Analog Switch Help

[vinit2100]

Please find the attached image

 

[KrisBlueNZ]

When both regulators are disabled, there is no voltage available on the B0 and B1 inputs of U21 so regardless of which pole is selected, its output cannot supply any voltage.

If you want a voltage of 0V/1.0V/1.5V there may be an easier way to achieve it. Post the schematic of the regulator part of the circuit.

 

[vinit2100]

0V is achieved by disabling both the regulator .... no doubt !!! . I was asking U21 is powered, and the E can be either connected to B1/B0 or no connected. will there be any voltage at A.. ? is the switch U21 normally open. ? This information is not provided in Datasheet :'(

 

[KrisBlueNZ]

The switch inside U21 is always in one position or the other postion. In other words, A is always connected to either B0 or B1. There is no option for "no connection".

U21 is an analogue switch and is not really intended to switch power. How much current are you going to draw from it?

If you want a voltage of 0V/1.0V/1.5V there may be an easier way to achieve it. Post the schematic of the regulator part of the circuit.

 

[vinit2100]

The switch inside U21 is always in one position or the other postion. In other words, A is always connected to either B0 or B1. There is no option for "no connection".

U21 is an analogue switch and is not really intended to switch power. How much current are you going to draw from it?

If you want a voltage of 0V/1.0V/1.5V there may be an easier way to achieve it. Post the schematic of the regulator part of the circuit.

around 100mA is the current to be drawn from the switch, U21 can carry 350mA , at 3.3V , and the regulator can provide 300mA current

 

[vinit2100]

around 100mA is the current to be drawn from the switch, U21 can carry 350mA , at 3.3V , and the regulator can provide 300mA current

Regulator 1 is connected to provide 1.5V and regulator 2 to get 1V respectively. 1.5V and 1V is required to operate a device in full voltage (1.5V) and low voltage(1.0V)

 

[KrisBlueNZ]

around 100mA is the current to be drawn from the switch, U21 can carry 350mA , at 3.3V , and the regulator can provide 300mA current

OK.

Regulator 1 is connected to provide 1.5V and regulator 2 to get 1V respectively. 1.5V and 1V is required to operate a device in full voltage (1.5V) and low voltage(1.0V)

Yes, I guessed that.

If you want a voltage of 0V/1.0V/1.5V there may be an easier way to achieve it, without using U21. If you want to investigate this possibility, post the schematic of the regulator part of the circuit.

 

[vinit2100]

OK.

Yes, I guessed that.

If you want a voltage of 0V/1.0V/1.5V there may be an easier way to achieve it, without using U21. If you want to investigate this possibility, post the schematic of the regulator part of the circuit.

 

[KrisBlueNZ]

What's the part number for U42 and U43?

 

[vinit2100]

ADP171 (adjustable) . im not getting you. when we disable both the regulator then 0 V will be the output volatge. My doubt was in analog switch side.

 

[KrisBlueNZ]

This is the simpler way to do what you want. This is a widely used trick. You only need one regulator, and no analogue switch.

When the voltage select line is low, the MOSFET is OFF and the output voltage is set by R105 and R113. Since the ADP171's reference voltage is 0.5V, the output voltage will be 1.0V.

When the voltage select line is high, the MOSFET is ON, and it connects the new 10 kΩ resistor in parallel with R113. Therefore there is 10 kΩ from the output to the ADJ pin, and 5 kΩ from the ADJ pin to 0V, so the output voltage will be 1.5V.

The enable pin operates as normal.

 

[vinit2100]

View attachment 18740
This is the simpler way to do what you want. This is a widely used trick. You only need one regulator, and no analogue switch.

When the voltage select line is low, the MOSFET is OFF and the output voltage is set by R105 and R113. Since the ADP171's reference voltage is 0.5V, the output voltage will be 1.0V.

When the voltage select line is high, the MOSFET is ON, and it connects the new 10 kΩ resistor in parallel with R113. Therefore there is 10 kΩ from the output to the ADJ pin, and 5 kΩ from the ADJ pin to 0V, so the output voltage will be 1.5V.

The enable pin operates as normal.

Why used MOSFET instead of BJT ?

 

[KrisBlueNZ]

A MOSFET behaves very much like a low-value resistor when biased ON. A BJT, even when saturated, doesn't pull its collector all the way down to 0V.

 

[vinit2100]

can i choose the first method of using analog switch ? i have a doubt in that, when both the regulator's are disabled. will there be any voltage in analog switch output ?

 

[KrisBlueNZ]

You want to use two regulators and an analog switch IC, instead of just one regulator?

 

[vinit2100]

You want to use two regulators and an analog switch IC, instead of just one regulator?

yes

 

[KrisBlueNZ]

Well, I can only show you the best way to do it. I can't force you to do it that way! It's your project!

 

[vinit2100]

yeah, the schematic is finalized , wha t about the switch output ? r u in facebbok ? give me the id

 

[KrisBlueNZ]

What about it? It will work.

 

[vinit2100]

What about it? It will work.

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