19-2188; Rev 1; 9/02
Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
General Description
The MAX1887/MAX1897 step-down slave controllers are
intended for low-voltage, high-current, multiphase DC-to-
DC applications. The MAX1887/MAX1897 slave con-
trollers can be combined with any of Maxim’s
Quick-PWM™ step-down controllers to form a multiphase
DC-to-DC converter. Existing Quick-PWM controllers,
such as the MAX1718, function as the master controller,
providing accurate output voltage regulation, fast tran-
sient response, and fault protection features.
Synchronized to the master’s low-side gate driver, the
MAX1887/MAX1897 include the Quick-PWM constant on-
time controller, gate drivers for a synchronous rectifier,
active current balancing, and precision current-limit cir-
cuitry.
The MAX1887/MAX1897 provide the same high effi-
ciency, ultra-low duty factor capability, and excellent
transient response as other Quick-PWM controllers. The
MAX1887/MAX1897 differentially sense the inductor
currents of both the master and the slave across cur-
rent-sense resistors. These differential inputs and the
adjustable current-limit threshold derived from an exter-
nal reference allow the slave controller to accurately
balance the inductor currents and provide precise cur-
rent-limit protection. The MAX1887/MAX1897’s dual-
purpose current-limit input also allows the slave
controller to automatically enter a low-power standby
mode when the master controller shuts down.
The MAX1887 triggers on the rising edge of the mas-
ter’s low-side gate driver, which staggers the on-times
of both master and slave, providing out-of-phase oper-
ation that can reduce the input ripple current and con-
sequently the number of input capacitors. The
MAX1897 features a selectable trigger polarity, allowing
out-of-phase or simultaneous in-phase operation.
o
Quick-PWM Slave Controller
o
Precise, Active Current Balance (±1.25mV )
o
Accurate, Adjustable Current-Limit Threshold
o
Optimized for Low-Output Voltages (≤2V)
o
4V to 28V Battery Input Range
o
Fixed 300kHz (MAX1887) or Selectable
200kHz/300kHz/550kHz (MAX1897) Switching
Frequency
o
Drive Large Synchronous-Rectifier MOSFETs
o
525µA (typ) I
CC
Supply Current
o
20µA Standby Supply Current
o
<1µA Shutdown (MAX1897) Supply Current
o
Small 16-Pin QSOP (MAX1887), Compact
20-Pin 5mm x 5mm QFN (MAX1897), or
20-Pin 5mm x 5mm Thin QFN (MAX1897)
Features
MAX1887/MAX1897
Ordering Information
PART
MAX1887EEE
MAX1897E
GP*
MAX1897ETP
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
20 QFN 5mm
✕
5mm
20 Thin QFN 5mm
✕
5mm
*Contact
factory for availability.
Pin Configuration
TRIG
LIMIT
ILIM
V+
17
TOP VIEW
Applications
Notebook Computers
CPU Core Supply
Single-Stage (BATT to V
CORE
) Converters
Two-Stage (5V to V
CORE
) Converters
Servers/Desktop Computers
Telecom
CM+
CM-
TON
CS-
CS+
1
2
3
4
5
20
19
18
16
15
14
LX
DH
SHDN
V
CC
V
DD
BST
13
12
11
10
DL
MAX1897
6
COMP
7
POL
8
GND
9
PGND
Typical Operating Circuit appears at end of data sheet.
Quick-PWM is a registered trademark of Maxim Integrated
Products, Inc.
THIN QFN 5mm x 5mm
Pin Configurations continued at end of data sheet.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
