TPS61256: Can not used as boost

Result When loading is above 5v/ 100 mA ,maybe  the softstart of TPS61256 stopped the rectifying switch, which protect the TPS61256?
//see spec page 17   ,The TPS6125x device has an internal softstart circuit that limits the inrush current during start-up.  The rectifying switch is current limited (approximately
200 mA) during this phase. This mechanism is used to limit the output current under short-circuit condition.///

we found that when the loading is about  5V and 100ma ,when power on the  tps61256 ,the tps61256' output is always  2.6v  , so maybe the tps61256's rectifying  is turned off ?

so the tps6125* family maybe not suitable for  the quick boost circuit .

Dir Sir,

TPS61256 minimum resistive load for start up is 55ohm. What if you wait for the output voltage is stable at 5V after startup, then adding a load current of 600mA? Will the output voltage still drop to 2.7V?

 What if you wait for the output voltage is stable at 5V after startup//How to wait the startup?  how long is the startup time? 

our system is connected to  output of  the tps61256 directly ,our system need  5V/300ma   .so when enable the tps61256  ,the output of  TPS61256 is always 2.6v . 

maybe the Tps61256 turned off the switcher in chip ,when startup? so the Tps 6125*can not used as the quick boost circuit?

Hi,

The soft-start of TPS61256 limits current to 200mA during pre-charge time, so when immediately add 300mA load will trigger current limit and lower output voltage.

What's you load? Can you control the load power sequence? So suggest to enable your load after the boost complete its pre-charge. You can refer to this pic from datasheet, but you need to test on your board because it depends on your output capacitance.

Please let me know if you have any questions.

hi  minqi:

thank you .

1 The soft-start of TPS61256  //After the soft-start time , the TPS61256's output is always  2.6v ?why ?

2 What's you load?      //The loading is the  Sensor  OS05A10   .when system  power on ,the sensor must start to work quickly   

3 Can you control the load power sequence?//the loading is connected to the TPS61256'S directly 

4 You can refer to this pic from datasheet, //From the datasheet ,  how long is the start up time? the mini time maybe 500us ? 

if the TPS61256 cannot work well with our system  It will be bad

lchaoyong 

Hi,

1. During pre-charge current limit, the output voltage will equals to Vin=2.6V, so you can increase Vo by increasing Vin. What's your power supply requirement of OS05A10?

2. Did you test with OS05A10 or 300mA E-load? Suggest to test with OS05A10. Normally sensor has UVLO and need some time to operate, so when start-up, maybe it doesn't need 300mA and won't trigger pre-charge current limit.

4. Based on TI' test condition, the start-up time is about 200us at 2.7Vin. But you need to test with your output capacitor.

Please let me know if you have any questions.

hi

1 During pre-charge current limit, the output voltage will equals to Vin=2.6V //when  increase the input  to  4.0v  the output  of the Tps61256 is always  2.6v

2 What's your power supply requirement of OS05A10? //  5v and 200-300mAsee mail before 

we found that when the loading is about  5V and 100ma ,when power on the  tps61256 ,the tps61256' output is always  2.6v  , so maybe the tps61256's rectifying  is turned off ?

3 Normally sensor has UVLO and need some time to operate, so when start-up, maybe it doesn't need 300mA and won't trigger pre-charge current limit. // YES Test it  when loading is about  100mA  , The tps61256 's output is always 2.6v  ,

4 After the soft-start time , the TPS61256's output is always  2.6v no 5 v  ?why ?

thank you

lchaoyong

Hi,

The tps61256 pre-charge current inductor limit should be about 200mA. I test with our EVM board at Vin=2.7V Iout=100mA, it works fine. So maybe your load start-up current exceeds 100mA. (Blue: Vout, Yellow:Vin, Green:Io)

No matter what, in your case, you need to change to another boost IC that supports higher pre-charge current limit, such as TPS61022 and TPS61023. If you need pin to pin, you can choose TPS61253A.

Please let me know if you have any questions.

hi :

thankyou .

our test :

1The output voltage is about  5v,   using the 3.5 R( footprint 0603)  as the loading  ,the TPS61256 outputvoltage is fixed to  2.6--2.7v( by capture)  why?   

