19-1426; Rev 0; 2/99
NUAL
KIT MA
ATION
ET
EVALU
TA SHE
WS DA
FOLLO
Step-Up DC-DC Converters with
Precise, Adaptive Current Limit for GSM
General Description
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
MAX1687 /MAX1688
†
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.
Ordering Information
PART*
MAX1687EUE
MAX1687ESA
MAX1688EUE
MAX1688ESA
*Ug.
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 TSSOP
8 SO
16 TSSOP
8 SO
Applications
GSM Phones
Wireless Handsets
PC Cards (PCMCIA)
Typical Operating Circuit
2.7V TO 6V
IN
LX1
LX2
OUT
V
OUT
UP TO 6V
Pin Configurations
TOP VIEW
IN 1
IN 2
LX1 3
LX1 4
LIM [CHG] 5
FB 6
REF 7
N.C. 8
[ ] ARE FOR MAX1688
16 OUT
15 OUT
14 LX2
1 Li-lon
OR
3 NiMH
OR
3 ALKALINE
ON
MAX1687
MAX1688
ON
(LIM)
REF
GND
MAX1687
MAX1688
13 LX2
12 PGND
11 PGND
10 AGND
9
ON
( ) ARE FOR MAX1687
[ ] ARE FOR MAX1688
OFF
0 TO 1V
CONTROL INPUT
FB
[CHG]
TSSOP
Pin Configurations continued at end of data sheet.
†
Pg
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
Step-Up DC-DC Converters with
Precise, Adaptive Current Limit for GSM
MAX1687/MAX1688
ABSOLUTE MAXIMUM RATINGS
IN, ON, LX1, CHG, LIM, FB, OUT, REF to GND .......-0.3V to +7V
LX2 to GND ..............................................................-0.3V to +8V
IN, LX1 Average Current..........................................................1A
Continuous Power Dissipation (T
A
= +70°C)
TSSOP (derate 5.7mW/°C above +70°C) ....................457mW
SO (derate 5.88mW/°C above +70°C) .........................471mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10sec) ............................+300° C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
IN
= V
ON
= +3V, V
LIM
= 1V (MAX1687), V
CHG
= 1V (MAX1688), V
FB
= 1.5V, V
OUT
= 6V,
T
A
= 0°C to +85°C,
unless otherwise noted.
Typical values are at T
A
= +25°C.)
PARAMETER
Input Voltage Range
Input Undervoltage Lockout
Output Voltage Range
V
FB
= 1.5V
Input Supply Current
Shutdown Delay
Reference Voltage
FB Set Voltage
FB Transconductance
I
CHG
Source Current
Peak Current
Ripple Current
Sense Resistor
ON Input Low Voltage
ON Input High Voltage
I
PEAK
I
RIPPLE
R
SENSE
V
IL
V
IH
I
FB
Input Current
I
ON
I
LIM
N-Channel On-Resistance
P-Channel On-Resistance
Precharge On-Resistance
LX2 Leakage Current
V
IN
= 2.7V
V
IN
= 6V
V
IN
= 4.2V
V
FB
= 1.5V
V
ON
= 0 or 3V
V
LIM
= 1V
V
IN
= 2.7V
V
IN
= 2.7V
V
IN
= 4V, V
FB
= 0, V
OUT
= 0
V
IN
= V
LX2
= 6V, V
OUT
= V
ON
= 0
T
A
= +25°C
T
A
= 0°C to +85°C
0.4
0.3
30
0.05
1.8
1.5
0.05
0.02
0.02
0.2
0.1
0.1
2
0.8
0.7
70
10
Ω
Ω
Ω
µA
µA
g
mFB
t
DELAY
V
REF
I
REF
= 0 to 10µA
V
FB
rising, 2% hysteresis
V
FB
= 1.125V, V
OUT
= 3V (MAX1688)
V
FB
= 0, V
OUT
= 3V (MAX1688)
V
LIM
= V
CHG
= 1V
V
LIM
= V
CHG
= 0.65V
V
LIM
= V
CHG
= 1V
Shutdown, V
IN
= 4.2V, LX2 connected to LX1,
V
OUT
= 0, ON = GND
0.7
1.225
1.212
0.18
60
0.744
0.46
170
IN rising, 1% hysteresis
SYMBOL
CONDITIONS
MIN
2.7
2.4
V
REF
2
3
1.2
1.25
1.250
0.2
110
0.8
0.5
200
0.1
0.856
0.54
230
0.18
0.6
2.5
TYP
MAX
6
2.6
6
4
10
1.8
1.275
1.288
0.22
UNITS
V
V
V
mA
µA
ms
V
V
mmho
µA
A
mA
Ω
V
V
2
_______________________________________________________________________________________
Step-Up DC-DC Converters with
Precise, Adaptive Current Limit for GSM
ELECTRICAL CHARACTERISTICS
(V
IN
= V
ON
= +3V, V
LIM
= 1V (MAX1687), V
CHG
= 1V (MAX1688), V
FB
= 1.5V, V
OUT
= 6V,
T
A
= -40°C to +85°C,
unless otherwise noted.)
