Interfacing current sense of H-Bridge IC to 3.3V MCU

Thread Starter

Dilby

Joined Jan 30, 2021
1
Hi,

I'm using the same BTS7960 H-Bridge driver as discussed in this thread https://forum.allaboutcircuits.com/...-h-bridge-for-its-protection-features.141724/. However, in my application I'm interfacing to a 3.3V STM32 MCU rather than an 5V Arduino.

1) Can Ris be a lower value than the 500ohms mentioned in the referenced post. On a fault condition 7mA is supplied to Ris - 7ma*500ohm =3.5V (too high for the STM32) ? If I use a lower resistor value, what are the downsides ? My assumption is the power usage of the application will go up, which isn't great for a battery powered circuit.

2) The datasheet page 20 refers to a maximum analog sense current of 7mA under a fault condition, with a Vs of 13.5V and Ris of 1Kohm. If my Vs is much lower, i.e. 7.4v, would the analog sense current be lower (it's not clear from the data sheet) ?

Generally the question I have is what Ris value should I use for a Vs of 7.4v to interface with a 3.3v MCU without risk of exceeding the 3.3V.

Thanks Dilby.
 

wayneh

Joined Sep 9, 2010
17,152
Generally the question I have is what Ris value should I use for a Vs of 7.4v to interface with a 3.3v MCU without risk of exceeding the 3.3V.
Is it practical to simply do the experiment? Simulate the fault condition and give it a try.

I'd also consider putting a zener diode on the input to protect your MCU from any overvoltage input.
 
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