AS3630 datasheet(28/72 Pages) AMSCO

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AS3630 – 28

8A Supercap Flash Driver

Note: If DCDC1 shall not be used during flash (the whole current

has to be delivered by DCDC2 using the Supercap only, no

current from VIN) set the registers as follows:

txmask_torch_mode = 01b (TXMASK/TORCH is used as TXMask

input),

pull TXMASK/TORCH to ‘1’,

coil1_peak = 000b.

The AS3630 will then always operate in TXMask mode and

switch off DCDC1 (as coil1_peak = 000b).

Battery and Flash LED Current Reductions in Flash Mode

Current Reduction by VIN Measurements In Flash Mode

Due to the load of the flash driver and the ESR of the battery

(especially critical at low temperatures), the voltage on the

battery drops. If the voltage drops below the system reset

threshold, the system would reset. To prevent this condition the

AS3630 monitors the battery voltage and keeps it above

vin_low_v as follows:

During flash, if the voltage on VIN drops below the threshold

defined by vin_low_v, coil1_peak current is reduced thus

reducing the current from the battery and preventing a system

shutdown. Due to the unique regulation scheme (see DCDC1 /

DCDC2 Operating Principle During Flash) more current is

automatically used from the Supercap and therefore the flash

current is kept constant.

This function can be disabled by setting vin_low_v = 000b.

DCDC1 and DCDC2 in Current Limit

See DCDC1 / DCDC2 Operating Principle During Flash operating

mode 3.

TXMASK

The coil LDCDC1 current limit is usually defined by coil1_peak. If

this current is too high to allow parallel operation of another

high power load (e.g. the RF power amplifier) without

overloading of the battery, the TXMask function can be used.

Set txmask_torch_mode = 01b (TXMASK/TORCH is used as

TXMask input) and connect the enable line of the other high

power load to the AS3630 pin TXMASK/TORCH.

In the event of TXMASK/TORCH=1 during flash, the coil1_peak

current is instantaneously reduced by coil1_txmask_curr_red

steps (coding as for coil1_peak). If coil1_peak minus

coil1_txmask_curr_red steps would be negative DCDC1 is

switched off during TXMask.

Once TXMASK/TORCH=0, the coil peak current is ramped to the

previous programmed value of coil1_peak.

Continuous LED Current Ramp Down During Flash

If the register led_current_rampdown is set, the LED current

during flash is continuously ramped down. This has the benefit

of using the Supercap energy most efficiently.

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