L99LDLH32 datasheet(33/142 Pages) STMICROELECTRONICS

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DS12879 Rev 6

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L99LDLH32

Functional description

141

As soon as the VS supply crosses the under-voltage reset threshold (VS_UV_RES) the device

is automatically re-activated.

5.3.7

Channel output - LED short circuit detection

The L99LDLH32 performs the LED short circuit fault detection – both in Bus mode as well

as Fail Safe / Stand Alone mode - based on voltage monitoring across the channel output

voltage: the detection is done by comparing the absolute output voltage versus a

configurable threshold.

The device features 2 groups of configurable short circuit threshold (VSHT_CH_TH and

VSHT_CH_DIN_TH, as showed in Table 9). This configurability allows short detection of one or

more LEDs within the string connected to a given channel mapped according to

DIN_MAP_CHx <0>.

The short circuit detection can be enabled /disabled through the SHT_DET_EN bit (see

FTP/RAM memory map, Chapter 7): if this bit is equal to “0”, the short circuit detection is

disabled, otherwise, the short circuit detection is enabled. In this latter case, two different

scenarios are possible: to enable or disable the channel output deactivation in case of short

circuit, by one dedicated bit (SHT_OFF_x – see FTP/RAM memory map, Chapter 7). If

SHT_OFF_x bit is set to 0, the faulty channel output is kept active in case of short circuit,

otherwise the faulty channel is latched off. The channel is recognized in short circuit as soon

as its output voltage - read by ADC - is less than the specified short circuit threshold

(VSHT_CH_TH or VSHT_CH_DIN_TH, see Table 9).

In Bus mode, the faulty channel output is latched off and the dedicated fault bit (SHT_CHx –

see RAM memory map, Chapter 7) is set. The channel output can be restarted and the fault

bit will be cleared by sending a read & clear command to address 28. Selective bitwise read

& clear is possible.

In case of fault in Fail Safe / Stand Alone mode:



for the channels configured with FS_OUT_EN = 0, the output is latched off and it is

cleared upon falling edge of DIN with tDIN_FALL settling time. This means that fault is

not cleared during PWM dimming with PWM off-time shorter than tDIN_FALL time.



for the channels configured with FS_OUT_EN = 1, after elapsing the tAUTORESTART, the

faulty channel is automatically re-activated and the SHT_CHx bit is cleared.

If outputs are permanently enabled by FS_OUT_ENx = [1], in case of short circuit, they will

be latched and the latch can be cleared only through a power on reset condition.

For all (and only) those channels mapped on DIN (DIN_MAP_CHx = 01), the L99LDH32

features the indication of short circuit on FAULT pin. If the bit SHT_EN (see FTP/RAM

memory map, Chapter 7) is equal to “0”, the short circuit fault detection is NOT propagated

on FAULT bus; whilst if SHT_EN = 1, the short circuit of the faulty channel is indicated on

associated FAULT bus (pulled low).

The channel short event is also reported in the Global Status Byte register, in particular

Functional Error 2 (FE2) bit is set.

Table 9. LED short circuit threshold - grouping

DIN_MAP_CHx <0>

Short circuit threshold group

VSHT_CH_TH

VSHT_CH_DIN_TH

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