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TPS62730 efficiency with CC430

Roger Liang
Expert 3510 points
Other Parts Discussed in Thread: TPS62730, TPS62740

To get maximum battery life we are thinking of using external DC-DC converter which will supply 2.1V to CC430 input supply. 

And increase the overall efficiency of the battery utilization.

 

We were looking into TPS62730 DC-DC converter efficiency. 

 

If we look at the CC430 operating range i.e voltage range (3.3V - 2.1) and current range (17mA - 25mA in active mode and less then that in sleep mode). 

In this range TPS efficiency will be between 80-90%. This is what we can get from the document suggesting usage of TPS with CC430 LDO.

 

TPS will bypass Vin voltage to Vout when Vin=2.2V.

 

1. Default bypass voltage is at Vin=2.2V.

2. If we take the 80% as the lower limit of the TPS efficiency , we found that it will be good to switch to bypass mode at Vin=2.6V.

3. And if we we take 90% efficiency for TPS, it is good to switch to bypass voltage at Vin=2.3V.

To bypass Vin to any other other value other than 2.2V default, it is needed to track Vin. 

We can use internal ADC for this, which consumes 0.6mA for 22 ADC10 clock cycles which will be about 1.5uW.

Query :

Can I get direction where I will get this answers ? any documents supporting following queries?

-  Can we schedule Vin tracking and get bypassed  Vin voltage at Vin=2.6V or 2.3V to get best out of the Battery ?    

-  Why TI recommends shifting to bypass voltage at 2.2V ?

 

  • 0
    TI__Guru**** 150790 points

    I believe the 80-90% number giving in the app note is for a general DC/DC converter (not the TPS62730).  If you look at figure 1 in the TPS62730 D/S, you will see that it is more like 87-93% efficiency in that range.

    You can use an ADC to switch the modes whenever you want.  While it may be slightly more efficient to keep bucking at lower Vins (instead of bypassing), the operating frequency typically decreases as Vin gets close to Vout.  This may cause a degradation in radio performance, so we incorporate an automatic 100% mode transition to prevent this.  No ADC monitoring needed for this functionality.

    Since the TPS62730 was released, we have released the TPS62740 which has 360 nA Iq.  With this, you can leave it running in buck mode all the time and still maintain a very high efficiency even in standby mode.

  • 0 in reply to Chris Glaser
    Prodigy 175 points

    Thank You Chris Glaser, 

    We are looking into the TPS62740 for its very small Iq. 

    We expect our system to work on CR2450 coin battery for 4-5 years. If we install TPS62730 with 22uA Iq, this alone wont last for 2 years. Either we need to BYPASS it whenever there is no operations at MCU or we need to TPS62740.

    We will get back to you we look at TPS62740 in detail. 

    Thanks for your support.

    Best Regards,

    Bharat

  • 0 in reply to BHARAT GEBISE
    Prodigy 110 points

    Hi Bharat,

    I was just wondering if you had success switching the modes of operation for the TPS62730 with your MCU and have you been able to verify that the quiescent current of the TPS62730 goes to 30nA while in bypass mode. I have difficulties lowering my CC430 power consumption down to 1-2uA which datasheet states for LPM3 and LPM4. As soon as I try to use the bypass mode on the DC/DC the current draw jumps by about 400uA. How did you interface your MCU with the TP62730? Did you still need to pull-down the ON/BYPASS pin? I really appreciate your response on this.

    Best Regards,

    Saeed