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PDF LT1512 Data sheet ( Hoja de datos )
| Número de pieza | LT1512 | |
| Descripción | SEPIC Constant-Current/ Constant-Voltage Battery Charger | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT1512
SEPIC Constant-Current/
Constant-Voltage Battery Charger
Features
n Charger Input Voltage May Be Higher, Equal to or
Lower Than Battery Voltage
n Charges Any Number of Cells Up to 30V*
n 1% Voltage Accuracy for Rechargeable Lithium
Batteries
n 500kHz Switching Frequency Minimizes
Inductor Size
n 100mV Current Sense Voltage for High Efficiency
n Battery Can Be Directly Grounded
n Charging Current Easily Programmable or Shut Down
Applications
n Battery Charging of NiCd, NiMH, Lead-Acid or
Lithium Rechargeable Cells
n Precision Current Limited Power Supply
n Constant-Voltage/Constant-Current Supply
n Transducer Excitation
*Maximum Input Voltage = 40V – VBAT
Description
The LT®1512 is a 500kHz current mode switching regulator
specially configured to create a constant-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 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.
Typical Application
WALL
ADAPTER
INPUT
+
C3
22µF
CHARGE
25V
SYNC
AND/OR
SHUTDOWN
SHUTDOWN
• L1 A*
VIN VSW
C2**
D1
2.2µF MBRS130LT3
LT1512
L1 B*
S/S FB •
GND GND S VC
IFB
C5
0.1µF
R4
24Ω
R5
1k
C4
0.22µF
R3
0.2Ω
R1
R2
*L1 A, L1 B ARE TWO 33µH WINDINGS ON A
SINGLE INDUCTOR: COILTRONICS CTX33-3
**TOKIN CERAMIC 1E225ZY5U-C203-F
Figure 1. SEPIC Charger with 0.5A Output Current
0.5A
+ C1
22µF
25V
1512 F01
Maximum Charging Current
1.0
SINGLE
LITHIUM
0.8 CELL (4.1V)
0.6 DOUBLE
LITHIUM
CELL (8.2V)
0.4 6V BATTERY
0.2 12V BATTERY
INDUCTOR = 33µH
0
0 5 10 15 20 25
INPUT VOLTAGE (V)
1512 TA02
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.
1512fc
For more information www.linear.com/LT1512
1
1 page  
LT1512
Pin Functions
VC: 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 VC voltage varies from
1V to 1.9V. Current out of the VC 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 VC 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).
IFB: 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 IFB 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 VIN
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.
VIN: 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 IFB 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.
VSW: 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
to minimize voltage spikes at switch turn-off.
For more information www.linear.com/LT1512
1512fc
5
5 Page 
LT1512
Applications Information
input to R5 is equal to the processor VCC level multiplied
by the inverse PWM ratio. This assumes that the PWM
signal is a CMOS output that swings rail-to-rail with a
source resistance less than a few hundred ohms. The
negative voltage is converted to a current by R5 and R6
and filtered by C7. This current multiplied by R4 generates
a voltage that subtracts from the 100mV sense voltage
of the LT1512. This is not a high precision technique
because of the errors in VCC and the diode voltage, but
it can typically be used to adjust charging current over a
20% to 100% range with good repeatability (full charg-
ing current accuracy is not affected). To reduce the load
on the logic signal, R4 has been increased from 24Ω to
200Ω. This causes a known increase in full-scale charging
current (PWM = 0) of 3% due to the 5k input resistance of
the IFB pin. Note that 100% duty cycle gives full charging
current and that very low duty cycles (especially zero!)
will not operate correctly. Very low duty cycle (<10%)
is a problem because the peak detector requires a finite
up-time to reset C6.
More Help
Linear Technology Field Application Engineers have a CAD
spreadsheet program for detailed calculations of circuit
operating conditions, and our Applications Department is
always ready to lend a helping hand. For additional informa-
tion refer to the LT1372 data sheet. This part is identical to
the LT1512 except for the current amplifier circuitry.
Package Description Dimensions in inches (millimeters) unless otherwise noted.
(Re8f-eLreena8c(d-LeLTCeLPaTDDdCWINPPDGNDPW(8#INaPGP0ca5a(k#rN-c0rakao08gar-5wrg1e-o5e0w.1830-001R.053ev10I00nI))cRhe)v I)
.400*
(10.160)
MAX
87 65
.255 ±.015*
(6.477 ±0.381)
.300 – .325
(7.620 – 8.255)
12
34
.045 – .065
(1.143 – 1.651)
.130 ±.005
(3.302 ±0.127)
.008 – .015
(0.203 – 0.381)
.065
(1.651)
TYP
.325
+.035
–.015
( )8.255
+0.889
–0.381
.100
(2.54)
BSC
NOTE:
1. DIMENSIONS
ARE
INCHES
MILLIMETERS
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
.120
(3.048)
MIN
.018 ±.003
(0.457 ±0.076)
.020
(0.508)
MIN
N8 REV I 0711
For more information www.linear.com/LT1512
1512fc
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet LT1512.PDF ] | |
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