Micrel, Inc.

MIC2174/MIC2174C

September 2010

3

M9999-091310-C

Pin Description (Continued)

Pin Number

Pin Name

Pin Function

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.