MIC2174 Datasheet, PDF (2/24 Pages) Micrel Semiconductor – 300kHz, Synchronous Buck Controller 300kHz, Synchronous Buck Controller

Micrel, Inc.
Ordering Information
Part Number
MIC2174-1YMM
Voltage
Adj.
Switching Frequency
300kHz
Junction Temp. Range
–40° to +125°C
Pin Configuration
Package
10-Pin MSOP
MIC2174
Lead Finish
Pb-Free
10-Pin MSOP (MM)
Pin Description
Pin
Number
1
2
3
4
5
6
7
8
9
10
Pin Name Pin Function
HSD
EN
FB
GND
IN
DL
PGND
DH
LX
BST
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.
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).
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.
Signal ground. GND is the ground path for the device input voltage VIN and the control circuitry. The loop
for the signal ground should be separate from the power ground (PGND) loop.
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.
Low-Side Drive (output): High-current driver output for external low-side MOSFET. The DL driving
voltage swings from ground to IN.
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.
High-Side Drive (output): High-current driver output for external high-side MOSFET. The DH driving
voltage is floating on the switch node voltage (LX). It swings from ground to VIN minus the diode drop.
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.
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.
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.
September 2009
2
M9999-090409-B