1. Overview & Core Technology

️· What it is: The iW1707 is a digital controller for AC/DC adapters. It's designed to replace traditional, more complex designs using opto-isolation.
️· Key Benefit: Lower cost and increased reliability due to its digital control.
️· Operation: It uses a peak current mode control system, where the controller dynamically adjusts the BJT (Bipolar Junction Transistor) switching frequency for efficiency, EMI (Electromagnetic Interference) reduction, and power consumption optimization.
️· Adaptive Multi-Mode PWM/PFM: The controller adjusts the BJT switching frequency dynamically, switching between Pulse Width Modulation (PWM) and Pulse Frequency Modulation (PFM) modes based on load conditions.
️· Digital Control Advantages: Facilitates faster dynamic response, tighter output regulation, and advanced protection features.
️· No Secondary-Side Components: The system regulates output voltage without requiring secondary-side feedback circuits.

2. Key Features and Functionality

️· Active Start-Up: A proprietary start-up scheme for fast, smooth voltage build-up, even with large capacitive loads. It dynamically adjusts the peak current to prevent damage during startup.
️· Adaptive Soft Start: The soft-start process adapts to various output loads and voltages, providing a balance between speed and stability.
️· Overvoltage Protection (OVP), SCP, OCP: Built-in protection against overvoltage, short circuit, and overcurrent conditions.
️· I SENSE fault detection: Provides an extra layer of safety by monitoring the current sensing circuit.
️· Suitable for Network Adapters: Particularly well-suited for ADSL modems and similar devices that need to drive large capacitive loads.
️· UVLO (Under Voltage Lockout): Shuts down the controller if the input voltage (VCC) drops below a certain threshold (VCC(UVL)).

3. How it Works - Core Principles

️· Peak Current Mode Control: The controller regulates the output voltage by controlling the peak current in the primary side. This is achieved through the I PEAK comparator.
️· I PEAK Comparator: It sets a threshold value for the primary current, using the I SENSE signal.
️· V SENSE: This pin provides the secondary voltage feedback, which is monitored by the digital controller.
️· Adaptive Control: The controller intelligently adjusts the BJT base current to regulate output voltage and manage startup.
️· Digital Error Amplifier: Provides automatic loop compensation without the need for external components.

4. Pin Descriptions & Functionality

️· Pin 1 (VCC): Power supply input. Requires a decoupling capacitor.
️· Pin 3 (ASU): Control signal for the active start-up device (e.g., depletion NFET or BJT).
️· Pin 4 (I SENSE): Primary current sense input.
️· Pin 5 (GND): Ground.
️· Pin 6 (OUTPUT): Base drive for the external BJT switch.
️· ENABLE: A control signal that initiates the soft start process, pulls down the ASU pin.

Table: Pin Summary

Pin	Description	Function
VCC	Power Supply Input	Provides power to the controller.
ASU	Active Start-Up Control	Controls the active start-up device.
I SENSE	Current Sense Input	Monitors primary current for control.
GND	Ground	Common ground reference.
OUTPUT	BJT Base Drive	Provides base drive signal for the external BJT.

Important Terms (Definitions as used in the document)

️· BJT: Bipolar Junction Transistor - A type of transistor used as a switch.
️· PWM: Pulse Width Modulation - A technique to control power by varying the pulse width.
️· PFM: Pulse Frequency Modulation - A technique to control power by varying the pulse frequency.
️· EMI: Electromagnetic Interference - Unwanted electromagnetic energy that can disrupt electronics.
️· UVLO: Under Voltage Lockout - A safety feature that disables the controller when the input voltage is too low.
️· V SENSE: A voltage feedback pin that is used to regulate the output voltage.
️· I SENSE: A pin that is used to measure primary current to create feedback and limit current.
️· I PEAK: A measurement and comparator for peak current, setting the maximum allowable current.