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目录fjM嘉泰姆

1.产品概述                       2.产品特点fjM嘉泰姆
3.应用范围                       4.下载产品资料PDF文档 fjM嘉泰姆
5.产品封装图                     6.电路原理图                   fjM嘉泰姆
7.功能概述                        8.相关产品fjM嘉泰姆

一,产品概述(General Description)      fjM嘉泰姆

                The CXSD6279B is a voltage mode and synchronous PWM controllerfjM嘉泰姆
which drives dual N-Channel MOSFETs. It inte-grates the control, monitoring,fjM嘉泰姆
and protection functions into a single package, provides one controlled powerfjM嘉泰姆
outputs with under-voltage and over-current protection.CXSD6279B providesfjM嘉泰姆
excellent regulation for output load variation. An internal 0.8V temperature-fjM嘉泰姆
compensated reference voltage is designed to meet the requirement offjM嘉泰姆
low output voltage applications. It includes a 200kHz free-runningfjM嘉泰姆
triangle-wave oscillator that is adjustable from 70kHz to 800kHz.fjM嘉泰姆
        The power-on-reset (POR) circuit monitors the VCC, EN,and OCSETfjM嘉泰姆
input voltage to start-up or shutdown the IC.The over-current protection (OCP)fjM嘉泰姆
monitors the output current by using the voltage drop across the upperfjM嘉泰姆
MOSFET’s RDS(ON), eliminating the need for a current sens-ing resistor.fjM嘉泰姆
The under-voltage protection (UVP) moni-tors the voltage of the FB pin forfjM嘉泰姆
short-circuit protection.The over-current protection trip cycle the soft-startfjM嘉泰姆
func-tion until the fault events be removed. Under-voltage pro-tection willfjM嘉泰姆
shutdown the IC directly.fjM嘉泰姆
二.产品特点(Features)fjM嘉泰姆

1.)Simple Single-Loop Control DesignfjM嘉泰姆
   Voltage-Mode PWM ControlfjM嘉泰姆
2.)Fast Transient ResponsefjM嘉泰姆
    Full 0–100% Duty RatiofjM嘉泰姆
3.)Excellent Output Voltage RegulationfjM嘉泰姆
   0.8V Internal ReferencefjM嘉泰姆
    ± 1% Over Line Voltage and TemperaturefjM嘉泰姆
4.)Over Current Fault MonitorfjM嘉泰姆
   Uses Upper MOSFETs RDS (ON)fjM嘉泰姆
5.)Converter Can Source and Sink CurrentfjM嘉泰姆
6.)Small Converter SizefjM嘉泰姆
    200kHz Free-Running OscillatorfjM嘉泰姆
   Programmable from 70kHz to 800kHzfjM嘉泰姆
7.)14-Lead SOIC PackagefjM嘉泰姆
8.)Lead Free and Green Devices Available (RoHS Compliant)fjM嘉泰姆
三,应用范围 (Applications)fjM嘉泰姆

Graphic CardsfjM嘉泰姆
DDR Memory Power SupplyfjM嘉泰姆
DDR Memory Termination VoltagefjM嘉泰姆
Low-Voltage Distributed Power SuppliesfjM嘉泰姆
四.下载产品资料PDF文档 fjM嘉泰姆

需要详细的PDF规格书请扫一扫微信联系我们，还可以获得免费样品以及技术支持！fjM嘉泰姆

 fjM嘉泰姆

五,产品封装图 (Package)fjM嘉泰姆

fjM嘉泰姆
RT (Pin1)fjM嘉泰姆
This pin can adjust the switching frequency. Connect a resistor from the RT to the GND for increasing the switch-fjM嘉泰姆
OCSET (Pin2)fjM嘉泰姆
This pin serves two functions: a shutdown control and the setting of over current-limit threshold. Pulling this pinfjM嘉泰姆
below 1.27V will shutdown the controller, forcing the UGATE and LGATE signals to be at 0V.fjM嘉泰姆
A resistor (Rocset) connected between this pin and the drain of the high side MOSFET will determine the over fjM嘉泰姆

current limit. An internal 200μA current source will flow through this resistor, creating a voltage drop, which fjM嘉泰姆

will be com-pared with the voltage across the high side MOSFET.fjM嘉泰姆
SS (Pin3)fjM嘉泰姆
Connect a capacitor from the pin to the GND to set the soft-start interval of the converter. An internal 10μA fjM嘉泰姆

current source charges this capacitor to 5.8V. The SS voltage clamps the error amplifier output, and Figure1fjM嘉泰姆

 shows the soft-start interval. At t1, the SS voltage reaches the valley of the oscillator’s triangle wave. ThefjM嘉泰姆