(Note 1)
PARAMETER
Input Voltage Range
Input Undervoltage Lockout
Output Voltage Range
I
IN
Input Supply Current
Shutdown Delay
Reference Voltage
FB Set Voltage
FB Transconductance
Peak Current
Ripple Current
Sense Resistor
ON Input Low Voltage
ON Input High Voltage
N-Channel On-Resistance
P-Channel On-Resistance
Precharge On-Resistance
gm
FB
I
PEAK
I
RIPPLE
R
SENSE
V
IL
V
IH
V
IN
= 2.7V
V
IN
= 6V
V
IN
= 4.2V
V
IN
= 2.7V
V
IN
= 2.7V
V
IN
= 4V, V
FB
= 0, V
OUT
= 0
1.8
1.5
0.8
0.7
70
I
SHDN
T
DELAY
V
REF
I
REF
= 0 to 10µA
FB rising, 2% hysteresis
V
FB
= 1.125V, V
OUT
= 3V (MAX1688)
V
LIM
= V
CHG
= 1V
V
LIM
= V
CHG
= 0.65V
V
LIM
= V
CHG
= 1V
V
FB
= 1.5V
Shutdown V
IN
= 4.2V, LX2 connected to LX1,
V
OUT
= 0, ON = GND
0.6
1.212
1.20
0.16
0.73
0.44
145
IN rising, 1% hysteresis
SYMBOL
CONDITIONS
MIN
2.7
2.35
V
REF
TYP
MAX
6
2.65
6
5
10
2
1.288
1.30
0.24
0.90
0.57
240
0.18
0.6
UNITS
V
V
V
mA
µA
ms
V
V
mmho
A
mA
Ω
V
V
Ω
Ω
Ω
MAX1687/MAX1688
Note 1:
Specifications to -40°C are guaranteed by design, not production tested.
Typical Operating Characteristics
(V
IN
= +3.3V, V
OUT
= 5V, V
LIM
= 1V, Figures 6b and 7, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. DC LOAD CURRENT
(V
OUT
= 5.5V)
MAX1687/88 toc01
EFFICIENCY vs. GSM BURST LOAD
(V
OUT
= 5.5V)
MAX1687/88 toc02
EFFICIENCY vs. LOAD CURRENT
(V
IN
= 2.7V, V
OUT
= 3.3V)
95
90
EFFICIENCY (%)
85
80
75
70
MAX1687/88 toc03
95
90
V
IN
= 5V
85
EFFICIENCY (%)
95
90
85
EFFICIENCY (%)
80
75
V
IN
= 2.7V
70
65
60
V
IN
= 6V
V
IN
= 3.3V
V
IN
= 5V
100
80
75
70
65
60
0
50
V
IN
= 3.3V
V
IN
= 2.7V
V
IN
= 6V
65
60
0
500
1000 1500 2000
LOAD CURRENT (mA)
2500
3000
0
50
100
150
200
250
300
350
LOAD CURRENT (mA)
100
150
200
250
300
350
LOAD CURRENT (mA)
_______________________________________________________________________________________
3
Step-Up DC-DC Converters with Precise,
Adaptive Current Limit for GSM
MAX1687/MAX1688
_____________________________
Typical Operating Characteristics (continued)
(
V
IN
= +3.3V, V
OUT
= 5V, V
LIM
= 1V, Figures 6b and 7, T
A
= +25°C, unless otherwise noted.
