MIC2178BWMTR - Micrel - Datasheet.Global

March 2005 1 M9999-031805

MIC2178 Micrel, Inc.

MIC2178

2.5A Synchronous Buck Regulator

General Description

The Micrel MIC2178 is a 200kHz synchronous buck (step-

down) switching regulator designed for high-efficiency, bat-

tery-powered applications.

The MIC2178 operates from a 4.5V to 16.5V input and

features internal power MOSFETs that can supply up to 2.5A

output current. It can operate with a maximum duty cycle of

100% for use in low-dropout conditions. It also features a

shutdown mode that reduces quiescent current to less than

5µA.

The MIC2178 achieves high efficiency over a wide output

current range by operating in either PWM or skip mode. The

operating mode is externally selected, typically by an intelli-

gent system, which chooses the appropriate mode according

to operating conditions, efficiency, and noise requirements.

The switching frequency is preset to 200kHz and can be

synchronized to an external clock signal of up to 300kHz.

The MIC2178 uses current-mode control with internal current

sensing. Current-mode control provides superior line regula-

tion and makes the regulator control loop easy to compen-

sate. The output is protected with pulse-by-pulse current

limiting and thermal shutdown. Undervoltage lockout turns

the output off when the input voltage is less than 4.5V.

The MIC2178 and is packaged in a 20-lead wide power SOIC

package with an operating temperature range of –40°C to

+85°C.

See the MIC2177 for automatic selection of PWM or skip-

mode operation.

Typical Application

Features

•4.5V to 16.5V input voltage range

•Dual-mode operation for high efficiency (up to 96%)

PWM mode for > 200mA load current

Skip mode for < 200mA load current

•100mΩ internal power MOSFETs at 12V input

•200kHz preset switching frequency

•Low quiescent current

1.0mA in PWM mode

600µA in skip mode

< 5µA in shutdown mode

•Current-mode control

Simplified loop compensation

Superior line regulation

•100% duty cycle for low dropout operation

•Current limit

•Thermal shutdown

•Undervoltage lockout

Applications

•High-efficiency, battery-powered supplies

•Buck (step-down) dc-to-dc converters

•Palmtop computers

•Laptop computers

•Cellular telephones

•Hand-held instruments

•Battery Chargers

BIASSGND

COMP

PGND

OUT

VIN

220µF

10V

OUT

5V/2.5A

L1, 33µH

6.8nF

0.01µFR2

10k

MIC2178-5.0

PWM

SYNC

10k

5.4V to 18V

22µF

35V U1

13 14–17 19

4–7

3,8

1,2,9

MBRS140

ENABLE

OFF

PWRGD

20k

Skip Mode

PWM Mode

Ouput Good

Output Low

220µF

10V

22µF

35V

100

10 100 1000 2500

EFFICIENCY (%)

OUTPUT CURRENT (mA)

5V Output

Efficiency

= 6V

SKIP

PWM

Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

MIC2178 Micrel, Inc.

M9999-031805 2March 2005

Pin Description

Pin Number Pin Name Pin Function

1, 2, 9 VIN Supply Voltage (Input): Requires bypass capacitor to PGND. All three pins

must be connected to VIN.

3, 8 SW Switch (Output): Internal power MOSFET output switches. Both pins must

be externally connected together.

4, 5, 6, 7 PGND Power Ground: Connect all pins to central ground point.

10 PWM PWM/Skip-Mode Control (Input): Logic-level input. Controls regulator

operating mode. Logic low enables PWM mode. Logic high enables skip

mode. Do not allow pin to float.

11 PWRGD Error Flag (Output): Open-drain output. Active low when FB input is 10%

below the reference voltage (VREF).

12 FB Feedback (Input): Connect to output voltage divider resistors.

13 COMP Compensation: Output of internal error amplifier. Connect capacitor or

series RC network to compensate the regulator control loop.

14, 15, 16, 17 SGND Signal Ground: Connect all pins to ground, PGND*.

18 SYNC Frequency Synchronization (Input): Optional. Connect an external clock

signal to synchronize the oscillator. Leading edge of signal above 1.7V

terminates switching cycle. Connect to SGND if not used.

19 BIAS Internal 3.3V Bias Supply: Decouple with 0.01µF bypass capacitor to

SGND. Do not apply any external load.

20 EN Enable (Input): Logic high enables operation. Logic low shuts down

regulator. Do not allow pin to float.

Pin Configuration

2VIN

3SW

4PGND

5PGND

6PGND

7PGND

1VIN

8SW

VIN

EN20

BIAS19

SYNC18

SGND17

SGND16

SGND15

PWM

11 PWRGD

COMP

SGND

20-Lead Wide Power SOIC

Ordering Information

Part Number

Standard* Pb-Free Voltage Junction Temp. Package

MIC2178BWM MIC2178YWM ADJ –40°C to +85°C20-lead WSOIC

MIC2178-3.3BWM MIC2178-3.3YWM 3.3V –40°C to +85°C20-lead WSOIC

MIC2178-5.0BWM MIC2178-5.0YWM 5.0V –40°C to +85°C20-lead WSOIC

* Standard product will be supported as Pb-Free IAW PPCN #040004 effective 1-1-2005.

