TPS54560: Split-Rail, Problems generating +-15V from Vin 24V

Qais Sunna

Part Number: TPS54560
Other Parts Discussed in Thread: LM5160

Tool/software:

Hello,

As shown in the schematics below, I am trying to generate +-15V using split rail configurations from TPS54560. The circuit behaves weirdly by drawing too much current without any signs of correct output voltages. Am I doing something wrong with the component values i.e too large output capacitance value? I

Tested with two different coupled Inductors:
YPRH1207C-150M
SRF1280-150M

Please let me know if more information is needed.

Any help or guidance is greatly appreciated. Thanks!

2 months ago

0 EricLee 2 months ago

TI__Guru 61891 points

Hello Qais

Please measure VIN, IIN, VOUT and IOUT when you think the circuit behaves weirdly by drawing too much current, and let me know the measurement results.

Also, please capture some waveforms for more investigation.

-EL

0 Qais Sunna 2 months ago

Prodigy 10 points

Hey EL,

Thanks for your reply.

@ No load connected:
V_in = 23.96V
I_in = 0A
V_out+ = 24V
V_out- = -5.56V
I_out = 0A

@ 430R 5W Resistor connected as load to +/-15V:
V_in = 23.96V
I_in = 0.059A

V_out+ = 22.06V
I_out+ = -0.051A

V_out- = -7.51V
I_out- = 0.017A

Here is the signals on each of the IC pins in order.

PIN 1: BOOT

PIN 2: VIN

PIN 3: ENA

PIN 4: RT/CLK

PIN 5: FB

PIN 6: COMP

PIN 7: GND

PIN 8: SW

0 EricLee 2 months ago in reply to Qais Sunna

TI__Guru 61891 points

Hello Qais

I think this split-rail configuration works properly only in CCM, especially when the loads on both sides are balanced .

If you'd like to have a good output regulation at light load, please consider LM5160 which supports FPWM mode at light load. If you have a question about LM5160 device, please create a new post.

-EL

0 Qais Sunna 2 months ago in reply to EricLee

Prodigy 10 points

Hey Eric,

Thanks for the reply. We have designed the split-rail buck converter based on the datasheet as well as the hints in this post:

TPS54560: Split-Rail Power Supply - Power management forum - Power management - TI E2E support forums

Since we have already invested a lot of time prototyping with this chip "TPS54560", could you please point us in the correct direction on how to test it in the CCM mode and how to possibly achieve the +-15V outputs?

I appreciate your support!

+1 EricLee 1 month ago in reply to Qais Sunna

TI__Guru 61891 points

Hello Qais

If you'd like to use TPS54560 in Split-Rail configuration, you may have to add dummy loads on both sides in order to make the converter works in CCM.

Also, by increasing L1, the converter will be able to enter CCM more easily.

If you'd like to have a good output regulation at light load, please consider LM5160 which supports FPWM mode at light load.

-EL

0 Qais Sunna 1 month ago in reply to EricLee

Prodigy 10 points

Thanks for the help. I will consider LM5160!

0 EricLee 1 month ago in reply to Qais Sunna

TI__Guru 61891 points

Thanks for choosing TI. Please feel free to contact us if you have any question.
-EL