INA169-Q1: residual charge on output

Hi Tsuji-san,

Once V+ drops below VOUT by ~0.8V, an ESD diode internal to the device will become active, and the voltage on VOUT will discharge through the device to V+ pin. There should be no damage to the device in this scenario.

The picture attachment does not load for me. However, there should be a resistor from VOUT to GND that will also help discharge the voltage from the capacitor in this scenario.

VOUT will be limited to V+ - 1.2V as shown in Table 6.5 of the datasheet. The absolute max VOUT rating is similar, it is referring to what the device is capable of driving at the output (if max V+ = 40V), not what can be applied to the output from a different voltage source. So you are correct that there should be no problem, but this spec does not represent that. 

Please let me know if you have any other questions.

Cierra

Hi Shinji,

when the decay time of supply voltage during power-down is much longer than the time constant of output filter, then there's no problem, because the output voltage will never exceed the supply voltage during power-down. Assume you have a 100kHz low pass filter at the output by paralleling a 150pF cap and 10k resistor. Then the time constant is 1.5µs. Unless you abruptly short circuit the supply voltage to 0V, the decay time of supply voltage during power-down should be much much bigger than this time constant. -> No problem.

If the time constant is longer than the decay time of supply voltage during power-down, on the other hand, and if a big filter cap is mounted at the output carrying sufficient charge to become risky, I would search for a suited protecting discharging path for this cap during power-down. In this case I would mount a diode clamp from the output to the supply voltage. Even if the INA169 already contains a protection diode at this place (which I do not know !), the external diode clamp would disburden the internal protection diode by shunting the most discharging current arround the INA169.

What sort of output low pass filter do you plan?

Kai

Hi Kai-san,

Here is the putput filter configuration.

Is there a need for bypass diode?

CL=1000pF、Ro=3.6kΩ

and V+= +5V

regards,

Hi SHinji,

1000pF and 3k6 results in a time constant of only 3.6µs. This should not present any problems.

Kai