Micrel, Inc.

MIC2174

September 2009

2

M9999-090409-B

Ordering Information

Part Number

Voltage

Switching Frequency

Junction Temp. Range

Package

Lead Finish

MIC2174-1YMM

Adj.

300kHz

–40° to +125°C

10-Pin MSOP

Pb-Free

Pin Configuration

10-Pin MSOP (MM)

Pin Description

Pin

Number

Pin Name

Pin Function

1

HSD

High-Side N-MOSFET Drain Connection (input): Power to the drain of the external high-side N-channel

MOSFET. The HSD operating voltage range is from 3V to 40V. Input capacitors between HSD and the

power ground (PGND) are required.

2

EN

Enable (input): A logic level control of the output. The EN pin is CMOS-compatible. Logic high or floating

= enable, logic low = shutdown. In the off state, supply current of the device is greatly reduced (typically

0.8mA).

3

FB

Feedback (input): Input to the transconductance amplifier of the control loop. The FB pin is regulated to

0.8V. A resistor divider connecting the feedback to the output is used to adjust the desired output

voltage.

4

GND

for the signal ground should be separate from the power ground (PGND) loop.

5

IN

Input Voltage (input): Power to the internal reference and control sections of the MIC2174. The IN

operating voltage range is from 3V to 5.5V. A 1µF and 0.1µF ceramic capacitors from IN to GND are

recommended for clean operation.

6

DL

Low-Side Drive (output): High-current driver output for external low-side MOSFET. The DL driving

voltage swings from ground to IN.

7

PGND

Power Ground. PGND is the ground path for the MIC2174 buck converter power stage. The PGND pin

connects to the sources of low-side N-Channel MOSFETs, the negative terminals of input capacitors,

and the negative terminals of output capacitors. The loop for the power ground should be as small as

possible and separate from the Signal ground (GND) loop.

8

DH

High-Side Drive (output): High-current driver output for external high-side MOSFET. The DH driving

Adding a small resistor between DH pin and the gate of the high-side N-channel MOSFETs can slow

down the turn-on and turn-off time of the MOSFETs.

9

LX

Switch Node and Current Sense input: High current output driver return. The LX pin connects directly to

the switch node. Due to the high speed switching on this pin, the LX pin should be routed away from

sensitive nodes.

LX pin also senses the current by monitoring the voltage across the low-side MOSFET during OFF time.

In order to sense the current accurately, connect the low-side MOSFET drain to LX using a Kelvin

connection.

10

BST

Boost (output): Bootstrapped voltage to the high-side N-channel MOSFET driver. A Schottky diode is

connected between the IN pin and the BST pin. A boost capacitor of 0.1μF is connected between the

BST pin and the LX pin. Adding a small resistor in series with the boost capacitor can slow down the

turn-on time of high-side N-Channel MOSFETs.