LTC3786 3V to 18V boost converter

Question

Hi EngineerZone community, 
 
 I'm designing a li-po battery booster with LPC3786 which is able to convert 3-4.2V battery voltage to 18V 5A, for this purpose I tried to customized one of the sample circuits from the datasheet, (3786 F13a ) I have changed a few of components and entered the values in the LTpowerCAD project file and it seems to work, the only problem I can see is that as the original sample circuit's output voltage is 5V the output of the circuit is connected to the output pin of the LTC1754 pin (through the body diode of mosfet Q), which has the maximum rate 6V of the pin voltage so now with the output voltage of 18V is there any other solution for that ? maybe just replacing mosfet with a simple diod ? 
 
 is there any other problem you can mention in the circuts ?

ADIApproved · Accepted Answer

Hi. one possible solution is to directly connect the Vout of LTC1754-5 to Vbias and remove D2. Hence, the Vbias will always come from LTC1754-5. By the way, may I know what company are you from? May I also know your estimated amount of usage (EAU)? 
 Regards,)

Hamed_ta · Answer

any idea ?

ADIApproved · Answer

Hi, the major problem that you would encounter here is that the output voltage limit of LTC1754-5 is only 6V. Putting an 18V across it would damage this IC. This suggested circuit in page 28 is designed for a lower Iq and low output voltage. Do you really need a lower Iq that's why you are attempting to use it? Maybe using the circuit you obtained from LTpowerCAD is enough. 
 
 Regards,

Hamed_ta · Answer

directly connecting the Vout of LTC1754-5 to Vbias doesn't affect the efficiency on higher output voltages ? actually I think this is a solution for low input voltage not low Iq, 
 
 I wan't to use this circuit on a free and open source project.

Fil · Answer

It is a solution for low input voltage. Low Iq in a sense that VBIAS will come from 5V after PGOOD is ok which is close to minimum requirement. 
 Make sure that output current of charge pump is enough to provide for VIAS pin.

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LTC3786 3V to 18V boost converter