charger. These topologies allow the current sense circuit
to be ground referred and completely separated from the
battery itself, simplifying battery switching and system
grounding problems. In addition, these topologies allow
charging even when the input voltage is lower than the
battery voltage.
Maximum switch current on the LT1512 is 1.5A. This allows
battery charging currents up to 1A 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.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Charger Input Voltage May Be Higher, Equal to or
Lower Than Battery Voltage
Charges Any Number of Cells Up to 30V*
1% Voltage Accuracy for Rechargeable Lithium
Batteries
500kHz Switching Frequency Minimizes
Inductor Size
100mV Current Sense Voltage for High Efficiency
Battery Can Be Directly Grounded
Charging Current Easily Programmable or Shut Down
APPLICATIONS
n
n
n
n
Battery Charging of NiCd, NiMH, Lead-Acid or
Lithium Rechargeable Cells
Precision Current Limited Power Supply
Constant-Voltage/Constant-Current Supply
Transducer Excitation
*Maximum Input Voltage = 40V – V
BAT
TYPICAL APPLICATION
Maximum Charging Current
WALL
ADAPTER
INPUT
CHARGE
•
L1 A*
C2**
D1
2.2μF MBRS130LT3
V
SW
L1 B*
FB
GND GND S V
C
I
FB
C5
0.1μF
R5
1k
C4
0.22μF
R3
0.2Ω
R4
24Ω
•
R2
R1
0.5A
CURRENT (A)
1.0
SINGLE
LITHIUM
CELL (4.1V)
+
C3
22μF
25V
V
IN
LT1512
S/S
0.8
SYNC
AND/OR
SHUTDOWN
SHUTDOWN
0.6
+
C1
22μF
25V
DOUBLE
LITHIUM
CELL (8.2V)
6V BATTERY
12V BATTERY
INDUCTOR = 33μH
0.4
0.2
0
*L1 A, L1 B ARE TWO 33mH WINDINGS ON A
SINGLE INDUCTOR: COILTRONICS CTX33-3
**TOKIN CERAMIC 1E225ZY5U-C203-F
0
5
15
10
INPUT VOLTAGE (V)
20
25
1512 TA02
1512 F01
Figure 1. SEPIC Charger with 0.5A Output Current
ACTUAL PROGRAMMED CHARGING CURRENT WILL BE INDEPENDENT OF INPUT
VOLTAGE AND BATTERY VOLTAGE IF IT DOES NOT EXCEED THE VALUES SHOWN.
THESE ARE ELECTRICAL LIMITATIONS BASED ON MAXIMUM SWITCH CURRENT.
PACKAGE THERMAL LIMITATIONS MAY REDUCE MAXIMUM CHARGING CURRENT.
SEE APPLICATIONS INFORMATION.
1512fa
1
LT1512
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
V
C
1
FB 2
I
FB
3
S/S 4
N8 PACKAGE
8-LEAD PDIP
8
7
6
5
V
SW
GND
GND S
V
IN
Input 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
Storage Temperature Range.................. –65°C to 150°C
Ambient Temperature Range
LT1512C (Note 2)..................................... 0°C to 70°C
LT1512I ................................................ –40°C to 85°C
Operating Junction Temperature Range
LT1512C (Note 2).............................. –20°C to 125°C
LT1512I .............................................. –40°C to 125°C
Short Circuit.......................................... 0°C to 150°C
Lead Temperature (Soldering, 10 sec) ................. 300°C
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 100°C/W (N)
T
JMAX
= 125°C,
θ
JA
= 130°C/W (S)
NOTE: CONTACT FACTORY CONCERNING 16-LEAD
FUSED-LEAD GN PACKAGE WITH LOWER THERMAL RESISTANCE
ORDER INFORMATION
LEAD FREE FINISH
LT1512CN8#PBF
LT1512CS8#PBF
LT1512IN8#PBF
LT1512IS8#PBF
LEAD BASED FINISH
LT1512CN8
LT1512CS8
LT1512IN8
LT1512IS8
TAPE AND REEL
LT1512CN8#TRPBF
LT1512CS8#TRPBF
LT1512IN8#TRPBF
LT1512IS8#TRPBF
TAPE AND REEL
LT1512CN8#TR
LT1512CS8#TR
LT1512IN8#TR
LT1512IS8#TR
PART MARKING*
1512
1512
1512I
1512I
PART MARKING*
1512
1512
1512I
1512I
PACKAGE DESCRIPTION
8-Lead PDIP
8-Lead Plastic SO
8-Lead PDIP
8-Lead Plastic SO
PACKAGE DESCRIPTION
8-Lead PDIP
8-Lead Plastic SO
8-Lead PDIP
8-Lead Plastic SO
TEMPERATURE RANGE
0°C to 70°C
0°C to 70°C
–40°C to 85°C
–40°C to 85°C
TEMPERATURE RANGE
0°C to 70°C
0°C to 70°C
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. 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
V
FB
Reference Voltage
FB Input Current
FB Reference Voltage Line Regulation
CONDITIONS
Measured at FB Pin
V
C
= 0.8V
V
FB
= V
REF
2.7V ≤ V
IN
≤ 25V, V
C
= 0.8V
l
l
l
ELECTRICAL CHARACTERISTICS
MIN
1.233
1.228
TYP
1.245
1.245
300
0.01
MAX
1.257
1.262
550
600
0.03
UNITS
V
V
nA
nA
%/V
1512fa
2
LT1512
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IREF
PARAMETER
I
FB
Reference Voltage
I
FB
Input Current
I
FB
Reference Voltage Line Regulation
g
m
Error Amplifier Transconductance
Error Amplifier Source Current
Error Amplifier Sink Current
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
–40°C ≤ T
J
< 0°C (LT1512I)
l
l
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 5V, V
C
= 0.6V, V
FB
= V
REF
, I
FB
= 0V, V
SW
and S/S pins open,
unless otherwise noted.
