TPS61021EVM-723: Re-chargeable Nimh battery 1.2v Usage

Hi Helen,

Thanks for your support and answer. Actually I added load after startup the boost converter. But ı think your answer is for my second paragraph. After I added load after startup I can get suitable voltage & current at output. But when I use battery cell as input source, I live problem which I defined at below paragraph as before. So, can you check the situation again for battery source input?

"I am using Re-chargeable Nimh AA battery (1.2v) at Input of "TPS61021EVM-723" Board and "5.5ohm" fixed load is connected to the output of Board to pull fixed current (approximately 600mA). Theoretically, I must pull 1.45A-1.65A from One AA cell. But Voltage output goes down to 0.1V-0.2V at "TPS61021EVM-723" Board Voltage Output. Also I tested my Cell' s current capacity and it is 2000mA when I did short circuit between (+) and (-) of cell. I am using "GP Batteries" rechargable Cell which details are at below web link. Can you inform me what is the point we missed? Why we can not get output voltage/current at TPS61021 when we used ReChargable Cell as Voltage source at Input?"

https://www.gpbatteries.com/int_en/batteries/2700aa 

Thanks.

Hİ Helen,

If you mean VOUT as on board Voltage, Yes as I said before it was 0.1V-0.2V. I couldn't get 3.3V Output Voltage.

Also, what is your suggested Re-chargeable Nimh AA battery product or Manufacturer for TPS61021A? With Which brand battery we can run TPS61021A?

Also, you said the start-up current is 100mA. So, is it input current or output/3.3V current?

I need exact solution and answer for rechargable battery usage to move with TPS61021A.

Thanks.

Hi,

TEST-1:
When I measured the voltage of AA Cell without connecting it to Boost, I see 1.35V-1.40V on AA Cell. When I connected Cell to Boost' s Input as source and also Load (5.5Ohm) is connected at output of Boost, I see Input Voltage (Cell Voltage) as 1.35V approximately. It was >0.9V. But I couldn't get 3.3V at output while Load is connected. After I disconnected the Load at Boost's output, I start to see 3.3V as Vout.

TEST-2:
I used 44Ohm (25W) Power Resistor to pull 50-100mA at output. I saw 3.3V as Vout and I pulled approximately 70mA when 44ohm (25W) Resistor connected. While circuit is running, I connected 5.5Ohm as parallel to 44ohm (25W) Resistor and Boost Vout goes down to 0.1V-0.2V. I couldn't understand situation. You said me the initial start-up load current should be 50-100mA. I provided this condition and while circuit running I tried to pull more current decreasing the load impedance. But I lived same problem. So, what is your suggestion at this situation?

Also, what is Texas (TI) suggested Re-chargeable Nimh AA battery product or Manufacturer for TPS61021A? With Which brand battery we can run TPS61021A? 

Thanks.

Dear Sir,

The maximum output capability of the TPS61021A at Vin=1.2V is 3.3V/0.8A. And this 1.2V is the on board voltage, which is tested at the TPS61021's Vin pin(inductor). 

The AA battery has big impedance, so with extra 5.5ohm resistive load, the on board Vin=Vbat-Iin* Rbat=1.4V-2A*0.25=0.9V. So even the impedance is only 0.25 ohm, it is already drop to the minimum startup voltage.  And the maximum output capability after startup at Vin=0.9V is around 0.5A.

Sorry, we have no experience of the AA battery selection. They need to check with the supplier for the impedance curve.

Unfortunately I couldn't get any solution from TI (Texas Inst) side. I was hoping to get solution about usage of AA NiMH cell with TPS61021A IC. I think ı couldn't move with TPS61021A. At this situation we can move to Li-Ion Battery type.

Hi,

It can be possible but your IC supports Max 1A@3.3Vout and 1.2Vin. Also my NiMH Cells support max 2000mA when I did short circuit between (+) and (-) polarity.

Thanks.