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PDF LT1505CG Data sheet ( Hoja de datos )
| Número de pieza | LT1505CG | |
| Descripción | Constant-Current/Voltage High Efficiency Battery Charger | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT1505
Constant-Current/Voltage
High Efficiency Battery Charger
FEATURES
s Simple Charging of Li-Ion, NiMH and NiCd Batteries
s Very High Efficiency: Up to 97%
s Precision 0.5% Charging Voltage Accuracy
s Preset Battery Voltages: 12.3V, 12.6V,
16.4V and 16.8V
s 5% Charging Current Accuracy
s Charging Current Programmed by Resistor or DAC
s 0.5V Dropout Voltage, Duty Cycle > 99.5%
s AC Adapter Current Limit* Maximizes Charging Rate
s Flag Indicates Li-Ion Charge Completion
s Auto Shutdown with Adapter Removal
s Only 10µA Battery Drain When Idle
s Synchronizable Up to 280kHz
U
APPLICATIO S
s Notebook Computers
s Portable Instruments
s Chargers for Li-Ion, NiMH, NiCd and Lead Acid
Rechargeable Batteries
DESCRIPTIO
The LT®1505 PWM battery charger controller fast charges
multiple battery chemistries including lithium-ion (Li-Ion),
nickel-metal-hydride (NiMH) and nickel-cadmium (NiCd)
using constant-current or constant-voltage control. Maxi-
mum current can be easily programmed by resistors or a
DAC. The constant-voltage output can be selected for 3 or 4
series Li-Ion cells with 0.5% accuracy.
A third control loop limits the current drawn from the AC
adapter during charging*. This allows simultaneous opera-
tion of the equipment and fast battery charging without over-
loading the AC adapter.
The LT1505 can charge batteries ranging from 2.5V to 20V
with dropout voltage as low as 0.5V. Synchronous
N-channel FETs switching at 200kHz give high efficiency
and allow small inductor size. A diode is not required in
series with the battery because the charger automatically
enters a 10µA sleep mode when the wall adapter is un-
plugged. A logic output indicates Li-Ion full charge when
current drops to 20% of the programmed value.
The LT1505 is available in a 28-pin SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
*US Patent No. 5,723,970
TYPICAL APPLICATION
VIN
(FROM
ADAPTER)
R5
4k
R6
4k
M3
Si4435
DBODY*
TO
SYSTEM POWER
RS4
0.025Ω
R7
500Ω
C1
1µF
CIN
47µF
35V
100k
VCC
CLN
CLP
INFET
UV
SYNC
SHDN
BOOST BOOSTC
GBIAS
TGATE
SW
BGATE
LT1505
VC
PROG
3 CELL
*BODY DIODE
POLARITY MUST
BE AS SHOWN
C6
0.1µF
R1
1k
C7
0.68µF
FLAG
CAP
COMP1
BAT2 BAT
VFB
4.2V
4.1V
AGND
PGND
SENSE SPIN
C4
0.1µF
D3
MMSD4148T1
C3 D2
2.2µF MMSD4148T1
5Ω
M1
Si4412
M2
Si4412
D4
MBRS140
C2
0.68µF
L1
15µH
RS1
0.025Ω
COUT
22µF
25V
×2
300Ω
CPROG
1µF
RPROG
4.93k
1%
RX4
3k
0.33µF
NOTE: DBODY IS THE BODY DIODE OF M3
CIN: SANYO OS-CON
L1: SUMIDA CDRH127-150
(CAN BE FROM 10µH TO 30µH)
RS2
200Ω
1%
RS3
200Ω
1%
VBAT
12.6V
BATTERY
1505 F01
Figure 1. Low Dropout 4A Lithium-Ion Battery Charger
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT1505
Efficiency of Figure 1 Circuit
105
VIN = 19V
VBAT = 12.6V
100
95
90
85
80
01 2 345
IBAT (A)
1505 G01
∆VFB 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)
1505 G04
PROG Pin Characteristics
6
CURRENT FEEDBACK
AMPLIFIER OPEN LOOP
125°C
0 25°C
–6
0 1234 5
VPROG (V)
1505 G07
VGBIAS vs IGBIAS
9.2
9.1
9.0
0°C
8.9
25°C
8.8
125°C
8.7
8.6
8.5
8.4
8.3
8.1
0
–2 –4 –6 –8 –10 –12 –14 –16 –18 –20
IGBIAS (mA)
1505 G02
Current Limit Amplifier
CL1 Threshold
98
VREF Line Regulation
0.003
0°C ≤ TJ ≤ 125°C
0.002
0.001
0
ALL TEMPERATURES
–0.001
–0.002
–0.003
0
5 10 15 20 25 30
VCC (V)
1505 G03
ICC vs VCC
15
96 14
94 13
92
90
88
0
25 50 75 100
TEMPERATURE (°C)
125
1505 G05
12
11
10
10
0°C
125°C
13 16 19
VCC (V)
25°C
22 25
1505 G06
VC Pin Characteristics
–1.2
–1.0
–0.8
–0.6
–0.4
–0.2
0
0.2
0.4
0.6
0.8
1.0
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
VC (V)
1505 G08
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
JUNCTION TEMPERATURE (°C)
