RT7205A
Functional Block Diagram
VREF_CC
OPTO
VFB
IFB
CS+
CC&CV
Shunt Regulator
10-bit DAC
CS Amplifier
CS-
VREF_CV
CC1
CC2
V_TR
OPTO
AGND
V_TR
OTP-ROM
Mask-ROM
SRAM
TMR
10-bit ADC
RT
RT
VDD
D+
D-
DP
DM
Synchronize Rectifier
Controller
MCU
2
I C
BLD
USBP
OVP
BLD
VG
IO
USBP
PGND
WDT
Program / Test
OVP
CC_GND
VCP
V9
CC1
CC2
CC1
CC2
Charge Pump
Power
Green Alarm
OSC
Protection
Operation
Constant-Voltage and Constant-Current (CV/CC)
Regulators
The RT7205A is a highly integrated secondary-side
programmable SMPS and USB Type-C controller with
various functions and protections for off-line AC-DC
converters.
Two regulators are paralleled and connected to an open-
drain output, OPTO pin. The operation of each feedback
loop is similar to that of the traditional TL431 shunt
regulator except that VOPTO operating range is wider, from
0.3V to 16.5V, which enables easy design of converters
with a wider output range. The OPTO pin will be in high-
impedance state, if the VDD voltage is still below a UVLO
threshold VVDD_ON, which ensures a smooth power-on
Power Structure
Biased by the VDD pin, the RT7205A has two regulated
DC output voltages, V5 and V2, to supply the internal circuit
and the internal microprocessor (MCU). The bypass
capacitors at the V2 and V5 pins are required to improve
stability of the internal LDO and to minimize regulated
ripple voltages. The RT7205A also integrates a charge
pump to generate a boost voltage V9 from V5 with VCP
pin for capacitor connection so that the V9 voltage can be
nearly 2 times of the V5 voltage and the VGpin can directly
drive the SR MOSFET. Besides, the charge pump allows
the controller to operate under low supply voltage condition
as long as the output voltage is not below the programmed
UVP level.
sequence. The reference voltages, VREF_CV and VREF_CC
,
for the voltage and current feedback loops, respectively,
are analog output voltages from the embeddedDAC, and
their digital counterparts are from the MCU. The analog
output range of the 10-bitDAC is from 0 to VDAC_MAX (typical
2.7V), which makes output voltage resolution as small as
13.2mV and 6.6mV for the RT7205A and RT7205AL,
respectively, to achieve high-precision CV regulation.
Copyright 2018 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS7205A-00 February 2018
www.richtek.com
5
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
