MAX1640D [MAXIM]
Adjustable-Output, Switch-Mode Current Sources with Synchronous Rectifier; 可调输出，开关模式电流源，内置同步整流器
| 型号： | MAX1640D |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Adjustable-Output, Switch-Mode Current Sources with Synchronous Rectifier |
| 文件： | 总11页 (文件大小：119K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1245; Rev 0; 7/97
Ad ju s t a b le -Ou t p u t , S w it c h -Mo d e
Cu rre n t S o u rc e s w it h S yn c h ro n o u s Re c t ifie r
0/MAX641
_______________Ge n e ra l De s c rip t io n
____________________________Fe a t u re s
♦ 95% Efficiency
The MAX1640/MAX1641 CMOS, a d jus ta b le -outp ut,
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 g round , e limina ting g round -p ote ntia l e rrors . The
MAX1641 incorporates a low-side current sense.
♦ +5.5V to +26V Input Supply Range
♦ 2V to 24V Adjustable-Output Voltage Range
♦ 100% Maximum Duty Cycle (Low Dropout)
♦ Up to 500kHz PWM Operation
♦ Optional Synchronous Rectifier
♦ 16-Pin QSOP Package
♦ Current-Sense Accuracy: 2% (MAX1641)
The MAX1640/MAX1641 step-down pulse-width-modu-
la tion (PWM) c ontrolle rs use a n e xte rna l P-c ha nne l
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.
5.3% (MAX1640)
______________Ord e rin g In fo rm a t io n
PART
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
Dice*
The MAX1640/MAX1641 are available in space-saving,
16-pin narrow QSOP packages.
MAX1640C/D
MAX1640EEE
MAX1641C/D
MAX1641EEE
-40°C to +85°C
0°C to +70°C
16 QSOP
Dice*
________________________Ap p lic a t io n s
-40°C to +85°C
16 QSOP
Battery-Powered Equipment
Laptop, Notebook, and Palmtop Computers
Handy Terminals
*Dice are specified at T = +25°C, DC parameters only.
A
Portable Consumer Products
Cordless Phones
__________Typ ic a l Op e ra t in g Circ u it
Cellular Phones
V
IN
= +5.5V TO +26V
PCS Phones
IN
LDOH
PDRV
Backup Battery Charger
D0
D1
P
__________________P in Co n fig u ra t io n
TOFF
REF
NDRV
PGND
CS+
R
TOFF
TOP VIEW
LDOL
TOFF
D1
1
2
3
4
5
6
7
8
16 IN
15 LDOH
14 PDRV
13 NDRV
12 PGND
11 CS+
10 CS-
SET
OUT
CS-
D0
MAX1640
MAX1641
CC
MAX1640
TERM
REF
SET
TERM
CC
GND
LDOL
9
GND
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.
Ad ju s t a b le -Ou t p u t , S w it c h -Mo d e
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ABSOLUTE MAXIMUM RATINGS
IN to GND...............................................................-0.3V to +28V
LDOH to IN...............................................................+0.3V to -6V
LDOL to GND ...........................................................-0.3V to +6V
PGND to GND.....................................................................±0.3V
Continuous Power Dissipation (T = +70°C)
A
QSOP (derate 8.30mW/°C above +70°C)................... 667mW
Operating Temperature Range
PDRV to GND .............................. (V
- 0.3V) to (V + 0.3V)
IN
LDOH
NDRV to GND .........................................-0.3V to (V
TOFF, REF, SET, TERM, CC to GND ......-0.3V to (V
D0, D1 to GND .........................................................-0.3V to +6V
CS+, CS- to GND ...................................................-0.3V to +28V
+ 0.3V)
+ 0.3V)
MAX164_EEE...................................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10sec) ............................ +300°C
LDOL
LDOL
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 = +12V, V
= 6V, Circuit of Figure 2, T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.)
