Micrel
MIC2172/3172
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 0.3
Ω
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 0.3
Ω
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
VIN
P GND 2
7
8
VSW
P GND 1
April 2006
3
M9999-041806
(408) 955-1690
MICREL [ MICREL SEMICONDUCTOR ]
