EVQ7228-QJ-00A Voltage Range Adjustment

[bruno]

Hi all,

We’re looking to drive 16 single 200ma LEDs with a forward voltage of 2.8-3.2V, and ran into the problem of how to adjust the EVQ7228 buck converter voltage down from the default 7V min to a reasonable voltage to drive the single LEDs.

Based on our understanding of the data sheet it’s:

• Change R3 to 20.1kΩ (from current 80.6kΩ)
• and/or
• Reprogram the OTP:
  (0x27, 0x22, 0x22), # PRE-VBIAS for 3.5V
  (0x28, 0x25, 0xB9), # DROP_BAND
  (0x01, 0x02, 0x00), # DEV_CFG_1
  (0x02, 0x60, 0x03) # DEV_CFG_2

Before toasting a couple of boards it’d be amazing if someone knows the answer off the top of their heads to get some guidance. It’s not even clear if it’s advisable to combine the hardware and OTP fix, or if one would do.

Much appreciated!

[eduardo.munoz]

Hello Bruno,

if you would like to reduce pre-Vbias I would simply use the register values in 0x27. The lowest value N here is shown as 0x0E or 14 and gives a pre-Vbias of 2.5. Every value increase by 1 in the register contributes to the Vbias increasing by 0.05V.

Changing resistors would most likely cause a different change in Vbias than the current 0.05V/(1 reg value) increase.