We have few questions about reference circuit and hope to get your kindly help.
a. Why needs 5V boost to 6V for VLED ? we can not direct input 5V ?
b. What is the reason that the circuit needs using three heating resistor ? it there dimensions for reference ?
c. In the circuit note, +6V is for VLED3(IR) ? it looks different with ADPD188BI datasheet.
Thanks for support.
The CN0537 includes a +6 V boost so users have the option of setting a higher LED current — this is needed because the bias voltage requirement goes up as the driver current is increased. As shown…
They needs 1W power rating resistors regarding the power rating of heating resistors ?
The CN0537 includes a +6 V boost so users have the option of setting a higher LED current — this is needed because the bias voltage requirement goes up as the driver current is increased. As shown in the ADPD188BI datasheet, this can go above +5 V at the higher LED current settings.
That said, a +5V supply should be sufficient if the driver current will only be around 200 mA or below. This is actually the typical VLED used in most ADPD188BI examples.
Regarding the heating resistors, the circuit uses three to more evenly spread the heat dissipation. You are correct in that they require at least 1 W power rating; the default resistors installed are rated for 1.5 W and are in a 0603 package size (dimensions: 0.063" x 0.032", or 1.60 mm x 0.81 mm).
Lastly, it seems there is a mistake regarding the supply connections on the CN0537 block diagram. +6 V is used for VLED1 and +3.3 V is used for VLED3. I apologize for the confusion — I'll have this corrected as soon as possible.
The 25 ohm heater resistors is a 0603 package size @ 1.5W on the circuit. but we still did not found out 1.5W resistor spec on 0603 package size. because 1/8 W is maximum power rating on 0603 package size.
Could you provide CN-0537 Bom list for reference ?
The BOM should have been uploaded to the design support package, but I did just check and it appears that it was missing. Apologizes for that. I have updated the design package to include it. Please try back here again.
Thank you for quick support.