Input Zener

[Aharon]

Hi,
i want to calculate the input Zener Diode CR1 value.
POWER_5V0 =5V
U1 is LDO to supply 3.3V
current is 300mA Max

 

[bertus]

Hello,

Do you expect higher voltages at the 5 Volts input?
The regulator will work upto 5.5 Volts.
A diode in series with the input will raise the input limit to about 6 Volts.

Bertus

 

[Tha fios agaibh]

I'd use a 5.1v zener.

 

[Aharon]

the POWER_5V0 is DC/DC output, should be stable.

 

[WHONOES]

Why do you have a choke in the supply line?

 

[Aharon]

hi Whonos,
what are you mean choke? the CR1?
for clamping

 

[Harald Kapp]

the POWER_5V0 is DC/DC output, should be stable.

So why do you need a zener anyway?

what are you mean choke? the CR1?

No, FB1. I think that is a Ferrite Bead.
There is no C_in at the input pin 1 of the LDO. This is recommended (see the datasheet). FB1 effectively decouples the capacitors C7 and C8 (which I think are meant to be C_in from the datasheet). This is no good practice. Place the input capacitor next to the regulator's pin.

 

[Aharon]

So why do you need a zener anyway?

No, FB1. I think that is a Ferrite Bead.
There is no C_in at the input pin 1 of the LDO. This is recommended (see the datasheet). FB1 effectively decouples the capacitors C7 and C8 (which I think are meant to be C_in from the datasheet). This is no good practice. Place the input capacitor next to the regulator's pin.

thank you, i will change the FB1 position.
regarding the CR1, it cam from previse schematic the power source was from USB VBUS.