MICREL MIC2178-5.0BWM, MIC2178BWM, MIC2178-3.3BWM Datasheet

MIC2178

Micrel

MIC2178

2.5A Synchronous Buck Regulator

General Description

The Micrel MIC2178 is a 200kHz synchronous buck (step­down) switching regulator designed for high-efficiency, bat­tery-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 intelli­gent 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 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 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 skip­mode 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
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

Typical Application

V

IN

6V to 16.5V

C1

22µF

35V

OUTPUT GOOD

OUTPUT LOW

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 [phone] • fax + 1 [phone] • http://www.micrel.com

June 1998 1 MIC2178

SKIP MODE

PWM MODE

C2

22µF

35V

R1
20k

U1

20

EN

11

PWRGD

10

PWM

18

SYNC

COMP

13 14–17 19

R2

15k

C6

10nF

1,2,9

VIN

MIC

2178-5.0

SW

PGND

FB

BIASSGND

3,8

4–7

12

C5

0.01µF

L1

33µH

D1
MBRS140

C3
220µF
10V

C4
220µF
10V

V

OUT

5V/2.5A

5V Output

100

95

90

85

80

EFFICIENCY (%)

75

70

10 100 1000 2500

Efficiency

VIN = 6V

SKIP

PWM

OUTPUT CURRENT (mA)

MIC2178

Ordering Information

Part Number Voltage Temperature Range Package

MIC2178BWM Adjustable –40°C to +85°C 20-lead Wide SOIC
MIC2178-3.3BWM 3.3V –40°C to +85°C 20-lead Wide SOIC
MIC2178-5.0BWM 5.0V –40°C to +85°C 20-lead Wide SOIC

Pin Configuration

Micrel

VIN

PWM

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

10

14
13
12
11

EN20
BIAS19
SYNC18
SGND17
SGND16
SGND15
SGND
COMP
FB
PWRGD

20-Lead Wide Power SOIC

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 (V
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.

REF

).

MIC2178 2 June 1998

MIC2178

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, PWM Control Voltage (VEN, V
Sync Voltage (V

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

SYNC

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

PWM

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, 600 750 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 MIC2178 [adj.]: V
Output Voltage MIC2178 [adj.]: V

5V ≤ VIN ≤ 16V, 10mA ≤ I

MIC2178-5.0: 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

MIC2178-5.0: 4.85 5.0 5.15

6V ≤ VIN ≤ 16V, 10mA ≤ I

MIC2178-3.3: I

= 0 3.20 3.3 3.40 V

LOAD

≤ 2A 4.75 5.25 V

LOAD

MIC2178-3.3: 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 3.90 4.15 V
Feedback Bias Current MIC2178 [adj.] 60 150 nA

MIC2178-5.0, MIC2178-3.3 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

June 1998 3 MIC2178

MIC2178

Micrel

Symbol Parameter Condition Min Typ Max Units

Enable Threshold 0.8 1.6 2.2 V

I

EN

Enable Leakage VEN = 0V to 5.5V –1 0.01 1 µA
PWM Threshold 0.6 1.1 1.4 V

I

PWM

PWM Leakage V

= 0V to 5.5V –1 0.01 1 µA

PWM

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 I
PWRGD Off Leakage V

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

= 1.0mA 0.25 0.4 V

SINK

= 5.5V 0.01 1 µA

PWRGD

MIC2178 4 June 1998

MIC2178

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)

Typical Characteristics

Micrel

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

MIC2178-5.0

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

Reference Voltage

vs. Temperature

MIC2178 [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

MIC2178-3.3

-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)

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

-60 -30 0 30 60 90 120 150

12

10

8

6

June 1998 5 MIC2178

4

2

SUPPLY CURRENT (mA)

0

24681012141618

Current Limit

vs. Temperature

TEMPERATURE (°C)

PWM-Mode

Supply Current

OUTPUT

SWITCHING

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

12V

SKIP

PWM

OUTPUT CURRENT (mA)

8V

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

5V Output
Efficiency

VIN = 6V

8V

12V

SKIP
PWM

85°C
25°C

0°C