LT1157 Logic Level Question

Question

I plan to use the LT1157 in my application PCB to act as a switch control from a micro controller side to control the On/Off state of 2 module boards which will be connected in the PCB.

• 1st Load is 5V 1A.
• 2nd Load is 3.3V 500mA.

The LT1157 will get a 5V input at the V_s terminal.

Does anyone know how much voltage is required to be used at the IN1 and IN2 pins? The datasheet doesn't say how much voltage can be used here. I am guessing it will be 5V, but can it do logic level with 3.3V? My microcontroller board gives an output of 3.3V and not 5V so I'll have to make a logic Level converter before feeding the pins IN1 and IN2 if it's not 3.3V tolerant.

Please confirm, if anyone has used this IC before.

Answer 1

The answer is on page 2 of the datasheet. The minimum "Input High Voltage" is listed as "70% × VS". Therefore, if you supply voltage (VS) is 5V, the minimum specified input voltage would be 3.5V. This value is for operation over the entire specified temperature range.

It MAY work with 3.3V inputs (probably unreliably), but it would be better to convert the inputs to 5V logic. If your application will allow you to use a low-side driver, you could power the LT1157 from 3.3V and use a low-side driver to switch power for your 5V load (similar to the "Mixed 3.3V and 12V High- and Low-Side Switching" example in the datasheet.