April 2005

3

M9999-042205

MIC2183

Micrel, Inc.

Pin Description

Pin Number

Pin Name

Pin Function

1

VINA

Analog voltage input voltage to the circuit. This powers up the analog

sections of the die and does not need to be the same voltage as Pin 16

(V

2

FreqOut

This provides a digital signal output signal at half the switching frequency.

This signal swings from 0 to 3V, and can be used to drive an external

capacitive doubler to provide a higher voltage to the V

3SS

Soft start reduces the inrush current and delays and slows the output voltage

capacitor will soft start the switching regulator in 1.5ms.

4

COMP

Compensation (Output): Internal error amplifier output. Connect to a

capacitor or series RC network to compensate the regulator’s control loop.

5

SGND

Small signal ground: must be routed separately from other grounds to the (-)

terminal of C

6FB

Feedback Input - the circuit regulates this pin to 1.245V.

7

EN/UVLO

Enable/UnderVoltage Lockout (input): A low level on this pin will power down

the device, reducing the quiescent current to under 5uA. This pin has two

separate thresholds, below 1.5V the output switching is disabled, and below

0.9V the part is forced into a complete micropower shutdown. The 1.5V

threshold functions as an accurate undervoltage lockout (UVLO) with 140mV

hysteresis.

8

CSL

The (-) input to the current limit comparator. A built in offset of 100mV

between CSH and CSL in conjunction with the current sense resistor sets

the current limit threshold level. This is also the (-) input to the current

amplifier.

9

CSH

The (+) input to the current limit comparator. A built in offset of 100mV

between CSH and CSL in conjunction with the current sense resistor sets

the current limit threshold level. This is also the (+) input to the current

amplifier.

10

VDD

3V internal linear-regulator output. V

chip. Bypass to SGND with 1µF.

11

SYNC

Frequency Synchronization (Input): Connect an external clock signal to

synchronize the oscillator. Leading edge of signal above 1.5V starts the

switching cycle. Connect to SGND if not used.

12

PGND

MOSFET driver power ground, connects to source of synchronous MOSFET

and the (-) terminal of CIN.

13

OUTN

High current drive for synchronous N channel MOSFET. Voltage swing is

from ground to V

14

OUTP

High current drive for high side P channel MOSFET. Voltage swing is from

ground to V

15

FREQ/2

When this is low, the oscillator frequency is 400KHz. When this pin is raised

to V

16

VINP

Power Input voltage to the circuit. The output gate drivers are powered from

this supply. The current sense resistor R

possible to this pin.