Micrel MIC2177 User Manual

MIC2177 MicrelMIC2177 Micrel

70

75

80

85

90

95

100

10 100 1000 2500

EFFICIENCY (%)

OUTPUT CURRENT (mA)

5V Output
Efficiency

VIN = 6V

SKIP

PWM

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MIC2177

2.5A Synchronous Buck Regulator

General Description

The Micrel MIC2177 is a 200kHz synchronous buck (step­down) switching regulator designed for high-efficiency, bat­tery-powered applications.

The MIC2177 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 MIC2177 achieves high efficiency over a wide output
current range by switching between PWM and skip mode.
Operating mode is automatically selected according to output
conditions. Switching frequency is preset to 200kHz and can
be synchronized to an external clock signal of up to 300kHz.

The MIC2177 uses current-mode control with internal current
sensing. Current-mode control provides superior line regula­tion and makes the regulator control loop easy to compen­sate. 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 MIC2177 is packaged in a 20-lead wide power SO
package with an operating temperature range of –40°C to
+85°C.

See the MIC2178 for externally selected PWM or skip-mode
operation.

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
500µA in skip mode
< 5µA in shutdown mode

• 100% duty cycle for low dropout operation

• Current-mode control
Simplified loop compensation
Superior line regulation

• Current limit

• Thermal shutdown

• Undervoltage lockout

Applications

• High-efficiency, battery-powered supplies

• Buck (step-down) dc-to-dc converters

• Cellular telephones

• Laptop computers

• Hand-held instruments

• Battery Charger

Typical Application

V

IN

6V to 16.5V

C1

22µF

35V

April 1999 1 MIC2177

22µF

AUTO

MODE

C2

35V

PWM
MODE

2.2nF

Mode

C6

OFF

U1

ON

ENABLE

20

EN

11

AUTO

18

SYNC

COMP

R7

15k
C5

10nF

1,2,9

VIN

OUT

MIC2177-5.0

13 14–17 19

SW

PGND

FB

BIASSGND

10

3,8

4–7

12

C4

0.01µF

L1, 33µH

D1
MBRS140

C7
220µF
10V

C3
220µF
10V

V

OUT

5V/2.5A

MIC2177 Micrel

Ordering Information

Part Output Switching Temperature
Number Voltage Frequency Range Package

MIC2177-3.3BWM 3.3V 200kHz –40°C to +85°C 20-lead wide SOP
MIC2177-5.0BWM 5.0V 200kHz –40°C to +85°C 20-lead wide SOP
MIC2177BWM adj. 200kHz –40 °C to +85°C 20-lead wide SOP

Pin Configuration

VIN

OUT

1VIN
2VIN
3SW
4PGND
5PGND
6PGND
7PGND
8SW
9

10

14
13
12
11

EN20
BIAS19
SYNC18
SGND17
SGND16
SGND15
SGND
COMP
FB
AUTO

20-Lead Wide SOP

Pin Description

Pin Number Pin Name Pin Function

1, 2, 9 VIN Supply Input: Controller and switch supply. Unregulated supply input to

internal regulator, output switches, and control circuitry. Requires bypass
capacitor to PGND. All three pins must be connected to VIN.

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

externally connected together.

4,5,6,7 PGND Power Ground: Output stage ground connections. Connect all pins to a

common ground plane.

10 OUT Output Voltage Sense (Input): Senses output voltage to determine minimum

switch current for PWM operation. Connect directly to V

11 AUTO Automatic Mode: Connect 2.2nF timing capacitor for automatic PWM-/skip-

mode switching. Regulator operates exclusively in PWM mode when pin is
pulled low.

12 FB Feedback (Input): Error amplifier inverting input. For adjustable output

version, connect FB to external resistive divider to set output voltage. For

3.3V and 5V fixed output versions, connect FB directly to output.

13 COMP Compensation: Internal error amplifier output. Connect to capacitor or series

RC network to compensate the regulator control loop.

14,15,16,17 SGND Signal Ground: Ground connection of control section. Connect all pins to

common ground plane.

18 SYNC Frequency Synchronization (Input): Optional clock input. Connect to

external clock signal to synchronize oscillator. Leading edge of signal above

1.7V terminates switching cycle. Connect to SGND if not used.

19 BIAS Bias Supply: Internal 3.3V bias supply output. 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.

OUT

.

