MAX1887 Datasheet, PDF (29/33 Pages) Maxim Integrated Products – Quick-PWM Slave Controllers for Multiphase, Step-Down

Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
Typical Operating Circuit
REF
(MASTER)
FLOAT
(300kHz)
ILIM
(MASTER)
FB
(MASTER)
( )* MAX1897 PINS ONLY
V_DD
V+
(V_CC)*
BST
(POL)*
DH
SHDN
LX
ILIM
DL
MAX1887
(MAX1897)*
(TON)*
PGND
CS+
LIMIT
CS-
COMP
CM+
CM-
GND
TRIG
5V BIAS
SUPPLY
INPUT
OUTPUT
MASTER CURRENT
SENSE RESISTOR
MASTER LOW-SIDE GATE DRIVER
V_DD bypass capacitor go; the master’s analog
ground plane where sensitive analog components,
the master’s GND pin and V_CC bypass capacitor
go; and the slave’s analog ground plane where the
slave’s GND pin, and V_CC bypass capacitor go.
The master’s GND plane must meet the PGND
plane only at a single point directly beneath the IC.
Similarly, the slave’s GND plane must meet the
PGND plane only at a single point directly beneath
the IC. The respective master and slave ground
planes should connect to the high-power output
ground with a short metal trace from PGND to the
source of the low-side MOSFET (the middle of the
star ground). This point must also be very close to
the output capacitor ground terminal.
5) Connect the output power planes (V_CORE and sys-
tem ground planes) directly to the output filter
capacitor positive and negative terminals with multi-
ple vias. Place the entire DC-DC converter circuit
as close to the CPU as is practical.
Pin Configurations (continued)
TOP VIEW
ILIM 1
TRIG 2
CM+ 3
CM- 4
CS- 5
CS+ 6
COMP 7
GND 8
MAX1887
QSOP
16 LIMIT
15 V+
14 BST
13 LX
12 DH
11 V_DD
10 DL
9 PGND
Chip Information
TRANSISTOR COUNT: 1422
PROCESS: BiCMOS
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