Richtek RT8461ZS Schematic [ru]
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RT8461
Off-Line Constant Voltage High Power Factor PWM Floating Buck Driver Controller
General Description
The RT8461 is an off-line, constant output voltage, active power factor, PWM floating buck driver controller. With an unique floating drive topology, the RT8461 simplifies offline high voltage system application design with minimum number and lower price of components.
To achieve high power factor, the AC power line voltage is sensed via the SIN pin. An internal power factor correction circuit follows the sensed sine waveform and modulates the external MOSFET duty cycle-by-cycle to achieve constant output voltage.
The output voltage is adjustable via an output resistor divider. By operating at 47kHz, the switching loss is kept minimal and the high frequency EMI is reduced. To drive industrial grade MOSFET switches, the RT8461 gate driver can deliver up to 0.8A output current with 12V gate output voltage. The RT8461 provides output short protection.
Features
zWide Input Voltage Range : 16V to 33V
zHigh Power Factor Correction with Simple System Circuits
zAdjustable Constant Output Voltage
zBuilt-in High Power Factor Correction Circuit
zTypical 250μA Start-Up Supply Current
zLow Quiescent Current : 0.1μA
zSOP-8 Package
zRoHS Compliant and Halogen Free
Applications
z E27,PAR30, Off-line LED Lamp
Marking Information
RT8461 |
RT8461ZS : Product Number |
YMDNN : Date Code |
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ZSYMDNN |
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Simplified Application Circuit
AC IN |
+ |
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D1 |
~ |
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Rstart |
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- |
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VCC |
RT8461 |
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R1 |
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R2 |
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SIN |
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C2 |
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FB |
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GATE |
M1 |
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ICOMP |
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R3 |
C3 |
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VCOMP |
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R4 |
R5 |
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C4 |
C5 |
SENSE |
GND |
RS |
L |
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VOUT |
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D2 |
C1 |
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Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS8461-01 March 2013 |
www.richtek.com |
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1 |
RT8461
Ordering Information
RT8461 
Package Type
S : SOP-8
Lead Plating System
Z : ECO (Ecological Element with Halogen Free and Pb free)
Note :
Richtek products are :
`RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`Suitable for use in SnPb or Pb-free soldering processes.
Pin Configurations
(TOP VIEW)
GND |
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8 |
VCOMP |
GATE |
2 |
7 |
SIN |
VCC |
3 |
6 |
ICOMP |
SENSE |
4 |
5 |
FB |
SOP-8
Functional Pin Description
Pin No. |
Pin Name |
Pin Function |
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1 |
GND |
Ground. |
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2 |
GATE |
Gate Driver for External MOSFET Switch. |
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3 |
VCC |
Power Supply. For good bypass, place a ceramic capacitor near the VCC pin. |
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Inductor Current Sense. The inductor current is sensed by a resistor between GND |
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4 |
SENSE |
and SENSE pins. The sense pin signal is used as the saw tooth signal to the PWM |
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comparator. The comparator output will modulate the GATE turn-on duty to |
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achieve the output voltage regulation. |
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Output Voltage Sense. The Output voltage is sensed through an external resistor |
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5 |
FB |
divider. The sensed voltage (which is tied to amplifier negative input) is compared |
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to an internal reference threshold at 1.2V (which is tied to amplifier positive input). |
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The output of this GM amplifier is the VCOMP pin. |
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Output of this Multiplier. To achieve high power factor, the voltage loop amplifier |
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6 |
ICOMP |
output signal is modulated with the sensed input voltage through the SIN pin by an |
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internal multiplier. A compensation capacitor between ICOMP and GND is needed. |
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7 |
SIN |
Input Power Voltage Sensing for PFC Function. An external resistor for input |
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voltage sensing is connected to the power input. |
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8 |
VCOMP |
Output of the Internal Voltage Loop GM Amplifier. A compensation network |
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between VCOMP and GND is needed. |
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Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
www.richtek.com |
DS8461-01 March 2013 |
2
RT8461
Function Block Diagram
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Chip |
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Enable |
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VCC |
16V/8V |
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12V |
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OVP |
OSC |
S |
Q |
GATE |
35V |
+ |
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R |
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200k |
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PWM |
R |
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GND |
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Control |
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SENSE |
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Circuit |
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ICOMP |
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VCOMP |
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PFC |
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1.2V |
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Control |
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SIN |
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FB |
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- |
Circuit |
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Operation
The RT8461 is a floating-GND Buck PWM current mode controller with an integrated low side floating gate driver. The start up voltage of RT8461 is around 10V. Once VCC is above 16V, the RT8461 will maintain operation until VCC drops below 8V.
