TPS65530: FBG7/8

Rolf Wendt

Part Number: TPS65530
Other Parts Discussed in Thread: BQ24196,

Trying to breath life into the TPS65530. It is being driven from a BQ24196, so VSYS is 3.3-4.3V (4.3V nom). It appears as if I don't ever go into PWM mode, and after about 1mSec, I have notice that the MosFet controlling FBG7/8 turns off, forcing FB to go to PS rail. There is no mention in the datasheet with respect to what FBG7/8 does or how it is controlled so that I have no idea why this is happening.

I have attached my implementation, and a scope capture that may be helpful.

over 6 years ago

0 Rolf Wendt over 6 years ago

Intellectual 470 points

I should also note that the connectivity around Q1 has been corrected:

Also, BRD_SLEEPn is tied to VSYS (4.3V)

0 Gavin Wang (Zejing) over 6 years ago in reply to Rolf Wendt

TI__Expert 3480 points

Hi Rolf,

Firstly, can you update your wrong schematic? Channel 8 is a boost controller inside. But in your schematic, it is buck.
Secondly, FBG7/8 is GND for CH7/8 feedback resistors. There is Mosfet inside connected with GND. Can you check the waveforms of XSLEEP and ENAFE?

0 Rolf Wendt over 6 years ago in reply to Gavin Wang (Zejing)

Intellectual 470 points

Thank you very much. I caught the buck/boost issue prior to the email (update in one of my replies. The AFE is tied low through 100K pulldown, and the XSLEEP is tied to CSYS (4.3V).

What controls the Mosfet for FBG7/8?

0 Rolf Wendt over 6 years ago in reply to Rolf Wendt

Intellectual 470 points

Attached is an updated drawing

0 Rolf Wendt over 6 years ago in reply to Rolf Wendt

Intellectual 470 points

VREF never achieves more than 500mV.

Would it be possible to escalate this issue, or open up a more direct dialog?

0 Rolf Wendt over 6 years ago in reply to Rolf Wendt

Intellectual 470 points

What controls the MOSFET of the FBG7/8. This is not described in the datasheet.

This is issue is now on the critical path on the development schedule. Is there any mechanism where one can avoid the message relay latencies?

0 Rolf Wendt over 6 years ago in reply to Rolf Wendt

Intellectual 470 points

R45 is actually 10k (fyi)

0 Rolf Wendt over 6 years ago in reply to Rolf Wendt

Intellectual 470 points

Reducing the LL8 current resistor to 10 ohms corrected the issue. This could have been accelerated with support from TI, which was lacking. Unfortunately, I will take this experience into consideration when designing my next project.

0 Rolf Wendt over 6 years ago in reply to Rolf Wendt

Intellectual 470 points

Nope. FBG7/8 is 1V consistently, though the voltage is switching.

0 Rolf Wendt over 6 years ago in reply to Rolf Wendt

Intellectual 470 points

Could someone send me a schematic example of a fully operational board?

0 Rolf Wendt over 6 years ago in reply to Rolf Wendt

Intellectual 470 points

Things run marginally. If I attempt to measure at FB8 using a DVM, 9 out of 10 times the chip stops regulating. I have added a 100pF Cap across the upper FB resistor to stabilize this. Onward.

0 Rolf Wendt over 6 years ago in reply to Rolf Wendt

Intellectual 470 points

HELLO?????

0 Gavin Wang (Zejing) over 6 years ago in reply to Rolf Wendt

TI__Expert 3480 points

Any concern? You can follow the sch shown as follows.

0 Rolf Wendt over 6 years ago in reply to Gavin Wang (Zejing)

Intellectual 470 points

That's directly from the datasheet. The value of the resistor (for example) is omitted. Origionally, it was 1K, but I reduced it to 10 ohm resistor, which limits the current to 500mA, less than the peak switch capabilities.

A real application datasheet would be appreciated.

Power management

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TPS65530: FBG7/8