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PDF LT1511 Data sheet ( Hoja de datos )
| Número de pieza | LT1511 | |
| Descripción | Constant-Current/ Constant-Voltage 3A Battery Charger with Input Current Limiting | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT1511
Constant-Current/
Constant-Voltage 3A Battery
Charger with Input Current Limiting
FEATURES
s Simple Design to Charge NiCd, NiMH and Lithium
Rechargeable Batteries—Charging Current
Programmed by Resistors or DAC
s Adapter Current Loop Allows Maximum Possible
Charging Current During Computer Use
s Precision 0.5% Accuracy for Voltage Mode Charging
s High Efficiency Current Mode PWM with 4A Internal
Switch
s 5% Charging Current Accuracy
s Adjustable Undervoltage Lockout
s Automatic Shutdown When AC Adapter is Removed
s Low Reverse Battery Drain Current: 3µA
s Current Sensing Can Be at Either Terminal of the Battery
s Charging Current Soft-Start
s Shutdown Control
U
APPLICATIO S
s Chargers for NiCd, NiMH, Lead-Acid, Lithium
Rechargeable Batteries
s Switching Regulators with Precision Current Limit
, LTC and LT are registered trademarks of Linear Technology Corporation.
*See LT1510 for 1.5A Charger
DESCRIPTIO
The LT®1511 current mode PWM battery charger is the
simplest, most efficient solution to fast charge modern
rechargeable batteries including lithium-ion (Li-Ion), nickel-
metal-hydride (NiMH) and nickel-cadmium (NiCd) that
require constant-current and/or constant-voltage charg-
ing. The internal switch is capable of delivering 3A* DC
current (4A peak current). Full-charging current can be
programmed by resistors or a DAC to within 5%. With 0.5%
reference voltage accuracy, the LT1511 meets the critical
constant-voltage charging requirement for Li-Ion cells.
A third control loop is provided to regulate the current
drawn from the AC adapter. This allows simultaneous
operation of the equipment and battery charging without
overloading the adapter. Charging current is reduced to
keep the adapter current within specified levels.
The LT1511 can charge batteries ranging from 1V to 20V.
Ground sensing of current is not required and the battery’s
negative terminal can be tied directly to ground. A saturat-
ing switch running at 200kHz gives high charging effi-
ciency and small inductor size. A blocking diode is not
required between the chip and the battery because the
chip goes into sleep mode and drains only 3µA when the
wall adapter is unplugged.
TYPICAL APPLICATIO
GND CLP
D1
MBRD340
L1**
20µH
D2
MBR0540T
C2
0.47µF
200pF
SW
BOOST
LT1511
COMP1
CLN
VCC
UV
PROG
SPIN
VC
OVP SENSE BAT
NOTE: COMPLETE LITHIUM-ION CHARGER,
NO TERMINATION REQUIRED. RS4, R7
AND C1 ARE OPTIONAL FOR IIN LIMITING
*TOKIN OR UNITED CHEMI-CON/MARCON
CERAMIC SURFACE MOUNT
**20µH COILTRONICS CTX20-4
†SEE APPLICATIONS INFORMATION FOR
INPUT CURRENT LIMIT AND UNDERVOLTAGE LOCKOUT
RS3
200Ω
1%
RS2
200Ω
1%
RS1
0.033Ω
BATTERY CURRENT
SENSE
50pF
R7†
500Ω
C1
1µF
++
10µF
CIN*
10µF
D3
MBRD340
RS4†
ADAPTER
CURRENT SENSE
VIN (ADAPTER INPUT)
11V TO 28V
TO MAIN
R5† SYSTEM POWER
UNDERVOLTAGE
LOCKOUT
1k
0.33µF
300Ω
CPROG
1µF
RPROG
4.93k
1%
R6
5k
R3
390k
0.25%
BATTERY
VOLTAGE SENSE
R4
162k
0.25%
+
COUT
22µF
TANT
+
4.2V
+
4.2V
VBAT
2 Li-Ion
1511 • F01
Figure 1. 3A Lithium-Ion Battery Charger
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT1511
Switching Frequency vs
Temperature
210
205
200
195
190
185
180
–20 0
20 40 60 80 100 120 140
TEMPERATURE (°C)
1511 • TPC04
IVA vs ∆VOVP (Voltage Amplifier)
4
3
2
125°C
1
25°C
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
IVA (mA)
1511• TPC07
PROG Pin Characteristics
6
125°C
0 25°C
–6
0 1234 5
VPROG (V)
1511 • TPC10
ICC vs VCC
7.0
MAXIMUM DUTY CYCLE
6.5 0°C
25°C
6.0
125°C
5.5
5.0
4.5
0
5 10 15 20 25 30
VCC (V)
1511 • TPC05
Maximum Duty Cycle
98
97
96
95
94
93
92
91
90
0 20 40 60 80 100 120 140
TEMPERATURE (°C)
1511 • TPC08
