TLC3702 output current

Hi Oliver,

TLC3702 data-sheet figures 13 and 14 show the output voltage V_OH and V_OL levels for a range of output current levels. Ten milliamperes is within the output range capability and it appears from the data-sheet and graphs that the TLC3702 can sink/source up to 20mA of output current depending on the V_DD being applied . The device can safely dissipate the internal power associated with the two states.

You are correct regarding the input impedance being very high. That is the case when the device is operated within its recommended operating input range. Where the Max Input Current comes into play is when the input voltage is driven to a level where it begins to exceed the rail voltages V_DD and V_GND. What typically takes place is normally "off" junction begin to become forward biased as the voltage level moves beyond a supply rail. This may be ESD protection cell or other circuits turning on. Figures 2 and 3 in the data-sheet show how the current increases as the input voltage is driven beyond the supply rails. Figure 2 appears to be correct, but I do think Figure 3 has errors. Actually, Figure 3 is the behavior when the input level is driven below V_GND, not V_DD. The curve follows a forward-biased diode response.

Regards, Thomas

PA - Linear Applications Engineering

Hi Thomas.

Thank you for your explanation.

Concerning Figure 14 (Vol vs Iol), it means that with a VDD = 15V and a 10 mA current drawn on low state, the output voltage will be approx. 0.25V ?

On figure 13, the datasheet shows a negative Voh on the scale. Is this the voltage under VDD ?

Best regards.

Hello Oliver,

Yes, the TLC3702 V_OL level will be about 0.25V above ground level when V_DD is 15V and I_OL is 10mA. And yes, your understanding of figure 13 is correct. When V_DD is set to 15V and I_OH is -10mA, V_OH will be about -0.35V below V_DD, and 14.65V above ground.

Regards, Thomas

PA - Linear Applications Engineering

I found this discussion to be very helpful in my comparator exploits, however have a question within the same context. I understand the Low-Level output voltage versus Low-Level output current well enough, but a tad confused with its sister High-Level graph. Could you clarify the y-axis? What is "High Input Level Output Voltage"? Also... For this test, should not one change the pull-up resistor to a pull-down from output vcc to gnd? Many sincere thanks...

Hello Bryan,

The High-Level Output Voltage vs. High-Level Current shown in data-sheet Figure 13 depicts the TLC3702 behavior when the output is sourcing output current. The output is in the high state and for current to flow the output load must be connected to a less positive potential. Thus, you are correct; the current would flow into a pull-down resistor, or an active circuit that can sink the current being sourced by the TLC3702 output.

The Figure 13 Y-axis provides the high-state output voltage level V_OH achieved when the output is sourcing different levels of output current represented by  the X-axis parameter I_OH. The curves are for different V_DD levels that may be used with the TLC3702. The Y-axis voltage V_OH is specified in terms of how much it drops relative to the applied V_DD as I_OH increases. The more current required by the load, the greater the voltage drop across the output MOS transistor and the more reduced V_OH becomes. The X-axis current is labeled in terms of minus current following the convention that current out of the comparator is negative.

I do think the Y-axis should have been labeled "V_OH - High-input Level Output Voltage." I do think the word "input" was incorrectly included within the line.

I hope this helps.

Regards, Thomas

PA - Linear Applications Engineering

Bryan,

Something odd occurred when I posted my TLC3702 response. Some subscripts became separated from their associated term. It looks odd, but the explanations still come through.

Regards, Thomas

PA - Linear Applications Engineering

HI Thomas... Thanks for your helpful assistance. It all make perfect sense and  was even able to duplicate Figures 13 and 14 in my Saber simulation model.

Regards,

Bryan