PAC5250_17 Datasheet, PDF (22/70 Pages) Active-Semi, Inc – Power Application Controller

Figure 10-4. AC/DC Flyback Mode
VHM
PAC5250
VP
DRM
CSM
PAC5250
Power Application Controller
V (120V/230V)
AC
V (12V default)
P
The MMSS detects and selects between high-side and low-side mode during start up based on the placement of the current
sense resistor and the CSM pin voltage. It employs a safe start up mode with 9.5kHz switching frequency until V P exceeds
4.3V under-voltage-lockout threshold, then transitions to the 45kHz default switching frequency for at least 6ms to bring VP
close to the target voltage, before enabling the linear regulators. Any extra load should only be applied after the supplies are
available and the microprocessor has initialized. The switching frequency can be reconfigured by the microprocessor to be
181kHz to 500kHz in the high switching frequency mode for battery-based applications, and to be 45kHz to 125kHz in the
low switching frequency mode for AC applications. Upon initialization, the microcontroller must reconfigure the MMSS to
the desired settings for VP regulation voltage, switching mode, switching frequency, and VHM clamp. Refer to the PAC
application notes and user guide for MMSS controller design and programming.
If a stable external 4.5V to 18V power source is available, it can power the V P main supply and all the linear regulators
directly without requiring the MMSS controller to operate. In such applications, VHM can be connected directly to VP and
the microcontroller should disable the MMSS upon initialization to reduce power loss.
10.3.2. Linear Regulators
The MMPM includes up to four linear regulators. The system supply regulator is a medium voltage regulator that takes the
VP supply and sources up to 200mA at REGO until VSYS, externally coupled to REGO, reaches 5V. This allows a properly
rated external resistor to be connected from REGO to VSYS to close the current loop and offload power dissipation between
VP and VSYS. Once VSYS is above 4V, the three additional 40mA linear regulators for VCCIO, VCC33, and VCC18 supplies
sequentially power up. Figure 10-5 shows typical circuit connections for the linear regulators. For 5V I/O systems, short the
VCCIO pin to VSYS to bypass the VCCIO regulator. For 3.3V I/O systems, the VCCIO regulator generates 3.3V. The VCC33 and
VCC18 regulators generate 3.3V and 1.8V, respectively. When VSYS, VCCIO, VCC33, and VCC18 are all above their respective
power good threshold, and the configurable power on reset duration has expired, the microcontroller is initialized.
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Rev 1.7‒April 15, 2016