General
Review and verify the following for the custom
schematic design:
- The sections
above, 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 allowed
or recommended).
- 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).
- Onboard 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 a processor IO.
- Leave the
processor VPP supply pin floating (HiZ) or grounded during
power-up sequences, power-down sequences, and normal device
operation.
Schematics Review
Follow the list below for the custom schematic
design:
- A
dedicated LDO or PMIC output is used.
- Nominal
voltage connected to VPP is 1.8V and supports
current rating 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 slew and use of over voltage
protection.
- A series
resistor is provided to isolate the processor VPP
supply from the LDO for testing the timing or LDO
output.
- Supply
rail connected follow the processor ROC.
Additional
- Always provide provision on the processor board
to connect VPP supply (onboard 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
allowed or recommended 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, then characterize the system 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
power-up slew rate limit of 6000V per second defined in the
data sheet.