F

RT7204E

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is a registered trademark of Richtek Technology Corporation.

RT7204E_DS-00

May 2024

www.richtek.com

33

16

Application Information

(Note 8)

16.1

Constant Voltage (CV) Loop

As shown in Figure 7, the RT7204E integrates two error amplifiers (EA), which are connected with the feedback

compensators to regulate the output voltage and current, respectively. The output voltage is determined by the

following equation:

VOUT = KFB x VREF_CV

where

KFB = (RFB1 + RFB2) / RFB2 = 10

Therefore, the VOUT is determined by VREF_CV, the analog output from the DAC, which is controlled by MCU.

16.2

Constant Current (CC) Loop

As shown in Figure 7, the RT7204E integrates a virtually zero input offset high-side current-sense amplifier with

differential mode inputs to minimize noise interference. The sensed signal, Io_signal, is fed into an 11-bit ADC for

monitoring and processing by the MCU. The reference voltage of the CC loop is determined by VREF_CC (from the

DAC), which is programmed according to the requirements of charger.

Both the constant voltage and the constant current compensation loops are connected to the OPTO pin. The

OPTO driver sinks current through an external resistor RD and an optocoupler that isolates the secondary side

from the primary side, and then feedbacks the compensation signal to the primary side. Note that for better linearity

of the loop compensation range, RD should be designed to cover the operation at the minimum output voltage.

−−



OUT_MIN

F

COMP_MAX

D

(V

V

0.3V)

CTR

I

R

where

CTR: Current transfer ratio of the optocoupler

VF: Forward voltage of the optocoupler

0.3V: The minimum OPTO voltage for the OPTO driver to sink the minimum OPTO sink current

ICOMP_MAX: The maximum COMP sourcing current of a traditional PWM controller in the primary side. It is a current

sourced from an internal bias through a built-in pull-up resistor connected to the COMP pin in the PWM controller.