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]

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

[Peter BENSCH]

RL and RLOAD are identical and are only alternative designations. They have nothing to do with the resistors connected internally to GND at the outputs visible in figure 1. Those resistors at GND are probably a copy'n'paste error, because they were also not included in older data sheet versions and are used for open load detection in other high-side switches, which is not realised in the VN808CM-32-E. You can therefore ignore these GND resistors at the outputs.

The switch-on resistance of the high-side MOSFETs is indeed max. 160 mohms measured at 0.5A and ambient temperature 25°C, or max. 280 mohms at 0.5A and ambient temperature 125°C, as shown in table 3.

The switch-on time tON specified in table 4 was determined with an external (regular) load resistance of 48 ohms, while the protective function specified in table 6 was actually tested with an external (short-circuit simulating) load of 10 mohms.

Finally: "Iout min is 1A," is confirmed by the protection function, the values of which are listed in table 6. The value of IPEAK mentioned there describes that the high-side switch is switched off at the earliest at min 1.1A and at the latest at 2.6A.

Summary: with the exception of the resistors at the outputs mentioned first and visible in fig 1, which are not present, all data correspond to the facts. On behalf of the company, I would like to apologise for the incorrect drawing in fig 1.

Hope it is clearer now?

Regards
/Peter

[Leon_show]

Hello, in theory the IC amplifies the capacitance for stabilization, while small capacitors are placed at the input and output to eliminate noise.Is there a need for any capacitors on the output terminal of this IC for the purpose of protecting the IC? ex:coupling capacitor  

if it is necessary , what's the suggested value for the capacitor?

 

 

 

Thanks a lot!

 

[Peter BENSCH]

It seems to me that you are confusing the function of this high side switch with something else - the VN808 does not amplify any capacitance. As with all digital IC, a capacitor is only required between VCC and GND, where you should connect 100nF...2.2µF.

[Leon_show]

hi, i have another question about this ic 

 

i had tested this ic on my pcb board, but there is a strange situation I can't  realize :

 

In common ,i turn on the ic per channel with 2.0v  in the input side, and then the output side will output the voltage which is similar to the VCC when the VCC is large or equal than 9V ,right?

So i tested each output channel to check out the output value about voltage and current, i recorded the common situation, when the output is successful turn on at VCC=9.2v, the output current will be almost 13mA  from the power supplier,  but there is a channel i turn on in same condition, the current up to 0.14A   from the power supplier !   and the output voltage can't detect the correct value ,also there is a strange noise from the ic, is that mean the channel in this ic was broken? Could you please give me any suggestion or explanation about this strange situation?

 

Thanks a lot!

[Peter BENSCH]

The VN808CM-E has an undervoltage cut-off that switches off the device below min. 7V, max. 10.5V. At VCC=9V the device may be able to work, but it is also possible that it is already in shutdown. You should therefore use a supply voltage of >10.5V.

As far as your other measurements are concerned, you have not specified any load conditions, so no statement can be made about this. I also don't know what you mean by ‘strange noise’.