IRS2452AM not switching when load is connected on power up in BTL Mode

[ee_guy21]

Hello, 

I am attempting to use the IRS2452AM Class D amplifier in the Full Bridge (BTL Mode) configuration to drive a step up transformer. Right now I am using the IRAUDAMP23 development kit to verify my design before laying out custom hardware. My current issue is that when I turn on the chip (i.e. when I flip the reset switch on the dev board to enable the chip) the device does not do any switching if a load is connected. If I disconnect the load, the device immediately starts switching as I would expect a full bridge amplifier to do so. In some cases I can re-connect the load and device continues switching and pushing power out to the load, in others it stops switching again. 

Right now I'm driving the bridge outputs directly into a resistor. I'm using +-20v for supply and have used a 4k and 180 ohm power resistors as load. 

At first I was suspicious of OCP (over current protection) triggering, but I see no evidence of that when I monitor the CSD pin. 

If I run the IC in half bridge mode it always works when I switch it on. 

Thanks,

[Guruprasad_A]

Hi @ee_guy21 ,

Thank you for posting in the Infineon community.

Is there a current limit on supply? if so, please recheck with the increased current limit on supply.

Are you following the "Test procedure" mentioned in the app note IRAUDAMP23.

Regards,

Guruprasad

[ee_guy21]

Thanks for the quick response Guruprasad,

I've been running with 1A current limits on my +-20v bipolar supply and took them up to 6A and saw the same behavior. I also monitored +B, -B, VAA, VSS, and VCC for droops during the switch on event and haven't seen any.

I'm following the "Test Procedure" as close as I am able to. I've gotten the same behavior to happen in half bridge mode if I run the bridge outputs directly across a 20 ohm resistor. However in this scenario if I apply an input signal the device starts switching and keeps switching if I remove the signal. If the input signal is there when I switch S1 (the enable switch) then the half bridge switches. If I have a 4k ohm resistor across the bridge outputs it always switches. So I agree it seems like some sort of in rush or startup condition.

As noted above I think it's worth noting here that I have removed the LC filter on the output and are driving the bridge outputs directly into a restive load.

Is there anything about the LC filter on the output that aides in the feedback or is the IC assuming that the there will be those reactive elements out there to filter some of the load current?

Thanks,

[Guruprasad_A]

Hi @ee_guy21 ,

We are analyzing possibilities that could result in the problem.

Please validate that using LC Filter produces the same outcome.

What is the input voltage at P1?

Regards,

Guruprasad

[ee_guy21]

Thanks Guruprasad,

I was not seeing the issue with the LC filter connected. I ended up coming up with a work around. If I pull R15A, B, C, and D that essentially disables the over current protection and at least in half bridge mode it is always switching when I turn on the device.

I'm guessing this is some type of in-rush on startup condition that was triggering the OCP. I do not really need the OCP in my application so I'm fine with running without it. 

Thanks,