If shutdown and power on is done when TIMER pin voltage is not zero, does TIMER pin voltage rise up from that voltage?
For example, it is the condition that Vin off and on is done during t3 period of datasheet Figure 23.
Or does LM25069 wait for TIMER pin voltage fall down to zero and start insertion time?
Best Regards,
Kohei Sasaki
Hi Kohei,
When the VIN is shut down (VIN = 0V), then the LM25069 will pull the gate low with a 260mA pull down current. As for the timer pin function, we decided to test this condition you described in our lab.
We took a new LM25069 and made a couple of modifications.
1) Added a high power, 25ohm resistor directly from VIN to GND. This would give us fast transients when we turn off and on the supply.
2) Added a 10,000uF output capacitor. This would force the LM25069 to go into a power limit and timeout after the insertion timer begins.
Attached are 3x waveforms we took:
In this test, the TIMER pin voltage decreased, but not to 0V. Instead it discharged down to ~0.5V and remained there until VIN came back up.
This test was taken while the insertion timer was still running (notice the output voltage never rose). This test also shows the timer discharge to ~0.5V and remain there until VIN came back up.
This test shows the TIMER voltage did fully discharge down to 0V
So overall, we do not have a clear answer on the TIMER behavior in this corner condition. In all cases, the pin is discharged but it may go to 0.5V or 0V. Note that these tests were looking at the VIN voltage at the header pins, and not directly the IC pins. We may be able to redo the tests next week, but overall it seems that when designing the application circuit, one should assume that either behavior may occur.
Do you have a specific application requirement you are trying to meet which depends on the behavior of the TIMER pin in this condition?
Thanks!
Alex
