Other Parts Discussed in Thread: TPS63070, TPS3703
I'm making a 5V and 3.3V power supply from 4x AA series batteries. The input range is thus between ~4V and ~6V, I'm using the TPS63070 buck-boost converter for the 5V supply, into an LDO (TVL70233) for the 3.3V supply. During my testing with a different power supply design, I saw the battery supply drop quickly after hitting ~4V. On my other power supply, this would disable the output of the converter, unloading the batteries. However, after the load is removed, the voltage will restore high enough to re-enable the supply. This results in a boot loop. Therefore, I would like to add a brownout latch that activates after the supply voltage drops below 4V, that resets only on power cycle. The supervisor I plan to use is the TPS3840.
I found this article about adding a latch to a supervisor IC: https://www.ti.com/lit/an/snva836a/snva836a.pdf
It notes that tying the CT pin on the related TPS3703 supervisor adds a latching function. However, it does not mention this capability with the TPS3840, even though it has a CT pin. Would I be correct in assuming I cannot ground the CT pin on the TPS3840 to add a latch reset by power cycling?
Secondly, I would like to use a power switch to turn on and off the converters, but not pass the full system current through the switch. So instead, I connected the supply of the supervisor to the power switch so the switch is only powering the supervisor. This can then control the Enable pin on the buck-boost with the /RESET output. When the TPS3840 is not powered, the /RESET pin is said to be "undefined" rather than low. I would like the default state of the TPS63070 to be off, so in order to achieve this, I used a pull-down resistor (R5) on the /RESET line (PSU_EN) to ensure the supply is off when the power switch is off.
Is this a suitable implementation of the supervisor IC?
(VCC = battery voltage in schematic)
