LT1513/LT1513-2
SEPIC Constant- or
Programmable-Current/
Constant-Voltage Battery Charger
FEATURES
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DESCRIPTION
The LT
®
1513 is a 500kHz current mode switching regula-
tor specially configured to create a constant- or program-
mable-current/constant-voltage battery charger. In addition
to the usual voltage feedback node, it has a current sense
feedback circuit for accurately controlling output current
of a flyback or SEPIC (Single-Ended Primary Inductance
Converter) topology charger. These topologies allow the
current sense circuit to be ground referred and completely
separated from the battery itself, simplifying battery switch-
ing and system grounding problems. In addition, these
topologies allow charging even when the input voltage is
lower than the battery voltage. The LT1513 can also drive
a CCFL Royer converter with high efficiency in floating or
grounded mode.
Maximum switch current on the LT1513 is 3A. This allows
battery charging currents up to 2A for a single lithium-ion
cell. Accuracy of 1% in constant-voltage mode is perfect
for lithium battery applications. Charging current can be
easily programmed for all battery types.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Charger Input Voltage May Be Higher, Equal to or
Lower Than Battery Voltage
Charges Any Number of Cells Up to 20V
1% Voltage Accuracy for Rechargeable Lithium
Batteries
100mV Current Sense Voltage for High Efficiency
(LT1513)
0mV Current Sense Voltage for Easy Current
Programming (LT1513-2)
Battery Can Be Directly Grounded
500kHz Switching Frequency Minimizes
Inductor Size
Charging Current Easily Programmable or Shut Down
APPLICATIONS
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Charging of NiCd, NiMH, Lead-Acid or Lithium
Rechargeable Cells
Precision Current Limited Power Supply
Constant-Voltage/Constant-Current Supply
Transducer Excitation
Universal Input CCFL Driver
TYPICAL APPLICATION
WALL
ADAPTER
INPUT
•
L1A*
C2**
4.7µF
V
SW
5
L1B*
V
FB
V
C
TAB
1
R5
270Ω
C5
0.1µF
I
FB
3
2
R4
39Ω
C4
0.22µF
R3
0.08Ω
LT1513 • TA01
2.4
D1
†
1.25A
CURRENT (A)
R1
+
C3
22µF
25V
7
V
IN
LT1513
6
S/S
GND
4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0
5
CHARGE
SYNC
AND/OR
SHUTDOWN SHUTDOWN
•
R2
+
C1
22µF
25V
×
2
* L1A, L1B ARE TWO 10µH WINDINGS ON A
COMMON CORE: COILTRONICS CTX10-4
** CERAMIC MARCON THCR40EIE475Z OR TOKIN 1E475ZY5U-C304
†
MBRD340 OR MBRS340T3. MBRD340 HAS 5µA TYPICAL
LEAKAGE, MBRS340T3 50µA TYPICAL
Figure 1. SEPIC Charger with 1.25A Output Current
INDUCTOR = 10µH
ACTUAL PROGRAMMED CHARGING CURRENT WILL BE
INDEPENDENT OF INPUT VOLTAGE IF IT DOES NOT
EXCEED VALUES SHOWN
LT1513 • TA02
sn1513 1513fas
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Maximum Charging Current
SINGLE Li-Ion CELL
(4.1V)
DOUBLE Li-Ion
CELL (8.2V)
12V
16V
20V
BATTERY
VOLTAGE
10
20
15
INPUT VOLTAGE (V)
25
30
1
LT1513/LT1513-2
ABSOLUTE
AXI U
RATI GS
Operating Junction Temperature Range
LT1513C ............................................... 0°C to 125°C
LT1513I ............................................ – 40°C to 125°C
Short Circuit ......................................... 0°C to 150°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Supply Voltage ....................................................... 30V
Switch Voltage ........................................................ 40V
S/S Pin Voltage ....................................................... 30V
FB Pin Voltage (Transient, 10ms) .........................
±10V
V
FB
Pin Current .................................................... 10mA
I
FB
Pin Voltage (Transient, 10ms) .........................
±10V
PACKAGE/ORDER I FOR ATIO
FRONT VIEW
7
6
5
4
3
2
1
R PACKAGE
7-LEAD PLASTIC DD
T
JMAX
= 125°C,
θ
JA
= 30°C/ W
WITH PACKAGE SOLDERED TO 0.5INCH
2
COPPER
AREA OVER BACKSIDE GROUND PLANE OR INTERNAL
POWER PLANE,
θ
JA
CAN VARY FROM 20°C/W TO
> 40°C/W DEPENDING ON MOUNTING TECHNIQUE
TAB
IS
GND
V
IN
S/S
V
SW
GND
I
FB
FB
V
C
ORDER PART
NUMBER
FRONT VIEW
LT1513CR
LT1513-2CR
LT1513IR
LT1513-2IR
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
V
IN
= 5V, V
C
= 0.6V, V
FB
= V
REF
, I
FB
= 0V, V
SW
and S/S pins open, unless otherwise noted.
