Regulator for micro SD card

Hi Ram,

I can help you pick a DC/DC if that's what you need. Do I understand that you have a coin cell battery and need a 2.2V and 2.7V rail? How much current will you need on each rail? What is the typical load and peak load for each?

The TPS82740A/B is worth looking at for these rails for a very small size and high efficiency.

Hi Chris,

Thanks for the quick reply.

my battery is CP503333 http://rechargeablelithiumbatteries.sell.curiousexpeditions.org/iz5091660-cp503333-limno2-lithium-manganese-dioxide-battery-for-sate-alarm-system-3v-1200mah-images 

I was thinking of TPS62740 that will outputs 2.7v.

1st rail (Vout) will enter LDO and to the circuit MCU, CC1121 and sensors. 2.2V with approx. current of 2.5mA.

2nd rail (Load) will be for the micro SD card. 2.7v with peak current of 100mA (write) and idle current of approx. 200uA.

Regards,

Ram

I could not find a voltage discharge curve at that link. This is needed to understand how long the battery needs to go before it is considered dead.

Yes, the TPS62740 can do the same thing as the TPS82740, but it will be much larger.

What voltage range can the SD card accept?

The TPS62740 family is a great choice at supplying that 2.2V rail with higher efficiency. You don't need an LDO there.

Hi Chris,

I added the voltage discharge curve. for some reason I can't attach the PDF datasheet..

Voltage range of the micro SD card is 2.7-3.6v.

Actually, I was considered to use the TPS62740 for the 2.2v rail, but I have three digital sensors (MEMS) on my board, so I decided maybe it will be better to use LDO.

Ram

Thanks for sending the D/S. It looks like below 2.2V on the battery, there is very little energy left so it is likely ok to use a step-down converter or LDO for the 2.2V and not lose too much energy.

The TPS62740 can power noise sensitive devices like sensors and LP RF devices. Its integrated load switch is ideal for sensors, etc. to reduce their leakage when off. See figure 7 in the D/S. You can order the EVM and test it with your sensors to see how it performs. The advantage is much lower battery current draw on the 2.2V rail.

For the SD, the TPS61291 is likely your best choice. Again, because it has extremely low leakage when it is off (15 nA). Not consuming any Iq when you are idling keeps the overall efficiency high. As the battery discharges to 2.7V, your MCU would enable the TPS61291 and it would boost to 3V. This would be like figure 9 in the D/S.

Wow, thanks Chris.

So, in your opinion it would be better to use the boost converter for the micro SD card and buck/LDO for the 2.2v rail than to locate a buck converter for the micro SD card connected to the LOAD output with LDO to the 2.2v rail. right? :)

BTW, the LOAD output needs Cout (10uF)? in the TPS62740 D/S it's no clear..

Regards,

Ram

OK, thanks a lot!