LP8860-Q1: VDDIO/EN pin internal Pull Up resistor or current source

Hi Peter,

Can your provide your schematic and waveforms? What is the relationship between VDDIO/EN and control line?

Hi,

I can not provide schematics unfortunately.  But control line has 0 ~ 3.3V amplitude, and is connected to VDDIO/EN pin through a 10K series resistor.  VDDIO/EN also has a 1 uF cap to the ground to delay turning ON/OFF  (tRC = 10K * 1 uF = 0.01 sec).

When control line is at 0V, VDDIO/EN pin is at 2.48V. 

Hi Peter,

VDDIO is also connected to VDD through a 10k resistor right?

There is no VDDIO pin on LP8860CQVFPRQ1 part.   

I connect VDD (pin 3) to 3.0V supply. 

VDDIO/EN  (pin 19) has a 1uF cap to ground, and  is connected to control line through 10K series resistor

Hi Peter,

I refer to the VDDIO/EN pin. Let me rephrase my understanding.

1. VDDIO/EN  (pin 19) has a 1uF cap to ground, and is connected to control line through 10K series resistor.

2. Pin19 is not connected to VDD, right?

3. Can you try to use the smaller resistor? For example, 10ohm. The settling time is big when you use 10kohm and 1uF capacitor. Can you provide the test waveforms?

Hi Peter,

Do you have any feedback?

I need to keep the series resistor at 10K for the proper system configuration - system connection details are too long to describe.

Do I get you right that the reason why VDDIO/EN pin is at 2.5V is due to gradual increase of the pin voltage because of the 10K/1uF circuit? I have never seen a digital input behaving like this...

Hi Peter,

It is just an assumption and need your help to debug on this. Could you also measure the VDDIO pin current? I am not sure whether there any other possible reasons or not since I can't see your schematic.

Hey Peter,

Any good news?

I need more time to get back to this issue. I will post update once I get more info.

I removed 1uF cap on VDDIO/EN pin to get sharp rise/fall time, and get the same behavior - VDDIO/EN pin is at 2.48V when control line with 10K series resistor is at 0V.  This tells me there is internal Pull Up resistor on VDDIO/EN pin.

Hi Peter,

Since I can't see the whole schematic and then can't find other possible reason. But it is not the expected behavior. Maybe you can try to use the smaller resistor. You can try with smaller resistor and bigger capacitor if it is for filter purpose.