TPS7A74: Low VIN VOUT without VBIAS

Hi Patrick,

It will be difficult to find many LDO's that meet these specs.  Most LDO's historically have required an external BIAS rail.  What you need is an LDO with an internal charge pump.  The TPS7A57 will meet this requirement.

Alternatively, can you use a small boost converter like the TPS61299 to take the 1.1V rail and generate a BIAS rail for the TPS7A74?  The noise on the BIAS rail will be heavily attenuated in the TPS7A74 (see figure 6-7 in the TPS7A74 datasheet).

Thanks,

Stephen

Hi Patrick,

I see this did not answer your question.  Was there something else I could assist you with?

Thanks,

Stephen

ZYNQ Main Ultrasound _ SHEET10 .pdfHi Stephen, 

The TPS7A5701RTER will work well for the 1V1 >> 0V9 as with 1V1 in the CP is not needed (assume ground CP_EN).

But I have another rail that needs to go 0V85 to 0V72 (for Xilinx). FOR THIS the VBIAS is required, and the only rail running at that time is the 0V85 itself.

I have DCIN rail at 9V-15V (battery main power in to device) that is running, but power loss just to make a 3V <> 11V for this would be power loss. Datasheet says VCP_EN = 1.8 V, 3.0 V ≤ VBIAS ≤ 11 V is 15ma max for VBIAS.

? Does TI have a part for battery (9-15VIN to 3V for BIAS and Bias and CP EN? Is it OK to run VBIAS from 9V to lower the LDO Loss in TPS7A5701RTER?

I have TPS7A57EVM-056  and TPSM82903EVM  ordered from TI.com to test next week.

Thanks for your support! - Patrick

I will attach current version of circuit above.

Circuit to discuss

Hi Patrick,

Your BIAS rail for the TPS7A57 just needs to be 3V higher than Vout (which is the same as Vref).  With Vout = 0.72V, Vbias can be 3.72V or higher. 

You won't get a reduction in BIAS pin current with higher BIAS pin voltage (see figures 6-135 and 6-136 in the TPS7A57 datasheet). 

The 15mA BIAS pin current happens at maximum junction temperature.  Your BIAS pin current will be less at lower temperatures.  See Figure 6-135 through Figure 6-139 in the TPS7A57 datasheet for typical BIAS pin current values.

It sounds like you are also in need of a switching converter which can take 9-15V input, and generate a BIAS rail (at least 3.72V) with 15mA current - let me know if this is correct, and I'll add the appropriate switching team to this E2E thread for additional support on selecting the right switching converter option.

Thanks,

Stephen

Hi Stephen,

Yes, please suggest a very small switcher to generate the 9-15V input, and generate a BIAS rail (at least 3.72V) with 15mA current.

Patrick

Hi Stephen, When the 7A570 is running 0V85 to 0V72, there are no other rails running..

IF I do a boost from 0V85 to 4V, will this suffice for BIAS needed? - Patrick

Hi Patrick,

Yes I expect this will work just fine, I would enable the TPS7A57 based on the power good from the TPS62122 boost converter.

Thanks,

Stephen

Hi Stephen, The TPS62122 has no PG pin, the SOT version TPS62120 has PG but both are Bucks, not Boost. The TPS61299 is boost and will work @0V85 >> VO = 4V5, but no PG pin. So when this 4V5 is generated, I would supply to BIAS Pin of TPSS7A5701 and ground Bias EN, "I think". Is this best way to go? - Patrick