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Part Number: PCA9306
I am using PCA9306 for level translation from 3.3 V to 1.8V on i2c Bus.
1. First doubt I have is on the orientation of the IC as the one supplied to me does not have a reference dot mentioned in the datasheet, it rather has a laser marked line on one side. Not sure this is for indicating pin1?
2. When used in the orientation shown in the schematic (laser marked line as reference for pin 1), we find LDO losses regulation. With changed orientation LDO starts working but the I2C master is unable to pull the input lines (pin 7, 8 on P1 CONNECTOR) to low, they always remain at high state.
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In reply to Eric Schott48:
Hi Eric, Yes the controller device driving pins 7 and 8 (at connector P1) has strong internal Pullup resistors. I am finding loss of regulation on the LDO output with regular orientation of PCA9306. I have done some measurements through the multi meter at LDO (TLV70018) output pin 5 with normal orientation below are the observations: Sample No. Vin Actual Vout Expected Vout Voltage Board1 2.993V 2.055V 1.8V 4.990V 3.917V 1.8V Board2 2.993V 2.046V 1.8V 4.990V 3.901V 1.8V Thanks for the response, I will try to share the waveforms too. Mohit.
In reply to Mohit Srivastav:
Below are the traces required :
attachment 1: EN or Vref2: Enable in blue trace, VCC in yellow.
attachment 2 : LDO input in Blue and output (Vref1) in yellow.
attachment 3 : SCL1 (PCA9306 Output) in blue and SCL2 (PCA9306 input) in yellow.
Above traces are recorded with normal orientation of PCA9306 (attachment 4):
0.1uF and 1uF capacitors for the LDO and the 200k at EN are as per the schematic.
I can confirm that Vcc was 3.3 Volts. As I am using a Digital multi-meter too at the supply output, it showed 3.3V at output.
Checked En and Vref2 continuity through multimeter and found that they are connected.
Checked 200K resistance, it is 199K by multimeter.
Also checked capacitance at Vout pin of TLV70018 found it 3uF.
I removed C5 to measure it's exact value but i think 100pF is too low for Multimeter i have.
Voltage at EN is 3.0V with 3.3V Vcc (after removing C5)
One more interesting thing i missed to tell, when we un-populate the PCA9306, LDO TLV70018 regains the regulation and Vout is set to 1.8V. Un-populating any other component does not make any impact.
Hi Mohit, I believe the loss of regulation could be from the LDO not being able to sink the current coming from the PCA9306 device's Vref1 pin. When idling, this pin leaks about 5uA of current. With not other path, this current may be sinking through high impedance paths creating the voltage that deregulates the LDO. To sink this current on the board you have, you could replace one of the LDO capacitors (C1) with a 300k-Ohm or smaller resistor. This would allow the current to dissipate and the LDO to maintain its set voltage. Let me know the results of this modification. Regards, Eric
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