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TPS568215: Power good thresholds were clear in device datasheet

malli arjun1
Intellectual 610 points
Part Number: TPS568215
Other Parts Discussed in Thread: TPS62088, TPS548A20, TPS53513, TPS51200

In our power ON sequencing, we are planning to use power good of one regulator to enable the other regulator.

Below is the power sequencing in order, IC's used.

Note: All Power goods are pulled up to 3.3V(1st rail in system)

1. 3.3V(TPS568215) enabled by default

2. 1.8V(TPS62088) enabled by 3.3V Power Good

3. 2.5V(TPS7A9001) enabled by 3.3V Power good

4. 1.0V (TPS548A20) enabled by 3.3V Power good.

5. 1.2V(TPS53513) enabled by 1.8V Power good

6. 0.6V(TPS51200) enabled by 1.2V Power good.

Questions:

1. From TPS568215 datasheet, there is no data for Vol value for Power good signal only recommendation is 10K pull-up required.

Can i get the VOL(max) value for Power Good signal.

2. Using 3.3V power good i am enabling 1.8V,1.0V & 2.5V regulators.

For all these regulators to Turn ON,

i am sure 3.3V Power good voltage is higher than VIH(min) (1.3V to 1.5V)of all regulators.

But, worst case enable VIL(max) = 0.4V(for 1.8V& 2.5V regulators) - which unless i know VOL(3.3V PGOOD), i can't say it works properly.

Please help to access this with proper data.

3. I am driving 1.0V,1.8V & 2.5V enables from 3.3V POWER GOOD - any precautions related to loading the 3.3V POWER GOOD needs to be taken?

As all outputs are enables of regulators- they should load much on 3.3V Power good.

4. For the last rail, 0.6V enabled by 1.2V Power good signal.

0.6V enable thresholds from TPS51200 datasheet are

VIH(MIN) - 1.7V

VIL(MAX)- 0.3V

1.2V Power good

VOH - 3.3V

VOL - 0.5V(with sink current 4 to 6mA)- There is no data on VOL(Max)

Now, here VOL = 0.5V > Vil(Max) - I can't use 1.2V POWER GOOD directly to drive 0.6V enable.

is Vol = 0.5V with Isink=4 to 6mA is the max value ?

  • 0
    TI__Mastermind 18510 points

    Hi,

    Basically I know your concern, let me explain the PGOOD function.

     Pgood is open-drain design, an internal Mosfet control the PGOOD to go high or low.

    1, when the internal Mosfet turns on, PGOOD will be pulled to low, the resistance to GND is <500 ohm for most part, for 568215, it is around 100 ohm, so if you pull high to 3.3V with 10K, the output equals 3.3*100/(10k+100), it is very close to 0..., that should be the Vol you mentioned.

    For 1.2V PGOOD, datasheet shows I sink 6mA@Vpood=0.5V,, it is not Vol=0.5V, it is just the test condition, based on this, you can calculate the resistance from PGOOD to GND when the internal mosfet turns on, for this, you can get 0.5/0.004=125 ohm.

    2, When the internal mosfet turns off, the resistance to Ground is very high, you can think it is open, so when PGOOD pull-high to 3.3V with 10K, the PGOOD will output 3.3V.

    You can refer to item1 and item2 to for all your sequence design.

    Yuchang

  • 0 in reply to Yuchang Zhang
    Intellectual 610 points

    Thanks Yuchang.

    It clears all my doubts.

    1.for TPS568215 , if datasheet specifies value like PGOOD typical low resistance as 100 Ohms or equivalent data It will be help to all.

    2. I am driving 1.0V,1.8V & 2.5V enables from 3.3V POWER GOOD - any precautions related to loading the 3.3V POWER GOOD needs to be taken?

    As enables will take very less current (in few uA). i don't see any loading problem here- just share your thoughts here

    Malli

  • 0 in reply to malli arjun1
    TI__Mastermind 18510 points

    Hi, No loading problem concerns as well.