L99LDLH32 datasheet(32/142 Pages) STMICROELECTRONICS

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Functional description

L99LDLH32

32/142

DS12879 Rev 6

As soon as the TJ drops below the thermal warning reset threshold (TTW-TTW_HYS), the

corresponding thermal warning status bit is automatically cleared.

Even if a temperature warning is detected, device as well as output channels are kept

functional.

5.3.4

Thermal shutdown

If the junction temperature of the L99LDLH32 rises above the shutdown temperature

threshold (TTSD), a thermal shutdown event is detected: all the output channels are switched off

and the thermal shutdown status bit (TSD – see RAM memory map, Chapter 7) is set. The

Fault pin is pulled low.

Thermal shutdown event is also reported in the Global Status Byte register, in particular

Functional Error 1 (FE1) bit is set.

As soon as the TJ drops below the thermal shutdown reset threshold (TTSD-TTSD_HYS), the

output channels are automatically re-activated. The corresponding thermal shutdown status

bit (TTSD) is automatically cleared as soon as TJ drops below the thermal shutdown reset

threshold, contemporarily to channel re-activation.

In case of thermal shutdown, device logic and state machine remain active.

5.3.5

LED current derating

In case of temperature increasing, the device performs an automatic LED current derating

based on the measurement of external NTC voltage as well as on the internal device

temperature (TJ).

An integrated thermal sensor is used to sense the device junction temperature (TJ) as well

as to detect thermal warning (TW) and thermal shutdown (TSD) thresholds, granting device

protection in case of temperature increasing. The sensed junction temperature (TJ) is

monitored by an 8-bit ADC with the aim of starting an automatic, downwards derating of the

LED string current as soon as the TTW - TTW_HYS threshold is reached. The derating ends

when the 50% of the nominal LED current is reached, which corresponds to TJ = 165°C.

The 8-bit ADC is also used to monitor the voltage on the NTC pin, where an external resistor

can be connected. If the monitored voltage – whose value depends on the temperature

detected by the NTC resistor itself - reaches the VNTC_TH threshold (programmable by 3

bits, see Table 78), a downwards derating of the LED string current automatically starts, till

50% of the nominal LED current is reached. This corresponds to a NTC temperature 20°C

higher than the one corresponding to VNTC_TH.

The monitoring of both TJ and NTC voltage is contemporarily active. The actual derating is

determined by the parameter which would require the most severe derating.

5.3.6

VS under voltage lockout

If the VS supply falls below VS under-voltage threshold (VS_UV), the device will be

deactivated - regardless of the operating mode – and the FAULT pin will be pulled low.

This feature is implemented, in order to avoid any operation outside the allowed VS

operating range.

If Supply under-voltage event is detected, the related flag (VS_UV – see RAM memory map,

Chapter 7

) is set and reported also in the Global Status Byte register, where Device Error

(DE) bit is set.

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