AS3630 datasheet(27/72 Pages) AMSCO

27 / 72 page

8A Supercap Flash Driver

AS3630 – 27

Figure AS3630 – 23:

Automatically Selected Operating Mode After Flash

DCDC1 / DCDC2 Operating Principle During Flash

In order to supply the required LED output current during flash

operation, DCDC1 (from VIN) and DCDC2 (from Supercap) are

used in parallel as shown in Figure 22.

Three different operating modes are used (automatically

selected by the AS3630):

DCCD1 alone can deliver the full flash current.

IDCDC1<coil1_peak, IDCDC2=0A

DCDC1 is regulated to deliver the flash LED current

alone; no current is used from DCDC2 or the Supercap.

DCDC1 and DCDC2 together deliver the flash current.

IDCDC1 hits coil1_peak, IDCDC2<coil2_peak

DCDC1 is operating in peak current limit (controlled by

coil1_peak) and DCDC2 is controlled to deliver the

remaining current for the LED. DCDC2 peak current is

below the setting coil2_peak.

DCDC1 and DCDC2 together cannot deliver the full flash

current.

IDCDC1 hits coil1_peak, IDCDC2 hits coil2_peak

In this operating mode both peak current settings

together (coil1_peak and coil2_peak) are not able to

deliver the programmed led_current. Therefore both

DCDCs are operating in coil current limit and the LED

current is the resulting sum of these two currents. If the

ramped down8 until DCDC2 leaves peak current limit

and operation continuous at mode 2. (DCDC1 and

DCDC2 together deliver the flash current) and

led_current_min is set to the reduced LED current.

If the voltage on VSUPERCAP drops below 2.4V, DCDC2

is disabled and the flash current drops to the current

supplied by DCDC1 only.

mode_after_flash

(see page 51)

mode_setting

updated to

Mode selected after flash has been finished

000b

Shutdown of AS3630, but leave Supercap at the voltage

at the end of the flash

001b

Shutdown AS3630 and discharge Supercap

010b

Discharge the Supercap to approximately VVIN-0.3V by

using RDIS_CHARGE. Afterwards the Supercap is charged to

VVIN as shown in Figure 19 and kept at this voltage

011b

Supercap is automatically recharged to

end_of_charge_voltage

8. fault_current_reduced is set to indicate this condition.

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