LT1510 datasheet(10/16 Pages) LINER

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LT1510/LT1510-5

where RPROG is the total resistance from PROG pin to

ground.

For example, 1A charging current is needed.

PROG =

()( )

2 465

2000

493

Charging current can also be programmed by pulse width

modulating IPROG with a switch Q1 to RPROG at a frequency

higher than a few kHz (Figure 4). Charging current will be

proportional to the duty cycle of the switch with full current

at 100% duty cycle.

When a microprocessor DAC output is used to control

charging current, it must be capable of sinking current

at a compliance up to 2.5V if connected directly to the

PROG pin.

APPLICATIONS INFORMATION

even this low current drain. A 47k resistor from adapter

output to ground should be added if Q3 is used to ensure

that the gate is pulled to ground.

With divider current set at 25

µA, R4 = 2.465/25µA = 100k

and,

BAT

2 465

4 0 05

100 8 4 2 465

2 465 100 0 05

240

= ()

−

()

−

()

µµ

Lithium-ion batteries typically require float voltage accu-

racy of 1% to 2%. Accuracy of the LT1510 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

LT1510 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.

External Shutdown

The LT1510 can be externally shut down by pulling the VC

pin low with an open drain MOSFET, such as VN2222. The

VC pin should be pulled below 0.8V at room temperature

to ensure shutdown. This threshold decreases at about

2mV/

°C. A diode connected between the MOSFET drain

and the VC pin will still ensure the shutdown state over all

temperatures, but it results in slightly different conditions

as outlined below.

If the VC pin is held below threshold, but above ≈ 0.4V, the

current flowing

into the BAT pin will remain at about

700

µA.PullingtheVCpinbelow0.4Vwillcausethecurrent

to drop to

≈ 200µA and reverse, flowing out of the BAT pin.

Although these currents are low, the long term effect may

need to be considered if the charger is held in a shutdown

state for very long periods of time, with the charger input

voltage remaining. Removing the charger input voltage

causes all currents to drop to near zero.

If it is acceptable to have 200

µA flowing into the battery

while the charger is in shutdown, simply pull the VC pin

directly to ground with the external MOSFET. The resistor

divider used to sense battery voltage will pull current out

Figure 4. PWM Current Programming

PWM

RPROG

4.64k

300

Ω

PROG

CPROG

µF

VN2222

LT1510

1510 F04

IBAT = (DC)(1A)

Lithium-Ion Charging

The circuit in Figure 2 uses the 16-pin LT1510 to charge

lithium-ion batteries at a constant 1.3A until battery volt-

age reaches a limit set by R3 and R4. The charger will then

automatically go into a constant-voltage mode with cur-

rent decreasing 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.

Current through the R3/R4 divider is set at a compromise

value of 25

µA to minimize battery drain when the charger

is off and to avoid large errors due to the 50nA bias current

of the OVP pin. Q3 can be added if it is desired to eliminate

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