CXSD6289两个同步降压型脉宽调制控制器脉冲宽度调制控制器设计用于同步驱动两个N通道mosfet buck拓扑

目录rsS嘉泰姆

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

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

          The CXSD6289 has two synchronous buck PWM control-lers with highrsS嘉泰姆
precision internal references voltage to of-fer accurate outputs. The PWMrsS嘉泰姆
controllers are designed to drive two N-channel MOSFETs in synchronousrsS嘉泰姆
buck topology. The device requires 12V and 5V power supplies.If the 5VrsS嘉泰姆
supply is not available, the device can offer an optional shunt regulatorrsS嘉泰姆
5.8V for 5V supply.Both outputs have independent soft-start and enablersS嘉泰姆
func-tions combined on the SS/EN pin. Connecting a capaci-tor from eachrsS嘉泰姆
SS/EN pin to the ground for setting the soft-start time, and pulling the SS/ENrsS嘉泰姆
pin voltage below 1V to disable regulator. The device also offers 180°phasersS嘉泰姆
shift function between OUT1 and OUT2.The default switching frequency isrsS嘉泰姆
300kHz (keep the FS pin open or short to GND), and the device also providesrsS嘉泰姆
the programmable switching frequency function to ad-just the switching frequencyrsS嘉泰姆
from 70kHz to 800kHz. Con-necting a resistor from FS pin to GND increases thersS嘉泰姆
switching frequency. Conversely, connecting a resistor from FS pin to VCC12rsS嘉泰姆
decreases the switching frequency.There is no current sensing or under-voltagersS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 pinsrsS嘉泰姆
exceed their trip point and the condition keeps for 1-2 internal clock cycles (3-6us atrsS嘉泰姆
300kHz), all regulators are latched off.rsS嘉泰姆
二.产品特点(Features)rsS嘉泰姆

1.)Two Synchronous Buck Converters(OUT1,OUT2)rsS嘉泰姆
2.)Converter Input Voltage Range up to 12VrsS嘉泰姆
3.)0.6V Reference for OUT1 with 0.8% AccuracyrsS嘉泰姆
4.)3.3V Reference for OUT2 with 0.8% AccuracyrsS嘉泰姆
5.)Both Outputs have Independent Soft-Start andrsS嘉泰姆
    Enable FunctionsrsS嘉泰姆
6.)Internal 300kHz Oscillator and ProgrammablersS嘉泰姆
    Frequency Range from 70 kHz to 800kHzrsS嘉泰姆
7.)180 Degrees Phase Shift etween OUT1 and OUT2rsS嘉泰姆
8.)Short-Circuit ProtectionrsS嘉泰姆
9.)Thermally Enhanced SOP-20 PackagersS嘉泰姆
10.)Lead Free and Green Devices AvailablersS嘉泰姆
(RoHS Compliant)rsS嘉泰姆
三,应用范围 (Applications)rsS嘉泰姆

Graphic CardsrsS嘉泰姆
Low-Voltage Distributed Power SuppliesrsS嘉泰姆
SMPS ApplicationrsS嘉泰姆
四.下载产品资料PDF文档 rsS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！rsS嘉泰姆

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五,产品封装图 (Package)rsS嘉泰姆
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六.电路原理图rsS嘉泰姆

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七,功能概述rsS嘉泰姆

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 work as the load hasrsS嘉泰姆

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

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

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

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

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

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