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TPS92643-Q1: TPS92643 output voltage not changing from 2.3V to 7V which is required when the input range is 9-16V

Febin sugathan
Prodigy 10 points
Part Number: TPS92643-Q1
Other Parts Discussed in Thread: TPS92643EVM-204

Tool/software:

Paramaeter MIN  TYP  MAX  
Vin Input voltage 9 13.5 16  
Ns Number of LEDs   2    
Vf(led) LED forward voltage drop 3 3.2 3.5  
rD LED string series resistance 0.2   0.5 Ω
VCSN Output voltage 6 6.4 7  
Iled LED current continuous   1.05    
ΔiLED LED current ripple     0.08 %
ΔiL Inductor current ripple   0.0651    
VIN(DO,RISE) Start input voltage   9   V
VIN(DO,FALL) Stop input voltage   7.9   V
fPWM PWM frequency   200   Hz
DPWM PWM dimming duty cycle 4   100 %
fSW Switching frequency   400000   Hz
TA Ambient temperature   25   °C

I have designed the TPS92643 with respect to above mentioned specification but not able to meet the desired output voltage,

Could you pleas help us with this ?

  • 0
    TI__Mastermind 18945 points

    Hello Febin,

    I am not sure I quite understand your question.  This is a constant current buck, so if programmed correctly then the output should be 1.05A and the output voltage will be a function of the Vf of the LED at that 1.05A.  If you have 2 LEDs then the output should be ~6.4V, but this depends on where on the Vf vs If curve of the LED that 1.05A is.  

    What are you seeing?  Give me scope shots of SW node, I_L (inductor current), UDIM (PWM singal), and V_LED.  

    Give me a schematic too, to make sure the components are appropriate.  Do you have the TPS92643EVM-204?  

    -fhoude