TPS7A26: VPP slew rate

Hi Skylar,

My reading of this datasheet is that the slew rate is not a load transient requirement, but rather it is a maximum slew rate for turn on of the LDO output.  A maximum rate of rise is a common spec that we sometimes see for our power supplies. 

I.E. the slew rate of the LDO output turn on time must not exceed 6E+4 V/s.  Please confirm and I can review the LDO's you have asked about and get back to you.

Thanks,

Stephen

Hi Stephen,

I confirm the slew rate of the LDO output turn on time must not exceed 6E+4 V/s. So, could you pls help confirm the LDO I mentioned? Thanks.

BR,

Skylar

Hi Stephen,

Thanks for your such detailed reply and test!

Considering promoting new products, do you have some recommendation about  the LDO which could satisfy that the slew rate of the LDO output turn on time must not exceed 6E+4 V/s? Thanks.

BR,

Skylar

Hi Skylar,

Can you gain clarify on whether the maximum rate of rise requirement is across the full range of turn on (I.E. 0V to steady state)?  Typically the rate of rise spec is a narrow set of voltages (I.E. it does not matter if the rate of rise is violated between Vout = 1mV and Vout = 100mV).  What other key requirements do you need (In addition to Vin and Vout. Iout, noise, PSRR, size?, etc).

I've spent this year writing a comprehensive white paper on turn on time, inrush and rate of rise for our LDO's.  It should be released by the end of the month but the bottom line is that there is no single answer to this question for many of our LDO's. 

• Many LDO's turn on exponentially (RC time constant) so technically speaking, at infinitesimally small voltages the "rate of rise" spec (6e+4 V/s here) cannot be met... but if the spec is across 2 intermediate voltages, these LDO's may still be used
• LDO turn on behavior is a function of external components such as NR/SS capacitors, Cff capacitor and feedback resistors.
• Some LDO's have a fast charge circuit which also influences turn on.
• etc

Thanks,

Stephen

Hi Stephen Ziel,

Stephen Ziel said:

Can you gain clarify on whether the maximum rate of rise requirement is across the full range of turn on (I.E. 0V to steady state)?  Typically the rate of rise spec is a narrow set of voltages (I.E. it does not matter if the rate of rise is violated between Vout = 1mV and Vout = 100mV). 

I will confirm the question for you later.

Could you pls help confirm if the LDO TLV1117-18IDCYR could satisfy the slew rate of the LDO output turn on time must not exceed 6E+4 V/s? Thanks.

BR,

Skylar

Hi Skylar,

I need to see if we can capture turn on measurements of this LDO in the lab.  Please give me a few business days to get back to you. If I need to order an EVM then it will take 5 business days for shipping and 1-2 business days for the measurement.

Thanks,
Stephen

Hi Stephen,

Thanks for your reply. Add information as below. The Vout of LDO needs to satisfy the VPP requirement of AM62x as below.

Here are some questions from my side.

1. Can customer modify the output capacitor or delay the EN pin high level of TPS7A26 to satisfy the 6E+4V/s?

2. Could TLV1117-18IDCYR satisfy the slew rate of the LDO output turn on time must not exceed 6E+4 V/s? Thanks.

BR,

Skylar

Hi Skylar,

The TLV1117 does not have an enable pin and thus will turn on with Vin.  If Vin turns on extremely fast, then the LDO may also turn on too fast.  If Vin turns on more slowly, but not slow, it is possible that the LDO will turn on while in dropout and overshoot.  I would tend to not recommend the TLV1117 here. I think you need a device with an enable pin.

We have the TLV773 which is a 300mA device that meets your requirements (except the current limit).  We have a 500mA version of this in work which I believe would be the perfect low cost solution for this application, if it meets the customer timeline.  First samples will be late 4Q and the RTM is anticipated around June 2025.  Let me know...

Thanks,

Stephen