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Original question:

TPS61169: output current

TPS61169: What is the minimum duty ratio of PWM signal which is input to CTRL?

Kazuya Nakai59
Guru 21505 points
Part Number: TPS61169

 Hello guys,

 One of my customers is considering using TPS61169 for their next products. They will use the device for a light source of CCD camera. So they want to use analog dimming mode (LED current control) not digital dimming mode (LED on/off duty control) to avoid flickering in camera image. I think TPS61169 has analog dimming mode which can be controlled by CTRL signal duty ratio.

 The customer has a few questions about the analog dimming mode as the follows.

 Q1. Their conditions are Vin = 5V, Vout (LED VF) = 6V, ILED(max) = 300mA.

       What is the minimum CTRL duty ratio which can control ILED correctly. Is it 10% (=30mA)? Or 1%(=3mA)? or more less?

 Q2. Do you have any graph, ILED current (Y axis) vs CTRL signal duty ratio (X axis)?

 Q3. Is ILED compleately zero when CTRL=0% (Low Level continuously)?

 Your reply would be much appreciated.

 Best regards,

 Kazuya. 

  • 0
    TI__Mastermind 22745 points

    Hi Kazuya,

        For TPS61169, the recommend minimum duty cycle is 0.5% for better linearity. Here is an AN for such kind of single-channel LED driver:

        

    Since for such kind of LED drive, if CTRL=0, the output current will be zero since it will enable the swithching and the output voltage is less than the LED forward voltage and there will no current except the very low leakage current.

    Regards

    Sean