Push-Pull Supervisor driving the AM3558 IOD WARMRSTn pin

[dion]

QUESTION

Instead of Push-Pull drive, should the supervisor not instead be Open-Drain to prevent a condition where supervisor NRESET drives HIGH while  AM3358 WARMRSTN drives LOW?

REFERENCES

AM3358 datasheet = SPRS717J –> see Table 4-1 on Page 48

AM3358 TRM =  SPRUH73P –> see Figure 8-20. PORz on Page 1236

—> WARMRSTn pin is a bidirectional open-drain pin (signalname = nRESETIN_OUT) and may be actively driven low by AM3358.

APX811 (Diodes Icc doc DS31960 APX811/812 Rev. 2.)

—> NRESET is a push-pull output.

 

 

[Eshtaartha Basu]

Hello Dion,

Good question. On all our reference designs, we have used a 1K resistor between the output of supervisor circuit and nRESETIN_OUT. As a result, this resistor will act as either pull up or pull down of nRESETIN_OUT depending on the output state of supervisor circuit.

When low, nRESETIN_OUT buffer can sink up to 4mA whereas the supervisor circuit can only source up to 3.3mA through 1K resistor (at 3.3V). As a result, the supervisor circuit will not be able to override the state of nRESETIN_OUT if AM335x were to assert nRESETIN_OUT due to an internally generated warm reset.

Hope this answers your question. Please let us know if you have any other concerns.

[Author]

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