LM2734: I use LM2734 as DC 5V IN, DC -4V output, The sch as below ,please help to check if ok ? many thanks ~

Andrew Liu74

Intellectual 970 points

Part Number: LM2734

I use LM2734 as DC 5V IN, DC -4V output, The sch as below ,please help to check if ok ? many thanks ~

over 7 years ago

0 Anthony F over 7 years ago

TI__Mastermind 35215 points

Hi Andrew,

I have two comments below.

You will need to add another diode from GND to the BST pin to keep the BOOST capacitor charged. The BOOST capacitor is charged when the schottky diode (D9303) is on so the SW node is near the -4V output. This diode will then keep the BOOST capacitor charged to near 4V - Vfwd.
Per datasheet recommendations, I suggest increasing the input capacitor C50187 to 4.7 uF.

Best Regards,

Anthony

0 Andrew Liu74 over 7 years ago in reply to Anthony F

Intellectual 970 points

Dears

many thanks ~, the correct sch as below ,please help to check ,many thanks~

0 Anthony F over 7 years ago in reply to Andrew Liu74

TI__Mastermind 35215 points

Hi Andrew,

The added diode should have pin 1 connected to ground and pin 2 connected to the BST pin. The purpose of this diode is to keep the capacitor connected between the BST and SW pins charged.

Anthony

Power management

Power management forum

LM2734: I use LM2734 as DC 5V IN, DC -4V output, The sch as below ,please help to check if ok ? many thanks ~