Tool/software:
Hi team,
My customer Valeo asked if TPS92638-Q1 can support 600Hz@0.4% duty cycle PWM Dimming. If not, what is the min duty cycle for 600Hz PWM dimming of TPS92638-Q1? Or can we recommend a similar device can meet 600Hz@0.4% duty cycle dimming requirement?
Thank you
Best Regards,
Xiaowei Zhang
Hi Xiaowei,
A 600Hz PWM signal at 0.4% dimming has an on-time of 6.7μs. According to TPS92638-Q1 datasheet, there is a 45μs (max) delay between PWM edge and current output response. With these limitations it is not possible to reliably achieve 6.7μs on-time.
0.4% dimming ratio is a very difficult target. What is the application? Is this for LED backlight?
Typically, very low dimming ratios result in poor linearity as the output waveform becomes triangular instead of square. In certain cases this can also affect fault detection as the internal fault monitor expects a square wave output and requires a certain on-time for accurate measurement. Therefore, the minimum PWM dimming is dependent on your linearity requirements and the fault detection, as well as other factors such as output capacitance and forward voltage.
To achieve the lowest possible dimming ratios, I recommend a device with a precise internal PWM control.
https://www.ti.com/product/TLC6C5724-Q1
https://www.ti.com/product/TLC6C5748-Q1
If this is backlight application, I recommend a device specifically designed for backlight.
https://www.ti.com/product/TLC69601-Q1
Regards,
Zach
Hi Xiaowei,
Thank you for the clarification. Much of my previous response is still relevant, even for a slightly relaxed duty cycle requirement.
Also notice that the fault deglitch time is 80μs (min) and 175μs (max). Therefore, for an on-time of 67μs you will not be able to use the internal fault diagnostics of the device. Do you require fault diagnostics for your application?
Regards,
Zach
