DS89C21: DS89C21TMX VIH/ VIL/ VCH/ VOL Min/typ/max

Hi Kazusa-san,

I'm working to get a hold of some characterization data for this device. I should be able to answer your question tomorrow. 

Regards,
Eric

Hi Kazusa-san,

We may not have char data available for this device. Because the conditions you listed are still within the recommended temperature and supply voltage range, we would expect all values to remain within the specified limits. 

Note we typically see a correlating trend in some values under slightly lower supply voltages. i.e. Lower Vcc will result in lower Vol 

Let me know if you have any more questions.

Regards,
Eric

Hi Eric,

I am sorry, I was asking VIH, VIL, VOH and VOL.

My understanding is all typicals are given for VCC = 5.0V and T A = 25°C and max and min are given for within the recommended temperature and supply voltage range.

I have additional questions.

Why Voh does not have max spec?

Why VOL does not have min spec?

Hi Kazusa-san,

There are many measurements that are taken into account when specifying Min/Typ/Max values for datasheets. On DS89C21's datasheet, it states that the Electrical Characteristics sections is specified over recommended supply voltage and operating temperature ranges. This means testing is done over a range of conditions and Min/Max values are specified as worst-case behavior within recommended ranges. This is important so the device can be implemented in a design and expected to never exceed these values as long as its requirements are met. i.e. DS89C21 can be expected to always output a logic LOW [Vol(Max)] of 0.3V or lower when within recommended conditions. This allows the device to be compatible with controller with an input LOW threshold [Vil(Max)] of 0.3V or above. 

Typical values are meant to show more common behaviors when the device is not operating at the extreme ends of recommended conditions. This is generally taken as a statistical average of different measurements and does not only based on values at nominal conditions such as Vcc = 5.0V, TA = 25C.

So to answer your initial question; Voh and Vol typical values are based on data taken at a range of operating conditions. The Min/Max values for Vih, Vil, Voh, and Vol are based on the worst-case behavior on extreme ends of recommended conditions. In the case where supply voltage is slightly below nominal (i.e. Vcc = 4.85V), Voh and Vol will likely be measured slightly below typical values. Since these are still within recommended conditions, measured values will still be within the Min/Max specifications. 

Why Voh does not have max spec?
Why VOL does not have min spec?

Output voltages are attempting to drive a potential equal to the device's supply Vio (HIGH) or ground potential (LOW). Because DS89C21 does not have internal power circuitry to boost voltage, it will not be able to drive an output HIGH greater than Vcc. Similarly it is not capable of generating a potential less than ground. It can be thought that the Max/Min values for Voh and Vol could be Vcc and GND respectively. These are not specified because there will be some drop between supply/ground and the driver pin due to the resistance of the device and the current it is sourcing. The maximum value of this voltage drop is specified in Min/Max (supply - Vdrop or GND + Vdrop). Minimum values of this drop would be 0V for ideal components (0 resistance) giving us our Max/Min of Vcc and GND. Because no real-life testing would yield ideal values, this is not specified on the datasheet. 

Let me know if this makes sense. 

Regards,
Eric