RT7204E datasheet(29/45 Pages) RICHTEK

29 / 45 page

RT7204E

is a registered trademark of Richtek Technology Corporation.

RT7204E_DS-00

May 2024

www.richtek.com

Operation

The RT7204E is a highly integrated secondary-side programmable controller, providing various functions and

comprehensive protections for off-line AC-DC converters.

15.1

Power Structure

The RT7204E features internal regulated voltages, V5 and V2, which are derived from VDD supply. These voltages

are utilized to power the internal circuit and the internal microprocessor (MCU), respectively.

15.2

Constant Voltage and Constant Current (CV/CC) Regulators

Two regulators are paralleled and connected to the OPTO pin, an open-drain output. Each feedback loop operates

similarly to the traditional TL431 shunt regulator. However, the VOPTO operating voltage range is broader,

extending from 0.3V to 25V.This extended range facilitates the design of converters with a wider output voltage

range. When the VDD voltage is below the turn-on threshold VVDD_ON, the OPTO pin remains in a high-impedance

state. This feature is critical for ensuring a smooth power-on sequence. The reference voltages, VREF_CV and

VREF_CC, for the voltage and current feedback loops are provided by the analog output voltages of an 11-bit DAC.

With a resolution of 10mV for the DAC

’s CV output voltage, the system is capable of achieving high-precision CV

and CC regulation.

15.3

Current Sense Amplifier

To minimize power loss of the current sense resistor, a low input offset amplifier with voltage gain of 32 is applied.

When the 5m

 (typical) RCS goes with the voltage gain of 32, the resolution of the output current is approximately

6mA. The operation of the CV and CC loops is shown in Figure 1. The sensed output current is amplified by the

current-

sense amplifier as “Io_signal”, which is then sent to the current-loop regulator for constant-current regulation

and also sent to the MCU, by way of an 11-bit ADC for analog-to-digital conversion, to update the output current

status for the MCU.

RFB1

RFB2

ROPTO_VDD

ROPTO_SINK

IOPTO_SINK

VCS_OFFSET

KCS

CS-

CS+

IFB

OPTO

VFB

VDD

UVLO

VDD

UVLO

VREF_CC

11-bit DAC

Io_signal

VREF_CV

11-bit DAC

Figure 1. CV and CC Loops

RT7204E Datasheet(PDF) 29 Page - Richtek Technology Corporation

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