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TPS54260: About enable circuit with zener diode

Tao_2199
Genius 5740 points
Part Number: TPS54260

Hello,

 

Regarding to EN pin on TPS54260, my customer is asking some question.

Due to supply constant voltage to EN pin for wide range Vin (5-50V),

They will set a zener diode(5.6V) in enable circuit.(Please refer below.)

 

 

(Question)

(1)They are asking whether there is any problem in their enable circuit with zener diode.

According to datasheet Figure 29 (page16), the zener diode is included in TPS54260

and it is used for wide range Vin. (Constant voltage(5.6V) is supplied.)

If so, I think that it is not needed a extarnal zener diode in their enable circuit.

My understanding is correct?

 


 

(2) Or if extarnal zener diode is needed, are ｒesistors(27k and 47k ) needed in their enable circuit?

I think that only resistors(82k and 91k ) is needed to current limit for zener diode.

 

Regards,

Tao2199

  • 0
    TI__Expert 4365 points

    Hello Tao2199,

    It is true there is an internal zener clamp on the enable input. However this is only an appropriate limiter when the Enable input is open circuited and the internal pull-up is used to always enable the device.

    If you are using an external resistive divider to establish a system UVLO then you must obey the data sheet Abs Max input voltage limit of 5V. My recommendation is to use a zener clamp circuit that guarantees EN will never exceed 5V and this might involve a zener selection less than 5V. Note that most zener diode families are specified at a test current that approaches the max power limit of the zener. In your case, the current through the divider may be substantially lower than the zener test current. I'd recommend zeners in the 200mW SOD-123 case such as the BZT52C series parts (Prefix letters may vary). Also be sure to choose one of the major diode vendors that will properly specify the parts with a quality data sheet and consistently characterized production parts. Be sure to test the circuit under worst-case temperature exremes because the zener voltage has temperature dependence.