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LT 6703 for Hysteretic Voltage Control

Question asked by IrishEng on Apr 10, 2018
Latest reply on Apr 16, 2018 by Jvillanu

Hi,

 

I have been working with the LT 6703 (in particular the LT 6703-3 Non-inverting input) chip for the past year and it has been working perfectly. I followed the steps on page 10 of the datasheet to create a wider band hysteresis control. For example I have R1 = 46KΩ, R2 = 835kΩ , R3 = 1.2 MΩ and R4 = 600kΩ with a Vs of 2.4 V, which in turn gives me a lower threshold of 0.363 V and an upper of 0.438 V. When I vary the input between these values I got the appropriate high (Approximately Vs) and low value (GND) on the output. However I recently got some more chips and when I try to replicate the existing working setup, I can never get a full high on the output of the LT 6703. By this I mean that the output never reaches Vs on the output when the output is high and rather reaches between 0.5 and 0.75 of the Vs. I have been looking into comparators and their operation with feedback (both inverting and non-inverting). It seems that featuring the feedback resistor R3 causes the comparator output to have a voltage drop for the high output state. I'm wondering if anyone knows of a solution to get a wider band on the hysteresis control while ensure that the high (Approximately Vs) and low (GND) outputs are achieved?

 

From here I'm hoping to use the LT6703-2 which has an inverting input as this chip draws a lower current draw when the input voltage is below the reference voltage versus the current draw when the input voltage is above the reference. Any help with this would be greatly appreciated.

 

Thanks.

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