STLED524 datasheet(49/72 Pages) STMICROELECTRONICS

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STLED524

Detailed description

4.10.3

Thermal protection

There are two thermal sensors inside the chip. The former protects boost and current

mirrors. The latter protects LDO. Boost thermal protection and current mirrors have

TSHDN1 threshold (150 °C) and 20 °C hysteresis, while LDO thermal protection has

TSHDN2 threshold (170 °C) and 20 °C hysteresis.

If the chip temperature reaches the first TSHDN1 threshold, boost and current mirrors are

automatically disabled (EN bit and BSTEN bit are reset). An interrupt is generated, if it is

enabled and THP in the latch register is set. If the chip temperature goes below thermal

shutdown hysteresis, an interrupt is generated, THP bit in the status register is reset and

THP bit in the latch register is set. Boost and current mirrors are not re-enabled

automatically; the microcontroller can do it.

If the microcontroller tries to re-enable boost and current mirrors, when THP is active, boost

and current mirrors stay off.

When LDO temperature reaches TSHDN2 threshold, it is turned off. If LDO supplies the

digital part, the content of patterns and all settings in the control registers are lost. LDO is re-

enabled automatically, as soon as its temperature goes below TSHDN2HYST

overtemperature hysteresis.

4.10.4

Open ISET protection

When EN bit is set to 1, REFSEL bit is set to 0 and ISET pin is opened or RSET resistor

value is higher than 270 k

Ω typically, then current mirrors are turned off. Boost operation is

not touched. OPEN bit is set in the status register and an interrupt is generated, if it is

enabled and OPEN bit in the latch register is set. EN bit is not touched, but current mirrors

are disabled. In this situation the microcontroller has the possibility to set REFSEL bit to 1 in

the clock register and run with the internal reference for the current mirrors.

4.10.5

Short ISET protection

When EN bit is set to 1, REFSEL bit is set to 0 and ISET pin is shorted or RSET value is

lower than 14 k

Ω, then current mirrors are turned off. Boost operation is not touched.

SHORT bit is set in the status register and an interrupt is generated, if it is enabled and

SHORT bit in the latch register is set. EN bit is not touched, but current mirrors are disabled.

In this situation the microcontroller has the possibility to set REFSEL bit to 1 in the clock

4.10.6

Row transistor protection

If any of 5-row pins is shorted to GND, current mirrors are disabled and EN bit is reset. An

interrupt is generated, if it is enabled and ROWSC bit in the latch register is set.

4.10.7

Boost output voltage OK

When boost output voltage reaches the target value given by VOUT register (VOUTSET),

BSTOK bit in the status register is set to 1. An interrupt is generated, if it is enabled. BSTOK

bit in the latch register is set to 1. When boost output voltage falls below VOUTSET,

VBSTOKHYST, BSTOK bit is reset and an interrupt is generated, if it is enabled. BSTOK bit

hasn’t any impact on boost or current mirrors. The microcontroller can decide whether to

stop operation of the display or not, if boost output voltage is not sufficient (BSTOK = 0).

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