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PDF SG6846B Data sheet ( Hoja de datos )
| Número de pieza | SG6846B | |
| Descripción | Highly Integrated Green-Mode PWM Controller | |
| Fabricantes | Fairchild Semiconductor | |
| Logotipo |  |
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www.DataSheet4U.com
October 2008
SG6846B
Highly Integrated Green-Mode PWM Controller
Features
Low Startup Current: 8µA
Low Operating Current: 3.7mA
Peak-Current Mode Operation with Cycle-by-cycle
Current Limiting
PWM Frequency Continuously Decreasing with
Burst Mode at Light Loads
VDD Over Voltage Protection (OVP)
AC Input Brownout Protection with Hysteresis
Constant Output Power Limit (Full AC Input Range)
Internal Latch Circuit for OVP, OTP, and OCP
(BLSY, BLSZ)
Two-level OCP Delay with 200ms
Programmable PWM Frequency with Frequency
Hopping
OCP Threshold is 2/3 Peak Current Limit
Soft Startup Time: 5ms
Applications
General-purpose switch-mode power supplies and
flyback power converters, including:
Power Adapters
Open-frame SMPS
SMPS with Surge-current Output, such as for
Printers, Scanners, Motor Drivers
Description
The highly integrated PWM controller, SG6846B,
provides several features to enhance the performance
of fly-back converters. To minimize standby power
consumption, a proprietary green-mode function
provides off-time modulation to continuously decrease
the switching frequency under light-load conditions.
Under zero-load conditions, the power supply enters
burst-mode. This completely shuts off PWM output. If
VFB is larger than around 1.6V, PWM pulses out. This
green-mode function enables power supplies to meet
international power conservation requirements.
The SG6846B is designed for SMPS with surge-current
output. It is incorporated with a two-level OCP function.
Besides, the cycle-by-cycle current limiting, if the
switching current is higher than OCP threshold and
lasts for 200ms, SG6846B stops gate immediately and
latches itself (BLSY version) or restarts after VDD
charges up to 16.5V (BCSY version). SG6846B also
integrates frequency-hopping function internally. The
frequency hopping function helps reduce EMI emission
of a power supply with minimum line filters. It has built-
in synchronized slope compensation, proprietary
internal compensation for constant output power limit
over universal AC input range. The gate output is
clamped at 18V to protect the external MOSFET from
over-voltage damage.
Protection include: AC input brownout protection with
hysteresis and VDD over-voltage protection. For over-
temperature protection, an external NTC thermistor can
be applied to sense the ambient temperature. When
OCP, VDD OVP, or OTP are activated, an internal latch
circuit is used to latch-off the controller. The latch resets
when VDD supply is removed.
SG6846B is available in 8-pin SOP package.
Ordering Information
Part Operating
Number Temperature Range
SG6846BLSY
SG6846BLSZ
SG6846BCSY
-40 to +105°C
-40 to +105°C
-40 to +105°C
SG6846BCSZ
-40 to +105°C
OCP
Latch
Yes
Yes
No
No
Eco
Status
Green
RoHS
Green
RoHS
Package
Packing
Method
8-Pin Small Outline Package (SOP)
8-Pin Small Outline Package (SOP)
8-Pin Small Outline Package (SOP)
Tape & Reel
Tape & Reel
Tape & Reel
8-Pin Small Outline Package (SOP) Tape & Reel
For Fairchild’s definition of “green” Eco Status, please visit: http://www.fairchildsemi.com/company/green/rohs_green.html.
© 2008 Fairchild Semiconductor Corporation
SG6846B • Rev. 1.3.3
www.fairchildsemi.com
1 page  
Absolute Maximum Ratings
wwwS.DtraetsasSehseeet4xUc.eceodming the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device
reliability. The absolute maximum ratings are stress ratings only. All voltage values, except differential voltages, are
given with respect to GND pin.
Symbol
Parameter
VDD
VL
PD
ΘJC
TJ
TSTG
TL
ESD
Supply Voltage
Input Voltage to FB, SENSE, VIN, RT, RI Pins
Power Dissipation at TA<50°C
Thermal Resistance (Junction-to-Case)
SOP
SOP
Operating Junction Temperature
Storage Temperature Range
Lead Temperature, Wave Soldering, 10 Seconds
Human Body Model, JESD22-A114
Charge Device Model, JESD22-C101
Min.
-0.3
-40
-65
Max.
30
7.0
400
54.4
+150
+150
+260
5.0
1.5
Unit
V
V
mW
°C/W
°C
°C
°C
kV
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended
operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not
recommend exceeding them or designing to Absolute Maximum Ratings.
Symbol
Parameter
TA Operating Ambient Temperature
Min.
