BQ24152 Datasheet, PDF(16/38 Page) Texas Instruments – Fully Integrated Switch-Mode One-Cell Li-Ion Charger with Full USB Compliance and USB-OTG Support

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bq24152

SLUS847 â JUNE 2008 ...................................................................................................................................................................................................... www.ti.com

PWM Controller in Charge Mode

The bq24152 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 bq24152 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.

Battery Charging Process

At the beginning of precharge, while battery voltage is below the V(SHORT) threshold, the bq24152 applies a

short-circuit current, I(SHORT), to the battery.

When the battery voltage is above V(SHORT) and below V(OREG), the charge current ramps up to fast charge

current, IO(CHARGE), or a charge current that corresponds to the input current of I(IN_LIMIT). The slew rate for fast

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

current limit (default at 100 mA), IIN_LIMIT, and fast charge current, IO(CHARGE), can be set by the host. Once the

battery voltage is close to the regulation voltage, V(OREG), the charge current is tapered down as shown in

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

and PGND pins. bq24152 is a fixed single-cell voltage version, with adjustable regulation voltage (3.5 V to 4.44

V) programmed through I2C interface.

The bq24152 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 bq24152 terminates charge. The

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

termination bit (I_Term) of charge control register to 0, see the I2C section for details.

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

â¢ The battery voltage falls below the V(OREG) â V(RCH) threshold.

â¢ VBUS Power-on reset (POR), if battery voltage is below the V(LOWV) threshold.

â¢ CE bit toggle or RESET bit is set (host controlled)

Safety Timer in Charge Mode

At the beginning of charging process, the bq24152 starts a 32-minute timer (T32min) that can be stopped by any

write-action performed by host through I2C interface. Once the 32-minute timer is stopped, a 32-second timer

(T32sec) is automatically started. The 32-second timer can be reset by host using I2C interface. Writing "1" to

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 bq24152 is normally in 32-second mode with host control, and 32-minute

mode without host control using I2C interface. The process repeats until the battery is fully charged. If the

32-minute timer expires, bq24152 turns off the charger and enunciates FAULT on the STATx bits of status

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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