TPS92692-Q1: Comp pin discharging time

Hi Taylor,

The answer to this is complex and depends on a lot of factors such as your input voltage, input capacitance, and current draw which will affect the time it takes to reach UVLO of Vcc. The COMP pin is likely falling to below 1.6V because the off time of your PWM signal is too long and the Voltage at the Vin/Vcc pin is likely droping below the 4.1V UVLO threshold. Please see the wave forms below. Fig 1. through Fig 3. represents an increase in input voltage, and thus, in increase in discharge time, prolonging the time it takes to reach UVLO. Fig 4. represents the Vin reaching the UVLO and triggering a fault. Fig 5. shows the nodes which were probed labeled with their respective names and colors.

Fig 1. Ch1: Vin PWM, Ch2: Vsw, Ch3: Vin at pin, CH4: Vcomp

Fig 2. Ch1: Vin PWM, Ch2: Vsw, Ch3: Vin at pin, CH4: Vcomp

Fig 3. Ch1: Vin PWM, Ch2: Vsw, Ch3: Vin at pin, CH4: Vcomp

Fig 4. Ch1: Vin PWM, Ch2: Vsw, Ch3: Vin at pin, CH4: Vfault


Fig 5. TPS92692 880 EVM Boost schematic, showing the nodes which were probed in the wave forms above

Best,
Daniel 

Hi Taylor,

I am investigating the new design today. I will reply to Yuto, your FAE, to adhere to proper NDA restrictions as this is a public forum.

Best,
Daniel