-40
Max.
+105
Unit
°C
© 2008 Fairchild Semiconductor Corporation
SG6846B • Rev. 1.3.3
5
www.fairchildsemi.com
5 Page 
Operation Description
www.DataSheet4U.com
Startup Operation
The turn-on/turn-off thresholds are fixed internally at
16.5V and 10.5V. To enable the SG6846B during
startup, the hold-up capacitor must first be charged to
16.5V through the startup resistor.
If an open-circuit or short-circuit to ground occurs at the
RI pin, the internal protection circuit immediately shuts
down the controller.
The hold-up capacitor continues to supply VDD before
energy can be delivered from the auxiliary winding of
the main transformer. The VDD must not drop below
10.5V during this startup process. This UVLO hysteresis
window ensures that the hold-up capacitor can
adequately supply VDD during startup.
The typical startup current is only 8µA, which allows a
high-resistance, low-wattage startup resistor to be used.
For constant output power limit over a universal input-
voltage range, the peak-current threshold is adjusted by
the voltage of the VIN pin. Since the VIN pin is
connected to the rectified AC input line voltage through
the resistive divider, a higher line voltage generates a
higher VIN voltage. The threshold voltage decreases as
the VIN increases, making the maximum output power at
high line input voltage equal to that at low line input.
The value of R-C network should not be so large it
affects the power limit (shown in Figure 20). R and C
should put on less than 300Ω and 1000pF, respectively,
to minimize power loss. A 1.5MΩ/0.25W startup resistor
and a 10µF/25V VDD hold-up capacitor are sufficient for
a universal input range.
The required operating current has been reduced to
3.7mA, which enables higher efficiency and reduces the
VDD hold-up capacitance requirement.
Green-Mode Operation
The proprietary green-mode function provides off-time
modulation to continuously decrease the switching
frequency under light-load conditions. Maximum on-time
is limited to provide protection against abnormal
conditions. To further reduce power consumption under
zero-load condition, the PWM oscillator is completely
turned off and the power supply enters burst-mode.
Green mode dramatically reduces power consumption
under light-load and zero-load conditions. Power
supplies using SG6846B can meet restrictive
international regulations regarding standby power
consumption.
Oscillator Operation
A resistor connected from the RI pin to GND generates
a internal reference current source used to determine
the PWM frequency. Increasing the resistance
decreases the amplitude of the current source and
reduces the PWM frequency. Using a 26kΩ resistor
results in a corresponding 65kHz switching frequency.
The relationship between RI and the switching
frequency is:
fPWM(kHz) =
1690
RI (kΩ)
(2)
If an open-circuit or short-circuit to ground occurs at the
RI pin, the internal protection circuit immediately shuts
down the controller.
Two-level Over-current Protection (OCP)
The cycle-by-cycle current limiting shuts down the PWM
immediately when the switching current is over the
peak-current threshold. Additionally, when the switching
current is higher than over-current threshold, the internal
counter counts down. When the total accumulated
counting time is more than ~200ms (RI = 26kΩ), the
controller is latched off and the internal counter counts
up. When the switching current is lower than over-
current threshold, the internal counter counts down.
When the total accumulated counting time is more than
~200ms (RI = 26kΩ), the controller is latched off.
This two-level OCP protection and up/down counter are
especially designed for SMPS with surge current output,
such as those for printers, scanners, and motor drivers.
Constant Output Power Limit
For constant output power limit over universal input-
voltage range, the peak-current threshold is adjusted by
the voltage of the VIN pin. Since the VIN pin is
connected to the rectified AC input line voltage through
the resistive divider, a higher line voltage generates a
higher VIN voltage. The threshold voltage decreases as
VIN increases, making the maximum output power at
high-line input voltage equal to that at low-line input.
Brownout Protection
Since the VIN pin is connected through a resistive
divider to the rectified AC input line voltage, it can also
be used for brownout protection. If the VIN voltage is
less than 0.7V, the PWM output is shut off. If the VIN is
over 0.9V, the PWM output is turned on again. The
hysteresis window for on/off is ~0.2V.
VDD Over-voltage Protection (OVP)
VDD over-voltage protection is built in to prevent
damage. If VDD is over 24V, SG6846B is latched off.
Over-Temperature Protection (OTP)
An external NTC thermistor can be connected from the
RT pin to GND. The impedance of the NTC decreases
at high temperatures. When the voltage of the RT pin
drops below 1.05V, the SG6846B is turned off. For
protection-mode options, see Ordering Information.
© 2008 Fairchild Semiconductor Corporation
SG6846B • Rev. 1.3.3
11
www.fairchildsemi.com
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet SG6846B.PDF ] | |
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