目录rZb嘉泰姆

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

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

          The CXSD6289 has two synchronous buck PWM control-lers with highrZb嘉泰姆
precision internal references voltage to of-fer accurate outputs. The PWMrZb嘉泰姆
controllers are designed to drive two N-channel MOSFETs in synchronousrZb嘉泰姆
buck topology. The device requires 12V and 5V power supplies.If the 5VrZb嘉泰姆
supply is not available, the device can offer an optional shunt regulatorrZb嘉泰姆
5.8V for 5V supply.Both outputs have independent soft-start and enablerZb嘉泰姆
func-tions combined on the SS/EN pin. Connecting a capaci-tor from eachrZb嘉泰姆
SS/EN pin to the ground for setting the soft-start time, and pulling the SS/ENrZb嘉泰姆
pin voltage below 1V to disable regulator. The device also offers 180°phaserZb嘉泰姆
shift function between OUT1 and OUT2.The default switching frequency isrZb嘉泰姆
300kHz (keep the FS pin open or short to GND), and the device also providesrZb嘉泰姆
the programmable switching frequency function to ad-just the switching frequencyrZb嘉泰姆
from 70kHz to 800kHz. Con-necting a resistor from FS pin to GND increases therZb嘉泰姆
switching frequency. Conversely, connecting a resistor from FS pin to VCC12rZb嘉泰姆
decreases the switching frequency.There is no current sensing or under-voltagerZb嘉泰姆
sensing on the CXSD6289. However, it provides a simple short-circuit protection by monitoring the COMP1 pin and COMP2 pin for over-voltage. When any of two pinsrZb嘉泰姆
exceed their trip point and the condition keeps for 1-2 internal clock cycles (3-6us atrZb嘉泰姆
300kHz), all regulators are latched off.rZb嘉泰姆
二.产品特点(Features)rZb嘉泰姆

1.)Two Synchronous Buck Converters(OUT1,OUT2)rZb嘉泰姆
2.)Converter Input Voltage Range up to 12VrZb嘉泰姆
3.)0.6V Reference for OUT1 with 0.8% AccuracyrZb嘉泰姆
4.)3.3V Reference for OUT2 with 0.8% AccuracyrZb嘉泰姆
5.)Both Outputs have Independent Soft-Start andrZb嘉泰姆
    Enable FunctionsrZb嘉泰姆
6.)Internal 300kHz Oscillator and ProgrammablerZb嘉泰姆
    Frequency Range from 70 kHz to 800kHzrZb嘉泰姆
7.)180 Degrees Phase Shift etween OUT1 and OUT2rZb嘉泰姆
8.)Short-Circuit ProtectionrZb嘉泰姆
9.)Thermally Enhanced SOP-20 PackagerZb嘉泰姆
10.)Lead Free and Green Devices AvailablerZb嘉泰姆
(RoHS Compliant)rZb嘉泰姆
三,应用范围 (Applications)rZb嘉泰姆

Graphic CardsrZb嘉泰姆
Low-Voltage Distributed Power SuppliesrZb嘉泰姆
SMPS ApplicationrZb嘉泰姆
四.下载产品资料PDF文档 rZb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！rZb嘉泰姆

 rZb嘉泰姆

五,产品封装图 (Package)rZb嘉泰姆
rZb嘉泰姆

六.电路原理图rZb嘉泰姆

rZb嘉泰姆
七,功能概述rZb嘉泰姆

Output Inductor Selection (Cont.)rZb嘉泰姆
Where Fs is the switching frequency of the regulator. Al-though increase the inductor value and frequencyrZb嘉泰姆
reduce the ripple current and voltage, but there is a tradeoff ex-ists between the inductor’s ripple current andrZb嘉泰姆
the regula-tor load transient response time.A smaller inductor will give the regulator a faster load transientrZb嘉泰姆
response at the expense of higher ripple current.Increasing the switching frequency (FS) also reduces therZb嘉泰姆
ripple current and voltage, but it will increase the switch-ing loss of the MOSFET and the power dissipationrZb嘉泰姆
of the converter. The maximum ripple current occurs at the maximum input voltage. A good starting point isrZb嘉泰姆
to choose the ripple current to be approximately 30% of the maxi-mum output current.Once the inductancerZb嘉泰姆
value has been chosen, select an inductor that is capable of carrying the required peak cur-rent without goingrZb嘉泰姆
into saturation. In some types of inductors, especially core that is made of ferrite, the ripple current will increaserZb嘉泰姆
abruptly when it saturates. This will result in a larger output ripple voltage.rZb嘉泰姆
Output Capacitor SelectionrZb嘉泰姆
Higher Capacitor value and lower ESR reduce the output ripple and the load transient drop. Therefore select highrZb嘉泰姆
performance low ESR capacitors that are intended for switching regulator applications. In some applications,rZb嘉泰姆
multiple capacitors have to be parallel to achieve the de-sired ESR value. A small decoupling capacitor in parallelrZb嘉泰姆
for bypassing the noise is also recommended, and the voltage rating of the output capacitors are also must berZb嘉泰姆
considered. If tantalum capacitors are used, make sure they are surge tested by the manufactures. If in doubt,rZb嘉泰姆
consult the capacitors manufacturer.rZb嘉泰姆
Input Capacitor SelectionrZb嘉泰姆
The input capacitor is chosen based on the voltage rating and the RMS current rating. For reliable operation, rZb嘉泰姆

