NCV78514

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13

When VBAT falls under P_BAT_LOW, ILED is derated

following

the

formula

with

a

minimum

of

P_ILED_CLAMP value:

ILED + ISET

(BAT ) 1)

10

(eq. 2)

IC Temperature Monitoring

The junction temperature of the IC is monitored thanks to

an internal thermometer.

In the situation where the junction temperature exceeds

gradually the P_TJWARN, a current de−rating is

immediately applied to the LED current, with a controlled

slope upon P_DTC_BAT timing.

If the junction temperature continues to increase and

crosses the P_TJ_REG threshold, the LED current is

maintained around P_ILED_TJ.

If the IC temperature exceeds the P_TJ_OFF, the current

into the LED is stopped, and an error is reported on DIM pin.

A power on reset is required to reset the error.

In case of a very fast temperature increase (no derating is

engaged) and P_TJ_OFF is crossed, the LED string will be

rearmed when the junction temperature falls below the

P_TJ_HYST threshold, and the error reporting on DIM pin

is stopped

.

The current derating and management are defined as

following:

Figure 9. LED Current Derating versus Junction Temperature

Normalized Output

Current

Junction Temperature

100%

60%

TJ_WARN

TJ_REG

ILED_TJ_STEP

TJ_OFF

LED String Temperature Monitoring

A derating is also applied to ISET in case the LED string

temperature is too high, and a temperature coefficient

resistor is used (same PCB or separate LED module).

Both negative temperature coefficient (NTC) or positive

temperature coefficient (PTC) can be used with a pull−up or

pull−down resistor respectively.

In case of a module approach, NTC is recommended to

save one wire on the connector between the controller and

the Led module.

Figure 10. NTC (left side) and PTC (right side) Connection Options

TCS

ADC

VDD

NTC

TCS

ADC

VDD

PTC

NCV78514

NCV78514

RPU

RPD

P_TCS_PD

P_TCS_PD

The sampling period of the temperature sensor is defined

by the sampling rate of the internal ADC.

RPUP and RNTC (or RPD and RPTC) ratio is selected to

start the ILED derating when VTCS is crossing VTCSTART.

During the derating time frame, AR_P_DER_SLOPE is

applied on the LED current to avoid glare or flickering

effect.