Buck-Boost Dual Output

Hi,

Thank you for posting.  This sound more easily to be achieved with a flyback topology, or dual output SEPIC with coupled inductor.  The power level and voltage level may need a converter other than a controller.  Let me forward this to our converter IC experts.

Thanks,

Youhao Xi, Applications Engineering

Hi 

if I understand correctly, the input power is lithium-ion battery or 12V, here my suggestion 

a boost converter TPS61089 to 6V output, then connect the 12V input to the output of the boost. the 12V is higher priority to power the downstream loading.

from 6V~12V input to 3.8V output, we need a 3.5A buck converter to generate 3.8V. the 3.5V output can be an LDO from 3.8V to 3.5V.

I think you have mistaken my question.

Input will be Li-Ion battery i.e. 2.85-4.2V and Outputs: a) 3.8V,2A and b) 3.3@250mA.

Hi 

then the solution is simpler. you can use a low voltage buck-boost  http://www.ti.com/lit/ds/symlink/tps63810.pdf for 3.8V, then a LDO to 250mA.

Thanks for your reply.

Is the I2C mandatory? If not used can be left open right?

Hi, Any updates?

Hi 

I would suggest to pull high through resistor, but you can't change the VOUT to 3.8V without the I2C.

what is 3.8V 2A is used for in this application?

3.8V,2A for the cellular module.

I thought the output voltage set through the feedback pin.

Hi,

Any updates?

Hi 

I think the device should be changed to TPS63802. however, the maximum output current of this device is approximately 2.1A from 2.85V input to 3.8V output. do you think 3V minimum input is OK for your application? otherwise it would need two buck-boost converter.

3V Minimum is fine and what about TPS63020QDS?

Hi Lakshminarayana,

As Jasper suggested, the TPS63802 can be used, with somewhat loosened requirements for the minimum input voltage.

Alternatively, you could consider the TPS63806 which can support up to 3 A at Vout = 3.6 V, Vin = 2.8 V. The TPS63806 is similar to the TPS63802, but with increased current limit and it comes in chip-scale package.

Do you expect continuous maximum output current of 2 A, or just a pulse?

Best regards,
Milos

Hi Milos,

2A is just a pulse and the average current will be less.

Hi Lakshminarayana,

Please take a look at the TPS63802 datasheet, Figure 14, and the TPS63806 datasheet, Figure 17, for maximum output currents at Vout = 3.6 V. The TPS63802 has higher output current capabilities than the TPS63020. The TPS63020 would not be able to support your load.

The TPS63806 should be able to handle your load, but is comes in chip-scale package which is not as easy to handle as the DFN package for the TPS63802. In any case I can test your load on both devices. Could you please tell me what is the length of your 2-A pulse? 

Best regards,
Milos

Hi Milos,

Thank you.

"  Could you please tell me what is the length of your 2-A pulse? " typically for few microseconds(us) - (cellular 2G).

One query on TPS63802, In the pin description, for the Mode pin - set Low for PFM(power saving mode-Highest efficiency for lower current) and High for PWM Mode.

But in the Figure 17-Efficiency versus Output Current graph, Mode is HIGH and PFM? and highest efficiency?

Thanks

Hi Lakshminarayana,

For power-save mode the MODE pin needs to be set LOW. The pin description table is correct, the description in the images is not and will be corrected in the next datasheet revision, sorry for this.

The length of a high current pulse can be limited by the thermal management. Therefore even though Figure 14 from the datasheet shows that the TPS63802 can support 2.5 A at Vin = 3 V, the current capability can be reduced if the device overheats. But if the pulse length is below ms, there should be no problems.

Best regards,
Milos

Hi,

Thanks for the information.

Can I send the Layout file as Gerber(through Private) when the design is completed?

:)