Switch Current vs Boost Current
vs Boost Voltage
50
45 VCC = 16V
40 VBOOST = 38V
28V
35 18V
30
25
20
15
10
5
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)
1511 • TPC11
VREF Line Regulation
0.003
0.002
0.001
0
ALL TEMPERATURES
–0.001
–0.002
–0.003
0
5 10 15 20 25 30
VCC (V)
1511 • TPC06
VC Pin Characteristics
–1.20
–1.08
–0.96
–0.84
–0.72
–0.60
–0.48
–0.36
–0.24
–0.12
0
0.12
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
VC (V)
1511 • TPC09
Reference Voltage
vs Temperature
2.470
2.468
2.466
2.464
2.462
2.460
2.458
0
25 50 75 100 125 150
TEMPERATURE
LT1511 • TPC12
5
5 Page 
LT1511
APPLICATIONS INFORMATION
LT1511
PROG
300Ω
5V
0V
PWM
IBAT = (DC)(3A)
RPROG
4.7k
Q1
VN2222
CPROG
1µF
1511 • F03
Figure 3. PWM Current Programming
Lithium-Ion Charging
The 3A Lithium Battery Charger (Figure 1) charges lithium-
ion batteries at a constant 3A until battery voltage reaches
a limit set by R3 and R4. The charger will then automati-
cally go into a constant-voltage mode with current de-
creasing to zero over time as the battery reaches full
charge. This is the normal regimen for lithium-ion charg-
ing, with the charger holding the battery at “float” voltage
indefinitely. In this case no external sensing of full charge
is needed.
Battery Voltage Sense Resistors Selection
To minimize battery drain when the charger is off, current
through the R3/R4 divider is set at 15µA. The input current
to the OVP pin is 3nA and the error can be neglected.
With divider current set at 15µA, R4 = 2.465/15µA = 162k
and,
R3 = (R4)(VBAT − 2.465) = 162k(8.4 − 2.465)
2.465
2.465
= 390k
Li-Ion batteries typically require float voltage accuracy of
1% to 2%. Accuracy of the LT1511 OVP voltage is ±0.5%
at 25°C and ±1% over full temperature. This leads to the
possibility that very accurate (0.1%) resistors might be
needed for R3 and R4. Actually, the temperature of the
LT1511 will rarely exceed 50°C in float mode because
charging currents have tapered off to a low level, so 0.25%
resistors will normally provide the required level of overall
accuracy.
When power is on, there is about 200µA of current flowing
out of the BAT and Sense pins. If the battery is removed
during charging, and total load including R3 and R4 is less
than the 200µA, VBAT could float up to VCC even though the
loop has turned switching off. To keep VBAT regulated to
the battery voltage in this condition, R3 and R4 can be
chosen to draw 0.5mA and Q3 can be added to disconnect
them when power is off (Figure 4). R5 isolates the OVP pin
from any high frequency noise on VIN. An alternative way is
to use a Zener diode with a breakdown voltage two or three
volts higher than battery voltage to clamp the VBAT voltage.
LT1511
OVP
R3
12k
0.25%
Q3
VN2222
R5
220k
R4
4.99k
0.25%
VIN
VBAT
+
4.2V
–
+
4.2V
–
LT1511 • F04
Figure 4. Disconnecting Voltage Divider
Some battery manufacturers recommend termination of
constant-voltage float mode after charging current has
dropped below a specified level (typically around 10% of
the full current) and a further time out period of 30 minutes
to 90 minutes has elapsed. This may extend the life of the
battery, so check with manufacturers for details. The
circuit in Figure 5 will detect when charging current has
dropped below 400mA. This logic signal is used to initiate
a timeout period, after which the LT1511 can be shut down
by pulling the VC pin low with an open collector or drain.
Some external means must be used to detect the need for
additional charging or the charger may be turned on
periodically to complete a short float-voltage cycle.
Current trip level is determined by the battery voltage, R1
through R3 and the sense resistor (RS1). D2 generates
hysteresis in the trip level to avoid multiple comparator
transitions.
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT1511.PDF ] | |
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