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TPS26600-02EVM: cannot make work correctly with 5V source

Allen Hunsaker
Prodigy 10 points
Part Number: TPS26600-02EVM

case cs2268231


T1/VIN1 = 5V 100mA
J1 - Jumper ON
J2 - Jumper ON
J3 - Jumper OFF
J4 - Jumper ON 1-2
J5 - Jumper 7-8 connecting R12 200mA.
J6 - Jumper OFF
J7 - Jumper OFF

TP4 SHDNb1: Attached to system Digital Output to control level 0V - 3.3V - used to power on and reset on fault (assuming latch on fault).
TP1 FLTb1: Attached to system Digital Input to observe value for fault detection.

also
1 - Changed R2 = 127K and R3 = 20K to give Vov = 7V and Vuv = 4.2V
2 - Changed R1 & R5 from 24.3K to 3.32K (to increase LED luminance).

T1/VIN1 = 24V 1.6A
J8 - Jumper OFF - 5V applied to Diode (D7) side to ensure TP10 is no more than 5V for System Digital Input.
J9 - Jumper ON
J10 - Jumper ON
J11 - Jumper ON 1-2
J12 - Jumper 1-2 connecting R21 2.23A.
J13 - Jumper ON
J14 - Jumper ON

TP13 SHDNb2: Attached to system Digital Output to control level 0V - 3.3V - used to power on and reset on fault (assuming latch on fault).
TP10 FLTb2: Attached to system Digital Input to observe value for fault detection.

Bottom line:

using for 24V works.
using for 5V does NOT work as expected.
      a. latch does not latch
      b. after SHDN is HI and output enabled, if I take SHDN Lo, the output does not go to zero but 1.4 - 2 V??
 have purchased, for development, a TI )TPS26600-02EVM: Evaluation Module for TPS2660x).
I intend to use it to detect over-current on a 24V and a 5V power supply.
The 24V works exactly as expected, but the 5 Volts is not working as expected.
I am only using the FLT and SHDN expecting overcurrent to disconnect the output if too much current exists on the output.
  1. When I power up the device, I have DO connected to the SHDN to control it's level with 3.3V.  But set to logic Lo on Power up, so the output is off until I am ready to turn it on.
  2. To test it, I raise SHDN to logic Hi (3.3V) which enables the input 5V to the Output. This works fine.
  3. If I create high current on the output, the FLT occurs (shows up on my DI) and the Output goes to zero as expected.
  4. I have the Mode (J4) set to 1-2 connected which should latch on fault but does not, when I remove the load it resets as though auto retry (J4 is connected to 2-3) but that is NOT how it is connected.
  5. If the load is within my limits and I have already done step 2 above to enable output, and I then set SHDN to Logic Lo, the output does not go to zero, but 1.4 or 1.7 Volts usually...Why does it not go to zero at this point? I've checked the voltage, and it is at 0V, but the output does not go to zero when SHDN is Zero,
This is how I intend to use it. To Power Up with SHDN LO, then when ready, SHDN HI to enable output.
The first test in my sequence is to determine if the resultant current caused by the device load is too high, indicating something is wrong before I start the rest of the test sequence. In which case, the TPS shuts the voltage down and the test aborts.
If it is too high, the TPS26600 will shut down the output and latch off.
When I have removed the source of the problem I then want to take SHDN LO to reset, and then back to  HI to enable output again.
This is how the 24V works, but not the 5V.
I have swapped sides and jumpers to ensure the module works on both sides the same and it does. 24V works on either side, 5V does not work on any side.
I bought this device because the spec indicates it will work 4.2V - 55V, so it should work at 5V. Perhaps I need to do something different to get it to work at 5V, the same way it works at 24V. 
  • 0
    Prodigy 10 points

    on the 24V - Copy paste mistake... T1/VIN1 = 24V 1.6A should be T3/VIN2 = 24V 1.6A

  • 0
    Prodigy 10 points

    Update, I have traced the voltage on the 5V output that does not go to zero to an external device on the same board I am putting the 5V on. By programming that external board differently, I can get the output to go to zero.

    So, the only remaining problem is to figure out why latch doesn't work. BTW, I have swapped sides of the board with 24V and 5V... 24 always latches as expected. 5 NEVER latches. 5 always does auto reset no matter how I set the mode input.

  • 0 in reply to Allen Hunsaker
    TI__Guru 57880 points

    Hi Allen,

    Welcome to e2e . I will get back by tomorrow EOD on this.

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    TI__Guru 57880 points

    Hi Allen,

    During current limit due to IR drop or when device suddenly turns off due to TSD there can be ringing on VIN causing it to go below UVP of 4.2V and causing reset. I think if you use high cap at input to make VIN stable you should not see this issue.

    Regards

    Kunal Goel