March 2005 3 M9999-031805

MIC2178 Micrel, Inc.

Absolute Maximum Ratings

Supply Voltage [100ms transient] (VIN) ......................... 18V

Output Switch Voltage (VSW) ........................................ 18V

Output Switch Current (ISW)......................................... 6.0A

Enable, PWM Control Voltage (VEN, VPWM)................. 18V

Sync Voltage (VSYNC)..................................................... 6V

Operating Ratings

Supply Voltage (VIN) ..................................... 4.5V to 16.5V

Junction Temperature Range (TJ) ........... –40°C to +125°C

Electrical Characteristics

VIN = 7.0V; TA = 25°C, bold indicates –40°C ≤ TA ≤ 85°C; unless noted.

Symbol Parameter Condition Min Typ Max Units

ISS Input Supply Current PWM mode, output not switching, 1.0 1.5 mA

4.5V ≤ VIN ≤ 16.5V

skip mode, output not switching, 600 750 µA

4.5V ≤ VIN ≤ 16.5V

VEN = 0V, 4.5V ≤ VIN ≤ 16.5V 1 25 µA

VBIAS Bias Regulator Output Voltage VIN = 16.5V 3.10 3.30 3.4 V

VFB Feedback Voltage MIC2178 [adj.]: VOUT = 3.3V, ILOAD = 0 1.22 1.245 1.27 V

VOUT Output Voltage MIC2178 [adj.]: VOUT = 3.3V, 3.20 3.3 3.40 V

5V ≤ VIN ≤ 16V, 10mA ≤ ILOAD ≤ 2A 3.14 3.46 V

MIC2178-5.0: ILOAD = 0 4.85 5.0 5.15 V

MIC2178-5.0: 4.85 5.0 5.15

6V ≤ VIN ≤ 16V, 10mA ≤ ILOAD ≤ 2A 4.75 5.25 V

MIC2178-3.3: ILOAD = 0 3.20 3.3 3.40 V

MIC2178-3.3: 3.20 3.3 3.40 V

5V ≤ VIN ≤ 16V, 10mA ≤ ILOAD ≤ 2A 3.14 3.46 V

VTH Undervoltage Lockout upper threshold 4.25 4.35 V

VTL lower threshold 3.90 4.15 V

IFB Feedback Bias Current MIC2178 [adj.] 60 150 nA

MIC2178-5.0, MIC2178-3.3 20 40 µA

AVOL Error Amplifier Gain 0.6V ≤ VCOMP ≤ 0.8V 15 18 20

Error Amplifier Output Swing upper limit 0.9 1.5 V

lower limit 0.05 0.1 V

Error Amplifier Output Current source and sink 15 25 35 µA

fOOscillator Frequency 160 200 240 kHz

DMAX Maximum Duty Cycle VFB = 1.0V 100 %

tON min Minimum On-Time VFB = 1.5V 300 400 ns

SYNC Frequency Range 220 300 kHz

SYNC Threshold 0.8 1.6 2.2 V

SYNC Minimum Pulse Width 500 ns

ISYNC SYNC Leakage VSYNC = 0V to 5.5V –1 0.01 1µA

ILIM Current Limit PWM mode, VIN = 12V 3.8 4.7 5.7 A

skip mode 600 mA

RON Switch On-Resistance high-side switch, VIN = 12V 90 250 mΩ

low-side switch, VIN = 12V 110 250 mΩ

ISW Output Switch Leakage VSW = 16.5V 1 10 µA

MIC2178 Micrel, Inc.

M9999-031805 4March 2005

Symbol Parameter Condition Min Typ Max Units

Enable Threshold 0.8 1.6 2.2 V

IEN Enable Leakage VEN = 0V to 5.5V –1 0.01 1µA

PWM Threshold 0.6 1.1 1.4 V

IPWM PWM Leakage VPWM = 0V to 5.5V –1 0.01 1µA

PWRGD Threshold MIC2178 [adj.]: measured at FB pin 1.09 1.13 1.17 V

MIC2178-5.0: measured at FB pin 4.33 4.54 4.75 V

MIC2178-3.3: measured at FB pin 2.87 3.00 3.13 V

PWRGD Output Low ISINK = 1.0mA 0.25 0.4 V

PWRGD Off Leakage VPWRGD = 5.5V 0.01 1µA

General Note: Devices are ESD sensitive. Handling precautions recommended.

March 2005 5 M9999-031805

MIC2178 Micrel, Inc.

