# 3.3V -> 5V level shifting with LOW output impedance?

Discussion in 'General Electronics Chat' started by trackuino, Jun 15, 2011.

1. ### trackuino Thread Starter New Member

Jun 15, 2011
2
0
Hi! I'm using the following level shifter to translate a 3.3v digital, PWM signal (left side) to a 5v device (right side):

Now, the 5V device (connected to TXD) has an input impedance Z = 100K, so both R3 and Z make a voltage divider which has a dropout Vd:

$V_d=5\cdot\frac{4.7}{100+4.7}\approx 0.22V$

Is there any way to minimize the dropout to 0 or just a few millivolts by using this or any other circuit?

The reason behind minimizing the dropout is that the 5V side device is actually an FM radio transmitter (a Radiometrix HX1 module), spec'ed for 0..5V operation. Any dropout from that will cause the FM deviation to diminish, and that will produce lower SINAD on the received audio output.

I could use a lower R3 to reduce the output impedance (and the dropout), but I'd also like to keep the current drain of the shifter to a minimum.

I've considered using a MAX4427, but I think it's overkill !

Feb 5, 2010
4,166
1,125
3. ### trackuino Thread Starter New Member

Jun 15, 2011
2
0
Kermit2: thanks. I think that's what I was looking for.