CONDITIONS
Measured at I
FB
Pin
V
FB
= 0V, V
C
= 0.8V
V
IFB
= V
IREF
(Note 3)
2.7V ≤ V
IN
≤ 25V, V
C
= 0.8V
ΔI
C
=
±25μA
V
FB
= V
REF
– 150mV, V
C
= 1.5V
V
FB
= V
REF
+ 150mV, V
C
= 1.5V
High Clamp, V
FB
= 1V
Low Clamp, V
FB
= 1.5V
l
l
l
l
l
l
MIN
–107
–110
10
1100
700
120
1.70
0.25
0.8
450
430
400
85
40
35
1.5
1.3
TYP
–100
–100
25
0.01
1500
200
1400
1.95
0.40
500
1
500
500
95
130
MAX
–93
–90
35
0.05
1900
2300
350
2400
2.30
0.52
1.25
550
580
580
260
UNITS
mV
mV
μA
%/V
μmho
μmho
μA
μA
V
V
V/V
V
kHz
kHz
kHz
%
ns
V
V
Maximum Switch Duty Cycle
Switch Current Limit Blanking Time
BV
V
SAT
I
LIM
ΔI
IN
ΔI
SW
Output Switch Breakdown Voltage
Output Switch ON Resistance
Switch Current Limit
Supply Current Increase During Switch ON Time
Control Voltage to Switch Current Transconductance
Minimum Input Voltage
I
Q
Supply Current
Shutdown Supply Current
2.7V ≤ V
IN
≤ 25V
2.7V ≤ V
IN
≤ 25V, V
S/S
≤ 0.6V
0°C ≤ T
J
≤ 125°C
–40°C ≤ T
J
≤ 0°C (LT1512I)
2.7V ≤ V
IN
≤ 25V
0V ≤ V
S/S
≤ 5V
0°C ≤ T
J
≤ 125°C
–40°C ≤ T
J
< 20°C (LT1512I)
I
SW
= 2A
Duty Cycle = 50%
Duty Cycle = 80% (Note 4)
47
0.5
1.9
1.7
15
2
0.8
2.7
2.5
25
Ω
A
A
mA/A
A/V
l
l
l
l
l
l
l
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
Shutdown Threshold
Shutdown Delay
S/S Pin Input Current
Synchronization Frequency Range
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
Commercial devices are guaranteed over 0°C to 125°C junction
temperature range and 0°C to 70°C ambient temperature range. These
parts are also designed, characterized and expected to operate over the
–20°C to 85°C extended ambient temperature range, but are not tested at
–20°C or 85°C. Devices with full guaranteed electrical specifications over
the ambient temperature range –40°C to 85°C are available as industrial
parts with an “I” suffix.
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 125°C limit. With high power dissipation, maximum ambient
temperature may be less than 70°C.
Note 3:
The I
FB
pin is servoed to its regulating state with V
C
= 0.8V.
Note 4:
For duty cycles (DC) between 50% and 85%, minimum guaranteed
switch current is given by I
LIM
= 0.667 (2.75 – DC).
1512fa
3
LT1512
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Saturation Voltage
vs Switch Current
1.0
SWITCH SATURATION VOLTAGE (V)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
SWITCH CURRENT (A)
1512 G01
Switch Current Limit
vs Duty Cycle
3.0
3.0
2.8
INPUT VOLTAGE (V)
25°C AND
125°C
–55°C
1.5
1.0
0.5
0
2.6
2.4
2.2
2.0
25°C
SWITCH CURRENT LIMIT (A)
Minimum Input Voltage
vs Temperature
150°C
100°C
2.5
2.0
–55°C
0
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
1512 G02
1.8
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1512 G03
Minimum Peak-to-Peak
Synchronization Voltage vs Temp
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)
800
700
600
500
400
300
200
100
0
25 50 75 100 125 150
TEMPERATURE (°C)
1512 G04
Feedback Input Current
vs Temperature
V
FB
= V
REF
NEGATIVE FEEDBACK INPUT CURRENT (μA)
0
Negative Feedback Input Current
vs Temperature
–10
–20
–30
–40
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1512 G05
–50
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1512 G06
PIN FUNCTIONS
V
C
:
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 1.8A 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:
The feedback pin is used for positive output voltage
sensing. This pin is the inverting input to the voltage
error amplifier. 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. 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 LT1512 ground pin (avoid ground loops).
1512fa
4
LT1512
PIN FUNCTIONS
I
FB
:
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
the programmed voltage. During constant-current opera-
tion, the 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 24Ω, 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.
S/S:
This pin can be used for shutdown and/or synchro-
nization. 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 switching frequency
to the external signal. Shutdown is avoided in this mode
with an internal timer.
V
IN
:
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 GND pin is connected.
GND S, GND:
The LT1512 uses separate ground pins for
switch current (GND) and the control circuitry (GND S).
This isolates the control ground from any induced volt-
age created by fast switch currents. Both pins should be
tied directly to the ground plane, but the external control
circuit components such as the voltage divider, frequency
compensation network and I
FB
bypass capacitor should be
connected directly to the GND S pin or to the ground plane
close to the point where the GND S pin is connected.
V
SW
:
The switch pin is the collector of the power switch,
carrying up to 1.5A of current with fast rise and fall times.
Keep the traces on this pin as short as possible to mini-
mize radiation and voltage spikes. In particular, the path
in Figure 1 which includes SW to C2, D1, C1 and around
to the LT1512 ground pin should be as short as possible
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