IN
OUT
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Input Voltage Range
V
IN
5.5
26
V
0/MAX641
Linear-Regulator Output
Voltage, V Referenced
IN
V
5.5
-
V
5.0
-
V
4.5
-
IN
IN
IN
V
V
= 5.5V to 26V, I
= 0 to 20mA
V
V
LDOH
IN
LOAD
Linear-Regulator Output
Voltage, Ground Referenced
V
LDOL
V
IN
= 5.5V to 26V, I
= 0 to 20mA
4.5
5.0
5.5
LOAD
MAX1640
MAX1641
MAX1640
MAX1641
142
147
36
150
150
42
158
153
48
Full-Scale Current-Sense
Threshold
mV
Quarter-Scale Current-Sense
Threshold
mV
%/V
%/V
34
37.5
0.03
0.1
0.1
2
41
Current-Sense Line Regulation
Output Current Compliance
V
IN
= V
+ 0.5V to 26V
OUT
MAX1640
MAX1641
0.4
4
V
OUT
= 2V to 24V
D0 or D1 = high
mA
µA
µA
V
Quiescent V Supply Current
IN
D0 = D1 = low (off mode)
D0 = D1 = low
500
Output Current in Off Mode
1
4.35
2.04
10
V
LDOL
Undervoltage Lockout
4.05
1.96
4.20
2.00
4
Reference Voltage
V
REF
V
Reference Load Regulation
I
= 0 to 50µA
mV
µA
Ω
REF
V
SET
Input Current
1
FET Drive Output Resistance
Off-Time Range
PFET and NFET drive
12
1
10
µs
Off-Time Accuracy
R
= 62kΩ
1.7
2.2
33
2.7
µs
TOFF
Pulse-Trickle Mode Duty-Cycle
Period
D0 = low, D1 = high, R
D0 = low, D1 = high, R
= 100kΩ
= 100kΩ
27
40
ms
%
TOFF
Pulse-Trickle Mode Duty Cycle
(Note 1)
12.5
TOFF
Note 1: This ratio is generated by a 1:8 clock divider and is not an error source for current calculations.
_______________________________________________________________________________________
2
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0/MAX641
ELECTRICAL CHARACTERISTICS (continued)
(V = +12V, V
= 6V, Circuit of Figure 2, T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.)
IN
OUT
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
PWM Maximum Duty Cycle
Input Low Voltage
100
%
V
V
D0, D1
D0, D1
D0, D1
0.8
±1
IL
Input High Voltage
V
IH
2.4
V
Input Leakage Current
I
IN
µA
ELECTRICAL CHARACTERISTICS
(V = +12V, V
= 6V, Circuit of Figure 2, T = -40°C to +85°C, unless otherwise noted.)
IN
OUT
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Input Voltage Range
V
IN
5.5
26
V
Linear-Regulator Output
Voltage, V Referenced
IN
V
= 5.5V to 26V,
= 0 to 20mA
V
5.5
-
V
4.5
-
IN
IN
IN
V
V
V
LDOH
I
LOAD
Linear-Regulator Output
Voltage, Ground Referenced
V
= 5.5V to 26V,
= 0 to 20mA
IN
V
LDOL
4.5
5.5
I
LOAD
MAX1640
MAX1641
MAX1640
MAX1641
141
146
34
159
154
48
Full-Scale Current-Sense
Threshold
mV
mV
Quarter-Scale Current-Sense
Threshold
33
42
0.4
4
Output Current Compliance
V
OUT
= 2V to 24V (MAX1640)
%/V
mA
Quiescent V Supply Current
IN
D0 or D1 = high
D0 = D1 = low
Output Current in Off Mode
1
4.4
2.06
10
1
µA
V
V
LDOL
Undervoltage Lockout
4.0
Reference Voltage
V
REF
1.94
V
Reference Load Regulation
I
= 0 to 50µA
mV
µA
Ω
REF
V
SET
Input Current
FET Drive Output Resistance
Off-Time Range
12
8
1.5
1.5
µs
Off-Time Accuracy
R
= 62kΩ
2.5
µs
TOFF
Pulse-Trickle Mode Duty-Cycle
Period
D0 = low, D1 = high, R
= 50kΩ
25
42
ms
TOFF
PWM Maximum Duty Cycle
Input Low Voltage
100
%
V
V
D0, D1
D0, D1
D0, D1
0.8
±1
IL
Input High Voltage
V
IH
2.4
V
Input Leakage Current
I
IN
µA
_______________________________________________________________________________________
3
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__________________________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s
(Circuit of Figure 2, T = +25°C, unless otherwise noted.)
