LTC1729 データシートの表示（PDF） - Linear Technology

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LTC1729

Li-Ion Battery Charger Termination Controllers

Linear Technology 

LTC1729 Series

APPLICATIO S I FOR ATIO

For a battery that has been deeply discharged, the LTC1729

provides a 12mA start-up current. This preconditioning

trickle charge begins when the battery voltage drops

below 2.7V/cell. Comparator COMP3 is used to determine

when this condition exists. The battery operating range is

summarized in Figure 4.

With a 10k negative TC thermistor connected to the NTC

pin, the LTC1729 will disable charging if the temperature

is not in the 0°C to 50°C range. A thermistor must be

present at this pin, or if the temperature qualification

feature is not used, a 10k resistor must be used in its place.

This pin should not be left open. The NTC thermistor

monitoring circuits consist of COMP4, COMP5 and COMP6.

The NTC pin voltage range is shown in Figure 5.

Comparators COMP4 and COMP5 signal the logic when

the temperature is below 0°C or above 50°C. The 100µA

bias current through the 10kΩ thermistor will generate

2.79V at 0°C and 0.405V at 50°C. The voltage hysteresis

on COMP4 and COMP5 is designed to give 10°C of

temperature hysteresis. If the voltage on the NTC pin

drops below 0.2V, the comparator COMP6 generates a

reset to the logic and timer block.

To provide accurate charge voltages, the internal resistor

divider is trimmed to provide a precise ±0.2% voltage of

2.465V at the OVP pin for the four battery voltage options

of 4.1V, 4.2V, 8.2V and 8.4V.

When the input supply is removed in step-down charger

designs, the VCC pin does not drop to 0V, but is held to a

diode drop below the battery voltage. This is due to the

internal parasitic diode from the SW pin to the VCC pin that

is present in the LT1510, LT1511, LT1769, and the body

diode of the top MOSFET in the LT1505 charger. Remov-

ing the input supply will result in the VCC pin dropping

below the UVLO threshold, thus shutting down the LTC1729

and minimizing battery drain. Once the input supply is

connected, the LTC1729 resets the timers and begins

another charge cycle. There is a disconnect transistor that

will remove the OVP resistor divider from the battery when

the VCC voltage drops below the UVLO threshold.

If external circuitry is connected directly to the VCC pin and

the input power is removed, battery current will flow

through the charger’s internal parasitic diode (SW pin to

VCC pin), discharging the battery and possibly damaging

the charger if currents greater than 1A are present. If

external circuitry is used, connect it directly to the input

power source (which is the anode of the input Schottky

diode).

The logic and timer block consists of a state machine,

oscillator and counter. The state machine will be dis-

cussed in detail in the next section. The oscillator is

internally trimmed to 131kHz. The counter is composed of

a chain of 25 flip-flops that includes self-test circuitry.

VMAX = 1V

VMIN = 0V

4.5V/CELL

VMAX = 0V

VMIN = 0V

2.7V/CELL

VMAX = 0V

VMIN = 1V

BATTERY CLAMP

PULL-DOWN

ON

NORMAL CHARGE

TRICKLE CHARGE

PRECONDITIONING

1729 F04

Figure 4. BAT Voltage Operating Range

HOLD MODE

2.79V

NORMAL CHARGE

0.405V

HOLD MODE

0.2V

RESET MODE

1729 F05

Figure 5. NTC Voltage Operating Range

8

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