Final Electrical Specifications
LT1571 Series
Constant-Current/
Constant-Voltage Battery Charger
with Preset Voltage and Termination Flag
April 2000
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
Fast Charging of Li-Ion, NiMH and NiCd Batteries
Simple Charge Current Programming Requires Only
One Low Cost, 1/32W Resistor
High Efficiency Charger with Up to
1.5A Charge Current
Precision 0.6% Internal Voltage Reference
Preset Battery Voltages: 4.1V, 4.2V, 8.2V, 8.4V
500kHz or 200kHz Switching Frequency
Minimizes Charger Size
Low Reverse Battery Drain Current: 5µA
Flag Indicates Li-Ion Charge Completion
5% Typical Charge Current Accuracy
Low Shutdown Current
LT1571-5: 500kHz, Fixed 4.1V or 4.2V
LT1571-1: 200kHz, Adjustable Voltage
LT1571-2: 200kHz, Fixed 8.2V or 8.4V
The LT
®
1571 PWM battery charger is a simple, efficient
solution to fast-charge rechargeable batteries including
lithium-ion (Li-Ion), nickel-metal-hydride (NiMH) and
nickel-cadmium (NiCd) using constant-current and/or
constant-voltage control. The internal switch is capable
of delivering 1.5A DC current (2A peak current). The
onboard current sense resistor (0.1Ω) allows simple
charge current programming to within 5% accuracy
using a low cost external resistor. The constant-voltage
output can be selected for 4.1V or 4.2V per cell with 0.6%
accuracy.
LT1571 can charge batteries ranging from 1V to 20V. A
saturating switch operating at 200kHz (LT1571-1,
LT1571-2) or 500kHz (LT1571-5) gives high efficiency
and small charger size. A logic output (flag) indicates
Li-Ion near full charge when the charge current drops to
20% of the programmed value. The LT1571-1 and
LT1571-2 are in a 28-pin fused lead narrow SSOP power
package. The LT1571-5 is in a 16-pin fused lead narrow
SSOP power package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
s
s
Cellular Phones, PDAs, Notebook Computers,
Portable Instruments
Cradle Chargers for Li-Ion, NiCd, NiMH and
Lead-Acid Rechargeable Batteries
TYPICAL APPLICATIO
V
IN
8.2V
TO 20V
D3
MBRM120T3
V
CC
C
IN
*
10µF
V
DD
1µF
100k
6.19k
300Ω
1k
0.33µF
V
C
FLAG
BAT
C
OUT
***
22µF
BAT2
SENSE
CAP
SELECT
GND
LT1571-5
PROG
BOOST
SW
D1
MBRM120T3
C1
0.22µF
L1**
10µH
D2
MMBD914L
CHARGE
COMPLETE
4.2V
Li-Ion
BATTERY
+
+
*TOKIN OR MARCON CERAMIC SURFACE MOUNT
**COILTRONICS TP3-100, 10µH, 2.2mm HEIGHT (0.8A CHARGING CURRENT)
COILTRONICS TP1 SERIES, 10µH, 1.8mm HEIGHT (<0.5A CHARGING CURRENT)
***PANASONIC EEFCD1B220
Figure 1. Compact Li-Ion Cellular Phone Charger (0.8A)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
0.1µF
1571 F01
U
U
1
LT1571 Series
ABSOLUTE
AXI U
RATI GS
Supply Voltage (V
CC
) .............................................. 28V
BOOST Pin Voltage with Respect to V
CC
................. 20V
FLAG Pin Voltage ..................................................... V
CC
I
BAT
(Average)........................................................ 1.5A
Switch Current (Peak) .............................................. 2A
Storage Temperature Range ................. – 65°C to 150°C
PACKAGE/ORDER I FOR ATIO
**GND
**GND
TOP VIEW
**GND 1
SW 2
BOOST 3
BAT2 4
FLAG 5
SELECT 6
SENSE 7
**GND 8
16 GND**
15 V
CC1
*
14 V
CC2
*
13 CAP
12 PROG
11 V
C
10 BAT
9 GND**
1
2
3
4
5
6
7
8
9
**GND
SW
BOOST
NC
FLAG
NC
V
FB
SENSE 10
**GND 11
**GND 12
**GND 13
**GND 14
GN PACKAGE
16-LEAD NARROW PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 75°C/ W
* V
CC1
AND V
CC2
SHOULD BE CONNECTED
TOGETHER CLOSE TO THE PINS
** FOUR CORNER PINS ARE FUSED TO
INTERNAL DIE ATTACH PADDLE FOR
HEAT SINKING. CONNECT THESE FOUR
PINS TO EXPANDED PC LANDS FOR
PROPER HEAT SINKING
GN PACKAGE
28-LEAD NARROW PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 40°C/ W
* V
CC1
AND V
CC2
SHOULD BE CONNECTED TOGETHER
CLOSE TO THE PINS
** ALL GND PINS ARE FUSED TO INTERNAL DIE ATTACH
PADDLE FOR HEAT SINKING. CONNECT THESE PINS TO
EXPANDED PC LANDS FOR PROPER HEAT SINKING
40°C/W THERMAL RESISTANCE ASSUMES AN INTERNAL
GROUND PLANE DOUBLING AS A HEAT SPREADER
ORDER PART NUMBER
LT1571EGN-5
Consult factory for Industrial and Military grade parts.
