TPA3111D1: SD pin low when power via 100k from VCC

Michael Gilge

Part Number: TPA3111D1

Hello,

we operate the TPA3111 from a 21.6V rail. The SD-pin is connected via a 100k resistor to the 21.6V, as suggested by the datasheet and also the EVM.

However, the amplifier will not start and the SD-pin stays low, even when there is no connection with the FAULT pin. How much current is the SD pin sinking?

When I connect SD with the 3.3V rail, the amplifier works fine.

Is there power sequencing required?

Best regards,

Michael

over 6 years ago

0 Yanming Gong over 6 years ago

TI__Mastermind 19880 points

Hi Michael,

The voltage slew rate of SD, FAULT, GAIN0, GAIN1, AVCC must be restricted to no more than 10 V/ms. You can try to change the 100K ohm resistor to 200K, and check if any improvement.

Regards,

Derek

0 Michael Gilge over 6 years ago in reply to Yanming Gong

Expert 1720 points

Hi Derek,

you mean I should double all 100k resistors to the slew rate sensitive pins to 200k?

Also, can you recommend an EMI filter for the power supply?

I am just back from conducted emission testing: We need an LC output filter!

Best regard,

Michael

0 Michael Gilge over 6 years ago in reply to Yanming Gong

Expert 1720 points

Hi Derek,

I did measure the slew rate for PVCC and find it far from 10V/ms:

Even the first fast rise to app. 2.5V is app. 5V/ms.

Best,

Michael

0 Yanming Gong over 6 years ago in reply to Michael Gilge

TI__Mastermind 19880 points

Hi Michael,

Can you share the schematic to us?

Regards,

Derek

0 Michael Gilge over 6 years ago in reply to Yanming Gong

Expert 1720 points

Hi Derek,

sure - see schematic attached. We use PLIMIT feature to lower power to app. 5W if only standard PoE is available.

Best regards,

Michael

0 Michael Gilge over 6 years ago in reply to Yanming Gong

Expert 1720 points

We will also swap the ferrite bead + C output filter aganist a 33uH + 1uF LC-Filter.

Can you recommend a power supply PI-filter design?

0 Alix Wan over 6 years ago in reply to Michael Gilge

TI__Genius 9995 points

Hi Michael,

Have you passed the CE test while fail passing RE test now?

Usually LC filter can help to pass RE test without pi filter in PVCC.

Regards,

Alix Wan.

0 Michael Gilge over 6 years ago in reply to Alix Wan

Expert 1720 points

Hello Alix,

we have passed CE test with the LC filter on the output. We will go to test RE on Thursday. I am concerned about RE test and wanted to be on the safe side.

Regards,

Michael

0 Yanming Gong over 6 years ago in reply to Michael Gilge

TI__Mastermind 19880 points

Hi Michael,

The schematic look fine. I suggest that monitor the PVCC, SD, Fault pins together to find the abnormal behavior compared with normal behavior.

Regards,

Derek

0 Michael Gilge over 6 years ago in reply to Yanming Gong

Expert 1720 points

Hi Derek,

can we connect the shutdown pin to a 3.3V rail in the system? We want the amplifier on all the time.

What resistor do you recommend for the 3.3V connection to the SD-pin?

Regards,

MIchael

0 Yanming Gong over 6 years ago in reply to Michael Gilge

TI__Mastermind 19880 points

Hi Michael,

Sure, you can connect the SD pin to 3.3V rail in the system. Please see the 6.3 Recommended Operating Conditions in datasheet.

Pull-up to 3.3V by 1.5K or 4.7K is fine.

Regards,

Derek

0 Michael Gilge over 6 years ago in reply to Yanming Gong

Expert 1720 points

Hi Derek,

can you shed some light on table 2 for the relationsship between PLIMIT and the output power.

I am trying to reproduce the calculations but I do not arrive at the values from the table.

I have Vcc=22V, RL=8 Ohms. If I roughly disregard Rdson and any resistance of the output filter and want 10W output power, I arrive at

Vp = 4 * PLIMIT = SQRT(10W x 2 x RL) = 12.65

PLIMIT = 3.16V

Is that correct?

Regards,

Michael

0 Michael Gilge over 6 years ago in reply to Yanming Gong

Expert 1720 points

We are down to 1.5K but the TPA3111 will not start. Only if we tie the SD-pin directly to 3.3V the TPA31111 will work.

Any ideas?

0 Alix Wan over 6 years ago in reply to Michael Gilge

TI__Genius 9995 points

Hello customer,

When 1.5K resistor is tied to 3.3V, can you check the voltage to judge whether it works or not?

Regards,

Alix Wan.

0 Michael Gilge over 6 years ago in reply to Alix Wan

Expert 1720 points

Hello Alix,

when we tie a 1.5K resistor from 3.3V to the SD-pin (pin 1) the voltage at the pin is 0.05 V and the amplifier does not work. When we tie the 3.3V directly to the pin, the amplifier is working but runs hot. It seems that pin1 is sinking a lot of current. We have NOT connected FAULT (pin 2) to pin 1.

Regards,

Michael

0 Michael Gilge over 6 years ago in reply to Yanming Gong

Expert 1720 points

I changed all 100k resistors to 200k resistor but this did not change anything.

The SD-pin (pin 1) stays low.

0 Michael Gilge over 6 years ago in reply to Michael Gilge

Expert 1720 points

I found that when power cycling, the TPA3111 starts (I see switching at the output), the speaker clicks and then the TPA3111 switches off.

I have 2 1uF capacitors at the inputs. Why would the amplifier switch off?

0 Yanming Gong over 6 years ago in reply to Michael Gilge

TI__Mastermind 19880 points

Hi Michael,

Please check the FAULT pin status, if any FAULT report?

TPA3111 can not pull SD pin to low, SD pin is controlled by peripheral circuit.

Regards,

Derek

0 Michael Gilge over 6 years ago in reply to Yanming Gong

Expert 1720 points

Hi Derek,

is there a chance that a DC signal at the inputs can cause the amplifier to switch off despite having the 2 capacitors in the input lines?

Regards,

MIchael

0 Yanming Gong over 6 years ago in reply to Michael Gilge

TI__Mastermind 19880 points

Hi Michael,

Yes, DC detect fault is also reported. Any fault issues happened, TPA3111 output will be Hi-Z.

DC Fault mostly is related to the DC caps offset.

Did you check the Fault pin?

Regards,

Derek

0 Michael Gilge over 6 years ago in reply to Yanming Gong

Expert 1720 points

Hi Derek,

I found the problem - hanks for your support. The SD# input was driven low by a GPIO from the Audio DSP, which was still configured as output.

The only issue left is the relationsship between PLIMIT voltage and output power. Somebody mentioned an excel sheet which would have the calculations. Table 2 and equation (1) in the datasheet do not match. Using the equation I do not get te values of the table.

Regards,

Michael

0 Yanming Gong over 6 years ago in reply to Michael Gilge

TI__Mastermind 19880 points

Hi Michael,

Good news!

The deviation between table 2 and actual value is related to the resistors and layout trace.

You can adjust according to you application.

Regards,

Derek

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TPA3111D1: SD pin low when power via 100k from VCC