Hello,
I went ahead and simulated the circuit in TI TINA, with a basic functional summary outlined below:
I'm currently working with the TPS54627, INA195 and the OPA2313, to construct a voltage controlled adjustable current source capable of 6A.
- The TPS54627 device output is connected to the load through a 0.010 current sense resistor. The INA195 uses the voltage across this sense resistor to provide the Feedback to the TPS54627
-The OPA2313 is connected to provide current control, using a resistor divider of 10k and 10k between the OPA2313 and the INA195. The center of this divider is connected to the TPS54627's feedback.
ASSUMING THE OPA2313 OUTPUT IS 0V,
- For the INA195, this would be a V_out = 100 * 0.010 * I_load
- Or V_out = I_load, i.e. 1V = 1A in this case
The target voltage of the TPS54627 is 0.765V, and my target current is 6A, so I have the INA195 output connected across another resistive divider with a 10k and 3.4k resistor.
Through the first resistor divider: V_fb = 0.765 = V_d * (10k)/(10k+10k)
V_d = 0.765 * (10+10)/(10) = 2*0.765 = 1.53 V
Through the second INA divider:
V_d = 1.53 = V_out * (3.4k/(3.4k+10k))
V_out = 1.53*(10+3.4)/(3.4) = 6.03 V
All of this works correctly in my simulations.
I have gone ahead and assembled a test circuit. This is where my issue is. I was getting an output of a mere 14mA. So I verified my connections and confirmed by result. SS was left unconnected in my simulations (and works fine in the model), so I started experimenting.
I was successful by simply increasing the SS capacitance on the TPS54627 brought the current up higher, to about 1.2A, at which point it visually shuts down
for a SS capacitance 10uF, this is a little over 1 second per the datasheet:
t_ss_(ms) = C_(nF) * 0.765 * 1.1 / 6
t_ss_(ms) = 10000 * 0.765 * 1.1 / 6 = 1402.5 ms = 1.4 sec
I wanted to ask about the TPS54627's hiccup mode and current limiting and how it works. Again per the datasheet, the internal current limit is a minimum of 6.3A, which my application is below.
My belief is, the target voltage of the INA195's V_out is demanding 6.03V, but because the TPS54627's feedback voltage is less than 65% of the target 0.765, it never actually reaches the target, and thus dramatically reduces the current, but NEVER shuts down. The voltage rises fine in either case of load or no load, but the current appears to be self limiting.
I believe something about the way the TPS54627 is modeled in the provided TI TINA simulation models does not include the behavior of the Over Current Protection or Under Voltage Protection behavior of the TPS54627.
Where should I go from here?