Typical Characteristics

175

180

185

190

195

200

205

-60 -30 0 30 60 90 120 150

FREQUENCY (kHz)

TEMPERATURE (°C)

Oscillator Frequency

vs. Temperature

1.238

1.240

1.242

1.244

1.246

1.248

1.250

1.252

-60 -30 0 30 60 90 120 150

REFERENCE VOLTAGE (V)

TEMPERATURE (°C)

Reference Voltage

vs. Temperature

MIC2178 [adj.]

3.280

3.285

3.290

3.295

3.300

3.305

3.310

3.315

3.320

-60 -30 0 30 60 90 120 150

REFERENCE VOLTAGE (V)

TEMPERATURE (°C)

Reference Voltage

vs. Temperature

MIC2178-3.3

4.970

4.980

4.990

5.000

5.010

5.020

5.030

-60 -30 0 30 60 90 120 150

REFERENCE VOLTAGE (V)

TEMPERATURE (°C)

Reference Voltage

vs. Temperature

MIC2178-5.0

16.0

16.5

17.0

17.5

18.0

18.5

19.0

-60 -30 0 30 60 90 120 150

AMPLIFIER VOLTAGE GAIN

TEMPERATURE (°C)

Error-Amplifier Gain

vs. Temperature

100

120

-60 -30 0 30 60 90 120 150

BIAS CURRENT (nA)

TEMPERATURE (°C)

Feedback Input Bias Current

vs. Temperature

4.0

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

5.0

-60 -30 0 30 60 90 120 150

CURRENT LIMIT (A)

TEMPERATURE (°C)

Current Limit

vs. Temperature

100

150

200

250

24681012141618

ON-RESISTANCE (mΩ)

INPUT VOLTAGE (V)

High-Side Switch

On-Resistance

125°C

85°C

25°C

0°C

100

150

200

250

300

350

24681012141618

ON-RESISTANCE (mΩ)

INPUT VOLTAGE (V)

Low-Side Switch

On-Resistance

125°C

85°C

25°C

0°C

24681012141618

SUPPLY CURRENT (mA)

INPUT VOLTAGE (V)

PWM-Mode

Supply Current

OUTPUT

SWITCHING

100

10 100 1000 2500

EFFICIENCY (%)

OUTPUT CURRENT (mA)

= 5V

12V

3.3V Output

Efficiency

SKIP

PWM

100

10 100 1000 2500

EFFICIENCY (%)

OUTPUT CURRENT (mA)

12V

5V Output

Efficiency

= 6V

SKIP

PWM

MIC2178 Micrel, Inc.

M9999-031805 6March 2005

Block Diagram

PGND

SENSE

Amp.

PWM/

Skip-Mode

Select

REF

1.245V

100mΩ

N-channel

100mΩ

P-channel

COMP

VIN

Skip-Mode

Comp.

LIMIT

Comp.

Output

Control

Logic

Power Good

Comp.

1.13V

200kHz

Oscillator

PWM

Comp.

3.3V

Regulator

UVLO,

Thermal

Shutdown

OUT

SGND

PWRGD

0.01µF10k

BIAS

4.5V to 16.5V

100µF

SYNC

OUT

MIC2178 [Adjustable]

internal

supply Voltage

Enable

Shutdown

Stop

14 15 16 17

Bold lines indicate

high current traces

LIMIT

Thresh.

Voltage

PWM

Skip Mode

PWM Mode 10

Output Good

20k

*Connect

GND

to P

GND

Reset

Pulse

Corrective

Ramp

VOUT 1.245 R1

R2 1

March 2005 7 M9999-031805

MIC2178 Micrel, Inc.

Functional Description

Micrel’s MIC2178 is a synchronous buck regulator that oper-

ates from an input voltage of 4.5V to 16.5V and provides a

regulated output voltage of 1.25V to 16.5V. Its has internal

power MOSFETs that supply up to 2.5A load current and

operates with up to 100% duty cycle to allow low-dropout

operation. To optimize efficiency, the MIC2178 operates in

PWM and skip mode. Skip mode provides the best efficiency

when load current is less than 200mA, while PWM mode is

more efficient at higher current. PWM or skip-mode operation

is selected externally, allowing an intelligent system (i.e.

microprocessor controlled) to select the correct operating

mode for efficiency and noise requirements.

During PWM operation, the MIC2178 uses current-mode

control which provides superior line regulation and makes the

control loop easier to compensate. The PWM switching

frequency is set internally to 200kHz and can be synchro-

nized to an external clock frequency up to 300kHz. Other

features include a low-current shutdown mode, current limit,

undervoltage lockout, and thermal shutdown. See the follow-

ing sections for more detail.

Switch Output

The switch output (SW) is a half H-bridge consisting of a high-

side P-channel and low-side N-channel power MOSFET.

These MOSFETs have a typical on-resistance of 100mΩ

when the MIC2178 operates from a 12V supply. Antishoot-

through circuitry prevents the P-channel and N-channel from

turning on at the same time.