select the capacitor voltage rating to be at least 1.3 times higher than the maximum input voltage.rZb嘉泰姆
The maximum RMS current rating requirement is approxi-mately IOUT/2, where IOUT is the load current. rZb嘉泰姆

During power up, the input capacitors have to handle large amount of surge current. If tantalum capacitors rZb嘉泰姆

are used, make sure they are surge tested by the manufactures. If in doubt, consult the capacitors rZb嘉泰姆

manufacturer. For high frequency decoupling, a ceramic capacitor 1uF can be connected between the rZb嘉泰姆

drain of upper MOSFET and the source of lower MOSFET. rZb嘉泰姆
MOSFET SelectionrZb嘉泰姆
The selection of the N-channel power MOSFETs are de-termined by the RDS(ON), reverse transfer rZb嘉泰姆

capacitance (CRSS) and maximum output current requirement. The losses in the MOSFETs have rZb嘉泰姆

two components: conduction loss and transition loss. For the upper and lower MOSFET, the rZb嘉泰姆

losses are approximately given by the following :rZb嘉泰姆
PUPPER=IOUT(1+TC)(RDS(ON))D+(0.5)(IOUT)(VIN)(tSW)FSrZb嘉泰姆
PLOWER=IOUT(1+TC)(RDS(ON))(1-D)rZb嘉泰姆
Where I is the load current OUT TC is the temperature dependency of RDS(ON) F is the switchingrZb嘉泰姆

 frequency St is the switching interval sw D is the duty cycle Note that both MOSFETs have rZb嘉泰姆

conduction losses while the upper MOSFET include an additional transition loss.The switching rZb嘉泰姆

internal, tsw, is a function of the reverse transfer capacitance CRSS. The (1+TC) term is to rZb嘉泰姆

factor in the temperature depen-dency of the RDS(ON) and can be extracted from the “RDS(ON)rZb嘉泰姆
vs Temperature” curve of the power MOSFET.rZb嘉泰姆
Short Circuit ProtectionrZb嘉泰姆
The CXSD6289 provides a simple short circuit protection function, and it is not easy to predict itsrZb嘉泰姆

 performance, since many factors can affect how well it works. Therefore, the limitations and rZb嘉泰姆

suggestions of this method must be pro-vided for users to understand how to work it well.TherZb嘉泰姆

 short circuit protection was not designed to work for the output in initial short condition. In this rZb嘉泰姆

case, the short circuit protection may not work, and damage the MOSFETs. If the circuit still works,rZb嘉泰姆

 remove the short can cause an inductive kick on the phase pin, and it may damage the IC and rZb嘉泰姆

MOSFETs.  If the resistance of the short is not low enough to cause protection, the regulator willrZb嘉泰姆

 work as the load hasrZb嘉泰姆

Short Circuit Protection (Cont.)rZb嘉泰姆
increased, and continue to regulate up until the MOSFETs is damaged. The resistance of the shortrZb嘉泰姆

 should include wiring, PCB traces, contact resistances, and all of the return paths.The higher duty rZb嘉泰姆

cycle will give a higher COMP voltage level, and it is easy to touch the trip point. The compensa-rZb嘉泰姆
tion components also affect the response of COMP voltage; smaller caps may give a faster response.rZb嘉泰姆
The output current has faster rising time during short;the COMP pin will have a sharp rise. However,rZb嘉泰姆

 if the cur-rent rises too fast, it may cause a false trip. The output capacitance and its ESR can affectrZb嘉泰姆

 the rising time of the current during short.rZb嘉泰姆

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