The LT1943 will heat up and burn out when connect a 180mA load(Capacitive sensor).

Hi Sirs!

  When I used LT1943  to provide 3.3V(less than 100mA), +15V(< 50mA),-15V(<50mA),+24V(Imax < 200mA, Istable < 20mA ). Below is the SCH of LT1943。

1. It works correctlly when no load on VCC24( Out of SW2). all the power out is in  right value. and the total input current(supply with 10V input) is  less than 20mA.

2. Below is the total load for VCC24. 1 LED with I < 7mA, and LM317 is power with VCC24 to provide a adaptive Power supply to the Sensor(When I power  the board with a 24V adapter out of the board. I measured the instantaneous current  Imax < 300mA  ).

Here is the issue I met.

1. When I connected the sensor to Board on SMA which connect to LM317 out with a 1uF capacity. The LT1943 began to heat up. the current of power in(10V input) went to about 180mA~200mA.

2. I disconnected the sensor from board after power down.

3. I re-power on the board with no sensor connected to board. The input current is still about 110mA(At first The current will less than 20mA with no sensor connected to borad). and the LT1943 heat up again.

According to LT1943 datasheet the maxium output currenti of SW2 is 2.6A.

1. why is the LT1943 burned out with less than 200mA instantaneous current?

2. how should I modified the schematic to resolve the issue?

Thanks for your any information.