MICREL MIC3172BM, MIC3172BN, MIC2172BM, MIC2172BN Datasheet

MIC2172/3172 Micrel

MIC2172/3172

100kHz 1.25A Switching Regulators

Preliminary Information

General Description

The MIC2172 and MIC3172 are complete 100kHz SMPS
current-mode controllers with internal 65V 1.25A power
switches. The MIC2172 features external frequency syn­chronization or frequency adjustment, while the MIC3172
features an enable/shutdown control input.

Although primarily intended for voltage step-up applications,
the floating switch architecture of the MIC2172/3172 makes
it practical for step-down, inverting, and Cuk configurations
as well as isolated topologies.

Operating from 3V to 40V, the MIC2172/3172 draws only
7mA of quiescent current making it attractive for battery
operated supplies.

The MIC3172 is for applications that require on/off control of
the regulator. The MIC3172 is externally shutdown by
applying a TTL low signal to EN (enable). When disabled, the
MIC3172 draws only leakage current (typically less than
1µA). EN must be high for normal operation. For applications
not requiring control, EN must be tied to VIN or TTL high.

The MIC2172 is for applications requiring two or more SMPS
regulators that operate from the same input supply. The
MIC2172 features a SYNC input which allows locking of its
internal oscillator to an external reference. This makes it
possible to avoid the audible beat frequencies that result from
the unequal oscillator frequencies of independent SMPS
regulators.

A reference signal can be supplied by one MIC2172 desig­nated as a master. To insure locking of the slave’s oscillators,
the reference oscillator frequency must be higher than the

slave’s. The master MIC2172’s oscillator frequency is in­creased up to 135kHz by connecting a resistor from SYNC to
ground (see applications information).

The MIC2172/3172 is available in an 8-pin plastic DIP or
SOIC for –40°C to +85°C operation.

Features

• 1.25A, 65V internal switch rating

• 3V to 40V input voltage range

• Current-mode operation

• Internal cycle-by-cycle current limit

• Thermal shutdown

• Low external parts count

• Operates in most switching topologies

• 7mA quiescent current (operating)

•<1µA quiescent current, shutdown mode (MIC3172)

• TTL shutdown compatibility (MIC3172)

• External frequency synchronization (MIC2172)

• External frequency trim (MIC2172)

• Fits most LT1172 sockets (see applications info)

Applications

• Laptop/palmtop computers

• Toys

• Hand-held instruments

• Off-line converter up to 50W
(requires external power switch)

• Predriver for higher power capability

• Master/slave configurations (MIC2172)

4

T ypical Applications

+5V

(4.75V min.)

V

IN

SYNC

N/C

MIC2172

COMP

C3
1µF

GND

P1 P2 S

R3

1k

* Locate near MIC2172 when supply leads > 2

V

FB

27µH

SW

L1

D1

1N5822

C1*
22µF

C2
470µF

V

OUT

+12V, 0.14A

R1

10.7k
1%

R2

1.24k
1%

"

Figure 1.

MIC2172 5V to 12V Boost Converter

1997 4-13

4V to 6V

Enable

Shutdown

R3

1k

* Optional voltage clipper (may be req’d if T1 leakage inductance too high)

V

R1

3.74k
1%

R2

1.24k
1%

OUT

5V, 0.25A

V

IN

C1

22µF

COMP

C2
1µF

EN

MIC3172

P1 P2 S

V

GND

R4*

IN

V

SW

L

FB

C3*

D1*

1:1.25

= 100µH

PRI

T1

D2

1N5818

C4

470µF

Figure 2.

MIC3172 5V Flyback Converter

MIC2172/3172 Micrel

Ordering Information

Part Number Temperature Range Package

MIC2172BN –40°C to +85°C 8-pin plastic DIP
MIC2172BM –40°C to +85°C 8-lead SOIC
MIC3172BN –40°C to +85°C 8-pin plastic DIP
MIC3172BM –40°C to +85°C 8-lead SOIC

Pin Configuration

S GND

*SYNC/

COMP

FB

†

EN

MIC2172*/3172

1
2

3
4

†

8
7

6
5

P GND 1
V

SW

P GND 2
V

IN

S GND

COMP

*SYNC/

MIC2172*/3172

1
2
3

FB

†

4

EN

†

8
7

6
5

P GND 1
V

SW

P GND 2
V

IN

8-lead SOIC (M)8-lead DIP (N)

Pin Description

Pin Number Pin Name Pin Function

1 S GND Signal Ground: Internal analog circuit ground. Connect directly to the input

filter capacitor for proper operation (see applications info). Keep separate
from power grounds.

