LP8550TLESLASHNOPB datasheet(20/49 Pages) TI2

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LP8550

SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014

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8.3.4.2 Undervoltage Detection

The LP8550 has detection for too-low VIN voltage. Threshold level for the voltage is set with EEPROM register

bits as seen in Table 3:

Table 3. Threshold Level for Voltage Set with EEPROM Register Bits

UVLO[1:0]

THRESHOLD (V)

OFF

2.7

5.4

8.1

When undervoltage is detected the LED outputs and boost shut down, FAULT pin is pulled down, and

corresponding fault bit is set in fault register. LEDs and boost start again when the voltage has increased above

the threshold level. Hysteresis is implemented to threshold level to avoid continuous triggering of fault when

threshold is reached.

Fault is cleared by setting EN pin low or by reading the fault register.

8.3.4.3 Overcurrent Protection

The LP8550 has detection for too-high loading on the boost converter. When overcurrent fault is detected, the

LP8550 shuts down.

Fault is cleared by setting EN pin low or by reading the fault register.

8.3.4.4 Device Thermal Regulation

The LP8550 has an internal temperature sensor which can be used to measure the junction temperature of the

device and protect the device from overheating. During thermal regulation, LED PWM is reduced by 2% of full

scale per °C whenever the temperature threshold is reached. Temperature regulation is enabled automatically

when chip is enabled. 11-bit temperature value can be read from Temp MSB and Temp LSB registers, MSB

should be read first. Temperature limit can be programmed in EEPROM as shown in Table 4.

Thermal regulation function does not generate fault signal.

Table 4. Temperature Limits Programmable in EEPROM

TEMP_LIM[1:0]

OVER-TEMP LIMIT (°C)

OFF

110

120

130

8.3.4.5 Thermal Shutdown

If the LP8550 reaches thermal shutdown temperature (150°C ) the LED outputs and boost shuts down to protect

it from damage. Also the FAULT pin is pulled down to indicate the fault state. The device activates again when

temperature drops below 130°C degrees.

Fault is cleared by setting EN pin low or by reading the fault register.

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