Start-up of MP100L

We are evaluating using the MP100L

The issue we have seen that the MP100L will not start-up with resitive load of 2.2 komh (Vout is 3.3V without this load - only 26kohm feedback resistor load)

In our application we have 230VAC input that is full-wave rectified

Vin on the MP100L Vin (pin 8) is connected to this full rectified voltage
(a 47nF x2 capacitor is connected between line and neutral before the full-bridge)

VB/VD (pin 3/5) is connected to 4*10uF 50V/X7R capacitors (effective capacitance for the charging voltage ~20uF).

The ouptut voltage (3.3V) is set using 16kohm resitor between Vout(pin 4) and VFB (pin6) and a 10kohm resitor between VFB (pin7) and GND.

Vout is also connected to a 1uF output capacitor.

With no load (apart from the feedback resistors) the output voltge rise to ~3.3V

If a 2.2 kohm resitor is connected between the Vout and GND the output voltage rise to about 0.4V.

It seems that there are some internal over-current or something not mentioned in the datasheet that stop regulation of the output voltage to the valid value of 3.3V.

The output current of a 2.2komh resistor at 3,3V is 1.5mA, the values used in our application should really be able to support this

Any suggestions ?

Hi Steolo,

Can you please confirm if you have the circuit configuration similar to the MP100L datasheet application circuit on on page 15?
The pin numbers that you mentioned for VFB and VB are incorrect.

Please post your schematic for this circuit if possible.