Combined current with the LM3532

Ben Rector

Other Parts Discussed in Thread: LM3532, LM3697

I am using a TFT display that has the LED backlight built into it (3 Parallel strings of 5 LEDs) . Unfortunately the manufacture tied all of the strings together and I only have access to the a single + and - supply leads. The baclklight requires 60mA at 19.2V.

Will the lm3532 allow me to combine all three sinks together so that I can sink the 60mA. The datasheet doesn't specify if this is a valid use of the device. I would assume if it is possible to parallel the current sinks then one could sink ~90mA by tying all 3 sinks togather?

If the pins can be paralleled to allow a higher current sink, would the max current setting (for my application) in the current register be 60mA/3 (20mA)

Thanks.

over 11 years ago

0 Travis Eichhorn over 11 years ago

TI__Intellectual 1040 points

Hello,

Yes you can tie all three current sink inputs together for a max of 60mA. See also the LM3697 if you don't need the ambient light sensor interface.

Thanks

Travis

0 Ben Rector over 11 years ago in reply to Travis Eichhorn

Prodigy 20 points

Since there are 3 ports and the data sheet says each of the 3 ports can handle 30mA so wouldn't the maximum current of all 3 ports be 90mA?

Any guests as to the settings? All sinks set to regulation and max current for each channel decided by 3?

0 Travis Eichhorn over 11 years ago in reply to Ben Rector

TI__Intellectual 1040 points

yes (sorry), max current is 90mA. I always think of typical as being 20mA per string. Have feedback enabled for all sinks, then you can set the current setting up 2 ways. Either all sinks controlled by a single brightness register, or with each sink having independent control. As far as how the LED current will route itself throug the LEDs is anyones guess. Does the display have ballast resistors in series with each string? This would help reduce the current hogging of a string. Probably the LEDs are matched well anyways, so the current will be very close.

0 Don Schelle over 10 years ago in reply to Travis Eichhorn

TI__Expert 4150 points

Hi Travis,

Please confirm that you can tie all 3 sinks on the LM3697 together as well.

Don

Power management

Power management forum

Combined current with the LM3532