PWM Controller in Charge Mode

Battery Charging Process

Safety Timer in Charge Mode

bq24150

bq24151

The bq24150/1 provides an integrated, fixed 3 MHz frequency voltage-mode controller with Feed-Forward

function to regulate charge current or voltage. This type of controller is used to help improve line transient

response, thereby, simplifying the compensation network used for both continuous and discontinuous current

conduction operation. The voltage and current loops are internally compensated using a Type-III compensation

scheme that provides enough phase margin for stable operation, allowing the use of small ceramic capacitors

with low ESR. There is a 0.5-V offset on the bottom of the PWM ramp to allow the device to operate between 0%

to 99.5% duty cycles.

The bq24150/1 has two back to back common-drain N-channel MOSFETs at the high side and one N-channel

MOSFET at low side. An input N-MOSFET (Q1) prevents battery discharge when VBUS is lower than

VAUXPWR. The second high-side N-MOSFET (Q2) behaves as the switching control switch (see Figure 21). A

charge pump circuit is used to provide gate drive for Q1, while a boot strap circuit with external boot-strap

capacitor is used to boost up the gate drive voltage for Q2.

Cycle-by-cycle current limit is sensed through the internal sense MOSFETs for Q2 and Q3. The threshold for Q2

is set to a nominal 1.9-A peak current. The low-side MOSFET (Q3) also has a current limit that decides if the

PWM Controller will operate in synchronous or non-synchronous mode. This threshold is set to 100mA and it

turns off the low-side N-channel MOSFET (Q3) before the current reverses, preventing the battery from

discharging. Synchronous operation is used when the current of the low-side MOSFET is greater than 100mA to

minimize power losses.

charge current is controlled to minimize the current and voltage over-shoot during transient. Both the input

Figure 24. The voltage regulation feedback occurs by monitoring the battery-pack voltage between the CSOUT

and PGND pins. bq24150/1 is a fixed single-cell voltage version, with adjustable regulation voltage (3.5 V to 4.44

The bq24150/1 monitors the charging current during the voltage regulation phase. Once the termination

threshold, ITERM, is detected and the battery voltage is above the recharge threshold, the bq24150/1 terminates

charge. The termination current level is programmable. To disable the charge current termination, the host can

A new charge cycle is initiated when one of the following conditions is detected:

• The battery voltage falls below the V

• VBUS Power-on reset (POR), if battery voltage is below the V

• CE bit toggle or RESET bit is set (host controlled)

At the beginning of charging process, the bq24150/1 starts a 32-minute timer (T32min) that can be stopped by

reset bit of TMR_RST in control register resets the 32-second timer and TMR_RST is automatically set to "0"

after the 32-second timer is reset. If the 32-second timer expires, the charge is terminated and charge

parameters are reset to default values. Then the 32-minute timer starts and the charge resumes.

During normal charging process, the bq24150/1 is normally in 32-second mode with host control, and 32-minute

32-minute timer expires, bq24150/1 turns off the charger and enunciates FAULT on the STATx bits of status

register. This function prevents battery over charge if the host fails to reset the safety timer. The safety timer flow

chart is shown in Figure 25. Fault condition is cleared by POR and fault status bits can only be updated after the

status bits are read out by the host.

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