A
MAX1640
MAX1640
OUTPUT CURRENT vs. OUTPUT VOLTAGE
EFFICIENCY vs. OUTPUT VOLTAGE
OUTPUT CURRENT vs. INPUT VOLTAGE
1.510
1.510
1.500
1.490
1.480
1.470
1.460
1.450
100
90
80
70
60
50
40
V
= 26V
IN
(V = 4V)
OUT
V
IN
= 18V
V
= 12V
IN
T = -40°C
A
T = -40°C
A
1.500
1.490
1.480
1.470
1.460
T = +85°C
A
T = +85°C
A
T = +25°C
A
T = +25°C
A
2
4
6
8
10 12 14 16 18 20 22 24
2
4
6
8 10 12 14 16 18 20 22 24
4
8
12
16
20
24
28
0/MAX641
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
MAX1641
OUTPUT CURRENT vs. INPUT VOLTAGE
MAX1641
QUIESCENT CURRENT
vs. INPUT VOLTAGE (NO-LOAD)
OUTPUT CURRENT vs. OUTPUT VOLTAGE
1.550
1.525
1.500
1.475
1.450
1.560
1.540
1.520
1.500
1.480
1.460
1.440
1.420
2.9
2.7
2.5
2.3
2.1
1.9
1.7
1.5
(V = 4V)
OUT
T = +85°C
A
T = -40°C
A
T = -40°C
A
T = +25°C
A
T = +25°C
A
T = +25°C
A
T = +85°C
A
T = +85°C
A
T = -40°C
A
4
8
12
16
20
24
28
2
4
6
8
10 12 14 16 18 20 22 24
4
8
12
16
20
24
28
INPUT VOLTAGE (V)
V
OUT
(V)
INPUT VOLTAGE (V)
OFF-MODE SUPPLY CURRENT
(NO-LOAD)
LINE-TRANSIENT RESPONSE
SWITCHING FREQUENCY vs. R
TOFF
10,000
1000
100
10
0.65
0.63
0.61
0.59
0.57
0.55
0.53
0.51
0.49
0.47
0.45
V
OUT
= +3V
A
T = +85°C
A
T = +25°C
A
0A
0V
V
OUT
= +6V
T = -40°C
A
B
1
0
50 100 150 200 250 300 350 400
(kΩ)
2ms/div
V
LOAD
= 3V
4
8
12
16
20
24
28
T
OFF
INPUT VOLTAGE (V)
A: OUTPUT CURRENT, D1 = D0 = 1 1A/div
B: INPUT VOLTAGE, 10V/div
4
_______________________________________________________________________________________
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0/MAX641
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(Circuit of Figure 2, T = +25°C, unless otherwise noted.)
A
CURRENT-MODE CHANGE RESPONSE TIME
EXITING OFF MODE
A
A
0A
0V
B
B
20µs/div
2ms/div
V = 12V, R
= 4Ω
IN
LOAD
V = 12V, V = 1V, R = 4Ω, NO OUTPUT CAPACITOR
LOAD
IN
SET
A: D0 = D1 = 1 2V/div
A: OUTPUT CURRENT, D0 = D1 = 0 1A/div
B: LOAD VOLTAGE, AC coupled, 500mV/div
B: OUTPUT CURRENT, 0.5A/div
______________________________________________________________P in De s c rip t io n
PIN
NAME
FUNCTION
Internal, Ground-Referenced Low-Dropout Linear Regulator Output.
Bypass with a 0.1µF capacitor in parallel with a 4.7µF capacitor to GND.
1
LDOL
Off-Time Select Input. A resistor (R ) connected from this pin to GND programs the off-time for the hys-
TOFF
2
TOFF
teretic PWM step-down converter. This resistor also sets the period in duty-cycle mode. See Duty-Cycle
Mode and Programming the Off-Time.
3, 4
5
D1, D0
CC
Digital Inputs. Select mode of operation (Table 1).
Constant-Current Loop Compensation Input. Bypass with a 0.01µF capacitor to GND.
6
REF
Reference Voltage Output (V
= 2V). Bypass with a 0.1µF capacitor to GND.
REF
Current Select Input. Program the desired current level by applying a voltage at SET between 0V and V
,
REF
7
8
SET
(I = V
/ 13.3R ). See Figure 3.
SENSE
SET
Maximum Output Voltage Termination Input. When V
exceeds the reference voltage, the comparator
TERM
TERM
resets the internal PWM latch, shutting off the external P-channel FET.
9
GND
CS-
Ground
10
11
12
13
14
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
CS+
PGND
NDRV
PDRV
Internal, Input-Referenced Low-Dropout Linear Regulator Output.
Bypass with a 0.33µF capacitor to IN.
15
16
LDOH
IN
Power-Supply Input. Input of the internal, low-dropout linear regulators.
