LT3598 Demo Board

Thread Starter

ELECTRONERD

Joined May 26, 2009
1,147
Greetings,

I just received the LT3598 demo board from Linear Technology and I have a few questions. Below you'll find the LT3598 datasheet and also the Demo circuit quick start guide.

http://cds.linear.com/docs/Datasheet/3598fa.pdf

http://internal.linear.com/demo/dc1285A.pdf

In the Quick Start Guide, they say to connect the PWM pin to VIN. I'm wondering how I can adjust the PWM? In the schematic if I put another resistor from the CTRL pin to ground it would form a voltage divider. Thus, varying voltage. Or, would I put a resistor from the PWM pin to ground? Would this adjust the PWM? Also, what are the OPENLED, and SYNC pins for?

Thanks!
 

Ron H

Joined Apr 14, 2005
7,063
The quickstart guide says
Tie PWM to VIN or a PWM signal.
The PWM signal cannot be a DC level, unless you want the LEDs full on or full off. You have to provide a variable duty cycle pulse waveform (PWM) to vary the LED brightness. You can generate this with a circuit such as SgtWookie's Simple PWM Circuit.
From the datasheet:
OPENLED (Pin 7/Pin 10): Open LED Flag When Any LED
String Opens. The output is open-collector. Tie a resistor
to other supply for open LED flag function.
SYNC (Pin 14/Pin 17): Frequency Synchronization Pin.
This input allows for synchronizing the operating frequency
to an external clock. The RT resistor should be chosen to
program a switching frequency 20% slower than SYNC
pulse frequency. This pin should be grounded if this
feature is not used.
 
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