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19-1245; Rev 0; 7/97
KIT
ATION
EVALU
BLE
AVAILA
Adjustable-Output, Switch-Mode
Current Sources with Synchronous Rectifier
____________________________Features
o
95% Efficiency
o
+5.5V to +26V Input Supply Range
o
2V to 24V Adjustable-Output Voltage Range
o
100% Maximum Duty Cycle (Low Dropout)
o
Up to 500kHz PWM Operation
o
Optional Synchronous Rectifier
o
16-Pin QSOP Package
o
Current-Sense Accuracy: 2% (MAX1641)
5.3% (MAX1640)
_______________General Description
The MAX1640/MAX1641 CMOS, adjustable-output,
switch-mode current sources operate from a +5.5V to
+26V input, and are ideal for microprocessor-controlled
battery chargers. Charging current, maximum output
voltage, and pulse-trickle charge are programmed with
external resistors. Programming the off-time modifies
the switching frequency, suppressing undesirable har-
monics in noise-sensitive circuits. The MAX1640’s high-
side current sensing allows the load to connect directly
to ground, eliminating ground-potential errors. The
MAX1641 incorporates a low-side current sense.
The MAX1640/MAX1641 step-down pulse-width-modu-
lation (PWM) controllers use an external P-channel
MOSFET switch and an optional, external N-channel
MOSFET synchronous rectifier for increased efficiency.
An internal low-dropout linear regulator provides power
for the internal reference and circuitry as well as the
gate drive for the N-channel synchronous rectifier.
The MAX1640/MAX1641 are available in space-saving,
16-pin narrow QSOP packages.
MAX1640/MAX1641
______________Ordering Information
PART
MAX1640C/D
MAX1640EEE
MAX1641C/D
MAX1641EEE
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
Dice*
16 QSOP
Dice*
16 QSOP
________________________Applications
Battery-Powered Equipment
Laptop, Notebook, and Palmtop Computers
Handy Terminals
Portable Consumer Products
Cordless Phones
Cellular Phones
PCS Phones
Backup Battery Charger
*Dice
are specified at T
A
= +25°C, DC parameters only.
__________Typical Operating Circuit
V
IN
= +5.5V TO +26V
IN
D0
D1
TOFF
R
TOFF
NDRV
PGND
CS+
SET
CS-
OUT
LDOH
PDRV
P
__________________Pin Configuration
TOP VIEW
LDOL 1
TOFF 2
D1 3
D0 4
CC 5
REF 6
SET 7
TERM 8
16 IN
15 LDOH
14 PDRV
REF
MAX1640
MAX1641
13 NDRV
12 PGND
11 CS+
10 CS-
9
GND
CC
GND
MAX1640
TERM
LDOL
QSOP
________________________________________________________________
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 408-737-7600 ext. 3468.
Adjustable-Output, Switch-Mode
Current Source with Synchronous Rectifier
MAX1640/MAX1641
ABSOLUTE MAXIMUM RATINGS
IN to GND ...............................................................-0.3V to +28V
LDOH to IN ...............................................................+0.3V to -6V
LDOL to GND ...........................................................-0.3V to +6V
PDRV to GND .............................. (V
LDOH
- 0.3V) to (V
IN
+ 0.3V)
NDRV to GND .........................................-0.3V to (V
LDOL
+ 0.3V)
TOFF, REF, SET, TERM, CC to GND ......-0.3V to (V
LDOL
+ 0.3V)
D0, D1 to GND .........................................................-0.3V to +6V
CS+, CS- to GND ...................................................-0.3V to +28V
PGND to GND.....................................................................±0.3V
Continuous Power Dissipation (T
A
= +70°C)
QSOP (derate 8.30mW/°C above +70°C) ................... 667mW
Operating Temperature Range
MAX164_EEE ...................................................-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
= +12V, V
OUT
= 6V, Circuit of Figure 2, T
A
= 0°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Input Voltage Range
Linear-Regulator Output
Voltage, V
IN
Referenced
Linear-Regulator Output
Voltage, Ground Referenced
Full-Scale Current-Sense
Threshold
Quarter-Scale Current-Sense
Threshold
Current-Sense Line Regulation
Output Current Compliance
SYMBOL
V
IN
V
LDOH
V
LDOL
V
IN
= 5.5V to 26V, I
LOAD
= 0 to 20mA
V
IN
= 5.5V to 26V, I
LOAD
= 0 to 20mA
MAX1640
MAX1641
MAX1640
MAX1641
V
IN
= V
OUT
+ 0.5V to 26V
V
OUT
= 2V to 24V
D0 or D1 = high
D0 = D1 = low (off mode)
D0 = D1 = low
4.05
V
REF
I
REF
= 0 to 50µA
PFET and NFET drive
1
R
TOFF
= 62kΩ
D0 = low, D1 = high, R
TOFF
= 100kΩ
D0 = low, D1 = high, R
TOFF
= 100kΩ
1.7
27
2.2
33
12.5
1.96
4.20
2.00
4
MAX1640
MAX1641
CONDITIONS
MIN
5.5
V
IN
-
5.5
4.5
142
147
36
34
V
IN
-
5.0
5.0
150
150
42
37.5
0.03
0.1
0.1
2
500
1
4.35
2.04
10
1
12
10
2.7
40
4
0.4
TYP
MAX
26
V
IN
-
4.5
5.5
158
153
48
41
UNITS
V
V
V
mV
mV
%/V
%/V
mA
µA
µA
V
V
mV
µA
Ω
µs
µs
ms
%
Quiescent V
IN
Supply Current
Output Current in Off Mode
V
LDOL
Undervoltage Lockout
Reference Voltage
Reference Load Regulation
V
SET
Input Current
FET Drive Output Resistance
Off-Time Range
Off-Time Accuracy
Pulse-Trickle Mode Duty-Cycle
Period
Pulse-Trickle Mode Duty Cycle
(Note 1)
Note 1:
This ratio is generated by a 1:8 clock divider and is not an error source for current calculations.