Current Limit

The MIC2178 uses pulse-by-pulse current limiting to protect

the output. During each switching period, a current limit

comparator detects if the P-Channel current exceeds 4.7A.

When it does, the P-channel is turned off until the next

switching period begins.

Undervoltage Lockout

Undervoltage lockout (UVLO) turns off the output when the

input voltage (VIN) is to low to provide sufficient gate drive for

the output MOSFETs. It prevents the output from turning on

until VIN exceeds 4.3V. Once operating, the output will not

shut off until VIN drops below 4.2V.

Thermal Shutdown

Thermal shutdown turns off the output when the MIC2178

junction temperature exceeds the maximum value for safe

operation. After thermal shutdown occurs, the output will not

turn on until the junction temperature drops approximately

10°C.

Shutdown Mode

The MIC2178 has a low-current shutdown mode that is

controlled by the enable input (EN). When a logic 0 is applied

to EN, the MIC2178 is in shutdown mode, and its quiescent

current drops to less than 5µA.

Internal Bias Regulator

An internal 3.3V regulator provides power to the MIC2178

control circuits. This internal supply is brought out to the BIAS

pin for bypassing by an external 0.01µF capacitor. Do not

connect an external load to the BIAS pin. It is not designed to

provide an external supply voltage.

Frequency Synchronization

The MIC2178 operates at a preset switching frequency of

200kHz. It can be synchronized to a higher frequency by

connecting an external clock to the SYNC pin. The SYNC pin

is a logic level input that synchronizes the oscillator to the

rising edge of an external clock signal. It has a frequency

range of 220kHz–300kHz, and can operate with a minimum

pulse width of 500ns. If synchronization is not required,

connect SYNC to ground.

Power Good Flag

The power good flag (PWRGD) is an error flag that alerts a

system when the output is not in regulation. When the output

voltage is 10% below its nominal value, PWRGD is logic low,

signaling that VOUT is to low. PWRGD is an open-drain output

that can sink 1mA from a pull-up resistor connected to VIN.

Low-Dropout Operation

Output regulation is maintained in PWM or skip mode even

when the difference between VIN and VOUT decreases below

1V. As VIN – VOUT decreases, the duty cycle increases until

it reaches 100%. At this point, the P-channel is kept on for

several cycles at a time, and the output stays in regulation

until VIN – VOUT falls below the dropout voltage (dropout

voltage = P-channel on-resistance × load current).

PWM-Mode Operation

Refer to “PWM Mode Functional Diagram” which is a simpli-

fied block diagram of the MIC2178 operating in PWM mode

and its associated waveforms.

When operating in PWM mode, the output P-channel and N-

channel MOSFETs are alternately switched on at a constant

frequency and variable duty cycle. A switching period begins

when the oscillator generates a reset pulse. This pulse resets

the RS latch which turns on the P-channel and turns off the

N-channel. During this time, inductor current (IL1) increases

and energy is stored in the inductor. The current sense

amplifier (ISENSE Amp) measures the P-channel drain-to-

source voltage and outputs a voltage proportional to IL1. The

output of ISENSE Amp is added to a sawtooth waveform

(corrective ramp) generated by the oscillator, creating a

composite waveform labeled ISENSE on the timing diagram.

When ISENSE is greater than the error amplifier output, the

PWM comparator will set the RS latch which turns off the P-

channel and turns on the N-channel. Energy is then dis-

charged from the inductor and IL1 decreases until the next

switching cycle begins. By varying the P-channel on-time

(duty cycle), the average inductor current is adjusted to

whatever value is required to regulate the output voltage.

The MIC2178 uses current-mode control to adjust the duty

cycle and regulate the output voltage. Current-mode control

has two signal loops that determine the duty cycle. One is an

outer loop that senses the output voltage, and the other is a

faster inner loop that senses the inductor current. Signals

from these two loops control the duty cycle in the following

way: VOUT is fed back to the error amplifier which compares

the feedback voltage (VFB) to an internal reference voltage

MIC2178 Micrel, Inc.

M9999-031805 8March 2005

(VREF). When VOUT is lower than its nominal value, the error

amplifier output voltage increases. This voltage then inter-

sects the current sense waveform later in switching period

which increases the duty cycle and the average inductor

current . If VOUT is higher than nominal, the error amplifier

output voltage decreases, reducing the duty cycle.

The PWM control loop is stabilized in two ways. First, the

inner signal loop is compensated by adding a corrective ramp

to the output of the current sense amplifier. This allows the

regulator to remain stable when operating at greater than

50% duty cycle. Second, a series resistor-capacitor load is

connected to the error amplifier output (COMP pin). This

places a pole-zero pair in the regulator control loop.

One more important item is synchronous rectification. As

mentioned earlier, the N-channel output MOSFET is turned

on after the P-channel turns off. When the N-channel turns

on, its on-resistance is low enough to create a short across

the output diode. As a result, inductor current flows through

the N-channel and the voltage drop across it is significantly

lower than a diode forward voltage. This reduces power

dissipation and improves efficiency to greater than 95%

under certain operating conditions.

