MP1542 20.5V Boost Converter Design Support

DC-DC Power Converters
1

Hi, we are an undergraduate student team in India building autonomous robots, so please excuse our level of understanding.

We aim to build a boost converter module using the MP1542 IC.
Following are the specifications:

  • Input - 16.8V (Lithium Polymer 4S Battery)
  • Output - 20.4V at 0.5A maximum. (To power an Ubiquiti R5AC-LITE)

In the datasheet for the device it is given that the maximum voltage the EN pin can sustain is 6.5V
Screenshot_44

Since our input voltage is 16.8V it was decided to use a voltage divider and bring down the EN voltage to 5V. However in the following text it says that when Vin crosses 6V, the EN pin has to be pulled up to Vin using a 100k resistor

EN - Regulator On/Off Control Input. A high input at EN turns on the converter, and a low input turns it off. When not used, connect EN to the input source (through a 100kΩ pull-up resistor if VIN > 6V) for automatic startup. EN cannot be left floating.

But will the EN pin be able to sustain Vin since it is at 16.8V ?

Thus we are at a crossroads of pulling the EN pin at 5V and at Vin(16.8V). Which one will be feasible?

Regards,
Nilabha

Project MANAS

2

What is happening at that pin is as follows
Actual threshold for operation is 1.5V and it looks like it is intended to be driven by a logic signal.

If you don’t want to do that and have it just enable when the power comes up, then you have to take precautions.

Specifically you have to use a resistor to limit the current into the EN pin once its voltage gets over 6.5V. Basically at that pin you have a zener diode to ground and the current has to be limited to avoid damage.

So you can put a 100k to Vin and then you will have a converter that self enables
Or you can put a voltage divider to Vin such that EN is at 1.5V with Vin of 10V or so. For efficiency reasons the upper resistor will like sill be 100k.

So put 100k Vin to the EN pin, put 20k EN to GND and if you don’t want to spend the 1/100 of a cent on that resistor don’t stuff it