2
_______________________________________________________________________________________
Adjustable-Output, Switch-Mode
Current Source with Synchronous Rectifier
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= +12V, V
OUT
= 6V, Circuit of Figure 2, T
A
= 0°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
PWM Maximum Duty Cycle
Input Low Voltage
Input High Voltage
Input Leakage Current
SYMBOL
V
IL
V
IH
I
IN
D0, D1
D0, D1
D0, D1
CONDITIONS
MIN
100
0.8
2.4
±
1
MAX1640/MAX1641
TYP
MAX
UNITS
%
V
V
µA
ELECTRICAL CHARACTERISTICS
(V
IN
= +12V, V
OUT
= 6V, Circuit of Figure 2, T
A
= -40°C to +85°C, unless otherwise noted.)
PARAMETER
Input Voltage Range
Linear-Regulator Output
Voltage, V
IN
Referenced
Linear-Regulator Output
Voltage, Ground Referenced
Full-Scale Current-Sense
Threshold
Quarter-Scale Current-Sense
Threshold
Output Current Compliance
Quiescent V
IN
Supply Current
Output Current in Off Mode
V
LDOL
Undervoltage Lockout
Reference Voltage
Reference Load Regulation
V
SET
Input Current
FET Drive Output Resistance
Off-Time Range
Off-Time Accuracy
Pulse-Trickle Mode Duty-Cycle
Period
PWM Maximum Duty Cycle
Input Low Voltage
Input High Voltage
Input Leakage Current
V
IL
V
IH
I
IN
D0, D1
D0, D1
D0, D1
2.4
±
1
SYMBOL
V
IN
V
LDOH
V
LDOL
CONDITIONS
MIN
5.5
TYP
MAX
26
V
IN
-
4.5
5.5
159
154
48
42
0.4
4
1
UNITS
V
V
V
mV
V
IN
= 5.5V to 26V,
I
LOAD
= 0 to 20mA
V
IN
= 5.5V to 26V,
I
LOAD
= 0 to 20mA
MAX1640
MAX1641
MAX1640
MAX1641
V
OUT
= 2V to 24V (MAX1640)
D0 or D1 = high
D0 = D1 = low
V
IN
-
5.5
4.5
141
146
34
33
mV
%/V
mA
µA
V
V
mV
µA
Ω
µs
µs
ms
%
4.0
V
REF
I
REF
= 0 to 50µA
1.94
4.4
2.06
10
1
12
1.5
R
TOFF
= 62kΩ
D0 = low, D1 = high, R
TOFF
= 50kΩ
1.5
25
100
8
2.5
42
0.8
V
V
µA
_______________________________________________________________________________________
3
Adjustable-Output, Switch-Mode
Current Source with Synchronous Rectifier
MAX1640/MAX1641
__________________________________________Typical Operating Characteristics
(Circuit of Figure 2, T
A
= +25°C, unless otherwise noted.)