The RT8461's main control loop consists of a 47kHz fixed frequency oscillator, an internal 1.2V feedback (FB) voltage sense threshold, and the PFC control circuit with a PWM comparator. In normal operation, the GATE turns high when the gate driver is set by the oscillator (OSC). When the feedback (FB) voltage is below the reference 1.2V
threshold, the VCOMP pin voltage will go high. The ICOMP signal is the result of VCOMP signal multiplied with SIN signal. Higher ICOMP voltage means longer GATE turnon period. The GATE does not always turn-off in each cycle. The GATE will be turned on again by OSC for the next switching cycle.
The RT8461 provides several fault protections, including input voltage Under Voltage Lockout (UVLO), Over Current Protection (OCP) and VCC Over Voltage Protection (OVP). Additionally, to ensure the system reliability, the RT8461 is built with internal thermal protection function.
Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS8461-01 March 2013 |
www.richtek.com |
3
RT8461
Absolute Maximum Ratings (Note 1)
z Supply Voltage, VCC ----------------------------------------------------------------------------------------------------- |
−0.3V to 40V |
z SIN ---------------------------------------------------------------------------------------------------------------------------- |
−0.3V to 40V |
z GATE (Note 6) ----------------------------------------------------------------------------------------------------------- |
−0.3V to 16V |
z VCOMP, ICMOP----------------------------------------------------------------------------------------------------------- |
−0.3V to 3.5V |
z FB ----------------------------------------------------------------------------------------------------------------------------- |
−0.3V to 2V |
z SENSE ---------------------------------------------------------------------------------------------------------------------- |
−1V to 0.3V |
z Power Dissipation, PD @ TA = 25°C |
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SOP-8 ------------------------------------------------------------------------------------------------------------------------ |
0.53W |
z Package Thermal Resistance (Note 2) |
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SOP-8, θJA ------------------------------------------------------------------------------------------------------------------ |
188°C/W |
z Junction Temperature ----------------------------------------------------------------------------------------------------- |
150°C |
z Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------- |
260°C |
z Storage Temperature Range -------------------------------------------------------------------------------------------- |
−65°C to 150°C |
z ESD Susceptibility (Note 3) |
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HBM (Human Body Model) ---------------------------------------------------------------------------------------------- |
2kV |
MM (Machine Model) ----------------------------------------------------------------------------------------------------- |
200V |
Recommended Operating Conditions |
(Note 4) |
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z Supply Voltage VCC ------------------------------------------------------------------------------------------------------ |
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16V to 33V |
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z Junction Temperature Range -------------------------------------------------------------------------------------------- |
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−40°C to 125°C |
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z Ambient Temperature Range -------------------------------------------------------------------------------------------- |
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−40°C to 85°C |
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Electrical Characteristics |
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(VCC = 24VDC, CLOAD = 1nF, RLOAD = 2.2Ω in series, TA = 25°C, unless otherwise specified) |
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Parameter |
Symbol |
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Test Conditions |
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Min |
Typ |
Max |
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Unit |
Input Start-Up Voltage |
VST |
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16 |
17 |
18 |
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V |
Under Voltage Lockout Threshold |
VUVLO |
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7 |
8 |
11 |
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V |
Under Voltage Lockout Threshold |
VUVLO |
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-- |
2 |
4 |
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V |
Hysteresis |
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Input Supply Current |
ICC |
After Start-Up, VCC = 24V |
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2 |
5 |
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mA |
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Input Quiescent Current |
IQC |
Before Start-Up, VCC = 7V |
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-- |
0.1 |
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μA |
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Oscillator |
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Switching Frequency |
fSW |
VSIN = 14V |
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38 |
47 |
52 |
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kHz |
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Maximum Duty in Transient |
DMAX(TR) |
VC = 3V |
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-- |
-- |
100 |
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% |
Operation |
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Maximum Duty in Steady State |
DMAX |
(Note 5) |
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-- |
97 |
-- |
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% |
Operation |
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Blanking Time |
tBLANK |
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-- |
300 |
-- |
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Minimum Turn-Off Time |
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(Note 5) |
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-- |
650 |
-- |
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Current Sense Amplifier |
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Current Sense Voltage |
VSENSE |
VCOMP = 1V, SIN = 15V |
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-- |
−100 |
-- |
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mV |
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Sense Input Current |
ISENSE |
Sense = 100mV (Note 5) |
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-- |
10 |
-- |
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μA |
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Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
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www.richtek.com |
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DS8461-01 March 2013 |
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4
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