Richtek RT8461ZS Schematic [ru]

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Richtek RT8461ZS Schematic

®

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

ZSYMDNN

 

 

 

Simplified Application Circuit

AC IN

+

 

 

 

 

 

 

 

D1

~

 

Rstart

 

 

 

 

 

 

 

 

 

 

 

 

 

-

 

 

 

 

 

 

 

 

 

 

 

VCC

RT8461

 

 

 

 

 

 

 

 

 

 

 

R1

 

 

 

 

 

 

 

 

R2

 

 

 

SIN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

C2

 

 

 

FB

 

GATE

M1

 

 

 

 

 

 

ICOMP

 

 

 

 

 

R3

C3

 

 

VCOMP

 

 

 

 

R4

R5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

C4

C5

SENSE

GND

RS

L

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VOUT

 

 

 

 

 

 

 

 

D2

C1

 

 

 

 

 

 

 

 

 

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8461-01 March 2013

www.richtek.com

 

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

 

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

 

 

 

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.

 

 

 

 

 

Output Voltage Sense. The Output voltage is sensed through an external resistor

5

FB

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

6

ICOMP

output signal is modulated with the sensed input voltage through the SIN pin by an

 

 

internal multiplier. A compensation capacitor between ICOMP and GND is needed.

7

SIN

Input Power Voltage Sensing for PFC Function. An external resistor for input

voltage sensing is connected to the power input.

 

 

8

VCOMP

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.

www.richtek.com

DS8461-01 March 2013

2

RT8461

Function Block Diagram

 

+

Chip

 

 

 

+

-

Enable

 

 

 

VCC

16V/8V

 

 

 

12V

 

 

 

 

 

 

 

 

 

 

OVP

OSC

S

Q

GATE

35V

+

 

R

 

200k

-

 

 

PWM

R

 

 

GND

 

 

 

 

Control

 

 

SENSE

 

 

Circuit

 

 

 

ICOMP

 

 

 

 

 

VCOMP

 

PFC

 

 

 

1.2V

+

 

 

 

Control

 

 

SIN

FB

 

 

-

Circuit

 

 

 

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

 

SOP-8 ------------------------------------------------------------------------------------------------------------------------

0.53W

z Package Thermal Resistance (Note 2)

 

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)

 

HBM (Human Body Model) ----------------------------------------------------------------------------------------------

2kV

MM (Machine Model) -----------------------------------------------------------------------------------------------------

200V

Recommended Operating Conditions

(Note 4)

 

 

 

 

 

z Supply Voltage VCC ------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

16V to 33V

z Junction Temperature Range --------------------------------------------------------------------------------------------

 

 

 

 

 

 

−40°C to 125°C

z Ambient Temperature Range --------------------------------------------------------------------------------------------

 

 

 

 

 

 

−40°C to 85°C

Electrical Characteristics

 

 

 

 

 

 

 

 

(VCC = 24VDC, CLOAD = 1nF, RLOAD = 2.2Ω in series, TA = 25°C, unless otherwise specified)

 

 

 

 

 

Parameter

Symbol

 

Test Conditions

 

Min

Typ

Max

 

Unit

Input Start-Up Voltage

VST

 

 

 

16

17

18

 

V

Under Voltage Lockout Threshold

VUVLO

 

 

 

7

8

11

 

V

Under Voltage Lockout Threshold

VUVLO

 

 

 

--

2

4

 

V

Hysteresis

 

 

 

 

Input Supply Current

ICC

After Start-Up, VCC = 24V

 

--

2

5

 

mA

Input Quiescent Current

IQC

Before Start-Up, VCC = 7V

 

--

0.1

--

 

μA

Oscillator

 

 

 

 

 

 

 

 

 

Switching Frequency

fSW

VSIN = 14V

 

38

47

52

 

kHz

Maximum Duty in Transient

DMAX(TR)

VC = 3V

 

 

--

--

100

 

%

Operation

 

 

 

 

 

 

 

 

 

 

 

 

Maximum Duty in Steady State

DMAX

(Note 5)

 

 

--

97

--

 

%

Operation

 

 

 

 

 

 

 

 

 

 

 

 

Blanking Time

tBLANK

 

 

 

--

300

--

 

ns

Minimum Turn-Off Time

 

(Note 5)

 

 

--

650

--

 

ns

Current Sense Amplifier

 

 

 

 

 

 

 

 

 

Current Sense Voltage

VSENSE

VCOMP = 1V, SIN = 15V

 

--

−100

--

 

mV

Sense Input Current

ISENSE

Sense = 100mV (Note 5)

 

--

10

--

 

μA

 

 

 

 

 

 

 

 

 

 

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

 

www.richtek.com

 

 

 

 

 

DS8461-01 March 2013

4

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