The device includes functionality to use the internal 1.8V Analog Supply as the source for
the VPP 1.7V Supply. This feature eliminates the need for an external LDO connection
to VPP in order to perform eFuse programming on the device. By taking advantage of
this added functionality, system BOM costs can be reduced by eliminating the
external 1.7V VPP source LDO from a design.
In order to use the 1.8V Analog Supply
as the VPP source, any factory programming sequence that requires the one-time
programmable eFuse necessitates a minor modification to account for the VPP power
requirements. First, the VPP_EN bit in the VPP_EN_MMR register needs to be set to 1.
To correctly program the eFuse, VPP requires a 1.7V supply. The default output of
the 1.8V Analog Supply must be re-programmed to output 1.7V. The flow of this
process is as follows:
- Lower the internal 1.8V Analog LDO supply to 1.7V before programming the
eFuse
- Program eFuse
- Raise the internal Analog LDO supply back to the default of 1.8V
Note: Step 3 above is critical, as the device will not function properly if this
step is not performed.
To enter eFuse programming and set the internal 1.8V Analog supply to 1.7V (all
registers are under TOP_CTRL):
- Read the TRIM_OFFSET from EFUSE_OVERRIDE_LDO_TRIM.
- Assert the Mask for the Ana
ISO SOC reset in the MASK_ANA_ISO register by setting the MASK field to
3b111. This prevents the lowering of the LDO voltage from triggering any
systems resets.
- Program the LDO_PROG field of
the EFUSE_OVERRIDE_LDO_TRIM register to 4b1110.
- Program the TRIM_OFFSET field
of the EFUSE_OVERRIDE_LDO_TRIM register to the value obtained in step
1.
- Enable the override by
setting the OVERRIDE field of the EFUSE_OVERRIDE_LDO_TRIM register to
3b111.
- Wait for the supply voltage to stabilize. 1 millisecond is the recommended
delay interval.
- Program eFuse and verify.
To exit eFuse programming and restore
the internal Analog LDO supply back to 1.8V (all registers are under TOP_CTRL):
- Disable the override by clearing all bits of the OVERRIDE field of the
EFUSE_OVERRIDE_LDO_TRIM register.
- Wait for the supply voltage to stabilize. 1 millisecond is the recommended
delay interval.
- The internal Analog LDO supply will now be back to normal operation at
1.8V.
- De-assert the Mask for the
Ana ISO SOC reset by clearing all the bits of the MASK field in the
MASK_ANA_ISO register.
- Exit the eFuse programming
routine.