MAX1640
OUTPUT CURRENT vs. INPUT VOLTAGE
MAX1640/41-TOC01
EFFICIENCY vs. OUTPUT VOLTAGE
100
90
EFFICIENCY (%)
80
70
60
50
40
2
4
6
8 10 12 14 16 18 20 22 24
OUTPUT VOLTAGE (V)
V
IN
= 12V
V
IN
= 18V
V
IN
= 26V
1.510
MAX1640
OUTPUT CURRENT vs. OUTPUT VOLTAGE
MAX1640/41 TOC02
MAX1640/41-TOC03
1.510
1.500
OUTPUT CURRENT (A)
1.490
1.480
1.470
1.460
1.450
T
A
= +25°C
T
A
= -40°C
T
A
= +85°C
(V
OUT
= 4V)
1.500
OUTPUT CURRENT (A)
T
A
= -40°C
1.490
T
A
= +85°C
T
A
= +25°C
1.470
1.480
1.460
4
8
12
16
20
24
28
INPUT VOLTAGE (V)
2
4
6
8 10 12 14 16 18 20 22 24
OUTPUT VOLTAGE (V)
MAX1641
OUTPUT CURRENT vs. INPUT VOLTAGE
MAX1640/41 TOC04
MAX1641
OUTPUT CURRENT vs. OUTPUT VOLTAGE
MAX1640/41-TOC05
QUIESCENT CURRENT
vs. INPUT VOLTAGE (NO-LOAD)
2.7
QUIESCENT CURRENT (mA)
2.5
2.3
2.1
1.9
1.7
1.5
T
A
= -40°C
T
A
= +25°C
T
A
= +85°C
MAX1640/41-TOC06
1.550
(V
OUT
= 4V)
OUTPUT CURRENT (A)
1.525
T
A
= -40°C
T
A
= +25°C
1.500
T
A
= +85°C
1.475
1.560
1.540
OUTPUT CURRENT (A)
1.520
T
A
= -40°C
1.500
1.480
T
A
= +85°C
1.460
1.440
T
A
= +25°C
2.9
1.450
4
8
12
16
20
24
28
INPUT VOLTAGE (V)
1.420
2
4
6
8 10 12 14 16 18 20 22 24
V
OUT
(V)
4
8
12
16
20
24
28
INPUT VOLTAGE (V)
OFF-MODE SUPPLY CURRENT
(NO-LOAD)
0.63
OFF-MODE SUPPLY CURRENT (mA)
0.61
0.59
0.57
0.55
0.53
0.51
0.49
0.47
0.45
4
8
12
16
20
24
28
INPUT VOLTAGE (V)
1
0
T
A
= +25°C
T
A
= -40°C
T
A
= +85°C
MAX1640/41-TOC07
SWITCHING FREQUENCY vs. R
TOFF
MAX1640/41 TOC 08
LINE-TRANSIENT RESPONSE
MAX1640/41 TOC 09
0.65
10,000
SWITCHING FREQUENCY (kHz)
1000
V
OUT
= +3V
A
0A
100
V
OUT
= +6V
10
B
0V
50
100 150 200 250
T
OFF
(kΩ)
300 350 400
V
LOAD
= 3V
2ms/div
A: OUTPUT CURRENT, D1 = D0 = 1 1A/div
B: INPUT VOLTAGE, 10V/div
4
_______________________________________________________________________________________
Adjustable-Output, Switch-Mode
Current Source with Synchronous Rectifier
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2, T
A
= +25°C, unless otherwise noted.)
CURRENT-MODE CHANGE RESPONSE TIME
MAX1640/41 TOC 10
MAX1640/MAX1641
EXITING OFF MODE
MAX1640/41 TOC11
A
0A
A
0V
B
2ms/div
V
IN
= 12V, V
SET
= 1V, R
LOAD
= 4Ω, NO OUTPUT CAPACITOR
A: OUTPUT CURRENT, D0 = D1 = 0 1A/div
B: LOAD VOLTAGE, AC coupled, 500mV/div
V
IN
= 12V, R
LOAD
= 4Ω
A: D0 = D1 = 1 2V/div
B: OUTPUT CURRENT, 0.5A/div
B
20µs/div
______________________________________________________________Pin Description
PIN
1
NAME
LDOL
FUNCTION
Internal, Ground-Referenced Low-Dropout Linear Regulator Output.
Bypass with a 0.1µF capacitor in parallel with a 4.7µF capacitor to GND.
Off-Time Select Input. A resistor (R
TOFF
) connected from this pin to GND programs the off-time for the hys-
teretic PWM step-down converter. This resistor also sets the period in duty-cycle mode. See
Duty-Cycle
Mode and Programming the Off-Time.
Digital Inputs. Select mode of operation (Table 1).
Constant-Current Loop Compensation Input. Bypass with a 0.01µF capacitor to GND.
Reference Voltage Output (V
REF
= 2V). Bypass with a 0.1µF capacitor to GND.
Current Select Input. Program the desired current level by applying a voltage at SET between 0V and V
REF
,
(I = V
SET
/ 13.3R
SENSE
). See Figure 3.
Maximum Output Voltage Termination Input. When V
TERM
exceeds the reference voltage, the comparator
resets the internal PWM latch, shutting off the external P-channel FET.
Ground
Negative Current-Sense Comparator Input
Positive Current-Sense Comparator Input
High-Current Ground Return for the output drivers
Gate Drive for an optional N-channel FET synchronous rectifier
Gate Drive for the P-channel FET
Internal, Input-Referenced Low-Dropout Linear Regulator Output.
Bypass with a 0.33µF capacitor to IN.
Power-Supply Input. Input of the internal, low-dropout linear regulators.
_______________________________________________________________________________________
5
2
3, 4
5
6
7
8
9
10
11
12
13
14
15
16
TOFF
D1, D0
CC
REF
SET
TERM
GND
CS-
CS+
PGND
NDRV
PDRV
LDOH
IN

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