10.13 EXT_PWR_ON

EXT_PWR_ON is a digital push-pull output. A logic 1, referenced to the Radio_B+ level is output when V

(nominally 3.00V) and CHRG_DETB = 0 (charger presence is detected) and BATT_DETB is low. Otherwise, EXT_PWR_ON is

held low to prevent the phone from attempting to turn on due to charger connection when there is either no battery present or

when the battery is not charged enough for the phone to operate.

11.0 Charge Control Functions

11.1 GENERAL OPERATION

The LM3655 circuit is able to operate with different types of charge power supplies with a wide range of input voltage and

currents, including but not limited to unregulated current limited wall adapters, regulated wall adapters and Vehicle Power

Adapters with 1A of current limit.

The IC protects itself from high voltages by using Q1 and Q2 to stand off these voltages. It also uses resistors to current limit the

V

charging the battery. Power dissipation in Q1 is controlled using a constant-power control circuit within the IC.

The LM3655 has multiple modes of operation for charging and protecting the embedded cell. The three basic modes of operation

are low voltage charging, full-rate charging, and trickle charging. During the charge process, the power dissipation in the pass

element Q1 is monitored and controlled to a safe maximum limit by reducing charge current as necessary.

Because of quantization error or power supply voltage fluctuations, the power-limiting circuit may (in some cases) reduce cell

current to a level lower than necessary for extended periods of time. To counteract this, the IC periodically activates a charger test

pulse during the full-rate and trickle charging modes. This allows the power supply to deliver full-rate current, although the cell

voltage is always regulated such that it does not exceed the termination voltage (4.10V or 4.16V as determined by the

CHEMISTRY pin). The test pulse allows the cell to be charged at the fastest possible rate by allowing the charge control to

re-enter the full-rate charge (Q1 saturated) mode whenever possible. The test pulses are enabled during full-rate and trickle/

top-off charge modes, have a nominal duration of 256 mS, and are repeated every 64 seconds. This is referred to as ‘burp’ mode.

Figure 1 shows the cell voltage thresholds used in the selection of the charging modes. The horizontal (time) axis is intended to

illustrate the progression of a complete charge/discharge cycle of operation.

11.2 EXTERNAL POWER SUPPLY DETECT

11.2.1 V

The V

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FIGURE 1. Voltage Thresholds

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