To prevent shoot through current, the output stage employs

break-before-make circuitry that provides approximately 50ns

of delay from the time one MOSFET turns off and the other

turns on. As a result, inductor current briefly flows through the

output diode during this transition.

Skip-Mode Operation

Refer to “Skip Mode Functional Diagram” which is a simplified

block diagram of the MIC2178 operating in skip mode and its

associated waveforms.

Skip-mode operation turns on the output P-channel at a

frequency and duty cycle that is a function of VIN, VOUT, and

the output inductor value. While in skip mode, the N-channel

is kept off to optimize efficiency by reducing gate charge

dissipation. VOUT is regulated by skipping switching cycles

that turn on the P-channel.

To begin analyzing MIC2178 skip mode operation, assume

the skip-mode comparator output is high and the latch output

has been reset to a logic 1. This turns on the P-channel and

causes IL1 to increase linearly until it reaches a current limit

of 600mA. When IL1 reaches this value, the current limit

comparator sets the RS latch output to logic 0, turning off the

P-channel. The output switch voltage (VSW) then swings from

VIN to 0.4V below ground, and IL1 flows through the Schottky

diode. L1 discharges its energy to the output and IL1 de-

creases to zero. When IL1 = 0, VSW swings from –0.4V to

VOUT, and this triggers a one-shot that resets the RS latch.

Resetting the RS latch turns on the P-channel, and this

begins another switching cycle.

The skip-mode comparator regulates VOUT by controlling

when the MIC2178 skips cycles. It compares VFB to VREF and

has 10mV of hysteresis to prevent oscillations in the control

loop. When VFB is less than VREF –5mV, the comparator

output is logic 1, allowing the P-channel to turn on. Con-

versely, when VFB is greater than VREF + 5mV, the P-channel

is turned off.

Note that this is a self oscillating topology which explains why

the switching frequency and duty cycle are a function of VIN,

VOUT, and the value of L1. It has the unique feature (for a

pulse-skipping regulator) of supplying the same value of

maximum load current for any value of VIN, VOUT, or L1. This

allows the MIC2178 to always supply up to 300mA of load

current when operating in skip mode.

Selecting PWM- or Skip-Mode Operation

PWM or skip mode operation is selected by an external logic

signal applied to the PWM pin. A logic low places the

MIC2178 into PWM mode, and logic high places it into skip

mode. Skip mode operation provides the best efficiency

when load current is less than 200mA, and PWM operation is

more efficient at higher currents.

The MIC2178 was designed to be used in intelligent systems

that determine when it should operate in PWM or skip mode.

This makes the MIC2178 ideal for applications where a

regulator must guarantee low noise operation when supply-

ing light load currents, such as cellular telephone, audio, and

multimedia circuits.

There are two important items to be aware of when selecting

PWM or skip mode. First, the MIC2178 can start-up only in

PWM mode, and therefore requires a logic low at PWM during

start-up. Second, in skip mode, the MIC2178 will supply a

maximum load current of approximately 300mA, so the

output will drop out of regulation when load current exceeds

this limit. To prevent this from occurring, the MIC2178 should

change from skip to PWM mode when load current exceeds

200mA.

March 2005 9 M9999-031805

MIC2178 Micrel, Inc.

PGND

SENSE

Amp.

REF

1.245V

100mΩ

N-channel

100mΩ

P-channel

COMP

VIN

Error

Amp.

200kHz

Oscillator

PWM

Comp.

OUT

SGND

4.5V to 16.5V

SYNC

OUT

MIC2178 [Adjustable] PWM-Mode Signal Path

Stop

14 15 16 17

Corrective

Ramp

Reset

Pulse

OUT

1.245 R1

R2 1

Reset

Pulse

SENSE

LOAD

∆I

Error Amp.

Output

PWM-Mode Functional Diagram

MIC2178 Micrel, Inc.

M9999-031805 10 March 2005

One

Shot SW

PGND

ISENSE

Amp.

VREF 1.245V

100mΩ

P-channel

VIN

Skip-Mode

Comp.

ILIMIT

Comp.

VOUT

SGND

VIN

4.5V to 16.5V

CIN

COUT

MIC2178 [Adjustable] Skip-Mode Signal Path

14 15 16 17

ILIMIT

Thresh.

Voltage

Output Control Logic

IL1

OUT

1.245 R1

R2 1

One-Shot

Pulse

REF

+ 5mV

REF

– 5mV

LIM

OUT

Skip-Mode Functional Diagram

March 2005 11 M9999-031805

MIC2178 Micrel, Inc.

