TPS60100 Current consumption

It's not clear where your currents are being measured but a simple power calculation can tell you if your results are reasonable: Pin * efficiency = Pout

Vin * Iin * efficiency = Vout * Iout

For a boost converter like this, the input current will always be greater than the output current.

From the D/S, we can see that at 3.6Vin, the efficiency is at most 70%.  This is rather poor, so I would recommend a newer boost converter for an improvement.  The TPS61070 is a good choice.  TPS61220 might also give you enough output power.

Hi Chris,

Thanks for the reply. I've measured the current between the battery and TPS60100 input. On a 60ohm resistive load. I expect a little over 55mA of current consumption based on simple I=V/R equation. The measurement shows around 115mA. A measurement between TPS60100 and the 60ohm load shows 55mA. So it looks to me that the chip is drawing about 60mA for its operation. May be for the 300KHz switching operation? So even for the chips you have suggested, I assume the same current consumption should be expected. I have used a TPS6300, a buck-boost converter to give good results. Should I still be looking at charge pumps or go down the route of buck-boost converters?

Ah, it seems that I misread your part number.  Now, things make more sense.

Yes, bucking from 3.6V to 3.3V, you would expect to see a lower input current.  But that is not how the TPS60100 works in order to achieve very low ripple.  Page 12 of the D/S explains that the switches always operate at 50% duty cycle, so the excess voltage must be dropped across a transistor to keep the output regulated.  This is inefficient.

I would recommend the TPS61220 or TPS61291 boost converter with bypass mode for your application.  You keep the boost converter off until your battery voltage drops too low, then you boost to 3.3V for the rest of its life.  Very long battery life is achieved this way.

The boost converter could have been used. But I need a stable 3.3V throughout. That is the reason why TPS63000 was of interest since it will regulate the load in buck mode as well as boost mode. Also, I have an 80mA fuse just after the battery and before the regulator. In order to prevent the fuses from blowing in the event of a short circuit or high load, I plan to use a current limiter such as TPS2552 before the regulator. I want power to cut off before the fuse blows (at 75mA may be?). My application uses a maximum of 60mA current at the moment. The load varies a lot when the transmitter on the system switches on.

Considering all these, do u think TPS2552(ILIM shorted to IN to obtain 75mA cut off) before a buck-boost such as TPS63000 could be a solution?

The system would look like this:

                ---Battery--------80mA Fuse --------TPS2552 ----- TPS63000----- Load ----
                |                                                                                                                              |
                |______________________________________________________|

Hmm, the 80 mA fuse sure adds a challenge.  What do you expect the voltage range on your battery to be?  How far do you want to discharge it?

Yes, a buck-boost would give a regulated Vout.  But they can have more output ripple.

What sort of output ripple/noise do you need?

The lowest possible. I'm happy with 5-10mV(p-p). The key is the load transient I feel. When the transmitter radio switches on, it draws about 30mA more all of a sudden and then turns off. I'd like to use the maximum juice out of the battery  as well - may be down to 2.5V?

Thanks. This looks like  a solution. Also, is there a current limit switch I can use which can be adjusted between about 60mA and a 120mA that can be used along with this regulator?

You would need to post in the power interface forum for this function.