ISOM8111-Q1: Application inquiry

HyunGun Choi

Prodigy 30 points

Part Number: ISOM8111-Q1
Other Parts Discussed in Thread: ISOM8110

Tool/software:

Hello. I am a HW engineer at Kyungshin.

I have a question about ISOM8111DFHRQ1.

1) If you have an ISOM8111DFHRQ1 Ic current formula, please let me know.

2) Can you confirm the threshold current value for the input stage operation?
→ The datasheet states min=0.7mA / Max=20mA, but I am inquiring because the threshold value has not been confirmed.

3) If I configure the following circuit, is there a recommended R1 resistance value?

→ When the PHOTOCOUPLER is turned on, I would like to know how much current should flow to make the circuit stable.
→ The output stage is designed to divide the 12V_B voltage so that the MCU can read the High / Low voltage. (High = 5V / Low = 0V)

2 months ago

0 Andrew J 2 months ago

TI__Mastermind 28505 points

Hello HyunGun,

Thank you for reaching out.

(+) [FAQ] What is Current Transfer Ratio (CTR)? - Isolation forum - Isolation - TI E2E support forums
The ISOM8110 is designed for analog behavior so the switching threshold is defined by the circuit design. For designs, like yours where the ISOM81 is being used as a switch, it is best to design it in saturation mode. Please see this related post where timing performance for switching applications is discussed. (+) [FAQ] ISOM8110: How do I design ISOM8110 to have the best timing performance for switching applications?
In order to turn the ISOM81xx on you need to meet the forward voltage VF of 1.4V and at least IF = 700uA of forward current.
1. The output side of your application can actually be lowered to 5V pull-up to more easily interface with the MCU. Simply limit the current into the collector with a resistor so that forward current times CTR is larger than the limited collector current (saturation mode is when IF >> Ic_limit / CTR). This will force the output transistor to switch between GND and VCC at the MCU's logic level

Best,
Andrew

Isolation

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ISOM8111-Q1: Application inquiry