Application Information

Feedback Resistor Selection (Adjustable Version)

The output voltage is programmed by connecting an external

resistive divider to the FB pin as shown in “MIC2178 Block

Diagram.” The ratio of R1 to R2 determines the output

voltage. To optimize efficiency during low output current

operation, R2 should not be less than 20kΩ. However, to

prevent feedback error due to input bias current at the FB pin,

R2 should not be greater than 100kΩ. After selecting R2,

calculate R1 with the following formula:

R1 = R2 V

1.245V

OUT























–1

Input Capacitor Selection

The input capacitor is selected for its RMS current and

voltage rating and should be a low ESR (equivalent series

resistance) electrolytic or tantalum capacitor. As a rule of

thumb, the voltage rating for a tantalum capacitor should be

twice the value of VIN, and the voltage rating for an electrolytic

should be 40% higher than VIN. The RMS current rating must

be equal or greater than the maximum RMS input ripple

current. A simple, worst case formula for calculating this

RMS current is:

I = I

RMS(max)

LOAD(max)

Tantalum capacitors are a better choice for applications that

require the most compact layout or operation below 0°C. The

input capacitor must be located very close to the VIN pin

(within 0.2in, 5mm). Also, place a 0.1µF ceramic bypass

capacitor as close as possible to VIN.

Inductor Selection

The MIC2178 is a current-mode controller with internal slope

compensation. As a result, the inductor must be at least a

minimum value to prevent subharmonic oscillations. This

minimum value is calculated by the following formula:

L = V 3.0 H/V

MIN OUT ×µ

In general, a value at least 20% greater than LMIN should be

selected because inductor values have a tolerance of ±20%.

Two other parameters to consider in selecting an inductor are

winding resistance and peak current rating. The inductor

must have a peak current rating equal or greater than the

peak inductor current. Otherwise, the inductor may saturate,

causing excessive current in the output switch. Also, the

inductor’s core loss may increase significantly. Both of these

effects will degrade efficiency. The formula for peak inductor

current is:

I = I I

L(peak) LOAD(max)

L(max)

+∆

Where:

∆I = V 1

L(max) OUT OUT

IN(max)

−











×µ

To maximize efficiency, the inductor’s resistance must be

less than the output switch on-resistance (preferably,

50mΩ or less).

Output Capacitor Selection

Select an output capacitor that has a low value of ESR. This

parameter determines a regulator’s output ripple voltage

(VRIPPLE) which is generated by ∆IL x ESR. Therefore, ESR

must be equal or less than a maximum value calculated for a

specified VRIPPLE (typically less than 1% of the output volt-

age) and ∆IL(max):

ESR = V

MAX RIPPLE

L(max)

∆

Typically, capacitors in the range of 100 to 220µF have ESR

less than this maximum value. The output capacitor can be

a low ESR electrolytic or tantalum capacitor, but tantalum is

a better choice for compact layout and operation at tempera-

tures below 0°C. The voltage rating of a tantalum capacitor

must be 2 × VOUT, and the voltage rating of an electrolytic

must be 1.4 × VOUT.

Output Diode Selection

In PWM operation, inductor current flows through the output

diode approximately 50ns during the dead time when one

output MOSFET turns off the other turns on. In skip mode, the

inductor current flows through the diode during the entire P-

channel off time. The correct diode for both of these condi-

tions is a 1A diode with a reverse voltage rating greater than

VIN. It must be a Schottky or ultrafast-recovery diode

(tR<100ns) to minimize power dissipation from the diode’s

reverse-recovery charge.

Compensation

Compensation is provided by connecting a series RC load to

the COMP pin. This creates a pole-zero pair in the regulator

control loop, allowing the regulator to remain stable with

enough low frequency loop-gain for good load and line

regulation. At higher frequencies, the pole-zero reduces

loop-gain to a level referred to as the mid-band gain. The mid-

band gain is low enough so that the loop gain crosses 0db

with sufficient phase margin. Typical values for the RC load

are 4.7nF to 10nF for the capacitor and 5kΩ to 20kΩ for the

resistor.

Printed Circuit Board Layout

A well designed PC board will prevent switching noise and

ground bounce from interfering with the operation of the

MIC2178. A good design takes into consideration compo-

nent placement and routing of power traces.

The first thing to consider is the locations of the input

capacitor, inductor, output diode, and output capacitor. The

input capacitor must be placed very close to the VIN pin, the

inductor and output diode very close to the SW pin, and the

output capacitor near the inductor. These components pass

large high-frequency current pulses, so they must use short,

wide power traces. In addition, their ground pins and PGND

are connected to a ground plane that is nearest the power

supply ground bus.

MIC2178 Micrel, Inc.