2 COMP Frequency Compensation: Output of transconductance type error amplifier.

Primary function is for loop stabilization. Can also be used for output voltage
soft-start and current limit tailoring.

3 FB Feedback: Inverting input of error amplifier. Connect to external resistive

divider to set power supply output voltage.

4 (MIC2172) SYNC Synchronization/Frequency Adjust: Capacitively coupled input signal greater

than device’s free running frequency (up to 135kHz) will lock device’s
oscillator on falling edge. Oscillator frequency can be trimmed up to 135kHz
by adding a resistor to ground. If unused, pin must float (no connection).

4 (MIC3172) EN Enable: Apply TTL high or connect to V

TTL low or connect to ground to disable the regulator. Device draws only
leakage current (<1µA) when disabled.

5V

IN

Supply Voltage: 3.0V to 40V

6 P GND 2 Power Ground #2: One of two NPN power switch emitters with 0.3Ω current

sense resistor in series. Required. Connect to external inductor or input
voltage ground depending on circuit topology.

7V

SW

Power Switch Collector: Collector of NPN switch. Connect to external
inductor or input voltage depending on circuit topology.

8 P GND 1 Power Ground #1: One of two NPN power switch emitters with 0.3Ω current

sense resistor in series. Optional. For maximum power capability connect
to P GND 2. Floating pin reduces current limit by a factor of two.

to enable the regulator. Apply

IN

4-14 1997

MIC2172/3172 Micrel

Absolute Maximum Ratings MIC2172

Input Voltage .................................................................40V

Switch Voltage ..............................................................65V

Sync Current ..............................................................50mA

Feedback Voltage (Transient, 1ms) ........................... ±15V

Operating Temperature Range

8-pin PDIP.................................................–40 to +85°C

8-pin SOIC ................................................–40 to +85°C

Junction Temperature ..............................–55°C to +150°C

Thermal Resistance

θJA 8-pin PDIP .................................................130°C/W

θJA 8-pin SOIC .................................................120°C/W

Storage Temperature ............................... –65°C to +150°C

Soldering (10 sec.) .................................................. +300°C

Electrical Characteristics MIC2172 Note 1. Unless otherwise specified, V

Parameter Conditions Min Typ Max Units
Reference Section Pin 2 tied to pin 3

Feedback Voltage (V

Feedback Voltage 3V ≤ V
Line Regulation

Feedback Bias Current (I

Error Amplifier Section

Transconductance (∆I

Voltage Gain (∆V
Output Current V

Output Swing High Clamp, V

Compensation Pin Duty Cycle = 0 0.8 0.9 1.08 V
Threshold 0.6 1.25 V

Output Switch Section

) 1.220 1.240 1.264 V

FB

≤ 40V 0.03 %/V

IN

) 310 750 nA

FB

/∆VFB) ∆I

COMP

/∆VFB) 0.9V ≤ V

COMP

= ±25µA 3.0 3.9 6.0 µA/mV

COMP

≤ 1.4V 500 800 2000 V/V

COMP

= 1.5V 125 175 350 µA

COMP

= 1V 1.8 2.1 2.3 V

Low Clamp, VFB = 1.5V 0.25 0.35 0.52 V

FB

= 5V.

IN

1.214 1.274 V

1100 nA

2.4 7.0 µA/mV

100 400 µA

4

ON Resistance I

Current Limit Duty Cycle = 50%, T

Breakdown Voltage (BV) 3V ≤ VIN ≤ 40V 65 75 V

= 1A, VFB = 0.8V 0.76 1 Ω

SW

≥ 25°C 1.25 3 A
Duty Cycle = 50%, T
Duty Cycle = 80% Note 2 1 2.5 A

ISW = 5mA

J

< 25°C 1.25 3.5 A

J

1.1 Ω

1997 4-15

MIC2172/3172 Micrel

Parameter Conditions Min Typ Max Units
Oscillator Section

Frequency (fO) 88 100 112 kHz

85 115 kHz

Duty Cycle [δ(max)] 80 89 95 %

Sync Coupling Capacitor VPP = 3.0V 22 51 120 pF
Required for Frequency Lock VPP = 40V 2.2 4.7 10 pF

Peak-to-Peak Voltage C
Required for Frequency Lock

Input Supply Voltage Section

Minimum Operating Voltage 2.7 3.0 V
Quiescent Current (IQ) 3V ≤ VIN ≤ 40V, V
Supply Current Increase (∆IIN) ∆ISW = 1A, V

Bold type denotes specifications applicable to the full operating temperature range.
Note 1 Devices are ESD sensitive. Handling precautions required.
Note 2 For duty cycles (δ) between 50% and 95%, minimum guaranteed switch current is given by ICL = 0.833 (2-δ) for the MIC3172.

