LP5569 datasheet(21/86 Pages) TI1

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LP5569

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SNVSAP8 – JULY 2017

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Thermal shutdown is most often triggered by self-heating, which occurs when there is excessive power

dissipation in the device and/or insufficient thermal dissipation. LP5569 power dissipation increases with

increased output current and input voltage. When self-heating brings on thermal shutdown, thermal cycling is the

typical result. Thermal cycling is the repeating process where the part self-heats, enters thermal shutdown

(where internal power dissipation is practically zero), cools, turns on, and then heats up again to the thermal

shutdown threshold. Thermal cycling is recognized by a pulsing output voltage and can be stopped by reducing

the internal power dissipation (reduce input voltage and/or output current) or the ambient temperature. If thermal

cycling occurs under desired operating conditions, thermal dissipation performance must be improved to

accommodate the power dissipation of the LP5569 device. The QFN package is designed to have excellent

thermal properties that, when soldered to a PCB designed to aid thermal dissipation, allows the LP5569 device to

operate under very demanding power-dissipation conditions.

8.3.5.2 Undervoltage Lockout (UVLO)

The LP5569 device has an internal comparator that monitors the voltage at VIN. If the input voltage drops to 2.2

V (nominal), undervoltage is detected, the LED outputs and the charge pump shut down, and the corresponding

fault bit is set in the fault register. Hysteresis is implemented for the threshold level to avoid continuous triggering

of a fault when the threshold is reached. If the input voltage rises above 2.3 V (nominal), the LP5569 device

resumes normal operation.

8.3.5.3 Power-On Reset (POR)

The LP5569 device has internal comparators that monitor the voltages at VIN and V1P8. When VVIN is below

TBD V or V1P8 is below TBD V, reset is active and the LP5569 device is in the DISABLED state.

8.3.5.4 LED Fault Detection

The LP5569 device contains both open-LED and shorted-LED fault detection. These fault detections are

designed to be used in production-level testing and not normal operation. For the fault flags to operate, they must

be enabled via the MISC2 register (address 33h) LED_OPEN_TEST and LED_SHORT_TEST bits. The fault

flags are shared by both open-LED and shorted-LED tests so only one can be enabled at a time. The default

LED-fault status is ready in the LED_FAULT1 and LED_FAULT2 registers (addresses 81h and 82h). The

following sections detail the proper procedure for reading back open and short faults in the LED strings.

8.3.5.4.1

Open LED

The LP5569 device features one fault flag per LED, indicating one or more of the active low-voltage LED strings

are open. An open in a low-voltage LED string is flagged if the voltage at the input to any active low-voltage

current sink goes below the drv_headroom[1:0] setting in the MISC2 register. The procedure for detecting an

open-LED fault is:

1. Set the LP5569 device in the STANDBY state.

2. Configure the charge pump in the 1.5× mode.

3. Set the LED_OPEN_TEST bit = 1 in the MISC2 register (address 33h).

4. Set the chip_en bit = 1 in the CONTROL register (address 0h) with the LP5569 device in the NORMAL state.

5. Wait at least 500 µs.

6. Enable all LEDs, and set all LEDs to 100% brightness.

7. Wait at least 500 µs.

8. Check the fault status of the LED_FAULT1 and LED_FAULT2 registers.

9. Set the LED_OPEN_TEST bit = 0 in the MISC2 register (address 33h).

10. Set all LEDs to 0% brightness.

8.3.5.4.2

Shorted LED

The LP5569 device features one fault flag per LED, indicating when any active LED is shorted (anode to

cathode). During the LED short test, the charge pump is forced to the 1× mode. A short in the LED is determined

when the LED voltage (VIN – LED VF) falls below 1 V. The procedure for detecting a shorted-LED fault is:

1. Set the LP5569 device in the STANDBY state.

2. Configure the charge pump in the 1× mode, set LED PWM (0x16-0x1E) and LED current (0x22–0x2A) to

maximum value. depending on the LED channel being tested.

LP5569 Datasheet(PDF) 21 Page - Texas Instruments

LP5569 Datasheet(HTML) 21 Page - Texas Instruments

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