M9999-031805 12 March 2005

The feedback resistors, RC compensation network, and

BIAS pin bypass capacitor should be located close to their

respective pins. To prevent ground bounce, their ground

traces and SGND should not be in the path of switching

BIASSGND

PWRGD

COMP

PGND

VIN

100µF

10V

OUT

3.3V/1A

50µH

6.8nF

0.01µF

10k

MIC2178

PWM

Skip Mode

PWM Mode

SYNC

20k

10k

4.5V to 16.5V

22µF

35V

13 14–17 19

4–7

3,8

1,2,9

MBRS130L

U1 Micrel MIC2178-3.3BWM

C1 AVX TPSE226M035R0300, ESR = 0.3Ω

C2 AVX TPSD107M010R0100, ESR = 0.1Ω

C3 Z5UorX7R Ceramic Dielectric Material

C4 X7RorNP0 Ceramic Dielectric Material

D1 Motorola MBRS130LT3

L1 Coiltronics CTX50-4P, DCR = 0.097 Ω

L1 Coilcraft DO3316P-473, DCR = 0.12Ω

L1 Bi HM77-11003, DCR = 0.073Ω

Figure 1. MIC2178 4.5V–16.5V to 3.3V/1A Regulator

BIASSGND

PWRGD

COMP

PGND

VIN

100µF

10V

VOUT

5V/1A

50µH

6.8nF

0.01µF

10k

MIC2178

PWM

Skip Mode

PWM Mode

SYNC

20k

10k

VIN

5.4V to 16.5V

22µF

35V

13 14–17 19

4–7

3,8

1,2,9

MBRS130L

U1 Micrel MIC2178-5.0BWM

C1 AVX TPSE226M035R0300, ESR = 0.3Ω

C2 AVX TPSD107M010R0100, ESR = 0.1Ω

C3 Z5UorX7R Ceramic Dielectric Material

C4 X7RorNP0 Ceramic Dielectric Material

D1 Motorola MBRS130LT3

L1 Coiltronics CTX50-4P, DCR = 0.097 Ω

L1 Coilcraft DO3316P-473, DCR = 0.12Ω

L1 Bi HM77-11003, DCR = 0.073Ω

Figure 2. MIC2178 5.4V–16.5V to 5V/1A Regulator

currents returning to the power supply ground bus. SGND

and PGND should be tied together by a ground plane that

extends under the MIC2178.

March 2005 13 M9999-031805

MIC2178 Micrel, Inc.

BIASSGND

PWRGD

COMP

PGND

VIN

68µF

20V

OUT

12V/1A

68µH

6.8nF

0.01µF

MIC2178

PWM

Skip Mode

PWM Mode

SYNC

174k

20k

10k

12.5V to 16.5V

22µF

35V

13 14–17 19

4–7

3,8

1,2,9

MBRS130L

U1 Micrel MIC2178BWM

C1 AVX TPSE226M035R0300, ESR = 0.3Ω

C2 AVX TPSE686M020R0150, ESR = 0.15Ω

C3 Z5UorX7R Ceramic Dielectric Material

C4 X7RorNP0 Ceramic Dielectric Material

D1 Motorola MBRS130LT3

L1 Coiltronics CTX68-4P, DCR = 0.238 Ω

L1 Coilcraft DO3316P-683, DCR = 0.016Ω

L1 Bi HM77-11003, DCR = 0.233Ω

10k

Figure 3. MIC2178 12.5V–16.5V to 12V/1A Regulator

BIASSGND

PWRGD

COMP

PGND

VIN

220µF

10V

OUT

3.3V/2.5A

33µH

6.8nF

0.01µF

MIC2178

PWM

Skip Mode

PWM Mode

SYNC

20k

10k

10V to 16.5V

22µF

35V

X2 U1

13 14–17 19

4–7

3,8

1,2,9

MBRS130L

U1 Micrel MIC2178-3.3BWM

C1 AVX TPSE226M035R0300, ESR = 0.3Ω

C2 AVX TPSE227M010R0100, ESR = 0.1Ω

C3 Z5UorX7R Ceramic Dielectric Material

C4 X7RorNP0 Ceramic Dielectric Material

D1 Motorola MBRS130LT3

L1 Bi HM77-18004, DCR = 0.075Ω

10k

Figure 4. MIC2178 10V–16.5V to 3.3V/2.5A Regulator

BIASSGND

PWRGD

COMP

PGND

VIN

100µF

10V

OUT

3.3V/1A

33µH

6.8nF

0.01µF

MIC2178

PWM

Skip Mode

PWM Mode

SYNC

20k

10k

4.5V to 10V

22µF

35V

13 14–17 19

4–7

3,8

1,2,9

MBRS130L

U1 Micrel MIC2178-3.3BWM

C1 AVX TPSE226M035R0300, ESR = 0.3Ω

C2 AVX TPSD107M010R0100, ESR = 0.1Ω

C3 Z5UorX7R Ceramic Dielectric Material

C4 X7RorNP0 Ceramic Dielectric Material

D1 Motorola MBRS130LT3

L1 Coiltronics CTX33-3P, DCR = 0.077 Ω

L1 Coilcraft DO3316-333, DCR = 0.088Ω

L1 Bi HM77-60002, DCR = 0.035Ω

10k

Figure 5. MIC2178 4.5V–10V to 3.3V/1A Regulator

MIC2178 Micrel, Inc.