COUPLING

= 12pF 2.2 12 30 V

= 0.6V, ISW = 0 7 9 mA

COMP

= 1.5V 9 20 mA

COMP

Absolute Maximum Ratings MIC3172

Input Voltage .................................................................40V

Switch Voltage ..............................................................65V

Enable Voltage..............................................................40V

Feedback Voltage (Transient, 1ms) ........................... ±15V

Operating Temperature Range

8-pin PDIP.................................................–40 to +85°C

8-pin SOIC ................................................–40 to +85°C

8-pin CerDIP ...........................................–55 to +125°C

Electrical Characteristics MIC3172 Note 1. Unless otherwise specified, V

Parameter Conditions Min Typ Max Units
Reference Section Pin 2 tied to pin 3

Feedback Voltage (V

Feedback Voltage 3V ≤ V
Line Regulation

) 1.224 1.240 1.264 V

FB

≤ 40V 0.07 %/V

IN

Junction Temperature ................................–55°C to 150°C

Thermal Resistance

θJA 8-pin PDIP .................................................130°C/W

θJA 8-pin SOIC .................................................120°C/W

θJA 8-pin CerDIP ..............................................100°C/W

Storage Temperature ................................. –65°C to 150°C

Soldering (10 sec.) .................................................... 300°C

= 5V.

IN

1.214 1.274 V

Feedback Bias Current (I

) 310 750 nA

FB

1100 nA

4-16 1997

MIC2172/3172 Micrel

Parameter Conditions Min Typ Max Units
Error Amplifier Section

Transconductance (∆I

COMP

/∆VFB) ∆I

= ±25µA 3.0 3.9 6.0 µA/mV

COMP

2.4 7.0 µA/mV
Voltage Gain (∆V
Output Current V

/∆VFB) 0.9V ≤ V

COMP

≤ 1.4V 500 800 2000 V/V

COMP

= 1.5V 125 175 350 µA

COMP

100 400 µA

Output Swing High Clamp, V

= 1V 1.8 2.1 2.3 V

FB

Low Clamp, VFB = 1.5V 0.25 0.35 0.52 V

Compensation Pin Duty Cycle = 0 0.8 0.9 1.08 V
Threshold 0.6 1.25 V

Output Switch Section

ON Resistance I

= 1A, VFB = 0.8V 0.76 1 Ω

SW

1.1 Ω

Current Limit Duty Cycle = 50%, T

Duty Cycle = 50%, T

≥ 25°C 1.25 3 A

J

< 25°C 1.25 3.5 A

J

Duty Cycle = 80% Note 2 1 2.5 A

Breakdown Voltage (BV) 3V ≤ VIN ≤ 40V 65 75 V

ISW = 5mA

Oscillator Section

Frequency (f

) 88 100 112 kHz

O

85 115 kHz

Duty Cycle [δ(max)] 80 89 95 %

4

Input Supply Voltage Section and Enable Section

Minimum Operating Voltage 2.7 3.0 V
Quiescent Current (IQ) 3V ≤ VIN ≤ 40V, V

= 0.6V, ISW = 0 7 9 mA

COMP

Shutdown, VEN = 0V 0.1 5 µA

Quiescent Current Increase (∆I

) ∆ISW = 1A, V

IN

= 1.5V 9 20 mA

COMP

Enable Input Threshold 0.4 1.2 2.4 V
Enable Input Current VEN = 0V –1 0 1 µA

VEN = 2.4V 2 10 µA

Bold type denotes specifications applicable to the full operating temperature range.
Note 1 Devices are ESD sensitive. Handling precautions required.
Note 2 For duty cycles (δ) between 50% and 95%, minimum guaranteed switch current is given by ICL = 0.833 (2-δ) for the MIC3172.

1997 4-17