SYMBOL
V
REF
PARAMETER
FB Reference Voltage
FB Input Current
FB Reference Voltage Line Regulation
V
IREF
I
FB
Reference Voltage (LT1513)
I
FB
Input Current
I
FB
Reference Voltage Line Regulation
I
FBVOS
I
FB
Voltage Offset (LT1513-2) (Note 3)
I
FB
Input Current
V
FB
Source Current
g
m
Error Amplifier Transconductance
Error Amplifier Source Current
Error Amplifier Sink Current
CONDITIONS
Measured at FB Pin
V
C
= 0.8V
V
FB
= V
REF
q
q
2.7V
≤
V
IN
≤
25V, V
C
= 0.8V
Measured at I
FB
Pin
V
FB
= 0V, V
C
= 0.8V
V
IFB
= V
IREF
(Note 2)
2.7V
≤
V
IN
≤
25V, V
C
= 0.8V
I
VFB
= 60µA (Note 4)
V
IFB
= V
IREF
V
IREF
= – 10mV, V
FB
= 1.2V
∆I
C
=
±25µA
V
FB
= V
REF
– 150mV, V
C
= 1.5V
V
FB
= V
REF
+ 150mV, V
C
= 1.5V
2
U
U
W
W W
U
W
ORDER PART
NUMBER
7
6
5
4
3
2
1
T7 PACKAGE
7-LEAD TO-220
T
JMAX
= 125°C,
θ
JA
= 50°C/ W,
θ
JC
= 4°C/W
V
IN
S/S
V
SW
GND
I
FB
FB
V
C
LT1513-2CT7
LT1513-2IT7
MIN
1.233
1.228
TYP
1.245
1.245
300
MAX
1.257
1.262
550
600
0.03
– 93
– 90
35
0.05
12.5
0
– 100
1900
2300
350
2400
UNITS
V
V
nA
nA
%/V
mV
mV
µA
%/V
mV
nA
µA
µmho
µmho
µA
µA
q
q
q
q
q
q
q
q
q
q
0.01
– 107
–110
10
– 7.5
– 200
– 700
1100
700
120
– 100
– 100
25
0.01
2.5
– 10
– 300
1500
200
1400
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LT1513/LT1513-2
ELECTRICAL CHARACTERISTICS
V
IN
= 5V, V
C
= 0.6V, V
FB
= V
REF
, I
FB
= 0V, V
SW
and S/S pins open, unless otherwise noted.
SYMBOL
PARAMETER
Error Amplifier Clamp Voltage
A
V
f
Error Amplifier Voltage Gain
V
C
Pin Threshold
Switching Frequency
Duty Cycle = 0%
2.7V
≤
V
IN
≤
25V
0°C
≤
T
J
≤
125°C
T
J
< 0°C
q
CONDITIONS
High Clamp, V
FB
= 1V
Low Clamp, V
FB
= 1.5V
MIN
1.70
0.25
0.8
450
430
400
85
40
35
q
q
q
TYP
1.95
0.40
500
1
500
500
95
130
MAX
2.30
0.52
1.25
550
580
580
260
UNITS
V
V
V/ V
V
kHz
kHz
kHz
%
ns
V
V
Maximum Switch Duty Cycle
Switch Current Limit Blanking Time
BV
Output Switch Breakdown Voltage
0°C
≤
T
J
≤
125°C
T
J
< 0°C
I
SW
= 2A
Duty Cycle = 50%
Duty Cycle = 80% (Note 1)
47
V
SAT
I
LIM
Output Switch ON Resistance
Switch Current Limit
0.25
3.0
2.6
3.8
3.4
15
4
0.45
5.4
5.0
25
Ω
A
A
mA/A
A/V
∆I
IN
/∆I
SW
Supply Current Increase During Switch ON Time
Control Voltage to Switch Current
Transconductance
Minimum Input Voltage
I
Q
Supply Current
Shutdown Supply Current
Shutdown Threshold
Shutdown Delay
S/S Pin Input Current
Synchronization Frequency Range
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
For duty cycles (DC) between 50% and 85%, minimum
guaranteed switch current is given by I
LIM
= 1.33 (2.75 – DC).
0V
≤
V
S/S
≤
5V
2.7V
≤
V
IN
≤
25V
2.7V
≤
V
IN
≤
25V, V
S/S
≤
0.6V, T
J
≥
0°C
T
J
< 0°C
2.7V
≤
V
IN
≤
25V
q
q
q
q
q
q
q
2.4
4
12
0.6
5
– 10
600
1.3
12
2.7
5.5
30
50
2
25
15
800
V
mA
µA
µA
V
µs
µA
kHz
Note 2:
The I
FB
pin is servoed to its regulating state with V
C
= 0.8V.
Note 3:
Consult factory for grade selected parts.
