LT1510IS8 データシートの表示（PDF） - Linear Technology

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LT1510IS8

Constant-Voltage/Constant-Current Battery Charger

Linear Technology 

LT1510/LT1510-5

APPLICATIONS INFORMATION

of the battery, canceling part or all of the 200µA. Note that

if net current is into the battery and the battery is removed,

the charger output voltage will float high, to near input

voltage. This could be a problem when reinserting the

battery, if the resulting output capacitor/battery surge

current is high enough to damage either the battery or the

capacitor.

If net current into the battery must be less than zero in

shutdown, there are several options. Increasing divider

current to 300µA - 400µA will ensure that net battery

current is less than zero. For long term storage conditions

however, the divider may need to be disconnected with a

MOSFET switch as shown in Figures 2 and 5. A second

option is to connect a 1N914 diode in series with the

MOSFET drain. This will limit how far the VC pin will be pulled

down, and current (≈ 700µA) will flow into the BAT pin, and

therefore out of the battery. This is not usually a problem

unless the charger will remain in the shutdown state with

input power applied for very long periods of time.

Removing input power to the charger will cause the BAT

pin current to drop to near zero, with only the divider

current remaining as a small drain on the battery. Even

that current can be eliminated with a switch as shown in

Figures 2 and 5.

R3

12k R5

LT1510

Q3

220k

VN2222

OVP

VIN

R4

4.99k

0.25%

+

VBAT

4.2V

–

+

4.2V

–

1510 F05

Figure 5. Disconnecting Voltage Divider

Some battery manufacturers recommend termination of

constant-voltage float mode after charging current has

dropped below a specified level (typically 50mA to 100mA)

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

7 will detect when charging current has dropped below

75mA. This logic signal is used to initiate a time-out

period, after which the LT1510 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 if needed, 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 internal LT1510 sense resistor

(≈ 0.18Ω pin-to-pin). D2 generates hysteresis in the trip

level to avoid multiple comparator transitions.

Nickel-Cadmium and Nickel-Metal-Hydride Charging

The circuit in Figure 6 uses the 8-pin LT1510 to charge

NiCd or NiMH batteries up to 12V with charging currents

of 0.5A when Q1 is on and 50mA when Q1 is off.

C1

D1

0.22µF 1N5819

SW

VCC +

D3

1N5819

CIN*

10µF

WALL

ADAPTER

L1**

33µH

D2

1N914

BOOST PROG

LT1510

1µF

300Ω

R1

100k

GND

VC

0.1µF

1k

IBAT

R2

11k

Q1

VN2222

SENSE

* TOKIN OR MARCON CERAMIC

SURFACE MOUNT

** COILTRONICS CTX33-2

BAT

+

+

COUT

22µF

TANT

2V TO

20V

ON: IBAT = 0.5A

OFF: IBAT = 0.05A

1510 F05.5

Figure 6. Charging NiMH or NiCd Batteries

(Efficiency at 0.5A ≈ 90%)

For a 2-level charger, R1 and R2 are found from:

( )( ) 2000 2.465

IBAT =

RPROG

( )( ) 2.465 2000

R1 =

ILOW

( )( ) 2.465 2000

R2 =

IHI − ILOW

All battery chargers with fast-charge rates require some

means to detect full charge state in the battery to terminate

the high charging current. NiCd batteries are typically

charged at high current until temperature rise or battery

11

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