Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
MAX1887/MAX1897
Pin Description
PIN
MAX1887
MAX1897
NAME
DESCRIPTION
Dual-Mode Current-Limit Adjustment and Standby Input. The current-limit threshold
voltage is 1/10 the voltage seen at ILIM (V
ILIM
) over a 400mV to 1.5V range. If V
ILIM
drops below 250mV, the slave controller enters a low-power standby mode, forcing
DL high and DH low.
Trigger Input. Connect to the master controller’s low-side gate driver. For the
MAX1887, a rising edge triggers a single cycle. For the MAX1897, the trigger input’s
polarity is pin selectable. POL = V
CC
or floating triggers on the rising edge (out-of-
phase operation), and POL = GND triggers on the falling edge (in-phase operation).
Master Controller’s Positive Current-Sense Input
Master Controller’s Negative Current-Sense Input
On-Time Selection Control Input. This is a three-level input used to determine the DH
on time (see
On-Time Control and Active Current Balancing).
For the MAX1897,
connect TON as follows for the indicated switching frequencies:
GND = 550kHz
floating = 300kHz
V
CC
= 200kHz.
For the MAX1887, the switching frequency is internally configured for 300kHz
operation. The slave controller’s switching frequency should be selected to closely
match the frequency of the master PWM controller.
Slave Controller’s Negative Current-Sense Input
Slave Controller’s Positive Current-Sense Input
Current Balance Compensation. Connect a series resistor and capacitor between
COMP and OUT. See the
Current Balance Compensation
section.
TRIG Polarity Select Input. Connect POL to V
CC
or float to trigger on the rising edge of
TRIG (out-of-phase operation). Connect POL to GND to trigger on the falling edge of TRIG
(in-phase operation). For the MAX1887, POL is internally connected to V
CC
.
Analog Ground. Connect the MAX1897’s exposed pad to analog ground.
Power Ground
Low-Side Gate-Driver Output. DL swings from PGND to V
DD
. DL is forced high
when the MAX1897 enters standby or shutdown mode.
Supply Voltage Input for the DL Gate Driver. For the MAX1887, V
DD
also serves as
the analog supply voltage input that powers the PWM core. Connect to the system
supply voltage (4.5V to 5.5V). Bypass to PGND with a 1µF or greater ceramic
capacitor, as close to the IC as possible.
Analog Supply Voltage Input for PWM Core. Connect V
CC
to the system supply
voltage (4.5V to 5.5V) through a series 10Ω resistor. Bypass to GND with a 0.22µF
or greater ceramic capacitor, as close to the MAX1897 as possible.
Active-Low Shutdown Input. A logic low shuts down the MAX1897 slave controller,
immediately pulling DL high and DH low. Connect to V
CC
for normal operation.
1
19
ILIM
2
20
TRIG
3
4
1
2
CM+
CM-
—
3
TON
5
6
7
4
5
6
CS-
CS+
COMP
—
8
9
10
7
8
9
10
POL
GND
PGND
DL
11
11
V
DD
—
12
V
CC
SHDN
—
13
10
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
