TPS61099: Vbatt voltage dropped when the boost started up

Hi Jianqiang,

I tried to search the case "CS0537905" in the e2e but no results. Could you please tell me where I can get the information? BTW, I cannot open your link.

The TPS61099 has integrated the soft-start mechanism inside, which limits the peak inductor current below 200mA until Vo reaches to 1.6V. You can find so in datasheet description 8.3.4 and waveform Figure.23.

My best guess is 100mA~200mA current needed by TPS61099 pulled battery voltage drops. You can do so by using a E-load externally and manually add 150mA load to this battery and see what happens.

-Wenhao 

Hi Wenhao,

Thanks for your information.

For this issue, the drops also happened without any loading on the output TPS61099. 

As you know, the Internal impedance is about 100 ohm which is very big. so we want to know the current when boost is powered on.

Thanks

Jianqiang Yuan

Hi Wenhao,

Thanks for your supports.

100mA charge current seems be larger for this system It can cause this drop. 

BTW, Do you have comments or solution for this Power supply solution? 

Thanks

Jianqiang Yuan

Hi Jianqiang,

 I think there are maybe three ways to help mitigate the issue below, but I need to think about the feasibility.

1.Increase input caps to sustain this 100mA charge current and prevent battery voltage from drop too deep;

2.Decrease the current consumption from TPS61099;

3.Increase the battery voltage;

I will get back on you before Tuesday. Thanks!

-Wenhao

Hi Wenhao,

Thanks for your  feedback quickly.

1. Yes. we tried to increase the caps. The drop voltage level can be decreased too. But the issue didn'tdisappear.

2. Yes. Please help to check if we can decrease the current from TPS61099. BTW, if you have any other boost for our requirement , please also share to us.

3. This requirement is from our end customer. they want to use the standard LiMn Battery (CR2032). And now we are discussing with them if they can change it to another one. 

Thanks

Jianqiang Yuan

Hi Jianqiang,

How are you controling the EN? I am wondering if we can delay EN and only start up the device after Vin has been fully established. 

-Wenhao

Hi Wenhao,

We are using one GPIO to control the TPS61099.  We can delay the EN. We tried the solution before, but still see the issue when we enable the EN pin.

Thanks

Jianqiang Yuan

Hi Jiangqiang,

I tested the start-up current for TPS610995 which is a fixed voltage version of TPS61099.

As you can see below, Ch2 is Vo, Ch4 is Inductor current. I used EN to ramp up the VO after VIN has been fully established. TPS61099 first ramps Vo with 100mA charge. After that, when the output voltage is charged above approximately 1.6 V, the device starts the hysteretic current mode operation. The current limit threshold is gradually increasing to 0.7× ILIM within 500 μs. So you can see here inductor current actually increased. This forced input current larger than 100mA after Vin>1.6V, which makes start-up more difficult with CR2032. The peak inductor current increases with current limit threshold gradually increases.

Theoretically, adding the input capacitor can actually works depends on how much capacitance you add. Suppose in the worst case there is no current from battery, the TPS61099 has to draw all the charge from CIN. If CIN is large enough to support VOUT to rise, then the final input voltage is VIN-COUT*VOUT/CIN. If this voltage is larger than UVLO, then the device is still alive.

Assume VIN=3.0V, VOUT=5V, COUT=20uF, to ensure the input voltage not exceed 0.5V (TPS61099's UVLO), the Cin should be larger than 40uF+some margin. I assume 20% margin here so 48uF can be used here.

Decrease current assumption cannot be used here. Even though I can extend the soft start up time after Vo rises to 1.6V (see SLVA307B), there is maybe no way we can decrease the 100mA charge when VOUT<1.6V.

I will check if there is any other DCDC which can meet your requirement. Please allow me two days.

-Wenhao

Hi Wenhao,

Thanks for your great supports.

Thanks

Jianqiang Yuan