RT7205A
Functional Block Diagram
OPTO
VFB
IFB
AGND
VREF_CC
CC&CV
Shunt Regulator
VREF_CV
10-bit DAC
CC1
OTP-ROM
CC2
10-bit ADC
VDD
Mask-ROM
V_TR
SRAM
Synchronize Rectifier
Controller
VG
IO
USBP
USBP
MCU
TMR
I C
2
CS+
CS Amplifier
V_TR
OPTO
RT
RT
D+
D-
CS-
DP
DM
BLD
BLD
PGND
WDT
Program / Test
OVP
OVP
CC_GND
VCP
Charge Pump
V9
Power
Green Alarm
OSC
Protection
CC1
CC2
CC1
CC2
VDD
Operation
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.
Power Structure
Biased by the VDD pin, the RT7205A has two regulated
DC output voltages, V
5
and V
2
, 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 V
9
from V
5
with VCP
pin for capacitor connection so that the V9 voltage can be
nearly 2 times of the V5 voltage and the VG pin 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.
Constant-Voltage and Constant-Current (CV/CC)
Regulators
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 V
OPTO
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 V
VDD_ON
, which ensures a smooth power-on
sequence. The reference voltages, V
REF_CV
and V
REF_CC
,
for the voltage and current feedback loops, respectively,
are analog output voltages from the embedded DAC, and
their digital counterparts are from the MCU. The analog
output range of the 10-bit DAC is from 0 to V
DAC_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.
VDD
V2
V5
is a registered trademark of Richtek Technology Corporation.
DS7205A-00
February 2018
www.richtek.com
5
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
