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PDF R7711A Data sheet ( Hoja de datos )
| Número de pieza | R7711A | |
| Descripción | Primary Feedback CC/CV PWM Controller | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
R7711A
Primary Feedback CC/CV PWM Controller for Flyback
Converters
General Description
Features
The R7711A is a current mode PWM controller which
includes primary side voltage feedback technology. It
controls the output voltage and current accurately without
shunt regulator and opto-coupler on secondary side to
reduce the part count and save costs.
The R7711A is designed especially for low power
applications, such as chargers for cell phones, PDAs,
and other mobile products. Complete protections are
provided, such as output Under- Voltage Protection, output
Over-Voltage Protection, VDD Over-Voltage Protection,
Over-Temperature Protection, and Secondary Rectifier
Short-circuit Protection. The ultra low start-up current and
operating current of the R7711A achieves low power
consumption in standby mode. The R7711A supports burst
switching green mode operation to meet CEC regulations
and Energy-Star requirements.
Programmable Primary-Side CC/CV Regulation
Low No Load Input Power (<30mW at 230VAC)
Burst Switching Green Mode PWM Operation
Low Start-up Current (<10mA)
Easy EMI Solution
Built-in Jittering Frequency
Built-in Soft Gate Driver
Programmable Cable Drop Compensation
Adjustable Propagation Delay Compensation
VDD Over-Voltage Protection (VDDOVP)
Output Over-Voltage Protection (OVP)
Output Under-Voltage Protection (UVP)
Secondary Rectifier Short-Circuit Protection (SRSP)
Internal Over-Temperature Protection (OTP)
RoHS Compliant and Halogen Free
Applications
Switching AC/DC Adaptor and Battery Charger
DVD Open Frame Power Supply
STB Power
Cell Phone Charger
Networking Power Supply
Simplified Application Circuit
L
AC Mains
(90V to 265V)
N
VDD DMAG
R7711A
COMP GATE
CS
GND
2
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
R7711A-06 May 2014
VOUT
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
R7711A
Programmable Cable Drop Compensation
The R7711A features a cable drop compensation to
adaptively compensate the output voltage drop effect due
to the output cable impedance. As shown in the figure 4,
The ICABLE, proportional to the converter output current,
creates an additional voltage offset (ΔVRDMAG2) into the
DMAG pin to achieve the cable compensation. The ICABLE
is calculated by using the following equation :
ICABLE = 8μA/V x VCOMP −11.2μA (ICABLE ≥ 0)
VIN
TX1 DO IDO VOPCB
VOUT
NP NS+ VDO -
RCABLE
VAUX
R7711A
+
VDMAG2
ICABLE DMAG -
Cable
Comp.
CDMAG
RDMAG2NA
VDMAG
RDMAG1
VCOMP
Figure 4. DMAG Current for Cable Compensation
Burst Switching Green Mode
To further reduce the switching losses in no load or very
light load condition, a burst switching green mode control
reduces the average switching frequency when the VCOMP
drops. A green-mode voltage threshold (VTH_Green = 1.1V
typ.) switches the operating frequency in either fBS_MIN
(1kHz typ.) or fGreen (250Hz typ.). The green mode
operation meets the CEC regulations and Energy-Star
requests.
Min. On-Time
To improve green power at light load or no load conditions,
the R7711A works with a minimum on-time (TON_MIN) and
the output voltage is regulated by the modulated switching
frequency. The TON_MIN, shown as the following equation,
is a function of the ICLAMP :
ICLAMP
VIN
RDMAG2
NA
NP
TON_MIN
0.7A ns
ICLAMP
Leading Edge Blanking (LEB) for VCS
Due to the device's parasitic capacitors, an initial current
spike appears at the rising edge of the GATE voltage
(VGATE). The spike of the CS voltage may incorrectly trigger
the peak current comparator, to turn off the power MOSFET,
resulting in running failure of the flyback converter. Thus,
the LEB, used to mask the initial voltage spike on the CS
pin, is a necessary design for successful PWM operation.
VDD Under-Voltage Lockout (UVLO) Protection
The R7711A automatically initializes upon receipt of the
supply voltage (VDD) on the VDD pin. The UVLO function
continually monitors the VDD. When the VDD exceeds its
rising UVLO threshold (VTH_ON = 14.5V typ.), the IC is
enabled. When the VDD falls below the falling UVLO voltage
threshold (VTH_OFF = 8.5V typ.), the GATE voltage is pulled
low to shut off the converter. The supply voltage (VDD)
must be below the absolute maximum rating for safety.
VDD Over-Voltage Protection (VDD OVP)
When the VDD exceeds the VDD over-voltage threshold
(VTH_VDDOV = 27V typ.) in abnormal conditions, the GATE
voltage is pulled low to shut off the converter and the
R7711A works in hiccup mode until the fault is removed.
This avoids permanent damage of the converter
components . The VDD over-voltage may be caused by
an incorrectly sensed feedback signal on the DMAG pin
or an output over-voltage condition.
Output Over-Voltage Protection (OVP)
The R7711A provides accurate output OVP. Once the
feedback voltage (VSH_DMAG), sampled on the DMAG pin,
is over 125% (typ.) of the reference voltage (VREF = 2.5V
typ.), the R7711A issues an output OVP signal to turn off
the controller and prevent the loading device and converter
from being damaged. Therefore, the OVP threshold on
the output is about 125% of the CV output voltage at the
end of the PCB. The R7711A works in hiccup mode until
the fault is removed.
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
R7711A-06 May 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
R7711A
Typical Operating Characteristics
VDD OVP Threshold vs. Junction Temperature
28.0
27.5
27.0
26.5
26.0
25.5
25.0
-50
-25 0
25 50 75 100
Junction Temperature (°C)
125
VDD Operating Current vs. Junction Temperature
800
700
600
500
400
300
200
100
0
-50
GATE = COMP = Open
-25 0 25 50 75 100 125
Junction Temperature (°C)
UVLO-On Threshold Voltage vs. Junction Temperature UVLO-Off Threshold Voltage vs. Junction Temperature
16 10.0
15 9.5
14 9.0
13 8.5
12 8.0
11 7.5
10
-50
-25 0
25 50 75 100
Junction Temperature (°C)
125
7.0
-50
-25 0 25 50 75 100 125
Junction Temperature (°C)
VDD Start-up Current vs. Junction Temperature
10
PPWWMMFFrreeqquueennccyy vs. JJuunnccttioionnTTeemmppeerartautruere
80
75
8
70
6
65
4
60
2
0
-50
VDD = VTH_ON − 0.1V
-25 0
25 50 75 100 125
Junction Temperature (°C)
55
50
-50
-25 0 25 50 75 100 125
Junction Temperature (°C)
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
R7711A-06 May 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet R7711A.PDF ] | |
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