Hi, I understood that CN0349 is running on 3.3v. Anyone knows the current needed?
The CN0349 hardware is no longer available for purchase.
However, the power dissipation can be calculated by adding up the contributions of the various components as taken from their respective data sheets:
AD5934 @ 3.3V: 15mA
AD8606 @ 3.3V: 2.8mA
ADG715 @ 3.3V: 20uA
FXO-HC536R-1 crystal oscillator @ 3.3V: 32mA
ADuM1250 @3.3V: 3mA/side, total = 6mA
Total not including ADuM5000: 55.82mA
ADuM5000 with 55.82mA load:
Efficiency of ADuM5000 supply is 28% and it must supply 55.82mA to the load.
Therefore you must supply 55.82/0.28 = 200mA to the ADuM5000 to get 55.82mA out.
The total power dissipation of the circuit is therefore approximately 200mA.
thank you for your reply. My current circuit can only power 80mA to ADum5000, does this slow the startup time for it?
If you can't supply at least 200mA to the ADuM5000, it won't regulate, the voltage output will be low, and the circuit simply won't work.
Since you only have 80mA for the circuit, I would eliminate the ADuM5000 and the ADuM1250 isolator. Maybe you don't really need the isolation?
Something strange is going on, because the LTC charge pump will not provide more than 40mA without the voltage dropping.
Are you sure that you don't have the AD5934 in the power-down mode? Is the entire circuit connected--including the oscillator?
Put a 1 ohm resistor in series with the output of the LTC charge pump. Measure the voltage across the resistor and you can calculate the current drawn by the ADuM5000. This will be the total circuit current including the ADuM5000.
Then the resistor in series with the output of the ADuM5000 and measure the current drawn by the actual circuit load. You should be able to track down your problem.
Something in the circuit is not drawing current.
Yes i totally agree with you, some strange things are happening.
I am certain that the AD5934 is running, because the circuit manage to return me the correct real and imaginary numbers when i measure the Calibration resistors(100ohm and 1k).
I will do the measurement for the current on ADum5000. Can i drop you a mail on my schematic, will give a better picture on the circuit.
One more piece of information. I connected my multimeter in series between my batt and board. The current i measure is at 30mA at peak. Other than ADum5000, my wireless MCU draws about 15mA.
I am really puzzled.
I place my multimeter in series with my 3.3v and the Vin for ADum1250 and ADum5000. The current is 125mA about there.
How is it possible that the charge pump can fit up to it?
I tried using CN0349 to measure the EC of a know solution, it works. The crystal is powered as well.
Hi Bryan: your LTC1754 working in abnormal status, please make sure the ADuM5000 can get enough power supply current for best performance.
Noted. I was suspecting as well.
Do you have any recommendation to replace LTC1745? THe voltage supply to LTC1745 is from a battery, hence i need a charge pump to regulate the Vout 3.3v to the rest of the circuit.
hi Bryan: please check with the buck switching regulators selector at:
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