2 What's your power supply requirement of OS05A10? //  5v and 200-300m loading Asee mail before 

3After the soft-start time , the TPS61256's output is always  2.6v no 5 v  ? Maybe the TPS61256 stopped the switcher in chip ?

4 The TPS61253A.  maybe suitble for oursystem   ,but Its current is too high .can you recommend 1A (PIN TO PIN ) boost chip TO us?

thank you

Thankyou .

lchaoyong

Hi,

1. The output voltage is about  5v,   using the 3.5 R( footprint 0603)  as the loading  ,the TPS61256 outputvoltage is fixed to  2.6--2.7v( by capture)  why? 

// I remember you said that you test with your actual sensor load OS05A10? For 3.5R load, the current is 1.42A and will trigger current limit.

The reason why is explained here. During current limit in pre-charge time, the high-side FET is operated like a controlled Rdson to limit the current flow into output.

3. After the soft-start time , the TPS61256's output is always  2.6v no 5 v  ? Maybe the TPS61256 stopped the switcher in chip ?

//Because it entered pre-charge current limit, until you reduce the load, the output voltage will stay low.

4. The TPS61253A.  maybe suitble for oursystem   ,but Its current is too high .can you recommend 1A (PIN TO PIN ) boost chip TO us?

//Sorry, for pin to pin device we only have TPS61253A to meet your start-up current need. But you can change to TPS61022.

HI

thank you

1 first test ;  change the loading to 1k  the tps61256's output is ok , then  change the  loading is 12R ,  the tps61256 's  output is always 2.7v ,then 3.7R , The output is  2.7v 

2 //Because it entered pre-charge current limit, until you reduce the load, the output voltage will stay low.//the  load ( os05a10 ) is about 300mA/5v  ,but after the tps61256's softstart  time ,the tps61256's output is always 2.7v .so the result confused us very much .there is no expaltion about the protection function  in spec  .

lchaoyong

hi :

the inductor current is limited to about 200mA//Whethere is it means the current is above 200ma ,so the tps6125* stopped to work , so the output voltage always is  3.6v -0.7v( Vrons)=2.9v ?

The reason why after the tps61256's softstart  time ,the tps61256's output is always 2.7v is Vout=2.7V<Vin, so you are still in pre-charge and didn't enter soft-start switching//1  wait for  5minutes , the output is always 2.7v  no 5v       how to  enter the soft-star switching?

thank you

lchaoyong

Hi,

so the tps6125* stopped to work , so the output voltage always is  3.6v -0.7v( Vrons)=2.9v ? // No, the high-side FET is still turned on, but not completely on because it's working in MOSFET linear mode, Rds.on is large that limit the current.

I wait for  5minutes , the output is always 2.7v  no 5v       how to  enter the soft-star switching?// To enter soft-start switching, your Vout is need to exceeds your Vin, then the control loop start to operate and switching.

hi  :

 wait for  5minutes , ^^^^^^^^  To enter soft-start switching, your Vout is need to exceeds your Vin,  //Our systme need  5v power     but the tps6125*'s output voltage is always 2.7v   ,so our system can not work . how to make the output of Tps6125* can exceed the vin?

thank  you

.

hi l

1I understand your means , The above 200mA loading must be added after the pre-charge time , or the tps61256's output can not boost up to 5v .because when soft-star time , the bigger loading will lead the tps61256 into protection status  even after the pre-charging time

  2 so the tps61256 can not  be suitable for the bigger loading system ( above 150mA loading ) 

lchaoyong

Hi,

Yes, you're correct. The easiest way is changing to TPS61022 or TPS61253A.

But if you are willing to add some external circuit, you can still use TPS61256: Use this circuit, more details are explained in this file: http://www.ti.com/lit/an/slvaed6/slvaed6.pdf

hi :

thankyou 

1: http://www.ti.com/lit/an/slvaed6/slvaed6.pdf//    from the pdf , one mosfet must  be addded  on the output of tps61256 

2can  you describe the protection principle of  tps61256  with the bigger loading current ,when soft -start?

Hi,

Is everything going well? Do you have problems about our discussion and what's your decision?