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LP8725: DVS pin settings & toggle settling time

Leo Chow
Expert 3120 points
Part Number: LP8725

Hi,

I have several queries with regards to LP8725. It is as follows:

1) The DVS voltage on the BUCK1, can it be set to any desired voltage that is set into the register REG 0x08[4.0] and REG 0x09[4:0]?

Eg: 

REG 0x08 programmed to 1.2V,  REG 0x09 programmed to 1.1V

Toggling the DVS pin will make the BUCK1 output to have 1.2V or 1.1V according to the high and low state

.

REG 0x08 programmed to 1.1V,  REG 0x09 programmed to 1.0V

Toggling the DVS pin will make the BUCK1 output to have 1.1V and 1.0V according to the high and low state

 

If my processor DVS needs 3 voltages 1.2V, 1.1V and 1.0V, are we able to load the desired voltage settings into the REG 0x08 or REG 0x09 and toggle the DVS pin to get the desired output voltage?

 

2) What is the time it takes to switch from one voltage to another voltage (Settling time)?

  • 0
    TI__Genius 10460 points

    Hi,

    1) Yes, the DVS pin state controls the Buck 1 output voltage based on registers 0x08 and 0x09. 

    Regarding the 3 voltage toggling via DVS - is this a good example for the procedure you are considering?

    1. Power up with DVS = 0 => Buck 1 = BUCK1_V1 = 1.0 V
    2. Set DVS = 1 => Buck 1 = BUCK1_V2 = 1.1 V
    3. Rewrite BUCK1_V1 = 1.2 V
    4. Set DVS = 0 => Buck1 = BUCK1_V1 = 1.2 V

    2) The typical settling time may depend on the operating conditions. Can you please share the following?

    • Two desired voltage settings
    • Input voltage
    • Output current

    Thanks,

    Gerard

  • 0 in reply to Gerard Copeland
    TI__Expert 3120 points

    Hi Gerard,

    1. yes the 3 voltage toggling via DVS is what I'm looking at. Is that possible?

    2. For the SW1 specs. The input is regulated 3.6V. Vout : DVS 1.2V, 1.1V 1.0V, I outmax : 300 to 500mA.

    Also referring to LP8725 datasheet on table for DVS1, DVS pin state: 

    When we use serial interface method for DVS control (DVS1 REG0x00 bit2) the output BUCK1_V2 and BUCK1_V1 are available for the same VS1 input value (0 or 1).  How is this achievable?

  • 0 in reply to Leo Chow
    TI__Genius 10460 points

    Hi,

    Thanks for the feedback on test conditions. It looks like table you are referring to does not match the bit description, which states DSV1_V = '1' drives the output to BUCK1_V1. 

    Table:

    Bit Description:

    Please allow me some time to confirm if I have a working EVM available in my lab. If so, I can test this behavior as well as the other DVS tests by the end of the week

    1. 3 voltage toggling via DVS
    2. DVS settling time
    3. DVS1_V control

    Thanks,

    Gerard

  • 0 in reply to Gerard Copeland
    TI__Genius 10460 points

    Hi, 

    I have an EVM that is powering up, but there are some issues with I2C communication. Please allow me some additional time to resolve before getting to these tests. Thank you for your patience!

    Gerard

  • 0 in reply to Gerard Copeland
    TI__Genius 10460 points

    Hi,

    Thanks again for your patience. I was able to test the following. Please keep in mind the following applies for one unit at room temperature. 

    1. Yes it is possible to toggle 3 voltages with the DVS pin with the procedure outlined in my first response. 

    2. DVS settling time for one unit tested is 20 us. The scope shot below shows a Buck 1 DVS from 1.2 V to 1.1 V at 500 mA output current. 

    3. The bit description is correct. The table is not correct - if DVS1_V = 0, the output voltage is BUCK1_V1 regardless of the DVS pin. 

    Thanks,

    Gerard

  • 0 in reply to Gerard Copeland
    TI__Expert 3120 points

    Hi Gerard,

    thank you testing this out & it's helpful indeed, as per your comment above it's tested on room temp hence DVS settling time obtained was 20us. In customer's application, end equipment may be subjected to extended temp conditions. Are there any other factors which we need to take note of assuming equipment might be operating in extended temp range such as 40C to 60C?

    BR,

    Leo

  • 0 in reply to Leo Chow
    TI__Genius 10460 points

    Hi Leo,

    Sorry, could you please clarify or provide examples of possible "factors which we need to take note of"? I'm not sure what you mean by that. 

    If you are referring to the topics tested, (1) DVS toggling and (3) DVS1_V behavior would not be affected by temperature within the recommended operating conditions - this is digital behavior. The settling time is an analog property that would have temperature dependency. Unfortunately, since this is not a specified datasheet parameter, it is not characterized, so we cannot say with certainty how much it will vary. 

    Thanks,

    Gerard