ORDER PART NUMBER
LT1571EGN-1
2
U
U
W
W W
U
W
(Note 1)
Operating Ambient
Temperature Range (Note 2) .................. – 40°C to 85°C
Operating Junction
Temperature Range .............................. – 40°C to 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
28 GND**
27 GND**
26 GND**
25 GND**
24 V
CC1
*
23 V
CC2
*
22 CAP
21 PROG
20 V
C
19 BAT
18 GND**
17 GND**
16 GND**
15 GND**
**GND
**GND
**GND
SW
BOOST
BAT2
FLAG
NC
SELECT
1
2
3
4
5
6
7
8
9
TOP VIEW
28 GND**
27 GND**
26 GND**
25 GND**
24 V
CC1
*
23 V
CC2
*
22 CAP
21 PROG
20 V
C
19 BAT
18 GND**
17 GND**
16 GND**
15 GND**
SENSE 10
**GND 11
**GND 12
**GND 13
**GND 14
GN PACKAGE
28-LEAD NARROW PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 40°C/ W
* V
CC1
AND V
CC2
SHOULD BE CONNECTED TOGETHER
CLOSE TO THE PINS
** ALL GND PINS ARE FUSED TO INTERNAL DIE ATTACH
PADDLE FOR HEAT SINKING. CONNECT THESE PINS TO
EXPANDED PC LANDS FOR PROPER HEAT SINKING
40°C/W THERMAL RESISTANCE ASSUMES AN INTERNAL
GROUND PLANE DOUBLING AS A HEAT SPREADER
ORDER PART NUMBER
LT1571EGN-2
LT1571 Series
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
V
CC
= 16V (LT1571-1, LT1571-2), V
CC
= 10V (LT1571-5), V
BAT
= 8V (LT1571-1,LT1571-2), V
BAT
= 4V (LT1571-5), maximum operating
V
CC
= V
MAX
= 26V, no load on any outputs unless otherwise noted. (Note 6)
PARAMETER
Overall
Supply Current
DC Battery Charging Current, I
BAT
V
PROG
= 2.7V
8V
≤
V
CC
≤
26V, 0V
≤
V
BAT
≤
20V (LT1571-1)
R
PROG
= 4.93k
R
PROG
= 4.93k, T
J
< 0°C
R
PROG
= 3.28k
R
PROG
= 49.3k
R
PROG
= 49.3k, T
J
< 0°C
V
CC
= 26V, V
BAT
= 20V (LT1571-1)
R
PROG
= 4.93k
Shutdown
Auto Shutdown, Reverse Current from Battery
(When Adapter in Figure 1 Circuit is Removed)
Shutdown Threshold at V
C
Pin
When V
CC
is Connected
Shutdown Supply Current
Reference
Reference Voltage (LT1571-1)
R
PROG
= 4.93k. Measured at V
FB
, with VA
Supplying I
PROG
and Switch Off
8V
≤
V
CC
≤
26V, 0°C
≤
T
J
≤
70°C
8V
≤
V
CC
≤
26V, 0°C
≤
T
J
≤
125°C
8V
≤
V
CC
≤
26V, T
J
< 0°C (Note 5)
R
PROG
= 4.93k. Measured at BAT2 Pin
T
J
= 25°C
8V
≤
V
CC
≤
26V, 0°C
≤
T
J
≤
125°C
Absolute Value, Not Matching
V
BAT2
= V
PRESET
– 1V
R
PROG
= 4.93k
R
PROG
= 4.93k, R
CAP
= 65.6k
Low-to-High Threshold
High-to-Low Threshold
V
CAP
= 4.5V, I
FLAG
≤
1mA
V
CAP
= 0.6V, V
CC
= 26V
Output Current from 100µA to 500µA
V
PROG
= V
REF
, V
FB
= V
REF
+ 10mV
At 0.75mA Output Current
Undervoltage Lockout
V
CC
– V
BOOST
≤
20V
20V < V
CC
– V
BOOST
≤
26V
2V
≤
V
BOOST
– V
CC
≤
8V (Switch ON)
8V < V
BOOST
– V
CC
≤
20V (Switch ON) (LT1571-1)
q
q
q
q
q
q
q
q
CONDITIONS
MIN
TYP
5.2
MAX
7
1.07
1.09
1.65
125
130
1.07
15
UNITS
mA
A
A
A
mA
mA
A
µA
mV
0.93
0.91
1.35
75
70
0.93
1.0
1.5
100
q
1.0
5
V
BAT
≤
20V, 0°C
≤
T
J
≤
70°C (LT1571-1)
q
40
V
C
≤
40mV
80
0.15
0.3
mA
q
q
q
2.446
2.441
2.430
2.465
2.465
