LM3532: Max current clarification: 1A 880mA 90mA ?

Hi Ilvedson,

880mA is the min. current limit while 1A is a typical value when VIN is between 2.7V and 5.5V.

Current flowing each channel is limited by the internal current source capability. 

So, there is no mistake about these values in the datasheet.

BR,

Robin

If the minimum current limit is 880mA, why does the full scale brightness register only allow a maximum of 30mA per channel? 

Robin, thanks for your patience. I'm clearly no expert on the matter.

In my hunt for an LED driver, I'm looking at how much current can be driven in each LED string. Other LED driver datasheets never talk about the boost converter current limit on the front page. They do state the current limit per LED string, which is the more useful information when selecting a driver. Would I be the only one to say that the "1 A Typical Current Limit" could be misleading?

Regardless, the LM3532 is my choice for the current design.

Hi Ilvedson,

For your requirements, you should be careful about max. current per string.

If the input voltage and output voltage are very different, then you have to pay attention to the inductor (also called FET current limit). Without considering of converter efficiency, IOUT=IINxVIN/VOUT, and the IIN must be lower than the mentioned current limit.

BR,

Robin

fsw?:

What does 'fsw' stand for in the formulas on page 36 & 37 of the datasheet?

FET Switching frequency?

A different question:

In my application I have a 'Bright' mode and 'Dim' mode.

'Bright' mode: 10mA  per string

'Dim' mode: 6mA (according to the exponential mapping chart)

According to the typical efficiency charts, when in 'dim' mode, it appears I should expect less than 50% efficiency (regardless of how many LEDs per string).

Given that my application lives in 'dim' mode most of the time, would you suggest a different LED driver that can handle the diverse current range or suggest a different way to use the LM3532?

EDIT to the former message:

'Dim' mode is  0.6mA, not 6mA.

Thanks Robin.

What do you mean the LM3532 doesn't output sometimes regarding dimming?  Are you saying the output is using PWM or simliar to manage dimming?  I did not see the details about how the device manages the dimming on the output side.