MAX1686 Datasheet, PDF (1/12 Pages) Maxim Integrated Products – Step-Up DC-DC Converters with Precise, Adaptive Current Limit for GSM

19-1426; Rev 0; 2/99
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Step-Up DC-DC Converters with
Precise, Adaptive Current Limit for GSM
General Description
The MAX1687/MAX1688 step-up DC-DC converters deliv-
er up to 2W from a single Li-Ion or three NiMH cells. The
devices are ideal for burst-load applications such as GSM
cell phones and wireless LANs, where the RF power
amplifiers require short, high current bursts. The
MAX1687/MAX1688 reduce battery surge current by slow-
ly charging a reservoir capacitor, which supplies the nec-
essary peak energy for the load current burst. As a result,
the peak battery current is limited, thus maximizing battery
life and minimizing battery voltage sag and transient dips.
An internal synchronous rectifier provides over 90% con-
version efficiency and eliminates the need for an external
Schottky diode. A logic shutdown mode reduces the shut-
down current to only 3µA. The devices can be disabled
during current bursts (RF transmit mode) to eliminate
switching noise.
The switching frequency of the MAX1687/MAX1688, con-
trolled by the selected inductor, can exceed 1MHz. Two
external resistors set the output voltage from 1.25V to 6V.
The MAX1687 controls peak battery current, while the
MAX1688 features a more advanced, adaptive constant-
recharge-time algorithm that maximizes battery life. The
MAX1687/MAX1688 are available in thin 16-pin TSSOP
(1.1mm max height) or standard 8-pin SO packages.
GSM Phones
Wireless Handsets
PC Cards (PCMCIA)
Applications
Features
o Low 450mA Peak Battery Current
Provides 2A, 5V GSM Burst
o 90% Efficiency
o Internal Power MOSFETs and Current-Sense
Resistor
o Output Disconnects from Input During Shutdown
o 3µA Shutdown Current
o Precise Voltage-Controlled Current Limit
(MAX1687)
o Adaptive Constant-Recharge-Time Capability
(MAX1688)
o 1.25V to 6V Adjustable Output
o 2.7V to 6V Input Range
(1 Li-Ion cell or 3 NiMH cells)
o Switching Frequency Can Exceed 1MHz
o Standby Mode Disables DC-DC During
Transmission Burst
o Low Inrush Current at Start-Up
Ordering Information
PART*
TEMP. RANGE
MAX1687EUE
-40°C to +85°C
MAX1687ESA
-40°C to +85°C
MAX1688EUE
-40°C to +85°C
MAX1688ESA
-40°C to +85°C
*U.S. and foreign patents pending.
PIN-PACKAGE
16 TSSOP
8 SO
16 TSSOP
8 SO
Typical Operating Circuit
Pin Configurations
TOP VIEW
IN 1
16 OUT
IN 2
15 OUT
LX1 3
14 LX2
LX1 4
LIM [CHG] 5
MAX1687
MAX1688
13 LX2
12 PGND
FB 6
11 PGND
REF 7
10 AGND
N.C. 8
9 ON
[ ] ARE FOR MAX1688
TSSOP
Pin Configurations continued at end of data sheet.
†_{Patent pending}
2.7V TO 6V
1 Li-lon
OR
3 NiMH
OR
3 ALKALINE
ON
OFF
0 TO 1V
CONTROL INPUT
IN ^LX1
LX2
OUT
MAX1687
MAX1688
FB
ON
(LIM)
REF
[CHG]
GND
( ) ARE FOR MAX1687
[ ] ARE FOR MAX1688
V_OUT
UP TO 6V
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