_______________________________________________________________________________________
5
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IN
LDOL
LDOH
REG
0/MAX641
A1
A2
CS+
PDRV
Gm
CS-
MODE
CONTROL
B
SET
NDRV
PGND
MUX
REF
A
SEL
MAX1640
MAX1641
TERM
D0, D1
CC
TOFF
Figure 1. MAX1640/MAX1641 Functional Diagram
6
_______________________________________________________________________________________
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0/MAX641
0.33µF
0.33µF
47µF
47µF
1/2 IR7309
1/2 IR7309
IN
LDOH
PDRV
IN
LDOH
PDRV
LDOL
P
LDOL
P
0.1µF
4.7µF
4.7µF
0.1µF
MAX1641
MAX1640
D0
D1
D0
D1
R
TOFF
R
TOFF
TOFF
REF
1/2 IR7309
TOFF
REF
1/2 IR7309
47µH
NDRV
PGND
N
NDRV
PGND
N
V
OUT
47µH
BATT
100mΩ
R3
R4
R1
CS+
CS+
R1
SET
0.1µF
100mΩ
SET
0.1µF
R2
CS-
R2
CS-
V
OUT
R3
R4
TERM
BATT
CC
GND
TERM
0.01µF
CC
GND
0.01µF
Figure 2a. Standard Application Circuit
Figure 2b. Standard Application Circuit
part operates for 12.5% of the period set by R
,
TOFF
_______________De t a ile d De s c rip t io n
resulting in a lower current for pulse-trickle charging.
Figure 1 is the MAX1640/MAX1641 functional diagram.
Figure 2 shows the standard application circuits.
The MAX1640/MAX1641 switch-mode current sources
utilize a hysteretic, current-mode, step-down pulse-
width-modulation (PWM) topology with constant off-
time . Inte rna l c omp a ra tors c ontrol the s witc hing
mechanism. These comparators monitor the current
Ch a rg e Mo d e : P ro g ra m m in g t h e
Ou t p u t Cu rre n t s
through a sense resistor (R
) and the voltage at
SENSE
The sense resistor, R , sets two charging current
SENSE
TERM. When inductor current reaches the current limit
[(V - V ) / R ], the P-channel FET turns off
levels. Choose between these two levels by holding
D0 high, and toggling D1 either high or low (Table 1).
CS+
CS-
SENSE
and the N-channel FET synchronous rectifier turns on.
Inductor energy is delivered to the load as the current
The fast-charge current level equals V
/ R
CS
SENSE
where V
is the full-scale current-sense voltage of
CS
ramps down. This ramp rate depends on R
and
TOFF
150mV. Alternatively, calculate this current by V
/
/
REF
SET
inductor values. When off-time expires, the P-channel
FET turns back on and the N-channel FET turns off.
(13.3R
). The top -off c urre nt e q ua ls V
SENSE
(13.3R ). A resistor-divider from REF to GND pro-
SENSE
grams the voltage at SET (Figure 3).
Two digital inputs, D0 and D1, select between four pos-
sible current levels (Table 1). In pulse-trickle mode, the
_______________________________________________________________________________________
7
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The voltage at SET is given by:
R1 = R2 (V
/ V
-1 ); 10kΩ < R2 < 300kΩ
REF
SET
L
MAX1641
whe re V
= 2V a nd V
is p rop ortiona l to the
REF
SET
desired output current level.
BATT
Table 1. Selecting Output Current Levels
R3
R4
CS+
CS-
D1
DO
MODE
OUTPUT CURRENT (A)
R
SENSE
0
0
OFF
0
0
1
Top-Off
V
/ (13.3R
/ (13.3R
)
)
SET
SENSE
V
SET
SENSE
1
1
0
1
Pulse-Trickle
Fast Charge
12.5% duty cycle
TERM
V
SET
/ (13.3R
)
SENSE
Figure 4b. Setting the Maximum Output Voltage Level
The MAX1640/MAX1641 a re s p e c ifie d for V
0/MAX641
SET
between 0V and V . For V
> V , output current
REF
SET
REF
inc re a s e s line a rly (with re d uc e d a c c ura c y) until it
clamps at V ≈ 4V.
MAX1640
MAX1641
SET
REF
SET
P u ls e -Tric k le Mo d e : S e le c t in g t h e
P u ls e -Tric k le Cu rre n t
R1
R2
Pulling D0 low and D1 high selects pulse-trickle mode.
This current equals V / (13.3R ) and remains
SET
SENSE
on for 12.5% of the period set by R
. Pulse-trickle
TOFF
current maintains full charge across the battery and
can slowly charge a cold battery before fast charging
commences.
