TPS61372: Customer inquires

Hi 

        please help to check sch.

/cfs-file/__key/communityserver-discussions-components-files/196/QI_5F00_SUB_5F00_BOARD_5F00_0926-1_2D00_TI.pdf

Hi Charles,

For TPS61372, when working in Vin = 2.7V, Vout = 5.2V, auto PFM mode, and L = 1μH, the guaranteed max Iout is around 1.28A.

If L = 4.7μH, the guaranteed max Iout is around 1.45A.

When working in FPWM mode, the max Iout will be a little smaller. The guaranteed max Iout is around 1.40A when Vin = 2.7V, Vout = 5.2V, FPWM mode, and L = 4.7μH.

The max Iout is a little smaller than the required max Iout. Please help check whether it will be a concern? Whether other solution such as TPS61033 will be considered?

Here are the comments for your 8 questions.

1) Red number means that to meet the needed Iout, the inductor peak current has exceeded the min peak current limit.

2) For TPS61372, the current limit means that the peak inductor current must below this limit.

3) The calculated max Iout of TPS612592 is a little bigger than that of TPS61372. Well, limited by the thermal, the max Iout of TPS612592 at Vin = 2.7V and Vout = 5.2V is less than 1.4A.

4) When Vin = 2.7V, the max output is around 7.5W even inductor with bigger inductance is used.

5) TPS61372 has switching peak current limit, no OCP. 

6) TPS61372 has hiccup output short protection

7) Please refer to this description in datasheet.

8) The phase margin is too small. The suggest Rc is 61.9kΩ.

Regards

Lei 

Hi Leo,

What's the Vin range? 2.7V to 4.4V?

What's the max Iout?

Regards

Lei 

Hi  zhong

           1)   VIN range is  2.7V TO 4.5V .

           2)   Vout  5.2V ,    We will use 1UH with forced PWM .

           3)   How  can  tps61372  support the peak current ?

Hi 

8) The phase margin is too small. The suggest Rc is 61.9kΩ.

Hi 

61.9K is based the L=1UH?,    in addition , we use 3*22uf cap ,but the effective cap is 18uF.

Hi Leo,

leo hua said:

61.9K is based the L=1UH?

Yes.

leo hua said:

How  can  tps61372  support the peak current ?

When Vin = 2.7V, Vout = 5.2V, Mode = FPWM, L = 1μH, the guaranteed max Iout is around 1.22A.

Regards

Lei 

Hi Lei

           1）  Calculate the phase margin with 61.9 K and 82 K,  61.9 K resistor corresponds to 68 degree phase margin，and 82 K resistor corresponds to 60 degree phase margin, So Should the appropriate phase margin be less than 60 degrees?    Don't to change the Cc1 Value?

           2)    Doesn't need to change the Cc1 Value?

           3)    Can you update the sch check results?

Hi Leo,

The most concerns is that the max Iout when Vin = 2.7V and Vout = 5.2V seems less than the max Iout needed in your application. Please double confirm.

Here are the comments for your questions.

leo hua said:

So Should the appropriate phase margin be less than 60 degrees?

When Rc = 82kΩ, the phase margin is 60.6º, it's OK. If the phase margin is several degrees less than 60º, it will still be OK.

leo hua said:

Doesn't need to change the Cc1 Value?

No need.

leo hua said:

Can you update the sch check results?

No concerns on the schematic. The Rc(R25) is 82kΩ, not 2k, so it's OK.

Regards

Lei

Hi 

       We update the R25 value to 62K, and add c44 22uF to Vout ,   It is  fine?

Hi

That's OK.

Hi Lei

           when the PEAK current is exceeding current limited,  how long does the exceeding current limited remain which can trigger SCP function.  

In addition, the C38's rating voltage is 10V , is it fine?

Hi Leo,

From the inductor current touches the current limit, to the inductor current begins to fall, the delay is very small, around 10~20ns.

10V DC rating of C38 is OK.

Regards

Lei

Hi  Lei

           C38（470PF） 's Capacitor accuracy is 10%，is it fine?

Hi Leo,

It's OK.

Regards

Lei

Hi Lei,

             When VIN is 4.7V , OUT is setting 5.2v,and forced PWM MODE ,can   the switch  work normally?  is there some the Constant on time or Constant off time limitation for  vin and vout ratio?

Hi Leo,

The TPS61372 can work normally when Vin = 4.7V and Vout = 5.2V.

This device has special function designed to make sure the Vout is still regulated when Vin is very close to the Vout.

Regards

Lei

Hello Please  help  share the formula for the transfer function of Bode plot. 

Hello Leo,

Please see the part "8.2.2.6 Loop Stability and Compensation" in datasheet, which contains all the formulas for the transfer function.

Regards

Lei

Hi Lei

    please give me your phone number, there is big drop at VIN ,when  transient  0mA to 500mA.

Hello Leo,

I've asked Charles's help to send my phone number to you.

Regards

Lei

Hello  Lei

                1) We add RC circuit for enable signal delay . the GPIO_QI_CH2_ BOOST_EN is 1.7V, So R21 3.3K  is OK?  

                2) At this point, what is the expected voltage for pin B4? Can I turn on ENABLE?

                3) How much current will B4 pin carry?

The RC circuit consists of 3.3K and 4.7UF capacitors.

Hi Leo,

1) The R21 and C45 are decided by the needed delay time. For the device itself, the 3.3k is OK.

2) Suppose the Vin is > UVLO, then as long as the EN pin(B4) voltage is > 1.2V, the device is enabled.

3) When the GPIO_QI_CH2_ BOOST_EN is 1.7V, the current flows into EN is around 2.1μA.

Regards

Lei

Hi Lei

          We measure the enable current ,  maybe ~10 uA , it is correct?

Hi Leo,

The 2.1μA refers to the current into the EN pin.

Does the 10μA current include the current flows from R23 to GND? If yes then it make sense.

Regards

Lei

Hi Lei

    I WILL CHECK 2uA.

the other questions, Please check the VIN IQ is  correct?

VIN2.8V,VOUT5.18V ,AUTO PFM   VIN IQ =168uA ,

VIN4.5V VOUT5.18V, AUTO PFM   VIN IQ =145UA, 

VIN2.8V,VOUT5.18V PWM   VIN IQ =25mA ,

VIN4.5V VOUT5.18V, PWM  VIN IQ =11mA,  

Hi Leo,

The IQ are tested when there is no switching. You data should be tested when no load, right? It will be much bigger than the real IQ in datasheet.

Regards

Lei