Logic compatibility for analog switch 74HCT4066 from Nexperia with STM32G431MBT6

[sreejithrnair]

 Hi @Peter BENSCH 

I have a query regarding voltage compatibility of Quad single-pole single-throw analog switch from Nexperia 74HCT4066.

The switch part is voltage compatible with STM32G431MB/ME series when analyzing VOH VIH VIL VOL relationships with ST MCU. This logic of analog switch part is TTL and the STM32G431 is CMOS logic. So, I would like to know whether the CMOS logic of ST MCU will be compatible with TTL logic of analog switch and how the ST MCU will behave to identify for both CMOS and TTL logic?

Please find attached datasheet URL of analog switch for your reference: Quad single-pole single-throw analog switch (nexperia.com)

Hoping for a clarity solution.

Kind Regards,
Sreejith

Design Engineer

Eaton

[Peter BENSCH]

Yes, the HCT family can be controlled directly from the CMOS outputs of the STM32, because the required TTL levels are well within the CMOS output voltage.

Hope that helps?

Regards
/Peter

[sreejithrnair]

Hi,

Many thanks for the response. Indeed, this is helpful solution.

By referring to HCT family, is the Analog Mux/Demux IC (74HCT4052) also compatible with CMOS logic?

Regards,
Sreejith

[Peter BENSCH]

The question is unspecific, as there are different implementations of CMOS Logic. With regard to inputs of HCT logic, the question can be answered in the affirmative; for HCT outputs, the thresholds of the CMOS inputs specified in the data sheet of the respective device must be considered carefully.

Regards
/Peter

[Danish1]

Any DIGITAL input on a 74HCTxx device running at Vcc = +5V is compatible with any DIGITAL output from any CMOS device including stm32gxxx that is running at Vdd = +3.3V

On the other hand, if a 74HCxx (without T) device is running at +5V, then it's DIGITAL inputs are NOT compatible with DIGITAL outputs of a CMOS device running at Vdd = +3.3V.

Please confirm the supply-voltages of your stm32g and 74HCT devices

[sreejithrnair]

Hi Danish,

Many thanks for the info.

Supply voltage for STM32G MCU is 3.3V

Supply voltage for 74HCT device is 5V.

Regards,
Sreejith

[sreejithrnair]

Hi @Peter BENSCH 

Will there be any impact in current consumption when using the TTL part compared with CMOS logic?

Best Regards,
Sreejith

[Peter BENSCH]

Does your question regarding the current consumption refer to the STM32G431 or the 74HCx?

The STM32G431 can only switch to one of three possibilities at its GPIO: Low, High or Floating (Analogue Input). Low and High correspond to voltage levels with which 74HCT can operate - as long as the STM32G431 has a VDD=3.3V. This does not affect the power requirement of the STM32G431. The situation would be different if you do not control a 74HCT (CMOS), but 74xx in bipolar technology, whose input current is not negligible.

For the current requirement of the 74HCx, please consult the data sheet of the respective manufacturer.

I would also like to take this opportunity to point out that you should always set the GPIO with which you drive 74HCT to low or high. If you also intend to set the GPIO to floating (analogue input), the subsequent 74HCT will no longer have a defined level and can capture noise, which leads to increased power consumption of the 74HCT. Such cases can be mitigated by activating an internal or adding an external pull resistor.

Regards
/Peter