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TPS546E25: VSEL/FB pins of the secondary device when operating in a stacked 2-phase configuration

Matsuse Ryosuke
Prodigy 10 points
Part Number: TPS546E25

Tool/software:

To generate Vout = 0.88V / 55A, we are using two TPS546E25 devices in a 2-phase setup.

The primary device uses an external feedback divider, with the FB pin connected between VOSNS and GOSNS, and resistor values of Rtop = 12kΩ and Rbot = 10kΩ, which sets the output voltage to 0.88V.

In this configuration, how should the VSEL/FB pins of the secondary device be connected?

Like Primary, should it be connected to the voltage divider resistor as an FB pin?
Should a value close to 0.85V or 0.90V be set as VSEL?

  • +1
    TI__Mastermind 23955 points

    Based on the information provided in the TPS546E25 datasheet, here's how to connect the VSEL/FB pin in a stack or multiphase configuration:

    1. For the primary device:

      • If using internal feedback divider: Connect a resistor from VSEL/FB to AGND to set the output voltage.
      • If using external feedback divider: Connect VSEL/FB to the midpoint of an external resistor divider between VOUT and AGND.

    2. For secondary devices:

      • The VSEL/FB pin should be connected to a resistor to AGND to select the appropriate VOUT_SCALE_LOOP value for the output voltage.
      • If the primary device is using an internal divider, use the same VSEL resistor value as the primary.
      • If the primary device is using an external divider, select the VSEL resistor with the lowest VOUT_MAX greater than the maximum expected output voltage.  section 6.4.5.4 Programming VSEL\FB

    3. In all cases:

      • Make sure the VSEL/FB pin connections are made near the device.
      • The return for the VSEL/FB resistor (when using internal feedback divider) should be to the quiet AGND island.

    It's important to note that in a stacked configuration, only the primary device directly controls the output voltage. The secondary devices are configured to match the primary's voltage setting to ensure proper current sharing and operation.

    For 0.88V external divider, the secondary VSEL to AGND can be 4.87kohm to 33.2kohm from the table 6-11.