2.465
2.480
2.489
2.480
V
V
V
Preset Battery Voltage
LT1571-2: 8.2V/8.4V
LT1571-5: 4.1V/4.2V
Voltage Setting Resistors Tolerance (R4, R5)
BAT2 Pin Input Current (LT1571-2, LT1571-5)
Charge Completion Flag (Comparator E6)
Charge Completion Threshold (Note 8)
Threshold on CAP Pin
FLAG (Open Collector) Output Low
FLAG Pin Leakage Current
Voltage Amplifier VA
Transconductance
Output Source Current
V
FB
Input Bias Current (LT1571-1)
Overall
Minimum Input Operating Voltage
Boost Pin Current
q
q
q
q
q
0.5
q
–1
–40
1
40
6
%
%
%
µA
A
A
V
V
V
µA
mho
mA
nA
V
µA
µA
mA
mA
0.14
0.05
0.6
0.20
0.085
4
0.28
0.13
4.5
0.3
3
0.3
1.3
0.6
±3
2.5
±15
7.8
20
30
11
14
6.2
7
0.10
0.25
6
8
3
LT1571 Series
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
V
CC
= 16V (LT1571-1, LT1571-2), V
CC
= 10V (LT1571-5), V
BAT
= 8V (LT1571-1,LT1571-2), V
BAT
= 4V (LT1571-5), maximum operating
V
CC
= V
MAX
= 26V, no load on any outputs unless otherwise noted. (Note 6)
PARAMETER
Switch
Switch ON Resistance
∆I
BOOST
/∆I
SW
During Switch ON
Switch OFF Leakage Current
Maximum V
BAT
with Switch ON
Minimum I
PROG
for Switch ON
Minimum I
PROG
for Switch OFF
Current Sense Amplifier Inputs (SENSE, BAT)
Sense Resistance (R
S1
)
Total Resistance from SENSE to BAT (Note 3)
BAT Bias Current (Note 4)
V
C
< 0.3V
V
C
> 0.6V
V
C
< 40mV
LT1571-1, LT1571-2
LT1571-5
All Conditions of V
CC
, Temperature,
LT1571-1, LT1571-2
LT1571-1, LT1571-2, T
J
< 0°C
LT1571-5
LT1571-5, T
J
< 0°C
LT1571-1, LT1571-2
LT1571-1, LT1571-2, T
A
= 25°C (Note 7)
LT1571-5
V
C
= 1V, I
VC
=
±1µA
q
q
q
q
q
q
q
q
q
CONDITIONS
I
SW
= 1.5A, V
BOOST
– V
SW
≥
2V
I
SW
= 1A, V
BOOST
– V
SW
< 2V (Unboosted)
V
BOOST
= (V
CC
+ 8V), I
SW
≤
1A
V
SW
= 0V, V
CC
≤
20V
V
SW
= 0V, 20V < V
CC
≤
26V
q
q
q
MIN
TYP
0.3
20
2
4
MAX
0.5
2.0
35
100
200
V
CC
– 2
27
UNITS
Ω
Ω
mA/A
µA
µA
V
µA
mA
1
1
4
2.4
0.08
0.2
– 200
700
0.12
0.25
– 375
1300
5
220
550
230
230
575
575
Ω
Ω
µA
µA
µA
kHz
kHz
kHz
kHz
kHz
kHz
%
%
%
Oscillator
Switching Frequency
Switching Frequency Tolerance
180
440
170
160
425
400
87
90
77
125
200
500
200
500
Maximum Duty Cycle
93
81
210
550
0.6
100
3
300
Current Amplifier (CA2)
Transconductance
Maximum V
C
for Switch OFF
I
VC
Current (Out of Pin)
V
C
≥
0.6V
0.2V < V
C
< 0.45V
V
C
< 40mV (Shutdown)
µmho
V
µA
mA
µA
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LT1571 is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the – 40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
Sense resistor R
S1
and package bond wires.
Note 4:
Current (≈ 700µA) flows into the pins during normal operation and
also when an external shutdown signal on the V
C
pin is greater than 0.3V.
Current decreases to
≈
200µA and flows out of the pins when external
shutdown holds the V
C
pin below 0.3V but above shutdown threshold.
