MAX1856 Datasheet, PDF (1/18 Pages) Maxim Integrated Products – Wide Input Range, Synchronizable, PWM SLIC Power Supply

19-1898; Rev 0; 2/01
Wide Input Range, Synchronizable,
PWM SLIC Power Supply
General Description
The MAX1856 offers a low-cost solution for generating a
SLIC (ringer and off-hook) power supply. Using standard
off-the-shelf transformers from multiple vendors, the
MAX1856 generates various output voltages: -24V and
-72V (dual output) for both ringer and off-hook supplies for
voice-enabled broadband consumer premises equipment
(CPE), -48V for IP phones and routers, -5V and -15V (sin-
gle or dual output) for DSL CO line drivers, or negative
voltages as high as -185V for MEMS bias supplies. The
output voltages are adjusted with an external voltage
divider.
Due to its wide operating voltage range, the MAX1856
operates from a low-cost, unregulated DC power supply
for cost-sensitive applications like xDSL, cable modems,
set-top boxes, LMDS, MMDS, WLL, and FTTH CPE. The
MAX1856 provides low audio-band noise for talk battery
and a sturdy output capable of handling the ring trip con-
ditions for ring battery.
The operating frequency can be set between 100kHz and
500kHz with an external resistor in free-running mode. For
noise-sensitive applications, the MAX1856’s operating fre-
quency can be synchronized to an external clock over its
operating frequency range.
The flyback topology allows operation close to 50% duty
cycle, offering high transformer utilization, low ripple cur-
rent, and less stress on input and output capacitors.
Internal soft-start minimizes startup stress on the input
capacitor, without any external components.
The MAX1856’s current-mode control scheme does not
require external loop compensation. The low-side current-
sense resistor provides accurate current-mode control
and overcurrent protection.
Applications
VoIP Ringer and Off-Hook Voltage Generators
Cable and DSL Modems
Set-Top Boxes
Wireless Local Loop
FTTH
LMDS/MMDS
Routers
Industrial Power Supplies
CO DSL Line Driver Supplies
MEMS Bias Supplies
Idle Mode is a trademark of Maxim Integrated Products.
Features
o Low-Cost, Off-the-Shelf Transformer
o 3V to 28V Input Range
o Low Audio-Band Noise on Talk Battery
o Effectively Handles Ring Trip Transients
o Powers 2-, 4-, or 12-Line Equipment
o High Efficiency Extends Battery Life During
Life-Line Support Conditions
o Adjustable 100kHz to 500kHz Switching
Frequency
o Clock Synchronization
o Internal Soft-Start
o Current-Mode PWM and Idle Mode™ Control
Scheme
o Logic-Level Shutdown
o 10-Pin µMAX Package
PART
MAX1856EUB
Ordering Information
TEMP. RANGE
-40°C to +85°C
PIN-PACKAGE
10 µMAX
Typical Operating Circuit
INPUT
3V TO 28V
V_CC
SYNC/SHDN
1
2
LDO
EXT
2
FREQ
CS
MAX1856
2
GND
FB
PGND
REF
OUT2
-72V
OUT1
-24V
________________________________________________________________ Maxim Integrated Products 1
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.