PWM comparator starts to generate a PWM signal to control logic, and thefjM嘉泰姆
COMP (Pin4)fjM嘉泰姆
This pin is the output of the error amplifier. Add an exter-nal resistor and capacitor network to provide thefjM嘉泰姆

 loop com- pensation for the PW M converter (see Application Information).fjM嘉泰姆
FB (Pin5)fjM嘉泰姆
FB pin is the inverter input of the error amplifier and it receives the feedback voltage from an external fjM嘉泰姆

resis-tive divider across the output (V OUT). The output voltage is determined by:fjM嘉泰姆
EN (Pin6)fjM嘉泰姆
Pull the pin higher than 2V to enable the device, and pull the pin lower than 0.8V to shutdown the fjM嘉泰姆

device. In shutdown, the SS is discharged and the UGATE and LGATE pins are held low. The EN pin fjM嘉泰姆

is the open-collector, and it will not be floating. fjM嘉泰姆
GND (Pin7)fjM嘉泰姆
Signal ground for the IC. fjM嘉泰姆
PHASE (Pin8)fjM嘉泰姆
This pin is connected to the source of the high-side MOSFET and is used to monitor the voltage dropfjM嘉泰姆

 across the high-side MOSFET for over-current protection. fjM嘉泰姆
UGATE (Pin9)fjM嘉泰姆
Connect the pin to external MOSFET, and provides the gate drive for the upper MOSFET.fjM嘉泰姆

BOOT (Pin 10)fjM嘉泰姆
This pin provides the supply voltage to the high side MOSFET driver. For driving logic level N-channel fjM嘉泰姆

MOSEFT,a bootstrap circuit can be used to create a suitable driver’s supply. fjM嘉泰姆
PGND (Pin11)fjM嘉泰姆
Power ground for the gate diver. Connect the lower MOSFET source to this pin. fjM嘉泰姆
LGATE (Pin 12)fjM嘉泰姆

Connect the pin to the external MOSFET, and provides the gate drive signal for the lower MOSFET.fjM嘉泰姆
PVCC (Pin13)fjM嘉泰姆
This pin provides a supply voltage for the lower gate drive, connect it to the VCC pin in common use. fjM嘉泰姆
VCC (Pin14)fjM嘉泰姆
This pin provides a supply voltage for the device. When the VCC is above the rising threshold 10.4V, fjM嘉泰姆

the device is turned on; conversely, when the VCC is below the falling threshold, the device is turned off.fjM嘉泰姆
六.电路原理图fjM嘉泰姆

fjM嘉泰姆
七,功能概述fjM嘉泰姆

Output Capacitor SelectionfjM嘉泰姆
The selection of COUT is determined by the required effec-tive series resistance (ESR) and voltage ratingfjM嘉泰姆

 rather than the actual capacitance requirement. Therefore, select highperformance low ESR capacitors fjM嘉泰姆

that are intended for switching regulator applications. In some applications,multiple capacitors have tofjM嘉泰姆

 be paralled to achieve the desired ESR value. If tantalum capacitors are used, makesure they are surgefjM嘉泰姆

 tested by the manufactures. If in doubt,consult the capacitors manufacturer.fjM嘉泰姆
 Input Capacitor SelectionfjM嘉泰姆
The input capacitor is chosen based on the voltage rating and the RMS current rating. For reliable fjM嘉泰姆

operation, select the capacitor voltage rating to be at least 1.3 times higher than the maximum inputfjM嘉泰姆

 voltage. The maximum RMS current rating requirement is approximately IOUT/2 , where IOUT is the fjM嘉泰姆

load current. During power up, the input capaci-tors have to handle large amount of surge current.fjM嘉泰姆

 If tanta-lum capacitors are used, make sure they are surge tested by the manufactures. If in doubt, fjM嘉泰姆

consult the capacitors manufacturer.For high frequency decoupling, a ceramic capacitor be-tweenfjM嘉泰姆

 0.1μF to 1μF can be connected between the VCC and the ground pin.fjM嘉泰姆
Inductor SelectionfjM嘉泰姆
The inductance of the inductor is determined by the out-put voltage requirement. The larger the fjM嘉泰姆

inductance, the lower the inductor’s current ripple. This will translate into lower output ripple voltage.fjM嘉泰姆

 The ripple current and ripple voltage can be approximated by:fjM嘉泰姆
where Fs is the switching frequency of the regulator.There is a tradeoff exists between the inductor’sfjM嘉泰姆

 ripple current and the regulator load transient response time. A smaller inductor will give the regulator fjM嘉泰姆

a faster load tran-sient response at the expense of higher ripple current and vice versa. The maximumfjM嘉泰姆

 ripple current occurs at the maximum input voltage. A good starting point is to choose the ripple fjM嘉泰姆

current to be approximately 30% of the maxi-mum output current.Once the inductance value has fjM嘉泰姆

been chosen, select an inductor that is capable of carrying the required peak cur-rent without going fjM嘉泰姆

into saturation. In some types of inductors, especially core that is make of ferrite, the ripplefjM嘉泰姆
current will increase abruptly when it saturates. This will result in a larger output ripple voltage.fjM嘉泰姆
CompensationfjM嘉泰姆
The output LC filter introduces a double pole, which con-tributes with –40dB/decade gain slope and fjM嘉泰姆

180 degrees phase shift in the control loop. A compensation network between the COMP pin and the fjM嘉泰姆

ground should be added. The simplest loop compensation network is shown infjM嘉泰姆
Figure 5.fjM嘉泰姆
The output LC filter consists of the output inductor and output capacitors. The transfer function offjM嘉泰姆

 the LC filter is given by:fjM嘉泰姆
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