Products Mentioned

MAX20039 Recommended for New Designs
The MAX20039/MAX20040 ICs are a small, synchronous buck-boost converter family with integrated high-side and low-side switches. The MAX20040 is designed...
Datasheet
MAX20039 on Analog.com

Thread Details

State Not Answered
Replies 5 replies
Subscribers 40 subscribers
Views 768 views
Users 0 members are here

MAX20039 whistling

CAPMT

on Oct 23, 2024

Category: Hardware

Product Number: MAX20039

I designed a CPU board with SMARC board and touch screen.

I am using the MAX20039 for the 12V backlight touch screen power supply. MAX20039 input is a 12.8 from battery.

The touchscreen have a pin ADJ to drive the brightness with PWM signal.

If the ADJ is place to 3.3V (without PWM), everything works well and the backlight is at 100%.

If I apply to ADJ a PWM (0 - 3.3V - 50%), the backlight is at 50%, but the CPU board generates an audible whistling sound.

Please find attached my schematics.

Brian1201
on Oct 23, 2024 8:26 PM
0
CAPMT said:
Please find attached my schematics.

The attached circuit doesn't has the backlight ADJ pwm circuit. Can you include it? What does the 12v output signal look like -- clean DC or tons of ripples -- when it's shistling?

Brian
Cancel
Up 0 Down

Verify Answer

Cancel
CAPMT
on Oct 24, 2024 3:36 AM in reply to Brian1201
0
ADJ PWM is only a wire bitween GPIO from SMARC (IMX8) and touchscreen LCD (with a levelshifter).
Cancel
Up 0 Down

Verify Answer

Cancel
CAPMT
on Oct 24, 2024 3:38 AM in reply to CAPMT
0
Power supply from MAX20039 comes here:
Cancel
Up 0 Down

Verify Answer

Cancel
Brian1201
on Oct 25, 2024 5:20 PM
0
CAPMT said:
If I apply to ADJ a PWM (0 - 3.3V - 50%), the backlight is at 50%, but the CPU board generates an audible whistling sound.

I would use another 12v power supply and connect to the LCD backlight 12v input to see if the whistling happens, then the issue is in the backlight circuit and not the 12v regulator.
Cancel
Up 0 Down

Verify Answer

Cancel
CAPMT
on Oct 28, 2024 4:31 AM in reply to Brian1201
0
I've already done that.

It comes from the MAX20039.
Cancel
Up 0 Down

Verify Answer

Cancel