TLC393: Current Consumption

Edgar
Can you share your schematic and under what condition you are measuring the quiescent current? The supply current values found in the TLC393 datasheet are when the outputs of the comparators are in a steady state (not switching).
Chuck

Hello Edgar,

The supply current is shown in Figure 12, and in the electrical table (40uA max at 5V).

The supply current vs Supply voltage graphs shows about 26uA at 12V. But this is at output low and no input signals.

Supply current will increase as the output toggle frequency increases. This is common to most comparators as there is usually a spike in the supply current corresponding to the output transitions (few 100ns - due to charging/discharging of internal node capacitance). The bypass cap integrates these current pulses, so you see the average current. The faster it goes, the more spikes occur, the more current.

Is the output toggling at the time you are making the measurement? Does this current include the pull-up resistor current?

Dear chuck,

The schematic is as follows. JP3 is closed and Vbat is varies between 8V and 12V.

Paul,

the issue is that on the test bench, some of the TLC393 show the consumption steady and as expected, but others show much higher and unstable values.

Hi Edgar,

I have some ideas:

1. Are you sure that the supply voltage is never exceeding the TLC393's maximum supply voltage of 16V, even briefly? Sits C5 directly at pin 8 of TLC393?

2. Are you sure that the LM2936 isn't oscillating? Take for C15 a 10µF/16V/X7R in a 1206 package to avoid a drastical capacitance drop at 5V. And connect a 0R22 series resistance (or similar) to this cap to keep the ESR of C15 in the allowed range. Keep these two components very close to the output of LM2936. Connect an input cap to the LM2936, also directly at the input pin, as recommended in the datasheet.

3. Insert a 1k8 resistor at the -input of TLC393. If C9 is big, the voltage at the -input can violate the input voltage maximum ratings during sudden power-down. The 1k8 resistor limits the input current then and prevents latch-up.

Kai

Hi Edgar,

Were you able to resolve the issue?

How did you measure the current? If you just used a DMM in ammeter mode across JP3, the resulting series resistance due to "voltage burden" of the ammeter may have caused the comparator to self oscillate since the bypass capacitor is on the supply side and not at the supply pin.

Comparators can be picky about their supplies due to the internal supply transients at the output transitions.

Try placing a 0.1uF cap directly across the comparator supply pins (0.1uF from JP3-1 to GND) and re-measure the current.