LT1945 Design for 100mA on -15V & +15V

I am designing a power supply using LT1945. Here is the environment:

Input :12V
Output +15V, -15V
Current: 100mA, -100mA

Please find the Schematics attached for reference.

Issue: I have designed the circuit taking cue from the datasheet, (all the application circuits shown are of lower currents viz, 10mA, 20mA), however, while simulating it, the negative rail is stable only for currents lower than 40mA, even though the datasheet mentions it can source currents upto 350mA. At 100mA, the voltage drops to ~10V or so, and I am not able to solve the problem nor make it work at 100mA. 

Can anyone help me with an explanation or tell me what I am missing?

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  • Hi,

    The datasheet says both converters are designed with a 350mA current limit, that however, is referring to the switch current limit, and not to the output current available.

    The schematics provided at the front and last pages of the datasheet are useful for providing an idea of the load current available for the input and output voltage shown on those applications. As a general rule, as the output voltage is increased, the output current available will drop.

    If you really need 100mA load for each output, you need to pick a converter that has at least 500mA switch current capability, guaranteed, for the positive output, and about 700mA for the negative. Please note the LT1945 has a minimum of 250mA of guaranteed switch current, so this part will not support your needs.

    The LT8330 has a 1A switch and can be used for positive or negative applications to provide the power you need, though it will require one part per output.

Reply
  • Hi,

    The datasheet says both converters are designed with a 350mA current limit, that however, is referring to the switch current limit, and not to the output current available.

    The schematics provided at the front and last pages of the datasheet are useful for providing an idea of the load current available for the input and output voltage shown on those applications. As a general rule, as the output voltage is increased, the output current available will drop.

    If you really need 100mA load for each output, you need to pick a converter that has at least 500mA switch current capability, guaranteed, for the positive output, and about 700mA for the negative. Please note the LT1945 has a minimum of 250mA of guaranteed switch current, so this part will not support your needs.

    The LT8330 has a 1A switch and can be used for positive or negative applications to provide the power you need, though it will require one part per output.

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