Note 4:
The I
FB
pin is sevoed to regulate FB to 1.245V
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LT1513/LT1513-2
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Saturation Voltage
vs Switch Current
1.0
6
150°C
100°C
25°C
SWITCH CURRENT LIMIT (A)
SWITCH SATURATION VOLTAGE (V)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
INPUT VOLTAGE (V)
–55°C
0
0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0
SWITCH CURRENT (A)
LT1513 • G01
Negative Feedback Input Current
vs Temperature
0
NEGATIVE FEEDBACK INPUT CURRENT (µA)
–10
BATTERY VOLTAGE (V)
–20
–30
–40
–50
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1513 • G06
Minimum Peak-to-Peak
Synchronization Voltage vs Temperature
MINIMUM SYNCHRONIZATION VOLTAGE (V
P-P
)
3.0
2.5
2.0
1.5
1.0
0.5
0
–50 –25
f
SYNC
= 700kHz
FEEDBACK INPUT CURRENT (nA)
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1513 • G04
4
U W
Switch Current Limit
vs Duty Cycle
3.0
2.8
Minimum Input Voltage
vs Temperature
5
4
–55°C
3
2
1
0
0
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
LT1513 • G02
25°C AND
125°C
2.6
2.4
2.2
2.0
1.8
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1513 • G03
Output Charging Characteristics
Showing Constant-Current and
Constant-Voltage Operation
12
MAXIMUM AVAILABLE
CHARGING CURRENT
10
WITH 12V INPUT
8
(A)
6
4
(C)
2
0
(B)
V
IN
= 12V
(A) 8.4V BATTERY
I
CHRG
= 0.5A
(B) 8.4V BATTERY
I
CHRG
= 1A
(C) 4.2V BATTERY
I
CHRG
= 1.5A
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
CHARGING CURRENT (A)
1513 G07
Feedback Input Current
vs Temperature
800
700
600
500
400
300
200
100
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1513 • G05
V
FB
= V
REF
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LT1513/LT1513-2
PIN FUNCTIONS
V
C
(Pin 1):
The compensation pin is primarily used for
frequency compensation, but it can also be used for soft
starting and current limiting. It is the output of the error
amplifier and the input of the current comparator. Peak
switch current increases from 0A to 3.6A as the V
C
voltage
varies from 1V to 1.9V. Current out of the V
C
pin is about
200µA when the pin is externally clamped below the
internal 1.9V clamp level. Loop frequency compensation
is performed with a capacitor or series RC network from
the V
C
pin
directly to the ground pin
(avoid ground loops).
FB (Pin 2):
The feedback pin is used for positive output
voltage sensing. The R1/R2 voltage divider connected to
FB defines Li-Ion float voltage at full charge, or acts as a
voltage limiter for NiCd or NiMH applications. FB is the
inverting input to the voltage error amplifier. Input bias
current is typically 300nA, so divider current is normally
set to 100µA to swamp out any output voltage errors due
to bias current. The noninverting input of this amplifier is
tied internally to a 1.245V reference. The grounded end of
the output voltage divider should be connected directly to
the LT1513 ground pin (avoid ground loops).
I
FB
(Pin 3):
The current feedback pin is used to sense
charging current. It is the input to a current sense amplifier
that controls charging current when the battery voltage is
below a programmed limit. During constant-current
operation, the LT1513 I
FB
pin regulates at – 100mV. Input
resistance of this pin is 5kΩ, so filter resistance (R4,
Figure 1) should be less than 50Ω. The 39Ω, 0.22µF filter
shown in Figure 1 is used to convert the pulsating current
in the sense resistor to a smooth DC current feedback
signal. The LT1513-2 I
FB
pin regulates at 0mV to provide
programmable current limit. The current through R5,
Figure 5, is balanced by the current through R4, program-
ming the maximum voltage across R3.
GND (Pin 4):
The ground pin is common to both control
circuitry and switch current. V
C
, FB and S/S signals must
be Kelvin and connected as close as possible to this pin.
The TAB of the R package should also be connected to the
power ground.
V
SW
(Pin 5):
The switch pin is the collector of the power
switch, carrying up to 3A of current with fast rise and fall
times. Keep the traces on this pin as short as possible to
minimize radiation and voltage spikes. In particular, the
path in Figure 1 which includes SW to C2, D1, C1 and
around to the LT1513 ground pin should be as short as
possible to minimize voltage spikes at switch turn-off.
S/S (Pin 6):
This pin can be used for shutdown and/or
synchronization. It is logic level compatible, but can be
tied to V
IN
if desired. It defaults to a high ON state when
floated. A logic low state will shut down the charger to a
micropower state. Driving the S/S pin with a continuous
logic signal of 600kHz to 800kHz will synchronize switch-
ing frequency to the external signal. Shutdown is avoided
in this mode with an internal timer.
V
IN
(Pin 7):
The input supply pin should be bypassed with
a low ESR capacitor located right next to the IC chip. The
grounded end of the capacitor must be connected directly
to the ground plane to which the TAB is connected.
TAB:
The TAB on the surface mount R package is electri-
cally connected to the ground pin, but a low inductance
connection must be made to both the TAB and the pin for
proper circuit operation. See suggested PC layout in
Figure 4.
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