[FAQ] TPS546E25: I write to registers 0x33 and 0x46, but the register values do not change. Why?

Several register values depend on both, see table at bottom:

 The PIN_DETECT_OVERRIDE (0xD8) setting and  The external pin-strap resistor values (MSEL1, MSEL2, VSEL, PMB_ADDR)

For the TPS546E25, the default value of PIN_DETECT_OVERRIDE is configured to use the pin-strap settings.

When this default is active, the device use the resistor-strapped configuration over the NVM-stored values.

Important Device Behavior

Certain commands are dependent on pin-strap configuration. Refer to the datasheet table listing commands affected by pin strap resistor values.

The effective register value depends on:

Primary internal divider configuration

Primary external divider configuration

Secondary configuration

Pin-strap settings

NVM contents

Example

After power-up:

If register 0x33 is written to 0x3806 (800 kHz)

And PIN_DETECT_OVERRIDE (0xD8) remains at its default (pin-strap mode)

The readback value will reflect the pin-strap resistor setting 0x3805 (MSEL2 <1.78kOhm), not the NVM value.

However:

If 0xD8 is changed to enable NVM control (for example, 0xD8 is  0x8E59 where Frequency_Switch and IOUT_OC_FAULT_LIMIT are sourced from NVM)

And register 0x33 is read as 0x3806 (800 kHz)

Then the value reflects the NVM configuration.

Similarly, if the MSEL1 pin-strap resistor is < 1.78 kΩ, the OC limit is set to 50 A, which will match the programmed NVM value.

Summary

If register values appear unchanged after STORE/RESTORE commands:

1. Check the value of PIN_DETECT_OVERRIDE (0xD8).
2. Verify the pin-strap resistor values.
3. Confirm whether the parameter is configured to use NVM or pin-strap control.

In default operation, pin-strap settings override NVM values.