I got a ST L294 solenoid driver and I am stuck on the enable input (TTL) currently using a sunx cx-24 @ 5v supply. The output is NPN. I've hooked everything up except the photo sensor (cx-24) and powered up using 20 v. When I hooked up the cx-24 I blew the L294.
I believe it is the input( or rather the output of the cx-24 ).
I've seen suggestion of an optocoupler, or should I look at something else.
The L294 specs on enable are L -0.3 - 0.8 v -100 uA H 2.4 - ?? v 100 uA
This means that the enable signal has to be able to pull down to below .3 volts while pulling 100 uA from the enable pin to perform the enable function (it is active when it is a logic low), and must be able to pull high to at least 2.4 volts while supplying 100uA to the enable pin to disable it. Voltages in between .3 and 2.4 are not guaranteed to act either as an enable or a disable.
This signal can be provided from any 5 volt powered logic family, or from an active pull down device, like an NPN transistor, whose emitter is grounded, with a pull up resistor connected to a 5 volt supply. The absolute maximum voltage that can be safety applied to the enable pin is 7 volts.
Not without learning a lot more about exactly what you are hooking together. For instance, I have no idea what "sunx cx-24 @ 5v supply" means. I gather that you are somehow connecting an L294 with a 20 volt supply and some sort of photo sensor and there might also be a 5 volt supply involved. If you email me a schematic of what you have, I will get back to you tonight.
thanks for the reply the cx-24 has 3 outputs +, 0, out. Although I am not sure, the 20v is to drive the solenoid. The 5v has a dual purpose, it powers the cx-24 as well as providing a reference voltage to the L294.
is the the reference with Fig. 7a as the test application. I believe that the cx-24 (connects to pin9) should be isolated from the circuit, as pin 9 is supposed to be TTL.
you guys make everything sound so easy, I actually have hooked up a different sensor, it does use 5v with NPN output, but I need to use the cx-24, which I have on hand. I'm going to try your circuit today. Let you know. The 5v on the L294 is to produce a voltage reference, which translates to the output current spike I need. There is no mention of a 5v supply for the L294 except for diagnostic
The diodes that they are referring to are regular diodes??
Yes I did note the fast switch diode, that is where I started to have trouble. I knew it wasn't zener, so I opted for a schottky, I suffer from limited resources on short notice.
I actually built the fig. 7a found in the app notes pages. There is no mention of the 5 volt. I have it set-up to try the led, but I didn't hook it up. That is funny because the L295 says it doesn't require externat 5v.
Sorry for the delay in my response, but I was called away, yesterday.
Thanks for the link to the data sheet and application note:
I can find no where on the data sheet or application note that specifically says that Vss (logic supply) is optional, but application note 7a implies that it is. I think you need to supply Vss with 5 volts if you want the diagnostic output to function, and that output isn't used in application note circuit, 7a.
As long as the sensor supplies only a pull down current path, then it should work with this circuit, with the possible exception that an external pull up resistor might be needed to get a full 5 volt swing on the RC and transistor network going into pin 7. A 10 k resistor between the top of the 5.1 volt zener and pin 9 should do it.
That said, I think the enable pin is not responsible for your L294 failures. I suspect a slow output diode, D2 or some other error in your circuit.
Got the enable ( pin 9 ) volts working fine, cost me a few chips along the way. Down to 3 chips left before I need to order from digi-key. Now everything seems to ok, the diodes that I have are schottky and standard. Would the schottky diodes work, if not please let me know what type I should look for
Schottkys should work fine, as long as they have the required voltage and current rating. One other possible problem occurs if the supply leads are long. Then the wiring inductance can generate large voltage spikes during switching. The ap note does not show any, but there should be a bypass capacitor between the point where D2 ties to pin 1 and the point where Rs ties to D2. Something on the order of 470 uF
35 volt electrolytic would probably work, if it is a low inductance type, like Panasonic type FC or FM.