MIC2177 2 April 1999

MIC2177 Micrel

Absolute Maximum Ratings

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

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

Operating Ratings

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

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

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

Enable, Output-Sense Voltage (VEN, V
Sync Voltage (V

) .....................................................6V

SYNC

) .................18V

OUT

Electrical Characteristics

VIN = 7.0V; TA = 25°C, bold indicates –40°C ≤ TA ≤ 85°C; unless noted.
Symbol Parameter Condition Min Typ Max Units

I

SS

V

BIAS

V

FB

V

OUT

V

TH

V

TL

I

FB

A

VOL

f

O

D

MAX

t

ON min

I

SYNC

I

LIM

R

ON

I

SW

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

4.5V ≤ VIN ≤ 16.5V
skip mode, output not switching, 500 650 µA

4.5V ≤ VIN ≤ 16.5V

VEN = 0V, 4.5V ≤ VIN ≤ 16.5V 1 25 µA
Bias Regulator Output Voltage VIN = 16.5V 3.10 3.30 3.4 V
Feedback Voltage MIC2177 [adj.]: V
Output Voltage MIC2177 [adj.]: V

5V ≤ VIN ≤ 16V, 10mA ≤ I

MIC2177-5.0: I

= 3.3V, I

OUT

= 3.3V, 3.20 3.3 3.40 V

OUT

LOAD

= 0 4.85 5.0 5.15 V

LOAD

= 0 1.22 1.245 1.27 V

LOAD

≤ 2A 3.14 3.46 V

MIC2177-5.0: 4.85 5.0 5.15

6V ≤ VIN ≤ 16V, 10mA ≤ I

MIC2177-3.3: I

= 0 3.20 3.3 3.40 V

LOAD

≤ 2A 4.75 5.25 V

LOAD

MIC2177-3.3: 3.20 3.3 3.40 V

5V ≤ VIN ≤ 16V, 10mA ≤ I

≤ 2A 3.14 3.46 V

LOAD

Undervoltage Lockout upper threshold 4.25 4.35 V

lower threshold 3.9 4.15 V
Feedback Bias Current MIC2177 [adj.] 60 150 nA

MIC2177-5.0, MIC2177-3.3 20 40 µA
Error Amplifier Gain 0.6V ≤ V

≤ 0.8V 15 18 20

COMP

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
Oscillator Frequency 160 200 240 kHz
Maximum Duty Cycle VFB = 1.0V 100 %
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
SYNC Leakage V

= 0V to 5.5V –1 0.01 1 µA

SYNC

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

skip mode 600 mA
Switch On-Resistance high-side switch, VIN = 12V 90 250 mΩ

low-side switch, VIN = 12V 110 250 mΩ
Output Switch Leakage VSW = 16.5V 1 10 µA

April 1999 3 MIC2177

MIC2177 Micrel

Symbol Parameter Condition Min Typ Max Units

Enable Threshold 0.8 1.6 2.2 V

I

EN

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

Enable Leakage VEN = 0V to 5.5V –1 0.01 1 µA
AUTO Threshold 0.8 1.6 V
AUTO Source Current VFB = 1.5V, V
Minimum Switch Current VIN – V

for PWM Operation

VIN – V

= 0V 220 mA

OUT

= 3V 420 mA

OUT

< 0.8V 7 11 15 µA

AUTO

MIC2177 4 April 1999

MIC2177 Micrel

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)

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)

0

50

100

150

200

250

24681012141618

ON-RESISTANCE (mΩ)

INPUT VOLTAGE (V)

70

75

80

85

90

95

100

10 100 1000 2500

EFFICIENCY (%)

OUTPUT CURRENT (mA)

8V

12V

5V Output
Efficiency

VIN = 6V

SKIP

PWM

Typical Characteristics

Oscillator Frequency

205

200

195

190

185

FREQUENCY (kHz)

180

175

vs. Temperature

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

Reference Voltage

5.030

5.020

5.010

5.000

4.990

4.980

REFERENCE VOLTAGE (V)

4.970

vs. Temperature

MIC2177-5.0

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

Reference Voltage

vs. Temperature

MIC2177 [adj.]

Error-Amplifier Gain

vs. Temperature

Reference Voltage

3.320

3.315

3.310

3.305

3.300

3.295

3.290

3.285

REFERENCE VOLTAGE (V)

3.280

vs. Temperature

MIC2177-3.3

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

Feedback Input Bias Current

120

100

BIAS CURRENT (nA)

vs. Temperature

80

60

40

20

0

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

April 1999 5 MIC2177

Current Limit

5.0

4.9

4.8

4.7

4.6

4.5

4.4

4.3

CURRENT LIMIT (A)

4.2

4.1

4.0

vs. Temperature

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

PWM-Mode

12

10

SUPPLY CURRENT (mA)

Supply Current

OUTPUT

SWITCHING

8

6

4

2

0

24681012141618

INPUT VOLTAGE (V)

High-Side Switch

On-Resistance

125°C

3.3V Output

100

95
90
85
80
75

EFFICIENCY (%)

70
65
60

10 100 1000 2500

Efficiency

VIN = 5V

8V

12V

SKIP

PWM

OUTPUT CURRENT (mA)

85°C
25°C

0°C

Low-Side Switch

On-Resistance

125°C

0

24681012141618

INPUT VOLTAGE (V)

ON-RESISTANCE (mΩ)

350
300
250
200
150
100

50

85°C
25°C

0°C