General
Review and verify the following for
the custom schematic design:
- Above sections, including
relevant application notes and FAQ links
- Pin attributes, signal
description and electrical specifications
- Electrical characteristics
and additional available information
- Implementation of on-board
supply or provision provided to connect external supply
- An LDO is recommended (use of FET switch or load
switch is not recommended or allowed)
- Choose on-board LDO that
supports a minimum of 400mA current, has excellent load current transient
response, and quick output discharge (active discharge)
- Required bulk and bypass
capacitors are provided (follow SK schematics)
- On-board LDO has provision to
be enabled by processor IO
- When external supply is
connected, add bulk and decoupling capacitor provision on the processor
board near to the processor VPP pin and provided a TP to connect the
external supply
- External supply follows the
recommended power sequence and slew rate requirements as per the data
sheet
- The external supply timing is controlled by the
processor IO
- Leave the processor VPP
supply pin floating (HiZ) or grounded during power-up sequences, power-down
sequences, and normal device operation
Schematic Review
Follow the below list for the custom
schematic design:
- A dedicated LDO or PMIC
output is used
- Nominal voltage connected to VPP is 1.8V and
supports current requirements as per data sheet
requirements
- Selected LDO specifications
including load current transient response is similar to the LDO used on the
SK schematics
- Processor IO is used to
control the EN of the LDO and the required pull is provided
- Verify the if EN pull holds
the LDO is in off-state during power cycling
- When an adjustable LDO is used, verify the output
voltage configuration, output voltage slew and use
of over voltage protection
- Series resistor is provided to isolate the
processor VPP supply from the LDO output for testing
the timing or LDO output
- Supply rail connected follows the processor
ROC
Additional
- Always provide provision on the processor board
to connect VPP supply (on-board or external supply).
- Select an LDO with fast transient
response and connect LDO output to the processor VPP pin with a low loop
inductance path to source the high transient load current, where the VPP pin
never drops below the minimum operating voltage.
- Enable the VPP only during eFuse programming.
Connecting the VPP supply to a continuous 1.8V supply rail
is not a recommended or allowed or supported option.
- Due to the transient load current
requirement during eFuse programming, using load switch or FET switch is not a
recommended approach. A load switch or FET switch is likely to have too much
voltage drop that is not compensated when using an LDO.
- If the use case requires use of load switch or
FET switch, characterize the board by measuring the voltage
on the processor VPP pin during programming and verify
supply never drops below the ROC minimum limit. Several
variables in the path of VPP can cause the supply to be out
of the ROC when using load switch or FET and must be without
characterized before implementing. Check or test if the load
switch or FET switch violates the maximum VPP supply slew
rate limit of 6000V per second defined in the data
sheet.