AS3630 datasheet(37/72 Pages) AMSCO

37 / 72 page

8A Supercap Flash Driver

AS3630 – 37

NTC - Flash LED Overtemperature Protection - fault_ntc

Figure AS3630 – 34:

NTC Internal circuit

The NTC input can be used to monitor the flash LED temperature

if ntc_on=1. A internal current source controlled by NTC_current

sources a current on pin NTC - see Figure 34. If the voltage on

pin NTC drops below VNTC_TH, fault_ntc is set, the DCDCs are

stopped and the flash current source (on pin LED_OUT ) is

disabled (instantaneous) by setting mode_setting depending

on register mode_after_flash. If mode_after_flash=001b then

mode_setting=001b (shutdown and discharge Supercap). All

other settings of mode_after_flash result in mode_setting=000b

(shutdown).

As the external NTC cannot measure the LED temperature in

real time during a short high current flash pulse (the duration

from heating up of the LED until the NTC recognizes a too hot

LED is usually too long), it is advisable to measure the LED

temperature before the flash pulse (with the ADC and

NTC_current) and judge how much current can be driven

through the LED (to be estimated depending on LED heat sink

and is usually specified by the LED manufacturer).

LED Current Reduction Triggered - fault_current_reduced

If during flash the LED current has been reduced (for conditions

when this can occur see DCDC1 / DCDC2 Operating Principle

During Flash operating mode 3.), the register bit

fault_current_reduced is set for indication and lled_current_min

is set to the reduced LED current.

The operating mode is not changed and the DCDCs and current

source continue operation.

AS3630 Datasheet(PDF) 37 Page - ams AG