M9999-031805 14 March 2005

BIASSGND

PWRGD

COMP

PGND

VIN

100µF

10V

OUT

3.3V/1A

50µH

6.8nF

0.01µF

MIC2178

PWM

Skip Mode

PWM Mode

SYNC

20k

10k

4.5V to 16.5V C1

22µF

35V

13 14–17 19

4–7

3,8

1,2,9

MBRS130L

U1 Micrel MIC2178-3.3BWM

C1 AVX TPSE226M035R0300, ESR = 0.3Ω

C2 AVX TPSD107M010R0100, ESR = 0.1Ω

C3 Z5UorX7R Ceramic Dielectric Material

C4 X7RorNP0 Ceramic Dielectric Material

D1 Motorola MBRS130LT3

Q1 Siliconix Si9435DY PMOS

L1 Coiltronics CTX50-4P, DCR = 0.097 Ω

L1 Coilcraft DO3316-473, DCR = 0.12Ω

L1 Bi HM77-11003, DCR = 0.073Ω

SI9435

0.01µF

Figure 6. MIC2178 Reversed Battery Protected Regulator

BIASSGND

PWRGD

COMP

PGND

VIN

100µF

10V

OUT

/+I

OUT

5V/0.5A

6.8nF

0.01µF

MIC2178

PWM

Skip Mode

PWM Mode

SYNC

20k

10k

8V to 16.5V

22µF

35V

13 14–17 19

4–7

3,8

1,2,9

MBRS130L

U1 Micrel MIC2178-5.0BWM

C1 AVX TPSE226M035R0300, ESR = 0.3Ω

C2 AVX TPSD107M010R0100, ESR = 0.1Ω

C3 AVX TPSD107M010R0100, ESR = 0.1Ω

C4 AVX TPSD107M010R0100, ESR = 0.1Ω

C5 Z5UorX7R Ceramic Dielectric Material

C6 X7RorNP0 Ceramic Dielectric Material

D1 Motorola MBRS130LT3

D2 Motorola MBRS130LT3

L1 Coiltronics CTX50-4P, DCR = 0.097 Ω

100µF

10V

50µH

MBRS130L

100µF

10V

–V

OUT

/-I

OUT

–5V/0.5A

OUT

+ (–I

OUT

) 1A

DC = + V

OUT

DC 40% then – I

OUT

DC 40% then – I

OUT

(1– DC)

10k

Figure 7. MIC2178 8V–16.5V to ±5V/500mA Regulator

March 2005 15 M9999-031805

MIC2178 Micrel, Inc.

Suggested Manufacturers List

Inductors Capacitors Diodes Transistors

Coilcraft AVX Corp. General Instruments (GI) Siliconix

1102 Silver Lake Rd. 801 17th Ave. South 10 Melville Park Rd. 2201 Laurelwood Rd.

Cary, IL 60013 Myrtle Beach, SC 29577 Melville, NY 11747 Santa Clara, CA 96056

tel: (708) 639-2361 tel: (803) 448-9411 tel: (516) 847-3222 tel: (800) 554-5565

fax: (708) 639-1469 fax: (803) 448-1943 fax: (516) 847-3150

Coiltronics Sanyo Video Components Corp. International Rectifier Corp.

6000 Park of Commerce Blvd. 2001 Sanyo Ave. 233 Kansas St.

Boca Raton, FL 33487 San Diego, CA 92173 El Segundo, CA 90245

tel: (407) 241-7876 tel: (619) 661-6835 tel: (310) 322-3331

fax: (407) 241-9339 fax: (619) 661-1055 fax: (310) 322-3332

Bi Technologies Sprague Electric Motorola Inc.

4200 Bonita Place Lower Main St. MS 56-126

Fullerton, CA 60005 Sanford, ME 04073 3102 North 56th St.

tel: (714) 447-2345 tel: (207) 324-4140 Phoenix, AZ 85018

fax: (714) 447-2500 tel: (602) 244-3576

fax: (602) 244-4015

Package Information

0.022 (0.559)

0.018 (0.457)

5°

TYP

0.408 (10.363)

0.404 (10.262)

0.509 (12.929)

0.505 (12.827)

0.103 (2.616)

0.099 (2.515)

SEATING

PLANE

0.027 (0.686)

0.031 (0.787) 0.016 (0.046)

TYP

0.301 (7.645)

0.297 (7.544)

0.094 (2.388)

0.090 (2.286)

0.297 (7.544)

0.293 (7.442)

10° TYP

0.032 (0.813) TYP

0.330 (8.382)

0.326 (8.280)

7°

TYP

0.050 (1.270)

TYP

0.015

(0.381) R

0.015

(0.381)

MIN

PIN 1

DIMENSIONS:

INCHES (MM)

20-Lead Wide SOP (WM)

MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com

This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use.

Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.

Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can

reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into

the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s

use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify

Micrel for any damages resulting from such use or sale.