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TPS61183: fails to drive isolation FET transistor

Part Number: TPS61183


I mounted led driver TPS61183 on a board using schematic with isolation FET transistor shown in page 10 of TPS61183 datasheet.

I also followed the recommendations in paragraph, page 18 of the same datasheet.

The input power is 5V connected to the Source of my PMOS (Si7617DN). 

A 100KR is between the Source and Gate. Gate is connected to FAULT pin, and the output (inverse diode and inductor) are connected to the Drain of the FET.

The PWMIN signal is controlled by the microcontroller with a frequency of 1KHz, and variable duty cycle.

4 leds strings are used (IFB1..IFB4) and IFB5 and IFB6 are pull to 0V via a 10-Kohms resistors.

EN signal is driven high by a microcontroller which also provides the PWM signal on PWMIN pin.

ISET is pulled down by a 200K resistor to get 6mA per string.

I put a voltage divider (100K/5,62K) towards OVP.

RFPWM/MODE is pulled high via a 1K resistor.

RFSW = 499Kohms

When I set EN signal to logical 1, I see a slight decrease (less than 200mV) on FAULT pin and it goes back to 5V.

I conclude that the FAULT pin of the TPS61183 fails to pull the Gate of the transistor to 0V.


With this schematic, the TPS61183 systematically goes into error and pulls its FPO pin to 0 and the output voltage (connected to the leds strings anode) is 0V.

Can you help me on what could cause this error ?