MICREL MIC2171BU, MIC2171BT Datasheet

MIC2171 Micrel

MIC2171

100kHz 2.5A Switching Regulator

Preliminary Information

General Description

The MIC2171 is a complete 100kHz SMPS current-mode
controller with an internal 65V 2.5A power switch.

Although primarily intended for voltage step-up applications,
the floating switch architecture of the MIC2171 makes it
practical for step-down, inverting, and Cuk configurations as
well as isolated topologies.

Operating from 3V to 40V, the MIC2171 draws only 7mA of
quiescent current, making it attractive for battery operated
supplies.

The MIC2171 is available in a 5-pin TO-220 or TO-263 for
–40°C to +85°C operation.

Features

• 2.5A, 65V internal switch rating

• 3V to 40V input voltage range

• Current-mode operation, 2.5A peak

• Internal cycle-by-cycle current limit

• Thermal shutdown

• Twice the frequency of the LM2577

• Low external parts count

• Operates in most switching topologies

• 7mA quiescent current (operating)

• Fits LT1171/LM2577 TO-220 and TO-263 sockets

Applications

• Laptop/palmtop computers

• Battery operated equipment

• Hand-held instruments

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

• Predriver for higher power capability

4

Typical Applications

+5V

(4.75V min.)

IN

MIC2171

COMP

3

1k

* Locate near MIC2171 when supply leads > 2

C3
1µF

GND

SW

FB

15µH

L1

MIC2171 5V to 12V Boost Converter

D1

1N5822

Figure 1.

C1*
47µF

C2
470µF

V

OUT

+12V, 0.25A

R1

10.7k
1%

R2

1.24k
1%

"

V

IN

4V to 6V

C1

47µF

IN

MIC2171

COMP

R3

1k

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

C2
1µF

GND

R4*

SW

FB

L

C3*

D1*

PRI

1:1.25

= 12µH

T1

D2

1N5818

470µF

Figure 2.

MIC2171 5V Flyback Converter

C4

R1

3.74k
1%

R2

1.24k
1%

V

OUT

5V, 0.5A

1997 4-3

MIC2171 Micrel

5IN
4SW
3 GND
2FB
1 COMP

Ordering Information

Part Number Temperature Range Package

MIC2171BT –40°C to +85°C 5-lead TO-220
MIC2171BU –40°C to +85°C 5-lead TO-263

Pin Configuration

5IN
4SW
3 GND
2FB
1 COMP

Tab GND

Pin Description

Pin Number Pin Name Pin Function

1 COMP Frequency Compensation: Output of transconductance-type error amplifier.

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

3 GND Ground: Connect directly to the input filter capacitor for proper operation

4 SW Power Switch Collector: Collector of NPN switch. Connect to external

5 IN Supply Voltage: 3.0V to 40V

5-lead TO-263 (BU)5-lead TO-220 (BT)

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

divider to set power supply output voltage.

(see applications info).

inductor or input voltage depending on circuit topology.

4-4 1997

MIC2171 Micrel

Absolute Maximum Ratings

Input Voltage (VIN) ........................................................40V

Switch Voltage (VSW)....................................................65V

Feedback Voltage (transient, 1ms) (VFB)................... ±15V

Operating Temperature Range ......................–40 to +85°C

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

Thermal Resistance

θJA 5-lead TO-220, Note 1.................................45°C/W

θJA 5-lead TO-263, Note 2.................................45°C/W

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

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

Electrical Characteristics

VIN = 5V; TA = 25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted.
Parameter Conditions Min Typ Max Units

Reference Section

Feedback Voltage (V

Feedback Voltage 3V ≤ V
Line Regulation V

Feedback Bias Current (I

Error Amplifier Section

Transconductance (g

Voltage Gain (AV) 0.9V ≤ V
Output Current V

)V

FB

)V

FB

) ∆I

m

COMP

COMP

= 1.24V 310 750 nA

FB

COMP

COMP

= 1.24V 1.220 1.240 1.264 V

1.214 1.274 V

≤ 40V .06 %/V

IN

= 1.24V

1100 nA

= ±25µA 3.0 3.9 6.0 µA/mV

2.4 7.0 µA/mV

≤ 1.4V 400 800 2000 V/V

COMP

= 1.5V 125 175 350 µA

100 400 µA

4

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

= 2A, VFB = 0.8V 0.37 0.50 Ω

SW

0.55 Ω

Current Limit Duty Cycle = 50%, T

Duty Cycle = 50%, T

≥ 25°C 2.5 3.6 5 A

J

< 25°C 2.5 4.0 5.5 A

J

Duty Cycle = 80%, Note 3 2.0 3.0 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 90 95 %

Input Supply Voltage Section

Minimum Operating Voltage 2.7 3.0 V
Quiescent Current (IQ) 3V ≤ VIN ≤ 40V, V
Supply Current Increase (∆IIN) ∆ISW = 2A, V

General Note Devices are ESD sensitive. Handling precautions required.
Note 1 Mounted vertically, no external heat sink, 1/4 inch leads soldered to PC board containing approximently 4 inch squared copper area

surrounding leads.

Note 2 All ground leads soldered to approximently 2 inches squared of horizontal PC board copper area.
Note 3 For duty cycles (δ) between 50% and 95%, minimum guaranteed switch current is ICL = 1.66 (2-δ) Amp (Pk).

COMP

= 0.6V, ISW = 0 7 9 mA

COMP

= 1.5V, during swich on-time 9 20 mA

1997 4-5