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  

[Leon_show]

Hello, I noticed that some test conditions in the data sheet use RL and Rload (figure.1)  for  testing. To avoid any misunderstandings about resistances, I annotated the internal schematic using the information provided by the company. Could you please help me confirm if it  (figure.2)  is accurate as indicated in the image? Then, is the situation you mentioned earlier, "Iout min is 1A," applicable regardless of the load resistance in any condition?

Thank you for long time reply

[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’.

[Leon_show]

Hi:

Sure! I'll try to explain my circuit in detail. I use the VN808CM-E mainly to switch the laser on the PCB board. I connect the output of the VN808CM-E to the positive terminal of the laser. When a high logic input is applied, the IC outputs VCC voltage to the positive terminal of the laser. The negative terminal of the laser is connected to an EPC IC, which generates a downward oscillating voltage in response to the input pulse. This way, when I apply a high logic input to the VN808CM-E, the laser is turned on. This is the basic structure of my circuit.

However, I have observed that for certain channel outputs, the current from the VCC power supply suddenly increases to 0.1A. Additionally, the output of the IC does not show the VCC voltage on the multimeter (operating around 10V in the conducting state), and the IC emits a beeping sound.

If it's still not clear, please let me know.

Thanks a lot  !!!!

[Peter BENSCH]

Well, a description via text can be helpful parallel to a schematics, but is not sufficient here. For example, I don't know which laser you are using and what kind of EPC IC it is (URLs to the PDF would be useful).

Also, the fact that the current to VCC should suddenly increase does not provide enough information to analyse the fault. The VN808CM-E is a high side driver that switches the current path from VCC to the respective output. If the connected load (in this case your laser and the rest of the circuit) draws more current for whatever reason, this change must of course also be measured at VCC. If you then hear a beeping sound, the load current limitation is probably active, switches the output off, switches it on again after a while, sees an overcurrent again and switches it off again and so on. This may well be noticeable as a beeping sound. Another possibility is the connected EPC IC, but I can't say anything about this yet due to a lack of precise information (data sheet).

It would also be helpful if you could record the output signals of the VN808CM-E with an oscilloscope and insert them here.

Regards
/Peter