Switching regulator problem

[catalyst]

Hello,

I have a design about switching regulator. It will be operated with 12/24Vdc supply. I have designed a circuit in the light of datasheet of AOZ1284PI.I have set the output voltage to 5Vdc.

But I have some problems about design. When I use a resistive load whose current consumption is approximately 2Adc or 1Adc, there is no response or output from AOZ1284PI.

Also there is no response or output from AOZ1284PI even if there is no load.

If there is someone who will check my design, could you please help me? The schematic can bee seen at attachment.

[thinkfat]

What's L3/D3 supposed to do? The switcher may not like a high inductance at it's VIN.

Also what's the voltage at the EN pin? Maybe R8 is a bit too large to actually have enough current flow through the 3.3V Zener?

EDITed for more remarks:

You're running it at 1MHz switching frequency, on purpose? 22µH is then maybe a bit high for the main coil, also, as you step down from 24V to 5V, the duty cycle is going to be small and the ripple current is going to be high. The SRP1038A-220M is rated at 5A. How much are you intending to pull from the regulator?

Note that the regulator should still output 5V even if the components are maybe not optimal.

[catalyst]

Yes, the main reason why I use D3 is protection for reverse polarity. Also, the reason why I use L3 is to suppress ripple currents. I have changed the inductor value with 4.7uH instead of 22uH. There is no change unfortunately.

[DannyTheGhost]

As stated above by another message, issue might actually be in EN pin circuitry
In general, for zener you need calculate your resistor according to its 'stabilizing current' (haven't found more exact words for this term yet; how much current zener diode must sink to hold its breakdown state). Typically - it's 20-30mA, so 120k resistor would be suited only if you have 200V+ input voltage. Try with 1k resistor.

[MagicSmoker]

R8 should be more like 10k, not 120k, and switching frequency should be more like 200kHz, not 1MHz. Otherwise it should work as-is.

[thinkfat]

Yes, the main reason why I use D3 is protection for reverse polarity. Also, the reason why I use L3 is to suppress ripple currents. I have changed the inductor value with 4.7uH instead of 22uH. There is no change unfortunately.

You can't suppress the ripple current. The switcher must be able to source those amps or it ain't gonna work