the information about VN808CM-E's output current

[Leon_show]

您好，實驗室有用到您們生產的VN808CM_E產品，關於產品規格表的電流-峰值輸出有疑問(圖一)， 0.7A是指八個通道總共的最大電流嗎? 然後我看這個產品每個通道的output一共有兩個是互相連接的(圖二)，這樣會導致輸出的電流變更小嗎?

(700mA / 8 / 2= 43..mA (每一個output的電流)) ，如果我打算在output連接端用電流去驅動的話，把同一個channel裡面兩個內部連接的output在外部利用PCB走線，再度連接成真正一個輸出端口的話，可以有助於電流的提升嗎?( 700mA / 8 = 87.5mA)   

 

 English version :

Hello, Currently, our laboratory is using the VN808CM-E product produced by your company. I have a question regarding the current peak output in the product specification sheet (Figure 1). Does the 0.7A refer to the total maximum current for all eight channels? Also, I noticed that there are two outputs connected to each other for each channel (Figure 2). Will this result in a smaller output current?

(700mA / 8 / 2 = 43.75mA for each output). If I intend to drive the output using current at the output connection terminal, by externally connecting the two internally connected outputs of the same channel through PCB traces to create a true single output port, would this help increase the current? (700mA / 8 = 87.5mA)

謝謝  

[Peter BENSCH · Accepted solution]

Welcome @Leon_show, to the community!

You have probably misunderstood the data sheet of the VN808CM-E:

• each of the 8 outputs can drive 0.7A - i.e. a total of 5.6A when all outputs are switched on
• each of the 8 outputs has two pins which must be connected to each other on the board if you want to drive the full current, i.e.:
  • OUT1 = pin 35 and 36 together
  • OUT2 = pin 33 and 34 together
  • OUT3 = pin 31 and 32 etc

Hope that answers your question?

Good luck!
/Peter

[Leon_show]

hello, 

Peter BENSCH      professor 

Thanks for your reply before !  i still have another question about VN808CM-E:

I want to deduce the voltage or current output conditions of a single channel of the IC in HIGH LOGIC through the specifications provided in the DATA SHEET. However, in Figure 1 of the datasheet, it only mentions that Iout is internally limited. Yet, in Figure 2, there is information indicating VCC: 45V, Iout: 1A.  And then i hope i can know the output current's value in each  VCC when the logic is high.  can you provide more detailed information for me to figure out my request.?

 

[Peter BENSCH]

The information on page 1 of the data sheet is intended to provide an overview of the device and the load range in which it can typically be used. Table 1 then shows the maximum permissible parameters, whereby the DC output current is correctly listed as Internally limited, as an internal protective circuit prevents the VN808CM-E from being exceeded and thus overloaded.

I don't understand your last question about the current. Can you please describe in more detail what you mean?

Regards
/Peter

[Leon_show]

hello,  Peter BENSCH      professor 

Certainly, I will provide a more detailed explanation below. Through the diagram below, we can ascertain that for a single channel of VN808CM-E, when VCC is 45V, the Iout is 1A. I would like to inquire, if I control VCC within the range of 10.5V  to  32.5V , will Iout vary with VCC, or will it remain at 1A?

Thank you for your sincere response!

[Peter BENSCH]

Firstly, a request: I am not a professor, just a member of staff at ST who wants to help you and others. It is sufficient to address me by name.

About the VN808CM-E:

• the maximum current is not voltage-dependent, so the current is limited in the same way with a smaller VCC
• only the VN808CM-32-E can switch an output current of min. 1A, the VN808CM-E is designed for typical loads of min. 0.7A. Even if a max DC short circuit current of 1.7A is specified in table 6 of the data sheet, this is only the upper limit of the current limitation, which varies depending on the specific example and temperature.

It would therefore be very wise to only use the minimum value of the current for your design so that you do not experience any unpleasant surprises. So if your loads draw up to 1A, you should use the VN808CM-32-E instead of the VN808CM-E.

Regards
/Peter

[Leon_show]

Hello, Peter Bensch

firstly,thank you for your response.

Due to the design considerations in the backend circuitry, I would prefer the output current to be as high as possible. Therefore, choosing the VN808CM-32-E with a minimum of 1A output current seems better.

Lastly, I have a question: Is the 1A output current continuous during the on-time, or is it generated based on short pulses given through a high logic input, depending on the duration of the signal input?

Thank you for your sincere response!

[Peter BENSCH]

Regarding your last question: the respective output is active when the corresponding input is active. The same applies to the inactive state. The device is not edge-triggered like a latch or flip-flop, but works like a transistor.

Regards
/Peter

[Leon_show]

Hello, Peter Bensch

firstly,thank you for your response.

Sorry, I don't quite understand and would like to confirm with you again. If today I use an FPGA to provide a high logic input pulse signal, wouldn't the output current type be in the form of a pulse? Additionally, when you mentioned "The same applies to the inactive state," does it mean that there will be current output even in the low logic state?

Thank you for your detailed response for a long time.

[Peter BENSCH]

Well, it's all in the data sheet, e.g. in table 9 (Truth Table). As the device is a high side switch, it can only actively switch high, the low state depends on the load resistance.

If the error states are not considered initially, the VN808CM attempts to follow the input signal and to allow the current to flow at the output when the input is high. Conversely, no current flows when the input is low. This probably corresponds to your question.

However, all other parameters in the data sheet must also be observed, e.g. the error states in table 9, as well as the switching speed, which is max. approx. 1kHz.