1. Overview & Functionality

️· Device: AS7620 (with versions A and B) – a DC-DC converter (likely step-up/boost).
️· Versions:
- AS7620-A: Adjustable output voltage.
- AS7620-B: Fixed 3.3V output voltage.
️· Control Method: Hysteric control in Discontinuous Current Mode (DCM). This offers high efficiency, stability, and simplicity.
️· Application: Primarily designed for portable devices and applications requiring efficient power conversion.

2. Key Features & Design Considerations

️· Soft Start: Limits inrush current during startup to prevent voltage spikes.
️· Current Limit: Three selectable current limit thresholds (240mA, 720mA, 1000mA) to protect the device and optimize performance. The maximum output current is half the current limit.
️· Power Fail/Power Good (PF/PG): Monitors input and output voltages and provides signals (PF and PG pins) to indicate power stability. Adjustable thresholds are possible.
️· Thermal Protection: Shuts down if temperature exceeds 150°C to prevent damage, with a reset mechanism.
️· Switching Frequency (fsw): Dynamically adjusts based on load conditions to maximize efficiency. A formula (EQ 3) is provided to estimate fsw.
️· Output Voltage Selection (AS7620-A): Uses a resistor divider. Formula (EQ 1) is given for calculating the output voltage based on reference voltage and resistor values.
️· Hiccup mode: The device will be shut down again if the over-temperature persists, resulting in a hiccup mode for the output power.

3. Pin Functions (Inferred from Description)

️· ILIM: Configures the current limit threshold.
️· PF: Power Fail indication (active low).
️· PG: Power Good indication.
️· VEPF: Input power fail monitoring.
️· FB: Feedback voltage (for regulation).
️· VOUT: Output voltage.
️· VDDH: Voltage supply for the external resistor network connected to EPF

4. Formulas & Equations

️· Output Voltage Selection (EQ 1): V_OUT = V_REF - 1 + Rh / Rl.
️· Estimated Switching Frequency (EQ 2):_I_ _OUT_ _=_ -------- _Tsw_ 1 - - 12 [-] [-] - -------------------------------------------------- ( _VILIM_ _IN_ – _V_ [2] _OUT_ - _L_ )•• _VV_ _INOUT_
️· Estimated Switching Frequency (EQ 3):_Fsw_ = ----------------------------------------------------------------------------2 - _I_ _OUT_ - ( _V_ _IN_ – _V_ _OUT_ ) - _V_ _OUT_

5. Tables

️· Table 2: Resistor values for EPF network selection based on input bus voltage (for configuring PF/PG functionality).

Important Notes & Key Takeaways

️· Detailed Design: This is a technical datasheet excerpt; it's intended for engineers designing circuits using the AS7620.
️· External Components: The design requires external resistors (for voltage selection), inductors, capacitors, and potentially other components, which aren’t covered in this excerpt.
️· Careful Selection: Resistor selection is critical for both output voltage adjustment and proper PF/PG functionality.