TPS55289EVM: tps55289 with output 6A for power LED

Hi Sakar,

Thanks for reaching out.

First, let me check the experiment results.

1. With DC power supply, TPS55289 can output 5V/6A, but can only output 4.2V/4A, not up to 6A.

2. With Panasonic NCR18650GA, TPS55289 can output 5V/5A, and can't increase the LED current even with higher output voltage.

Below are my comments:

#1. It's strange that the output current can't be 6A with 4.2Vout and 4.5Vin, can you share the waveforms of inductor current, SW1, SW2 and Vout?

#2. Assuming the battery voltage is 3.7V, the input current would be about 5V*5A/0.95/3.7V=7.1A, the average inductor current limit can be triggered. What is the output voltage/output current requirement for LED?

BRs,

Bryce 

Reply to #2:

I have tested the Panasonic NCR18650GA battery with a full charge of 4.2V. The LED I am working with requires an output voltage of 5V and a current of 6A. This means that I can drive the LED with a current of 6A while maintaining a voltage of 5V.

My goal is to operate the LED at a constant current of 6A, and the voltage output is not a critical factor. To achieve this, I will incorporate an r-shunt small value in serie to the LED to measure the LED current and provide feedback to the MCU. The MCU will then control the TPS55289 through i2c to ensure a stable output of 6A.

After the LED has been powered with a maximum current of 6A for 30 seconds, next is to lower the output voltage of the TPS55289, maintaining the LED current at 1A.


btw, I used the TPS55289EVM during my testing and successfully control it by the USB2ANY via the IT web software


Best regard,
Sakar

Hi Sakarin,

Glad to know that you can do it with EVM now.

However, from the calculation, assuming the battery voltage is 4.2V, the input current would be about 5V*6A/0.95/4.2V=7.5A which is higher than the minimum value of average inductor current limit, so it is possible that some silicon can't output 30W with 4.2Vin.

BRs,

Bryce

When utilizing a DC power supply set to an output of 7V and 10A to provide power to the TPS55289EVM, I observed that the output, when connected to an LED load, reached 6A. This has caused confusion and raised concerns regarding the performance, especially when compared to using a battery or a low DC power supply set to 4.5V/10A.

Hi Sakarin,

It makes sense because when you increase the input voltage to 7V, the device would work in buck mode with 5Vo, it means the average inductor current limit would be the output current limit, so it can increase up to 7A loading.

But if you use the 4.2V battery, the device would work in Boost mode with 5Vout, it means the average inductor current limit would be the input current limit, so it can support up to 7A input current, but can't support 5Vo/6A loading if the input voltage is low.

BRs,

Bryce

if I supply voltage 4.5 to the TPS55289EVM, it's ok if the output does not reach 6A. The problem is the output of the the TPS55289EVM is ON and OFF immediately when I set the output voltage of the TPS55289EVM to 5V

Can I set the TPS55289EVM to have output always even the output does not reach 5V?
Because, if I supply with battery we will not know the battery voltage during operation. Or do I need to create battery profile to set the TPS55289EVM accordingly based on the vary of battery voltage?

Hi Sakarin,

I think you can use the output current limit function in this application. If you set the ISP-ISN voltage limit to 60mV, the output current limit will be 6A with 10mohm Rsense. Same for 1A output current limit.

BRs,

Bryce