I'm trying to design a SLA battery charger with the LTC4020, and I'm not clear as to what the SHDN pin does.
According to the datasheet:
SHDN (Pin 9): Precision Threshold Shutdown Pin. Enablethreshold is 1.225V (rising), with 100mV of inputhysteresis. When in shutdown, all charging functions aredisabled and input supply current is reduced to 27.5μA.Typical SHDN pin input bias current is 10nA
The language suggests that the SHDN pin trips as the voltage on it rises from below 1.225V to above 1.225V, but this makes no sense: why would you disable charging when the voltage is going up (unless it's for an over-voltage condition, which the LTC4020 is specifically designed to avoid doing in the first place)?
Does this description actually mean that the LTC4020 enables charging when the SHDN pin crosses the threshold from below 1.225V to above it? I think this is how the part actually operates, but that means that SHDN is either misleadingly named or is an active low-signal that isn't marked as such.
Please elaborate on how the SHDN pin is meant to function.
SHDN asserts (i.e., the part shuts down) with the voltage on SHDN less than the 1.225V threshold.
I believe your argument is that a more correct pin designation would be .
Thank you. That's what I thought.
i have another questions which seems to fit perfect here:What function does the SHDN pin actually control?It disables charging as the datasheet says: "When in shutdown, all charging functions are disabled and input supply current is reduced to 27.5μA."So for me this mean that the BGATE-pin is instant pulled high to disable the battery P-FET.But is the DC/DC converter also completly disabled? (Input voltage is of course still present)I would assume that the converter should be still operating to power the system load?