MIC2172/3172
Micrel, Inc.
Ordering Information
Part Number
Standard
Pb-Free
MIC2172BN
MIC2172BM
MIC3172BN
MIC3172BM
MIC2172YN
MIC2172YM
MIC3172YN
MIC3172YM
Temperature
Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Package
8-pin plastic DIP
8-lead SOIC
8-pin plastic DIP
8-lead SOIC
Pin Configuration
MIC2172*/3172
†
S GND 1
COMP 2
FB 3
*SYNC/
†
EN 4
8 P GND 1
7 V
SW
6 P GND 2
5 V
I N
S GND 1
COMP 2
FB 3
*SYNC/
†
EN 4
MIC2172*/3172
†
8 P GND 1
7 V
SW
6 P GND 2
5 V
I N
8-pin DIP (N)
8-lead SOIC (M)
Pin Description
Pin Number
1
Pin Name
S GND
Pin Function
Signal Ground: Internal analog circuit ground. Connect directly to the input
filter capacitor for proper operation (see applications info). Keep separate
from power grounds.
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.
Feedback: Inverting input of error amplifier. Connect to external resistive
divider to set power supply output voltage.
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).
Enable: Apply TTL high or connect to V
IN
to enable the regulator. Apply
TTL low or connect to ground to disable the regulator. Device draws only
leakage current (<1µA) when disabled.
Supply Voltage: 3.0V to 40V
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.
Power Switch Collector: Collector of NPN switch. Connect to external
inductor or input voltage depending on circuit topology.
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.
2
COMP
3
4 (MIC2172)
FB
SYNC
4 (MIC3172)
EN
5
6
V
IN
P GND 2
7
8
V
SW
P GND 1
M9999-042205
2
April 2005
MICREL [ MICREL SEMICONDUCTOR ]
