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Product Specification
Highly Integrated Green-Mode PWM Controller
OPERATION DESCRIPTION
Start-up Current
SG5842A/JA
System General Corp.
Version 1.4.2 (IAO33.0026.B6)
- 9 -
www.sg.com.tw www.fairchildsemi.com
October 30, 2007
The typical start-up current is only 14μA, which allows a
high-resistance, low-wattage start-up resistor to be used to
minimize power loss. A 1.5M
Ω
, 0.25W, start-up resistor
and a 10μF/25V V
DD
hold-up capacitor are sufficient for an
AC/DC adapter with a universal input range.
Operating Current
The required operating current has been reduced to 4mA.
This results in higher efficiency and reduces the V
DD
hold-up capacitance requirement.
Green-Mode Operation
The proprietary green-mode function provides off-time
modulation to continuously decrease the PWM frequency
under light-load conditions. To avoid acoustic noise
problems, the minimum PWM frequency is set above
22KHz. This green-mode function dramatically reduces
power consumption under light-load and zero-load
conditions. Power supplies using a SG5842A/JA
controller can meet even the most restrictive international
regulations regarding standby power consumption.
Oscillator Operation
A resistor connected from the RI pin to the GND pin
generates a constant current source for the SG5842A/JA
controller. This current is used to determine the center
PWM frequency. Increasing the resistance reduces PWM
frequency. Using a 26K
Ω
resistor, R
I
, results in a
corresponding 65KHz PWM frequency. The relationship
between R
I
and the switching frequency is:
(KHz)
1690
)
(K
R
Ω
=
PWM
f
----------------------------
(1)
The range of the PWM oscillation frequency is designed
as 47KHz ~ 109KHz.
SG5842JA also integrates frequency hopping function
internally. The frequency variation ranges from around
62KHz to 68KHz for a center frequency of 65KHz. The
frequency hopping function helps reduce EMI emission
of a power supply with minimum line filters.
Leading-Edge Blanking
Each time the power MOSFET is switched on, a turn-on
spike occurs 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 cannot switch off
the gate drive.
Under-Voltage Lockout (UVLO)
The turn-on/turn-off thresholds are fixed internally at
16.5V/10.5V. To enable a SG5842A/JA controller during
start-up, the hold-up capacitor must first be charged to
16.5V through the start-up resistor.
The hold-up capacitor continues to supply V
DD
before
energy can be delivered from the auxiliary winding of the
main transformer. V
DD
must not drop below 10.5V during
this start-up process. This UVLO hysteresis window
ensures that the hold-up capacitor can adequately supply
V
DD
during start-up.
Gate Output / Soft Driving
The SG5842A/JA BiCMOS output stage is a fast totem
pole gate driver. Cross-conduction has been avoided to
minimize heat dissipation, increase efficiency, and
enhance reliability. The output driver is clamped by an
internal 18V Zener diode to protect the power MOSFET
transistors from any harmful over-voltage gate signals. A
soft driving waveform is implemented to minimize EMI.
Slope Compensation
The sensed voltage across the current sense resistor is
used for peak-current-mode control and cycle-by-cycle
current limiting. The built-in slope compensation
function improves power supply stability and prevents
peak-current-mode control from causing sub-harmonic
oscillations.
Within every switching cycle,
SG5842A/JA controller produces a positively sloped,
synchronized ramp signal.
the
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| SG5842JADZ | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 BiCMOS Green-Mode PWM Controller RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| SG5842JASY | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 HI-INTEGRD GRN-MODE PWM CONTROLLER RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| SG5842JASZ | 功能描述:IC REG CTRLR FLYBK ISO PWM 8-SOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
| SG5842JDSY | 功能描述:電流型 PWM 控制器 HI-INTEGRD GRN-MODE PWM CONTROLLER RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| SG5842JDSZ | 制造商:Rochester Electronics LLC 功能描述: 制造商:Fairchild Semiconductor Corporation 功能描述: |
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