RL1632R-R100-F datasheet(14/22 Pages) ONSEMI

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NCV78514

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PTC choice makes the derating more direct due to the

exponential intrinsic variation of this resistor type. The

derating slew rate is then blended with the TDISDER slope

control.

For safety reasons, an internal pull−down resistor is

connected between TCS pin and and GND. Indeed, in case

of a floating pin, the TCS pin is automatically tied to GND,

and a maximum derating is applied on the LED current.

If the LED temperature stays excessive longer than

TFAULT timer, with a maximum derating applied, a fault is

reported on DIM pin.

Derating example with a positive temperature coefficient

sensor.

PTC ref: PRF18BE471QS5RB (470

W @ 25 C, 4700 W @

85C)

RPD + RPTC@85C*

VTCSSTART

VDD * VTCSSTART

[ 6250 W

(eq. 3)

Temperature calculation at ISTOP value (60% of ISET by

default).

RPTC@END + RPD(6250 W)*

VTCSSTART

VDD * VTCSSTART

+ 9775 W [ 90C with&a PRF18BE471

(eq. 4)

Because the PTC value changes by 50% with 5C

temperature difference, the same temperature difference

creates larger change of output current than NTC.

Derating example with a negative temperature coefficient

sensor: NCG18XH103F0SRB

RPU + RNTC@85C*

VDD * VTCSstart

VTCSSTART

[ 1100 W

(eq. 5)

Temperature calculation at ISTOP value (60% of ISET by

default).

RNTC@END + RPD(1100 W)*

VDD * VTCSSTART

VTCSSTART

+ 698 W [ 115C with&a NCG18XH103

(eq. 6)

If unused, TCS pin is to be connected with an external

resistor divider, to set TCS pin voltage to half of VLDO.

In case both junction temperature and LED temperature

required current derating, the current is controlled by the

thermal sensor (NTC/PTC or TJ) which requires the higher

current derating (whichever results in lower LED current).

Optional Behavior: STOP Over VTCSEND Threshold

Optionally, it is proposed to the end user to reshape the

derating profile by turning off the DCDC in case of

VTCS_END threshold is exceeded longer than TSTOP. If

so, the profile is expressed below

Figure 11. Current Derating TCS Voltage

VTCS_START

P_ISTOP

VTCS (V)

VTCS_END

Normalized

Output Current

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