Noggin
Member
I have a project on which we made the unfortunate decision to slap a super cap on the Vcc rail to ensure there is enough power available to allow the system to shut down properly without corrupting an SD card. Unfortunately, this severely dampens the Vcc rise when power is applied, which can cause the MCU to not start up properly. Asserting reset does not let the MCU recover. I've read that the sharp rise of the Vcc rail is used to start the crystal oscillating properly, if the rise is too slow then then crystal isn't guaranteed to start.
I'm also seeing other issues with the Real Time Clock (off-chip) not responding to I2C commands until a full power cycle. I suspect that this may also be due to a slowly rising Vcc.
I've been searching for a voltage supervisory (V-Sup) IC that passes through Vcc instead of just asserting a reset pin, but haven't had any luck. I imagine it should be relatively simple to put a couple of FETs in circuit to disconnect Vcc using the V-Sup's reset output, but it would be great to have a 1 component solution. This is a very tight board design already using two double sided, stacked boards. Something like an SOT-23-6 with an adjustable threshold would be the best fit.
Is there such a device?
I'm also seeing other issues with the Real Time Clock (off-chip) not responding to I2C commands until a full power cycle. I suspect that this may also be due to a slowly rising Vcc.
I've been searching for a voltage supervisory (V-Sup) IC that passes through Vcc instead of just asserting a reset pin, but haven't had any luck. I imagine it should be relatively simple to put a couple of FETs in circuit to disconnect Vcc using the V-Sup's reset output, but it would be great to have a 1 component solution. This is a very tight board design already using two double sided, stacked boards. Something like an SOT-23-6 with an adjustable threshold would be the best fit.
Is there such a device?