LED1202: LED channel damage

[SunilHD]

Hi Team,

We have used LED1202 in our board where one LED driver is connected to Microprocessor and one LED driver is connected to MCU.
We are seeing random LED channel damages (with LED driver which is connected to MCU) while device is in running state, and LED channel damage issue is random that any or all channels get damage which are connected to LEDs only. LED turns ON permanent which channel got damaged.

We had debugged the operating voltage fluctuations, ground bounce effects but nothing happens during the LED channel failure.

We have limited LED channel current to 6mA and using LED function as ON and OFF only. No PWM functionality os being used here.

Could you please let us know what can be the root cause here behind LED channel damage?

Thank you

[AScha.3]

Hi,

Can you show the circuit, so less guessing game?

[SunilHD]

Hi,
Please find the below circuit.

[AScha.3]

Hi,

Your circuit doesn't show the connection to the LED and what kind of LEDs used.

But from your findings with constant on driven LEDs: looks like the driver was overloaded, too high current or induction of a spike .

Which kind of LEDs, forward voltage?

And line/wire length from driver to GND return, = loop length: driver -- led-- gnd at driver?

I would at first increase the 100 resistors, maybe 330 ohms, to be sure, no over current can happen.

[SunilHD]

Hi,

LEDs are on Membrane keypad so it's not in the schematic design. We are connecting keypad to connector. On keypad, LED Anode is connected to +3.3V and Cathode is connected to LED driver IC pin through 100Ohm resistor.

We have set 100% PWM and 6.7mA current limit on each LED Driver channel using internal registers. Do you still suggest to increase series resistor to >100Ohm value?

Thank you

[AScha.3]

Hi,

Just what I would do: 

- supply LED1202 with 3v3, not 5v.

- try 330 ohm series resistors 

- add freewheeling diodes on all lines to LEDs, driver side output to 3v3, to prevent any spike here. Diodes just small fast types, like 1N4148 or anything like that.

[SunilHD]

Hi,

Currently we are using 3.3V power supply in the field and also mounted U65, U66 and U67 ESD diodes on the board. ESD diodes will work in place of Freewheeling diode, right?
Also, we will check with 1K resistor in series with LED.

Thank you

[AScha.3]

U65... Can you show actual circuit?

And type of esd diodes?

[SunilHD]

Hi,

You can check the ESD diode implementation in below circuit. Grey color parts are ESD diodes (P/N# DT6250-06MR-13) on LED lines which were not mounted earlier. We have mounted these parts now on board but still are seeing failure issues.

Thank you

[AScha.3]

Grey...ok.

>but still are seeing failure issues

So they are useless here. Breakdown at 8 V, useless to protect 5v max chip.

So just try 1n4148 or similar, as freewheeling diodes to 3v3, on all lines to LEDs, at the driver chip.

I had similar problem with driving a LED strip at 200mA , the 6A driver mosfet dead after some hours. With freewheeling diode to vcc, running for years now.