HUSB251

Data Sheet

©2023 Hynetek Semiconductor Co., Ltd. All rights reserved.

Page 12 of 21

THEORY OF OPERATION

HUSB251 is a MCU-based USB PD DRP controller. It integrates a MCU core with necessary functions for USB PD

protocol, legacy charging protocols and power regulation. By modifying the firmware, the HUSB251 can be employed

in different applications. The integrated protections including OCP, OVP, UVP, SCP, OTP, CCOV, TSD and DPDMOV

can enhance the system reliability significantly.

MCU

HUSB251 integrates a 32-Bit RISC-V MCU core for the main operation. This subsystem implements the standard

RISC-V structure. It features:



Support RV32 commands



Support the programs in C format



Support interruptions



Internal communication BUS



With 8 kB ROM, 8 kB RAM, 32 kB Flash peripherals

VIN PIN

VIN pin is the power supply input, which is derived from the output of the AC-DC or DC-DC converter. Connect a 1 μF

decoupling MLCC between VIN pin and GND pin.

The VIN pin is also connected to an internal MOSFET and discharge resistor, which is used as a bleeder to help

discharge the energy stored in the output capacitor. With this bleeder, VIN can be regulated to vSafe5V upon the

detachment of a connected device, or to a lower desired output voltage level upon a request command received from

the Sink, such as from 20 V to 5 V.

VDD PIN

An internal liner regulator is used to provide 1.5 V for internal circuits. Connect a 1 μF MLCC to VDD pin for

decoupling.

CONTROL LOOP COMPENSATION CIRCUIT (VFB, CS+, CS

−, IFB, OPTO PINS)

In the HUSB251, the constant voltage loop (CV loop) compensation and constant current loop (CC loop)

compensation are implemented. VIN voltage is scaled by a resistor divider to be as the feedback voltage. It is

compared with the internal voltage reference to generate an error signal. The CV loop can compensate this error

signal. And then the compensated signal is employed to drive the primary side of the opto-coupler and control the AC-

DC power loop.

CURRENT SENSE RESISTOR

The recommended current sense resistor is 5 mΩ. The sensed current information is employed to perform OCP, SCP

and Constant Current Control.

CC1 AND CC2 PINS

CC1 and CC2 pins are used to detect Type-C connection, BMC communication.

TYPE-C CC FUNCTION

CC1 and CC2 are the Configuration Channel pins used for connection and attachment detection, plug orientation

determination and system configuration management across USB Type-C cable.

The HUSB251 monitors the status of CC1 and CC2 pins and decide which state should enter.

CC1 and CC2 can be configured as Source, Sink and DRP by firmware. And default state of CC with Rd resistor.

CC1 and CC2 are configured as Source only mode with 1.5 A and 3 A current advertising. The default Rp current on

CC1 and CC2 is ICC_3P0, which means 3 A current advertising.

The CC1 and CC2 can tolerance a voltage up to 30V. This is helpful for the HUSB251 to survive in the failure when

the CC1 or CC2 is shorted to the VBUS pin.