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PDF LT1571-1 Data sheet ( Hoja de datos )
| Número de pieza | LT1571-1 | |
| Descripción | Constant-Current/ Constant-Voltage Battery Charger with Preset Voltage and Termination Flag | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT1571 Series
Constant-Current/
Constant-Voltage Battery Chargers
with Preset Voltage and Termination Flag
FEATURES
s Fast Charging of Li-Ion, NiMH and NiCd Batteries
s Simple Charge Current Programming Requires
Only One Low Cost, 1/32W Resistor
s High Efficiency Charger with Up to
1.5A Charge Current
s Precision 0.6% Internal Voltage Reference
s Preset Battery Voltages: 4.1V, 4.2V, 8.2V, 8.4V
s 500kHz or 200kHz Switching Frequency
Minimizes Charger Size
s Low Reverse Battery Drain Current: 5µA
s Flag Indicates Li-Ion Charge Completion
s 5% Typical Charge Current Accuracy
s Low Shutdown Current
s LT1571-1: 200kHz, Adjustable Voltage
LT1571-2: 200kHz, Fixed 8.2V or 8.4V
LT1571-5: 500kHz, Fixed 4.1V or 4.2V
U
APPLICATIO S
s Cellular Phones, PDAs, Notebook Computers,
Portable Instruments
s Cradle Chargers for Li-Ion, NiCd, NiMH and
Lead-Acid Rechargeable Batteries
DESCRIPTIO
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.
TYPICAL APPLICATION
VIN
8.2V TO 20V
(ADAPTER
OUTPUT)
D3
MBRM120T3
CIN*
10µF
D1
MBRM120T3
VCC SW
LT1571-5
100k
6.19k
CHARGE
COMPLETE
4.2V
Li-Ion
BATTERY
+
1µF
300Ω
PROG
0.33µF
VC
1k
+ COUT***
22µF
FLAG
BAT
BAT2
BOOST
SENSE
CAP
SELECT
GND
C1
0.22µF
D2
MMBD914L
L1**
10µH
0.1µF
*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
1571 F01
Figure 1. Compact Li-Ion Cellular Phone Charger (0.8A)
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency of Figure 4 Circuit
100
98 VCC = 15V (EXCLUDING DISSIPATION
ON INPUT DIODE D3)
96 VBAT = 8.4V
94
92
90
88
86
84
82
80
0.1 0.3 0.5 0.7 0.9 1.1
IBAT (A)
Switching Frequency vs
Temperature
1.3 1.5
1571 G01
510
505
LT1571-5
500
495
205
LT1571-1, LT1571-2
200
195
190
–20
0 20 40 60 80 100 120 140
JUNCTION TEMPERATURE (°C)
1571 G04
Maximum Duty Cycle
98
LT1571-1, LT1571-2
97 (VX = 5V)
96
95
94
93
92
91
90
0 20 40 60 80 100 120 140
JUNCTION TEMPERATURE (°C)
1571 G09
Reference Voltage vs Junction
Temperature
2.470
2.468
2.466
2.464
2.462
2.460
2.458
0
25 50 75 100 125 150
JUNCTION TEMPERATURE (°C)
1571 G02
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)
1571 G05
VC Pin Characteristic
–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)
1571 G08
LT1571 Series
Boost Current vs Switch Current
40
VCC = 16V
35
30
VBOOST = 26V
(VX = 10V)
25
20
VBOOST = 21V
15 (VX = 5V)
10
5
0
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
SWITCH CURRENT (A)
1571 G03
∆VOVP vs IVA (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)
1571 G06
PROG Pin Characteristic
6
125°C
0 25°C
–6
0 1234 5
VPROG (V)
1571 G09
5
5 Page 
LT1571 Series
APPLICATIO S I FOR ATIO
For example, if 10% threshold is needed for the 1A charger
(see Figure 4), then with RPROG = 4.93k:
RCAP
=
1.331• 4.93k
0.20 – 0.10
=
65.6k
Because of low level errors, as the threshold level is
reduced, the accuracy is also reduced. It is not recom-
mended to program a level less than 7.5%.
Preset Battery Voltage Settings
The LT1571-2 operates at 200kHz and is preset for 8.2V
battery voltage with SELECT pin floating and 8.4V with
SELECT pin grounded.
The LT1571-5 operates at 500kHz and is preset for 4.1V
battery voltage with SELECT pin floating and 4.2V with
SELECT pin grounded.
BAT2 pin is for Kelvin sensing the battery voltage and
should be connected to the battery.
Other Battery Voltage Settings
For battery voltages other than the preset voltages, the
LT1571-1 should be used. It operates at 200kHz and the
battery voltage is programmed with R3 and R4 divider at
VFB pin (Figure 6).
LT1571-1
VFB
VBAT
R3
R4
1571 F06
Figure 6. Programming Other Battery Voltages
Current through the R3/R4 divider is set at a compromise
value of 25µA to minimize battery drain when the charger
is off. The VFB pin input current of 3nA contributes very
little output voltage error and can be neglected.
With divider current set at 25µA, R4 = 2.465/25µA = 100k
and,
R3 = (R4)(VBAT − 2.465)
2.465
Lithium-ion batteries typically require float voltage accu-
racy of 1% to 2%. Accuracy of the LT1571-1 VFB 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 LT1571-1 rarely exceeds 50°C in float mode
because charge currents have tapered off to a low level, so
0.25% resistors normally provide the required level of
overall accuracy.
External Shutdown
The LT1571 can be externally shut down by pulling the VC
pin low with an open-drain N-FET, such as 2N7002. The VC
pin should be pulled below 0.6V to stop switching. When
VC is pulled below 40mV, LT1571 supply current drops to
typical 150µA.
Removing input power to the charger puts the LT1571 into
a sleep mode and draws only 5µA from the battery.
Nickel-Cadmium and Nickel-Metal-Hydride Charging
The circuit in Figure 7 uses the LT1571-1 to charge NiCd
or NiMH batteries up to 20V with charge currents of 0.5A
when Q1 is on and 50mA when Q1 is off.
For a 2-level charger, R1 and R2 are found from:
IBAT
=
(2000)(2.465)
RPROG
R1= (2.465)(2000)
ILOW
R2 = (2.465)(2000)
IHI − ILOW
All battery chargers with fast-charge rates require some
means to detect full charge in the battery and terminate the
high charge current. NiCd batteries are typically charged at
high current until the battery temperature begins to in-
crease or until the battery voltage reaches a peak and
begins to decrease (– dV/dt). This is an indication of near
full charge. The charge current is then reduced to a much
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT1571-1.PDF ] | |
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| LT1571-5 | Constant-Current/ Constant-Voltage Battery Charger with Preset Voltage and Termination Flag | Linear Technology |
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