- Sat Sep 21, 2013 12:18 pm
#163748
Hi - I'm working with an autopilot that three of its eleven servo outputs produce a 3.3V amplitude PWM (they're constrained at 3.3V because they can be configured for different uses). I need to boost that to 5V which is what most servos expect. I have built a small board that all the servo outputs go to and boosts just the three that need to be. Originally it used the design from Sparkfun (https://www.sparkfun.com/products/8745), but the servo outputs of the autopilot have very low current limits (< 1mA) which even with tweaking the resistor values to limit current caused that design to not work.
My most recent attempt (image links below) is to use the TI TXB0104PWR chip which works better, but can still be noisy and cause the servos to jitter, probably due to the low current limit of the autopilot output. Any suggestions on a single chip that can do this?
Requirements:
Input:3.3V Output: 5V
I don't care about an output enable pin (if it has one, it will be permanently tied to whatever the enable voltage level is)
Unidirectional is fine, bidirectional is ok if that's all that's available, but only one way will be used.
The autopilot has a 5V power supply which I feed through a voltage divider (a 12k and 22k resistor) for the needed 5V and 3.3V references, so both Vcca and Vccb are ramped up simulataneously. I don't know and don't have a way to tell whether the power or ground side will be applied to the chip first, so I've tried to just look at chips that don't care about power on sequencing. (Does that really matter?)
The PWM typically operates at 50Hz but can go as high as 200-250 Hz if we wanted to, but probably won't.
Thanks for any suggestions
https://www.dropbox.com/s/zy8y8f4w1j0zd ... 0Board.jpg
https://www.dropbox.com/s/c6nungc5dol5n ... ematic.png
My most recent attempt (image links below) is to use the TI TXB0104PWR chip which works better, but can still be noisy and cause the servos to jitter, probably due to the low current limit of the autopilot output. Any suggestions on a single chip that can do this?
Requirements:
Input:3.3V Output: 5V
I don't care about an output enable pin (if it has one, it will be permanently tied to whatever the enable voltage level is)
Unidirectional is fine, bidirectional is ok if that's all that's available, but only one way will be used.
The autopilot has a 5V power supply which I feed through a voltage divider (a 12k and 22k resistor) for the needed 5V and 3.3V references, so both Vcca and Vccb are ramped up simulataneously. I don't know and don't have a way to tell whether the power or ground side will be applied to the chip first, so I've tried to just look at chips that don't care about power on sequencing. (Does that really matter?)
The PWM typically operates at 50Hz but can go as high as 200-250 Hz if we wanted to, but probably won't.
Thanks for any suggestions
https://www.dropbox.com/s/zy8y8f4w1j0zd ... 0Board.jpg
https://www.dropbox.com/s/c6nungc5dol5n ... ematic.png
