LP3947

SNVS298B – NOVEMBER 2004 – REVISED APRIL 2013

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Table 3. LED Indicator Summary

RED LED

GREEN LED (EOC)

(CHG)

Charger Off

OFF

OFF

Charging Li Ion Battery(1)

ON

OFF

Maintenance Mode

OFF

ON

Charging Li Ion Battery after Passing Maintenance Mode

OFF

ON

EN Pin = LOW

OFF

ON

LDO Mode

OFF

OFF

5.6 Hr Safety Timer Flag/Battery Temperature Violation

ON

ON

(1)

Charging Li Ion battery for the first time after VCHG-IN insertion.

Ts PIN

The LP3947 continuously monitors the battery temperature by measuring the voltage between the Ts pin and

ground. Charging stops if the battery temperature is outside the permitted temperature range set by the battery’s

internal thermistor RT and the external bias resistor RS. A 1% precision resistor should be used for RS. A curve 2

type thermistor is recommended for RT. The voltage across RT is proportional to the battery temperature. If the

battery temperature is outside of the range during the charge cycle, the LP3947 will suspend charging. As an

example, for a temperature range of 0°C to 50°C, a 10k

Ω for the thermistor and a 4.1kΩ for Rs should be used.

When battery temperature returns to the permitted range, charging resumes from the beginning of the flow chart

and the 5.6 hr safety timer is reset. Refer to Figure 4. LP3947 Charger Flow Chart for more information.

In absence of the thermistor, Ts pin will be pulled high to VT and the LP3947 goes into LDO mode. In this mode,

the internal power FET provides up to 1.2 amp of current at the BATT pin. The LDO output is set to 4.1V or 4.2V,

depending on the programmed battery regulation voltage. When operating at higher output currents, care must

be taken not to exceed the package power dissipation rating. See “Thermal Performance of WSON Package”

section for more detail.

Table 4. Charger Status in Relation to Ts Voltage

Voltage on the Ts Pin

Charger Status

Ts

≥ 2.7V

LDO Mode

2.427v

≤ Ts < 2.7V

Charger Off

0V

≤ Ts ≤ 1.39V

1.39V < Ts < 2.427V

Charger On

LDO MODE

The charger is in the LDO mode when the Ts pin is left floating. This mode of operation is used primarily during

system level testing of the handset to eliminate the need for battery insertion. CAUTION: battery may be

damaged if device is operating in LDO mode with battery connected.

The internal power FET provides up to 1.2 amp of current at BATT pin in this mode. The LDO output is set to

4.1V. When operating at higher output currents, care must be taken not to exceed the package power dissipation

rating. See “Thermal Performance of WSON Package” section for more detail.

EN PIN

The Enable pin is used to enable/disable the charger, in both the charger mode and the LDO mode, see Figure 6

Figure 7. The enable pin is internally pulled HIGH to the CHG-IN pin. When the charger is disabled, it draws less

than 4 µA of current.

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