Richtek RT8461ZS Schematic [ru]
®
Off-Line Constant Voltage High Power Factor PWM
Floating Buck Driver Controller
RT8461
General Description
The RT8461 is an off-line, con stant output voltage, a ctive
power factor , PWM floating buck driver controller. With an
unique floating drive topology , the RT8461 simplifies of fline high voltage system application de sign with minimum
number and lower price of components.
T o a chieve high power factor , the AC power line voltage is
sensed via the SIN pin. An internal power fa ctor correction
circuit follows the sensed sine waveform a nd 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
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z Wide Input Voltage Range : 16V to 33V
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z High Power Factor Correction with Simple System
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Circuits
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z Adjustable Consta nt Output Voltage
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z Built-in High Power Factor Correction Circuit
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z T ypical 250
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z Low Quiescent Current : 0.1
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z SOP-8 Package
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z RoHS Compliant and Halogen Free
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μμ
μA Start-Up Supply Current
μμ
μμ
μA
μμ
Applications
z E27,PAR30, Of f-line LED La mp
Marking Information
RT8461ZS : Product Number
RT8461
ZSYMDNN
YMDNN : Date Code
Simplified Application Circuit
AC IN
Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
©
+
~
-
C2
R2
R3
R1
C3
Rstart
R4
C4
R5
C5
VCC
SIN
FB
ICOMP
VCOMP
RT8461
GNDSENSE
GATE
M1
DS8461-01 March 2013 www.richtek.com
D2
RS
D1
L
C1
V
OUT
1
RT8461
Ordering Information
Pin Configurations
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 require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.
Functional Pin Description
Pin No. Pin Name Pin Function
1 GND Ground.
2 GATE Gate Driver for External MOSFET Switch.
3 VCC Power Supply. For good bypass, place a ceramic capacitor near the VCC pin.
Inductor Current Sense. The inductor current is sensed by a resistor between GND
4 SENSE
and SENSE pins. The sense pin signal is used as the saw tooth signal to the PWM
comparator. The comparator output will modulate the GATE turn-on duty to
achieve the output voltage regulation.
GND
GATE
VCC
SENSE
(TOP VIEW)
8
2
3
4
7
6
5
SOP-8
VCOMP
SIN
ICOMP
FB
5 FB
6 ICOMP
7 SIN
8 VCOMP
Output Voltage Sense. The Output voltage is sensed through an external resistor
divider. The sensed voltage (which is tied to amplifier negative input) is compared
to an internal reference threshold at 1.2V (which is tied to amplifier positive input).
The output of this GM amplifier is the VCOMP pin.
Output of this Multiplier. To achieve high power factor, the voltage loop amplifier
output signal is modulated with the sensed input voltage through the SIN pin by an
internal multiplier. A compensation capacitor between ICOMP and GN D is needed.
Input Power Voltage Sensing for PFC Function. An external resistor for input
voltage sensing is connected to the power input.
Output of the Internal Voltage Loop GM Amplifier. A compensation network
between VCOMP and GND is needed.
Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
2
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DS8461-01 March 2013www.richtek.com
Function Block Diagram
RT8461
+
-
+
VCC
35V
GND
ICOMP
VCOMP
1.2V
FB
16V/8V
OVP
+
-
+
-
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, a n 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
Chip
Enable
12V
OSC
PWM
Control
Circuit
PFC
Control
Circuit
S Q
R
R
200k
GATE
SENSE
SIN
threshold, the VCOMP pin voltage will go high. The ICOMP
signal is the result of VCOMP signal multiplied with SIN
signal. Higher ICOMP voltage mean s longer G ATE turnon period. The GATE does not always turn-off in each
cycle. The G ATE will be turned on again by OSC for the
next switching cycle.
The RT8461 provides several fault protections, including
input voltage Under V oltage Lockout (UVLO), Over Current
Protection (OCP) and VCC Over V oltage Protection (OVP).
Additionally , to ensure the system reli ability, 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 V oltage, VCC----------------------------------------------------------------------------------------------------- −0.3V to 40V
z SIN ---------------------------------------------------------------------------------------------------------------------------- −0.3V to 40V
z GA TE (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, P
SOP-8------------------------------------------------------------------------------------------------------------------------ 0.53W
z Package Thermal Re sistance (Note 2)
SOP-8, θJA------------------------------------------------------------------------------------------------------------------ 188 °C/W
z Junction T emperature----------------------------------------------------------------------------------------------------- 150°C
z Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------------- 260°C
z Storage T emperature Range -------------------------------------------------------------------------------------------- −65°C to 150°C
z ESD Susceptibility (Note 3)
HBM (Human Body Model)---------------------------------------------------------------------------------------------- 2kV
MM (Machine Model) ----------------------------------------------------------------------------------------------------- 200V
@ T
D
= 25°C
A
Recommended Operating Conditions
z Supply V oltage VCC------------------------------------------------------------------------------------------------------ 16V to 33V
z Junction T emperature Range-------------------------------------------------------------------------------------------- −40°C to 125°C
z Ambient T emperature Range-------------------------------------------------------------------------------------------- −40°C to 85°C
(Note 4)
Electrical Characteristics
(VCC = 24VDC, C
Inpu t Start- Up Vol tage VST 16 17 18 V
Under Voltage Lockout Threshold V
Under Voltage Lockout Threshold
Hysteresis
Inpu t Supply Curre nt ICC After Start-Up, VCC = 24V -- 2 5 mA
Inpu t Quiesc ent Current IQC Before Start-Up, VCC = 7V -- 0.1 -- μA
Oscillator
Switching Frequency fSW V
Maximum Duty in Transient
Operation
Maximum Duty in Steady State
Operation
Blanking Time t
Mini mum T urn- Off Time (Note 5) -- 650 -- n s
Current Sense Amplifier
Current Sense Voltage V
Sense Input Current I
Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
4
©
LOAD
= 1nF, R
= 2.2Ω in series, TA = 25°C, unless otherwise specified)
LOAD
Parameter Symbol Test Conditions Min Typ Max Unit
7 8 11 V
UVLO
ΔV
D
D
BLANK
SENSE
-- 2 4 V
UVLO
= 14V 38 47 52 kHz
SIN
MAX(TR)
MAX
VC = 3V -- -- 100 %
(Note 5) -- 97 -- %
-- 300 -- ns
SENSE
V
= 1V, SIN = 15V -- −100 -- mV
COMP
Sense = 100mV (Note 5) -- 10 -- μA
DS8461-01 March 2013www.richtek.com
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