)
MAX1688 PEAK BATTERY CURRENT
vs. R
CHG
(1A GSM LOAD)
MAX1687/88 toc04
NO-LOAD BATTERY INPUT CURRENT vs.
TEMPERATURE (V
OUT
= 5V, V
LIM
= 1V )
MAX1687/88 toc05
REFERENCE VOLTAGE vs. REFERENCE
CURRENT (V
IN
= 3.3V, V
OUT
= 5V)
1.245
1.240
1.235
V
REF
(V)
1.230
1.225
1.220
1.215
MAX1687/88 toc06
800
700
PEAK BATTERY CURRENT (mA)
600
500
400
300
200
100
0
15
20
25
30
35
4.5
4.0
SUPPLY CURRENT (mA)
3.5
3.0
2.5
2.0
1.5
V
IN
= 5V
V
IN
= 3.3V
V
IN
= 2.7V
V
IN
= 6V
1.250
1.210
1.205
1.200
80
100
1
10
I
REF
(µA)
100
1000
40
-40
-20
0
20
40
60
R
CHG
(kΩ)
TEMPERATURE (°C)
REFERENCE VOLTAGE vs. TEMPERATURE
(V
IN
= 3.3V, V
OUT
= 5V)
MAX1687/88 toc07
SWITCHING FREQUENCY vs. INDUCTANCE
(V
IN
= 3.3V, V
OUT
= 5V,
I
LOAD
= 100mA, V
LIM
= 1V)
MAX1687/88 toc08
1.253
1200
1000
FREQUENCY (kHz)
800
600
400
200
REFERENCE VOLTAGE (V)
1.251
1.249
1.247
1.245
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
0
1
10
INDUCTANCE (µH)
100
MAX1688
I
PEAK
vs. V
OUT
DROOP
750
700
650
I
PEAK
(mA)
600
550
500
450
400
350
300
100
150
200
250
300
350
400
V
OUT
DROOP (mV)
R
CHG
= 40.2k
MAX1687/88 toc09
MAX1688 PEAK INDUCTOR CURRENT
vs. R
CHG
(1A GSM LOAD)
700
PEAK INDUCTOR CURRENT (mA)
600
500
400
300
200
100
0
15
20
25
30
35
40
R
CHG
(kΩ)
MAX1687/88 toc10
800
800
4
_______________________________________________________________________________________
Step-Up DC-DC Converters with
Precise, Adaptive Current Limit for GSM
Typical Operating Characteristics (continued)
(
V
IN
= +3.3V, V
OUT
= 5V, V
LIM
= 1V, Figures 6b and 7, T
A
= +25°C, unless otherwise noted.
)
MAX1688
SWITCHING WAVEFORMS
(GSM PULSED LOAD 1A, R
CHG
= 40.2kΩ)
MAX1687/88 toc11
MAX1687/MAX1688
SWITCHING WAVEFORMS
(FIXED I
LOAD
= 300mA)
MAX1687/88 toc10a
500mA/div
500mA/div
I
LX
I
LX
500mA/div
I
LOAD
V
OUT
100mV/div
200mV/div
V
OUT
500µs/div
1ms/div
R
CHL
= 40.2kΩ, L = 10µH
MAX1688
SWITCHING WAVEFORMS
(GSM PULSED LOAD 1A, R
CHG
= 18kΩ)
MAX1687/88 toc12
INDUCTOR CURRENT
MAX1687/88 toc13
500mA/div
I
LX
I
LX
500mA/div
I
LOAD
V
LIM
= 1V
V
OUT
200mV/div
200mA/div
0A
I
LX
V
LIM
= 0
2µs/div
1ms/div
R
CHG
= 18kΩ, L = 10µH
POWER-UP WAVEFORM
(R
LOAD
= 15Ω C
OUT
= 2000µF)
MAX1687/88 toc14
V
ON
vs. BATTERY CURRENT
MAX1687/88 toc15
V
ON
2V/div
V
OUT
V
ON
1V/div
I
BATTERY
200mA/div
1V/div
5ms/div
10µs/div
_______________________________________________________________________________________
5
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