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PDF CR6842 Data sheet ( Hoja de datos )
| Número de pieza | CR6842 | |
| Descripción | Green Power PWM Controller | |
| Fabricantes | Chip Rail | |
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 1. - Green Power PWM Controller  Hay una vista previa y un enlace de descarga de CR6842 (archivo pdf) en la parte inferior de esta página. Total 9 Páginas | ||
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CR6842
Green-Power PWM Controller with Freq. Jittering
Features
z Low Cost, Green-Power Burst-Mode PWM
z Very Low Start-up Current ( about 7.5µA)
z Low Operating Current ( about 3.0mA)
www.DataSheet4U.zcom Current Mode Operation
z Under Voltage Lockout (UVLO)
z VDD Over Voltage Protection(OVP)
z programmable over-temperature protection
z Internal Latch Circuit(OTP,OVP)
z Built-in soft start with 1ms
z Built-in Frequency jitter for better EMI Signature
z Soft Clamped gate output voltage 16.5V
z VDD over voltage protect 25.5V
z Cycle-by-cycle current limiting
z Sense Fault Protection
z Output SCP (Short circuit Protection)
z Built-in Synchronized Slope Compensation
z Leading-edge blanking on Sense input
z Programmable PWM Frequency
z High-Voltage CMOS Process with ESD
z DIP-8 & SOP-8 Pb-Free Package
z Compatible with SG6842J&LD7552&OB2269
Applications
z Power Adaptor
z Battery Charger Adapter
z Open Frame Switching Power Supply
z LCD Monitor
General Description
The CR6842 is a low startup current , low cost, current
mode PWM controller with Green-Power & burst-mode
power-saving operation. The integrated functions such as
the leading-edge blanking of the current sensing, internal
slope compensation provide the users a high efficiency,
low external component counts, and low cost solution for
AC/DC power applications. The special Green-Power
function provides off-time modulation to linearly decrease
the switching frequency under light-load conditions. And
under zero-load conditions, the power supply enters
burst-mode to further reduce power consumption by
shutting off PWM output. When the output of power
supply is short or over loaded, the FB voltage will
increase ,and if the FB voltage is higher than 5.2V for
longer than 56msec the PWM output will be turned off. A
external NTC resistor connected from pin RT to ground
can be applied to over-temperature protection. Pulse by
pulse current limit ensures a constant output current even
under short circuit. PWM output will be disabled as long
as VDD exceeds a threshold. When internal latch circuit is
used to latch-off the controller, the latch will be reset when
the power supply VDD is disabled.
Dec.2006 V 1.3
Chengdu Chip-Rail Tech.Co.,Ltd
1
1 page  
CR6842
OPERATION DESCRIPTION
Start-Up Current & Operating Current
The typical start-up current is only 8µA. This allows a high resistance, low-wattage start-up resistor to
be used, to minimize power loss. A 1.5MOhms, 0.25W, start-up resistor and a 10µF/40V VDD hold-up
capacitor would be sufficient for an AC/DC adapter with a universal input range.
The required operating current has been reduced to 3.4mA. This results in higher efficiency and
www.DataSheet4U.rceodmuces the VDD hold-up capacitance requirement.
Green-Power Mode Operation
The proprietary green-power mode function provides off-time modulation to continuously decrease the
PWM frequency under light-load conditions. To avoid acoustic-noise problem, the minimum PWM
frequency set above 25KHz. This green-power mode function dramatically reduces power consumption
under light-load and zero-load conditions. Power supplies using a CR6842 controller can easily meet even
the most restrictive international regulations regarding standby power consumption.
Oscillator Operation
A resistor connected from the RI pin to GND pin generates a constant current source for the CR6842
controller. This current is used to determine the center PWM frequency. Increasing the resistance will
reduce PWM frequency. Using a 26KΩ resistor RI results in a corresponding 67KHz PWM frequency. The
relationship between RI and the switching frequency is:
f PWM
=
1742 (KHz)
RI (KΩ)
CR6842 also integrates frequency jittering function internally. The frequency variation ranges from
around 63KHz to 70KHz for a center frequency 67kHz. The frequency jittering function helps reduce EMI
emission of a power supply with minimum line filters.
I RT
=
70µA * 26
RI (KΩ)
Leading Edge Blanking
Each time the power MOSFET is switched on, a turn-on spike will inevitably occur at the sense-resistor.
To avoid premature termination of the switching pulse, a leading-edge blanking time is built in. During this
blanking period, the current-limit comparator is disabled, and it cannot switch off the gate drive.
Under-Voltage Lockout (UVLO)
The turn-on/turn-off thresholds are fixed internally at 12.4V/16.5V. To enable a CR6842 controller
during start-up, the hold-up capacitor must first be charged to 16.5V through the start-up resistor.
The hold-up capacitor will continue to supply VDD before energy can be delivered from the auxiliary
winding of the main transformer. VDD must not drop below 12.4V during this start-up process. This UVLO
Dec.2006 V 1.3
Chengdu Chip-Rail Tech.Co.,Ltd
5
5 Page | ||
| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet CR6842.PDF ] | |
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