MIC2124 Datasheet, PDF (2/24 Pages) Micrel Semiconductor – Constant Frequency, Synchronous Current Mode Buck Controller

Micrel, Inc.
Ordering Information
Part Number
MIC2124YMM
Voltage
Adj.
Switching Frequency
300kHz
Junction Temp. Range
–40° to +125°C
Pin Configuration
Package
10-Pin MSOP
MIC2124
Lead Finish
Pb-Free
10-Pin MSOP (MM)
Pin Description
Pin Number
1
2
3
4
5
6
7
8
9
10
Pin Name
HSD
EN/COMP
FB
GND
IN
DL
PGND
DH
LX
BST
Pin Function
High-Side N-MOSFET Drain Connection (Input): Input voltage for the internal sensing of external
power stage supply. The HSD operating voltage range is from 3V to 18V. Input capacitors between
HSD and the power ground (PGND) are required.
Enable (Input): Floating = enable, logic low = shutdown. In the off state, supply current of the device is
greatly reduced (typically 1mA).
COMP (Output): Output of the gm error amplifier and connects to the components for the external
compensation.
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 MIC2124. The IN
operating voltage range is from 3V to 5.5V. A 2.2µF ceramic capacitors from IN to GND are
recommended for clean operation. Connect IN to HSD when VHSD < 5.5V.
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 MIC2124 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 VLX to VBST.
Switch Node (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.
Current Sense input (Input): LX pin also senses the current for the current mode control and short
circuit protection 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 at BST pin can slow down the turn-on time of high-
side N-Channel MOSFETs.
June 2010
2
M9999-060810-D