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LP5562: Double expected current draw

Michael Durian
Prodigy 210 points
Part Number: LP5562

I'm using the LP5562 to drive 4 display backlight LEDs. I've configured the LP5562 for 15mA current and set the PWM to 100% (255). Each time I change the PWM value for one of the LEDs from 0 to 255, I see about double the current draw I'm expecting. My bench power supply shows an increase in current of 28-31mA when I'd expected about 15mA. Since I'm measuring at the bench supply, I expect slightly higher numbers due to power loss in the on-board regulator, but not that much. I'm using a TPS610997 which is a switching regulator. At these current draw levels, the efficiency should be in the 90s.

The LP5562 registers are set as follows:

ENABLE = 0xc0
OP_MODE = 0x00
B_PWM = 0xff
G_PWM = 0xff
R_PWM = 0xff
B_CURRENT = 0x96
G_CURRENT = 0x96
R_CURRENT = 0x96
CONFIG = 0x01
STATUS = 0x00
W_PWM = 0xff
W_CURRENT = 0x96
LED_MAP = 0x00

Does the LP5562 consume that much current in addition to the current going through the LED?

  • 0
    TI__Genius 14295 points

    Let us check this and reply you soon.

  • 0 in reply to Kenneth Du
    Prodigy 210 points

    Thank you.

    I collected some more data by incrementally increasing the current value for one driver. It is very linear and seems to increase about 180uA per current value (instead of the expected 100uA). Changing the current value from 0 to 150 changes the mA reading from 21mA to 49mA (with 21mA going to other parts of my circuit). I don't have a way to measure the current flowing through the LED, so these readings are coming from my bench supply. Perhaps the current through the LED is accurate and something else is accounting for the extra 80% draw, but I'm not sure what it would be.

  • 0 in reply to Michael Durian
    Prodigy 210 points

    Okay. I think I'm just being dumb. In my two tests, I've either powered the display from 5V or from 3.3V out of an LDO driven by the 5V. My input into the boost regulator that generate the 5V is 3V, The higher current I'm seeing at the 3V bench supply is required to meet the same current level at 5V. The power is roughly the same. I think this is a non-issue.

    Thanks,

    mike

  • 0 in reply to Michael Durian
    TI__Genius 14295 points

    So it seems you have figured out the cause.

    Anyhow if you have more questions just let us know.