• TI Thinks Resolved

# ISO7721-Q1: Condition of the Electrical Characteristics

Part Number: ISO7721-Q1

I just would like to confirm one thing.

ISO7721 will satisfy the Electrical Characteristics in the datasheet page 10 when Vcc1 = Vcc2. Is this correct?

Or this device will satisfy the Electrical Characteristics even if Vcc1 and Vcc2 is different (e.g. Vcc1=2.5V, Vcc=5V). Is this correct?

• Hi Mamoru,

ISO7721 like many other digital isolators has two dice, one on Side1 and another on Side2. Side1 is powered by VCC1 and Side2 is powered by independently and these two dice and power supplies are isolated from each other. Hence, most electrical characteristics specified in datasheet are applicable to each die irrespective of the other die.

For example, ICC1 will only depend on VCC1 and doesn't depend on the value of VCC2. So if one would like to know device power consumption for VCC1 = 2.5V & VCC2 = 5V then they can simply refer to ICC1 values for VCC1 = 2.5V table from datasheet and ICC2 values for VCC2 = 5V table. Adding these two values will give the total power consumption of device.

The above explanation holds good for most of the electrical characteristics. This cannot be said for switching characteristics in datasheet. For example, propagation delay tPLH is a spec of the whole device and cannot be defined for individual dice.

I hope that answers your question, thanks.

Regards,
Koteshwar Rao

• In reply to Koteshwar Rao:

I understood that the dice on each side specification will depend on each Vcc. for example, Icc1 will depend Vcc1.

May I double-check meaning of following?

>This cannot be said for switching characteristics in datasheet. For example, propagation delay tPLH is a spec of the whole device and cannot be defined for individual dice.

the Electrical Characteristics on the datasheet is defined under the condition that Vcc1=Vcc2. so if Vcc1 is not same as Vcc2 (e.g. Vcc1 = 2.5V & Vcc2 = 5V), Actual Electrical Characteristics will not always be value what the datasheet showed. is this correct?

• In reply to Mamoru_Uozu:

Hi Mamoru,

The device characteristics of ISO7721 are grouped into three categories - Electrical Characteristics, Supply Current Characteristics & Switching Characteristics.

For electrical and supply current characteristics (sections 6.9 to 6.14 in datasheet), most of the parameters apply to individual dice. The example I provided earlier clarifies how to use this data to find ICC values for individual dice with different supplies.

For switching characteristics (sections 6.15 to 6.17), the above rule cannot be applied because the parameters covered under switching characteristics are the specs that apply to the whole device and cannot be defined for individual die. Please note switching characteristics only includes timing parameters like propagation delays and is provided only for VCC1 = VCC2 conditions in the datasheet.

Let me know if this clarifies your confusion, thanks.

Regards,
Koteshwar Rao