1505 G09
5
5 Page 
LT1505
APPLICATIONS INFORMATION
EMI considerations usually make it desirable to minimize
ripple current in the battery leads. Beads or inductors may
be added to increase battery impedance at the 200kHz
switching frequency. Switching ripple current splits be-
tween the battery and the output capacitor depending on
the ESR of the output capacitor and the battery imped-
ance. If the ESR of COUT is 0.2Ω and the battery impedance
is raised to 4Ω with a bead or inductor, only 5% of the
ripple current will flow in the battery.
Soft Start and Undervoltage Lockout
The LT1505 is soft started by the 0.33µF capacitor on the
VC pin. On start-up, the VC pin voltage will rise quickly to
0.5V, then ramp up at a rate set by the internal 45µA pull-
up current and the external capacitor. Battery charge
current starts ramping up when VC voltage reaches 0.7V
and full current is achieved with VC at 1.1V. With a 0.33µF
capacitor, time to reach full charge current is about 10ms
and it is assumed that input voltage to the charger will
reach full value in less than 10ms. The capacitor can be
increased up to 1µF if longer input start-up times are
needed.
In any switching regulator, conventional timer-based soft
starting can be defeated if the input voltage rises much
slower than the time out period. This happens because the
switching regulators in the battery charger and the com-
puter power supply are typically supplying a fixed amount
of power to the load. If input voltage comes up slowly
compared to the soft start time, the regulators will try to
deliver full power to the load when the input voltage is still
well below its final value. If the adapter is current limited,
it cannot deliver full power at reduced output voltages and
the possibility exists for a quasi “latch” state where the
adapter output stays in a current limited state at reduced
output voltage. For instance, if maximum charger plus
computer load power is 30W, a 15V adapter might be
current limited at 2.5A. If adapter voltage is less than
(30W/2.5A = 12V) when full power is drawn, the adapter
voltage will be pulled down by the constant 30W load until
it reaches a lower stable state where the switching regu-
lators can no longer supply full load. This situation can be
prevented by setting undervoltage lockout higher than the
minimum adapter voltage where full power can be achieved.
+
CL1
–
92m+V
LT1505
CLP
1µF
CLN 500Ω
VCC RS4*
+
CIN
UV
AC ADAPTER
OUTPUT
VIN
R5
*RS4
=
ADAPTER
92mV
CURRENT
LIMIT
R6
1505 F02
Figure 2. Adapter Current Limiting
A resistor divider is used to set the desired VCC lockout
voltage as shown in Figure 2. A typical value for R6 is 5k
and R5 is found from:
R5 = R6(VIN – VUV )
VUV
VUV = Rising lockout threshold on the UV pin
VIN = Charger input voltage that will sustain full load power
Example: With R6 = 5k, VUV = 6.7V and setting VIN at 16V;
R5 = 5k (16V – 6.7V)/6.7V = 6.9k
The resistor divider should be connected directly to the
adapter output as shown, not to the VCC pin to prevent
battery drain with no adapter voltage. If the UV pin is not
used, connect it to the adapter output (not VCC) and
connect a resistor no greater than 5k to ground. Floating
the pin will cause reverse battery current to increase from
10µA to 200µA.
Adapter Current Limiting
(Not Applicable for the LT1505-1)
An important feature of the LT1505 is the ability to
automatically adjust charge current to a level which avoids
overloading the wall adapter. This allows the product to
operate at the same time batteries are being charged
without complex load management algorithms. Addition-
ally, batteries will automatically be charged at the maximum
possible rate of which the adapter is capable.
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT1505CG.PDF ] | |
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