Datasheet IL4622E, IL4685E (NVE) - 9

IL4622E / IL4685E Device Operation
The IL4685 / IL4622 detailed block diagram is shown below. The major elements are a DC-DC convertor, an RS-485 / RS-422 transceiver, and GMR isolation: Freq Refer- Hop ence EMI Shield Overcurrent VDD1A Oscil- Reg- Amp lator ulator VDD2B IsoLoopR VF transformer Brownout VDD2A Detector 1 M nominal DE Refresh Clock
IsolationBarrier
Y D Z A R B nominal 500k RE Failsafe GND1
Figure 1. IL4685 / IL4622 detailed block diagram. DC-DC Convertor Operation
A 113 MHz oscillator drives a high-frequency power amplifier, which in turn drives an IsoLoop® microtransformer primary. Frequency hopping reduces EMI peak amplitudes, and embedded magnetic shielding further reduces radiated EMI. A unique ceramic/polymer composite barrier provides full 2.5 kV isolation with virtually unlimited barrier life. On the other side of the isolation barrier, the transformer secondary output is filtered, rectified, and regulated by a low-EMI low drop- out regulator with a precision bandgap voltage reference. Simple Capacitive Decoupling The only external parts required are a 0.1 µF capacitor placed as close as possible to the VDD1B supply pin, a 10 µF ceramic capacitor for the VDD2 or VDD2B pin, and a 0.1 µF/16 V filter capacitor near the VF pin. This low external parts count reduces board area and cost. Start-Up Current The input power supply to the DC-DC convertor must be able to supply a start-up surge current of 750 mA for at least 700 ns for the DC-DC convertor to start up properly. If the input current is supplied by a regulator, a one-amp regulator provides adequate current. Short-Circuit Protection The DC-DC convertor output will shut down at a current of approximately 120 mA. Short-circuit protection automatically resets and the output recovers when the fault is removed. 9 NVE Corporation 11409 Valley View Road, Eden Prairie, MN 55344 (952) 829-9217 www.nve.com YouTube.com/NveCorporation iso-apps@ www.nve.com