-7
PERIOD = 3.2 x 10 x R
(sec)
TOFF
Figure 3. Adjusting the Output Current Level
Off Mo d e : Tu rn in g Off t h e Ou t p u t Cu rre n t
Pulling D0 and D1 low turns off the P-channel FET and
hence the output current flow. This mode also controls
end of charge and protects the battery against exces-
sive temperatures.
L
MAX1640
CS+
R
S e t t in g t h e Ma x im u m Ou t p u t
Vo lt a g e Le ve l
The maximum output voltage should be programmed to
SENSE
CS-
BATT
a level higher than the output/battery voltage (I
x
LOAD
R3
R
). An external resistor-divider between the output
LOAD
TERM
and ground (Figure 4) sets the voltage at TERM. Once
the voltage at TERM exceeds the reference, the internal
comparator turns off the P-channel FET, terminating
current flow. Select R4 in the 10kΩ to 500kΩ range.
R3 is given by:
R4
Figure 4a. Setting the Maximum Output Voltage Level
R3 = R4 (V
/ V
) -1
OUT
TERM
8
_______________________________________________________________________________________
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0/MAX641
where V
voltage.
= 2V and V
is the desired output
generating increased ripple at the output. Select C
to optimize the ripple vs. loop response.
TERM
OUT
CC
P ro g ra m m in g t h e Off-Tim e
S yn c h ro n o u s Re c t ific a t io n
Synchronous rectification reduces conduction losses in
the rectifier by shunting the Schottky diode with a low-
resistance MOSFET switch. In turn, efficiency increases
by about 3% to 5% at heavy loads. To prevent cross-
conduction or “shoot-through,” the synchronous rectifier
turns on shortly after the P-channel power MOSFET
When programming the off-time, consider such factors
as maximum inductor current ripple, maximum output
voltage, inductor value, and inductor current rating. The
output current ripple is less than the inductor current rip-
ple and depends heavily on the output capacitor’s size.
Perform the following steps to program the off-time:
1) Select the maximum output current ripple. I (A)
R
Table 2. Component Manufacturers
2) Select the maximum output voltage. V (MAX)(V)
OUT
COMPONENT
MANUFACTURER
CDRH125 series
3) Calculate the inductor value range as follows:
= (V x 1µs) / I
Sumida
L
MIN
Inductor
Coilcraft
Coiltronics
International Rectifier
Siliconix
Dale
D03316P series
UP2 series
OUTMAX
R
L
MAX
= (V
x 10µs) / I
OUTMAX R
IRF7309
4) Select an inductor value in this range.
5) Calculate t as follows:
MOSFETs
S14539DY
OFF
WSL-2010 series
LR2010-01 series
TPS series
Sense Resistor
Capacitors
IRC
L x I
R
t
=
OFF
AVX
V
OUTMAX
Sprague
595D series
MBAR5340t3
IN5817-IN5822
NSQ03A04
6) Program t
by selecting R
from:
OFF
TOFF
Motorola
Nihon
Rectifier
R
= (29.3 x 109) x t
TOFF
OFF
7) Calculate the switching frequency by:
fs = 1 / (t + t
turns off. The synchronous rectifier remains off for 90%
of the off-time. In low-cost designs, the synchronous
rectifier FET may be replaced by a Schottky diode.
)
OFF
ON
where t
= (I x L) / (V - V
) and I = (V
IN
x
ON
R
IN
OUT
R
OUT
Co m p o n e n t S e le c t io n
t ) / L. L is the inductor value, V is the input volt-
OFF
External Switching Transistors
The MAX1640/MAX1641 drive an enhancement-mode
P-c ha nne l MOSFET a nd a s ync hronous -re c tifie r N-
channel MOSFET (Table 2).
age, V
is the output voltage, and I is the output
R
OUT
peak-to-peak current ripple.
Note that R
trickle charge period.
sets both the off-time and the pulse-
TOFF
When selecting a P-channel FET, some important para-
Re fe re n c e
meters to consider are on-resistance (r
), maxi-
DS(ON)
The on-chip reference is laser trimmed for a precise 2V
at REF. REF can source no more than 50µA. Bypass
REF with a 0.1µF capacitor to ground.
mum d ra in-to-s ourc e volta g e (V
ma x), ma ximum
DS
g a te -to-s ourc e volta g e (V
ma x), a nd minimum
GS
threshold voltage (V min).
TH
In high-current applications, MOSFET package power
dissipation often becomes a dominant design factor.
