TL2843B: No output on pin6 (output pin).

Hi,

How much capacitance is on Isense pin? The capacitance on Isense pin will make minimum width of pulse which may demand higher minimum load? Can you keep increase the minimum load until the Vout is ok, and decide if the minimum load is too high or not?

Hi. There is a 56pF cap on Isense. just to be clear it is pin6 that is 0V (not the converter's output, which of course is 0V because the FET driver has no input right now). I don't see a single pulse out of pin 6 after powering up. I will try smaller pull-dn on pin 6.

Hi,

Can you provide your schematics for review?

I incrementally lowered the pin 6 pull down resistor to 550ohm to no effect.

I'm not seeing a reason from the block diagram why the output would be low. VCC is good because the 5Vref is outputting. The 5Vref measures at 4.99V. FB is <2.5V, Isense is <1V.

What should this controller be doing at start-up? Is there a reset or enable that kicks start this thing?

this picture is of the RT/CT pin.

This pic is of the schematic section of the controller.

Hi,

Is pin 6 high?

Hi,

Can you try increase VCC above 17V to see if pin 6 becomes high?

pin 6 is low. I will increase VCC above 17V and check pin 6.

At VCC=17.4V, pin 6 is low. 

with the circuit unpowered, I measured the resistance from pin 6 to ground: .1ohm. I think this part is trashed. I'll replace it and check pin 6 again.