Team - I am helping my customer verify their operating points before they design it in. We modified the EVM as indicated below and the resulting OV trip point is lower than calculated. What are we missing? Notes from the customer as follows:
I was able to get into the lab this morning to take a look at the TPS1663 development board. I have made the following modifications to this board to mimic what is going to be present in the final design. During the testing I observed that the OV trip point was not working as designed. Below is the configuration of the development board:
|
Required Modifications |
|||||
|
Ref. Des |
Rockwell Part Number |
Value |
Tolerance |
Voltage |
Package Size |
|
R2 |
LAB STOCK |
330kΩ |
1% |
|
603 |
|
R3 |
PN-412491 |
82.5kΩ |
1% |
|
603 |
|
R4 |
LAB STOCK |
10kΩ |
1% |
|
603 |
|
R5 |
PN-412489 |
34kΩ |
1% |
|
603 |
|
R6 |
PN-202416 |
5.76kΩ |
1% |
|
603 |
|
C4 |
21505-162-09 |
0.056ɥ |
10% |
25V |
603 |
|
Min. Calculated Operating Points |
Nom. Calculated Operating Points |
Max. Calculated Operating Points |
||||||||
|
Under-Voltage/Over-Voltage Setpoints |
Under-Voltage/Over-Voltage Setpoints |
Under-Voltage/Over-Voltage Setpoints |
||||||||
|
Parameter |
Value |
Units |
Parameter |
Value |
Units |
Parameter |
Value |
Units |
||
|
OVset(rising) |
15.530 |
VDC |
OVset(rising) |
15.847 |
VDC |
OVset(rising) |
16.164 |
VDC |
||
|
OVset(falling) |
14.394 |
VDC |
OVset(falling) |
14.817 |
VDC |
OVset(falling) |
15.187 |
VDC |
||
|
UVset(rising) |
4.844 |
VDC |
UVset(rising) |
4.943 |
VDC |
UVset(rising) |
5.042 |
VDC |
||
|
UVset(falling) |
4.490 |
VDC |
UVset(falling) |
4.622 |
VDC |
UVset(falling) |
4.737 |
VDC |
||
|
Current Limit Setpoints |
Current Limit Setpoints |
Current Limit Setpoints |
||||||||
|
Parameter |
Value |
Units |
Parameter |
Value |
Units |
Parameter |
Value |
Units |
||
|
IR1,R2,R3 > 2ɥAmps |
11.009 |
ɥAmps |
IR1,R2,R3 > 2ɥAmps |
11.009 |
ɥAmps |
IR1,R2,R3 > 2ɥAmps |
11.343 |
ɥAmps |
||
|
Current Limit Setpoints |
Current Limit Setpoints |
Current Limit Setpoints |
||||||||
|
Parameter |
Value |
Units |
Parameter |
Value |
Units |
Parameter |
Value |
Units |
||
|
Ilimit |
3.094 |
Amps |
Ilimit |
3.125 |
Amps |
Ilimit(max) |
3.157 |
Amps |
||
Circuit produced a fault condition when the input voltage reaches 15.1VDC, which is much less than the above set point of 15.847VDC. If I push the reset button, this fault is repeatable at 15.1VDC. I also noticed if I didn’t reset the IC when reducing the voltage, the fault condition wouldn’t go away until the voltage was somewhere in the range of 13V. I didn’t write this down due to the initial trip point being way off. So I can have the lab tech rerun this test if you feel this information is important to know. When reviewing the data sheet, I noticed there was a falling threshold value associated with this part, which more or less causes the device to reset at a much lower value than the initial trip point. What I am trying to figure out here is why the calculated over voltage value doesn’t fall within the over voltage trip point window from my spreadsheet? The part is a comparator more or less so this is a little bit of a mystery. I can simply just adjust the resistor values so the voltage is much higher than operating range and it would correct things; however, I would like to understand why the trip point isn’t falling in my calculated range. I also ran a test on the over current protection and it did fall in the range I have calculated so that portion of the circuit is working. Please let me know if you have any ideas here as I am going to still investigate this further by reading through the data sheet; however, I will need to know what is going on with this circuit prior to designing this into my product.