I R power losses are the greatest heat contributor for
both high-side and low-side MOSFETs. Switching loss-
es affect the upper MOSFET only (P-channel), since the
Schottky rectifier or the N-FET body diode clamps the
switching node before the synchronous rectifier turns on.
Co n s t a n t -Cu rre n t Lo o p : AC Lo o p
Co m p e n s a t io n
2
The constant-current loop’s output is brought out at CC.
To reduce noise due to variations in switching currents,
bypass CC with a 1nF to 100nF capacitor to ground. A
large capacitor value maintains a constant average out-
put current but slows the loop response to changes in
switching current. A small capacitor value speeds up
the loop response to changes in switching current,
Rectifier Diode
If an N-channel MOSFET synchronous rectifier is not
used, a Schottky rectifier is needed. The MAX1640/
_______________________________________________________________________________________
9
Ad ju s t a b le -Ou t p u t , S w it c h -Mo d e
Cu rre n t S o u rc e w it h S yn c h ro n o u s Re c t ifie r
DC IN
PDRV
P
MAX1640
I/0
I/0
D0
D1
NDRV
N
LOW-SIDE IS SHORTED
PGND
CS+
R
SENSE
CH0
CH1
CS-
0/MAX641
R3
R4
T
TERM
BATT
GND
Figure 5. Microcontroller Battery Charger
MAX1641’s high switching frequency demands a high-
speed rectifier (Table 2). Schottky diodes such as the
1N5817–1N5822 are recommended. Make sure the
Schottky diode’s average current rating exceeds the
p e a k c urre nt limit a nd tha t its b re a kd own volta g e
ind uc tor va lue , off-time , outp ut c urre nt rip p le , a nd
switching frequency.
__________Ap p lic a t io n s In fo rm a t io n
All-P u rp o s e Mic ro c o n t ro lle r Ba t t e ry
Ch a rg e r: NiCd , NiMH
exceeds the output voltage (V
). For high-tempera-
OUT
ture applications, Schottky diodes may be inadequate
due to their high leakage current; high-speed silicon
diodes such as the MUR105 or EC11FS1 can be used
instead. At heavy loads and high temperatures, the
benefits of a Schottky diode’s low forward voltage may
outweigh the disadvantage of high leakage current. If
the application uses an N-channel MOSFET synchro-
nous re c tifie r, a p a ra lle l Sc hottky d iod e is us ua lly
unnecessary except with very high charge current (> 3
a mp s ). Be s t e ffic ie nc y is a c hie ve d with b oth a n
N-channel MOSFET and a Schottky diode.
In applications where a microcontroller is available, the
MAX1640/MAX1641 can be used as a low-cost battery
c ha rg e r (Fig ure 5). The c ontrolle r ta ke s ove r fa s t
charge, pulse-trickle charge, charge termination, and
other smart functions. By monitoring the output voltage
at V
, the controller initiates fast charge (set D0 and
OUT
D1 high), terminates fast charge and initiates top-off
(set D0 high and D1 low), enters trickle charge (set D0
low and D1 high), or shuts off and terminates current
flow (set D0 and D1 low).
La yo u t a n d Gro u n d in g
Due to high current levels and fast switching wave-
forms, proper PC board layout is essential. High-cur-
re nt g round p a ths s hould b e c onne c te d in a s ta r
Inductor Value
Refer to the section Programming the Off-Time to select
the proper inductor value. There is a trade-off between
10 ______________________________________________________________________________________
Ad ju s t a b le -Ou t p u t , S w it c h -Mo d e
Cu rre n t S o u rc e w it h S yn c h ro n o u s Re c t ifie r
0/MAX641
configuration to PGND. These traces should be wide to
reduce resistance and as short as possible to reduce
___________________Ch ip In fo rm a t io n
stray inductance. All low-current ground paths should
TRANSISTOR COUNT: 1233
be connected to GND. Place the input bypass capaci-
tor as close as possible to the IN pin. See MAX1640 EV
kit for layout example.
________________________________________________________P a c k a g e In fo rm a t io n
______________________________________________________________________________________ 11
相关型号：
MAX1640EEE+T
Switching Controller, Current-mode, 0.02A, 500kHz Switching Freq-Max, CMOS, PDSO16, 0.150 INCH, 0.025 INCH PITCH, QSOP-16
MAXIM
MAX1640EEE-T
Switching Controller, Current-mode, 0.02A, 500kHz Switching Freq-Max, CMOS, PDSO16, 0.150 INCH, 0.025 INCH PITCH, QSOP-16
MAXIM
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