TPS61230A: TPS61230A capacitor load ability?

Hi Feng:

May you confirm if the load is enable at beginning or enable after startup completed? And what's the type of load? 

The load is the 40mF capacitor to drive a PMIC with >1.5A current, it is enabled at the beginning.

Thanks and best regards,

Feng

What is the start up time, is around 1.5mS? I try to use boost converter calculator from TI, the model of the converter seems not working with a capacitor larger than 1.5mF, what do you think about TPS61022, which one is better? Do you mean enable the load through Enable pin of the boost converter or another switch for the load?

Thanks,

Feng

Hi Feng:

The soft start time could be calculated by Equation(1) in datasheet if it didn't meat the current limitation. But before that, there is a pre-charge phase. It has much smaller current limit. You could check the value in datasheet.  

For TPS61022, there is also "7.3.7 Output Short-to-Ground Protection" limit the current when the Vout is too low. 

There is a application note for improve the startup capability. You could have a look. http://www.ti.com/lit/an/slvaed6/slvaed6.pdf

Will the PMIC drain so much current before the Vout reach the target? Generally speaking, there is a min startup voltage limit for PMIC or its load. Please share the part number of PMIC, better with the information of the load of PMIC. We may could recommend solution for you.

Thanks Minqiu for the help, PMIC is disconnected before reaching to the target voltage, I calculated the output current, both parts are okay, but by using TI's boost converter simulation tool, TPS61230A seems not good to charge a large capacitor load, is this true?

Thanks,

Feng

Hi Feng,

I have several questions for you:

1. What's the reason that you put a 40mF super cap at output of TPS61230A?

2. TPS61230A has two phases during the start up. When the device is enabled, the high-side FET turns on to charge the output linearly by a DC current which is called the pre-charge phase. This pre-charge current limit spec min value is 1.0A. The pre-charge startup phase terminates until the output voltage being close to the input voltage (typically VOUT=VIN-115mV). After that, the device starts switching which is called the boost soft start phase. So TPS61230A cannot support 1.5A load current during the pre-charge phase. Please make sure the PMIC UVLO voltage is higher than 2.8V.

3. Which kind of simulation tool are you using? Can you share the model to us?

1. 40mF are used to store energy to provide the power for PMIC

2. If 40mF super CAP not reach to 5V, PMIC not on.

3. I use the Pspice model from TI' website

Thanks,

Hi Feng,

1. It's not necessary to put a super cap. The boost converter would provide the energy constantly. 

2. If you add a 40mF super capacitor is Pspice model, you need to set the simulation end time long enough. Probably 200ms. It will cost very long simulation time. 

3. My suggestion is you could use TPS61230A or TPS61022 directly. Input is 2.8V and output is 5V/1.5A. Super cap is not necessary.

1. The reason for using 40mF is our power board is not able to provide the high peak power for our application.

2. The reason is not the simulation time is not long enough, it is because the SW current goes to 0A after soft start, do you tried by yourself?

What's the output peak current in your application? If it's really needed, I can do a quick bench test and let you know the result.

Thanks! We bought both EVM and will test on our side.

Feng

Hi Feng,

I test the TPS61230A EVM with a 5mF output capacitor on bench. The boost circuit works well at Vin=2.8V, Vout=5V,1.5A condition. And it could start up well.

Sorry I didn't find the 40mF in lab. I think it will also work well with 40mF super cap. You can do a test on your side.