LM3550: feedback is 80mV

Hi Ben,

     I'm sorry that I'm snot clear about your problem, coudl you describe clearly? Does your board works fine? Have you turned on the device yet?

     I think may be you need to check your regs setting carefully to make sure all regs setting are right!

BR

Sean

Hello,

I have made these boards. my issue is the feedback pin (pin 5) is regulating to 75mV - 80mV. I have tried setting register A0 to FF and E0 but this made no effect.

Please can you advise on any ideas for this?

Target address is 0x53

10 D2 

[this should have turned on the capacitor charging]

the only registers changed from default are:

Target address is 0x53

B0 0F   [this should increase the flash LED on time to 512ms]

Kind regards,

Ben

Hello,

please see the trace below. this shows the capacitor volts in rd and the feedback sense voltage in blue.

Any ideas would be very welcome. 

Hi Ben,

    Please provide the schematic, I want to check the schematic first.

BR

Sean

Hello,

Please see Schematic below

Hi Ben,

     The schematic image seems damaged, I can't see it form this forum. From the waveforms that you have shown, it seems the device has worked, but it seems you need to check the regs setting and I would suggest you read the datasheet carefully, especially for the setting of the reg. 

BR

Sean

hello,

it doesn't seem to have uploaded properly, see below.

Hi Ben,

     Several suggestions for you:

    1. Check the I2C interface whether it can communicate correctly?

    2. Could you send me the regs list that you send to LM3550?

    3. Schematic seems ok from my side.

BR

Sean

Hello,

I am using the TI USB-TO-GPIO adaptor to send the below messages. I do get an ACK reply.

see below

Hi Ben,

     You can try with below regs:

     0x10: 0x99;

     0xA0: 0x3F;

     0xB0: 0xFF;

     0xC0: 0xFF;

     0xD0: 0x0F;

BR

Sean

Hello,

this appears to set torch mode, the average voltage was impossible to measure as it is so low.

Driving the strobe high turned off the torch mode.

Is this what you expected?

However, when I set 

0x10, 0xD2
0x0B, 0x0F

along with the other registers you recommended this seems to have corrected the issue! 

Admittedly this is now running in edge trigger mode, but I think that this has resolved the issue - must be something in the other registers.

I will go away and try and work out the edge triggering and what setting made this work and come back to resolve this issue.

Hello,

On reviewing the registers you have instructed me to write 3F to bank A0, but this sets 0011 1111, the datasheet states that the bit 6 and 7 should always be 1, can you explain why this has been changed?

to correct my level vs edge trigger mode I should have been writing 8F to bank B0, that was my mistake.

please can you confirm register A0 what setting bits 6 and 7 to 0 does?

Hi Ben,

    I'm sorry that's my mistake, for A0, bit 6 and bit7 should be 11. I don't have more suggestions now, it is really strange that you may need to try with MCU to send the I2C command? Or you may need to check the regs setting and hardware connection.

BR

Sean

Hi Sean,

it seems to have fixed the issue so I am not complaining. I now know the hardware works and that there is a set of register settings which will allow us to achieve what was needed.

I will continue to investigate and update this thread once I have an answer.

Kind regards,

Ben Strawbridge

Hi Ben,

    Sure, I'm sorry that I can't provide more suggestions here, please let me know if you have found something.

BR

Sean