Current drops to near zero when input voltage collapses. See External
Shutdown in Applications Information section.
Note 5:
A linear interpolation can be used for reference voltage
specification between 0°C and – 40°C.
Note 6:
Maximum allowable ambient temperature may be limited by power
dissipation. Parts may not necessarily be operated simultaneously at
maximum power dissipation and maximum ambient temperature.
Temperature rise calculations must be done as shown in the Applications
Information section to ensure that maximum junction temperature does
not exceed the 125°C limit. With high power dissipation, maximum
ambient temperature may be less than 70°C.
Note 7:
91% maximum duty cycle is guaranteed by design if V
BAT
or V
X
(see Figure 7 in Application Information) is kept between 3V and 5V.
Note 8:
See “Lithium-Ion Charging Completion” in the Applications
Information section.
4
LT1571 Series
PI FU CTIO S
GND:
Ground Pin.
SW:
NPN Power Switch Emitter. The Schottky catch diode
must be placed with very short lead length in close
proximity to SW pin and GND.
V
CC1,
V
CC2
:
Input Supply. For good bypass, a low ESR
capacitor of 10µF or higher is required, with the lead length
kept to a minimum. V
CC
should be between 8V and 26V
and at least 2V higher than V
BAT
for V
BAT
less than 10V, and
2.5V higher than V
BAT
for V
BAT
greater than 10V. Under-
voltage lockout starts and switching stops when V
CC
goes
below 7V (typical). Note that there is an internal parasitic
diode from SW pin to V
CC
pin. Do not force V
CC
below SW
by more than 0.7V with battery present. All V
CC
pins
should be shorted together close to the pins.
BOOST:
This pin is used to bootstrap and drive the NPN
switch to a low on-voltage for low power dissipation. V
BOOST
= V
CC
+ V
BAT
when switch is on. For less power dissipation
use V
BOOST
= 3V to 6V (see Applications Information).
SENSE:
Current Amplifier CA1 Input. Sensing can be at
either terminal of the battery. Note that current sense
resistor R
S1
(0.08Ω) is between SENSE and BAT pins.
BAT:
Current Amplifier CA1 Input.
BAT2 (LT1571-2, LT1571-5):
This pin is used to connect
the battery to the internal preset voltage setting resistor.
An internal switch disconnects the internal divider from
the battery when the device is in shutdown or when input
power is disconnected. This disconnect function
eliminates current drain due to the resistor divider. This
pin should be connected to the positive node of the
battery if the internal preset divider is used. Otherwise
this pin should be grounded. Maximum voltage on this
pin is 20V.
PROG:
This pin is for programming the charge current
and for system loop compensation. Charge current is
regulated to 2000× the current drawn from the PROG
pin. During normal operation, V
PROG
stays close to
2.465V. If it is shorted to GND, switching will stop. When
a microprocessor-controlled DAC is used to program
charge current, it must be capable of sinking current at a
compliance up to 2.465V.
V
C
:
This is the inner loop control signal of the current mode
PWM. Switching starts at 0.9V. In normal operation, a
higher V
C
corresponds to a higher charge current. A
capacitor of at least 0.1µF to GND filters out noise and
controls the rate of soft-start. To shut down switching, pull
this pin below 0.6V. Typical current out of this pin is 60µA.
When V
C
is pulled below 40mV, LT1571 supply current
drops to typical 150µA.
SELECT (LT1571-2, LT1571-5):
This pin is used to select
the preset battery voltage. For the LT1571-2, leave this pin
open for 8.2V and ground it for 8.4V. For the LT1571-5,
leave this pin open for 4.1V and ground it for 4.2V. For
other battery voltages, use the adjustable LT1571-1.
V
FB
(LT1571-1):
This is the input to the amplifier VA (see
Block Diagram) with a threshold of 2.465V. Typical input
current is about 3nA. When charging batteries, VA moni-
tors the battery voltage and reduces charging current
when battery voltage reaches the preset value. If it is not
used (constant-current only mode), the V
FB
pin should be
grounded.
CAP:
A 0.1µF capacitor from CAP to ground is needed to
filter the sampled charge current signal. This filtered
signal is used to set the FLAG pin when the charge current
drops to 20% of the programmed maximum charge cur-
rent. This threshold level can be set as low as 7.5% of the
programmed maximum charge current by adding a resis-
tor on the CAP pin.
FLAG:
This pin is an open-collector output that is used to
indicate end of charge. The FLAG pin is driven low when
the charge current drops below a certain percentage of the
programmed charge current as explained in the CAP pin
function. A pull-up resistor is required if this function is
used. This pin is capable of sinking at least 1mA. Maxi-
mum voltage on this pin is V
CC
.
U
U
U
5
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