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CXSD62679 high voltage and high current step-down chip: the core scheme of innovating electric vehicle power supply system

In the field of electric vehicle power supply design,CXSD62679 high voltage step-down chipWith its 600V input capability and synchronous rectification technology, it is becoming the preferred solution for electric bicycle/motorcycle converters. This SOP16 packaged DC-DC power management chip integrates multiple protection mechanisms and flexible frequency configuration functions to provide high reliability support for high-voltage and high-current applications.uDi嘉泰姆

1. Core Characteristics and Technological Innovation

1. High voltage and high current support:Internal integrated half-bridge drive circuit, with external MOS tube can withstand up600V input voltageThe output current is up to 10A (typical application) to meet the stringent power supply requirements of electric vehicles.uDi嘉泰姆

2. Intelligent synchronous rectificationuDi嘉泰姆

a. The conversion efficiency is significantly improved by using synchronous MOSFET instead of traditional freewheeling diode. Support:uDi嘉泰姆

B. Cycle-by-cycle current limit control (180mV comparison threshold)uDi嘉泰姆

c. Output short circuit protection (automatic restart triggered by VCC undervoltage)uDi嘉泰姆

d. Adjustable working frequency (0-300KHz through external capacitor configuration)uDi嘉泰姆

3. Multiple safety protectionuDi嘉泰姆

a.UVLO undervoltage lockout (CXSD62679: 16.5V on/8V off)uDi嘉泰姆

B. Dual current comparator (SDHIN/SDLIN pin)uDi嘉泰姆

c.95% maximum duty cycle outputuDi嘉泰姆

d.200ns dead time controluDi嘉泰姆

Analysis of 2. Typical Application Scenarios

1. Electric vehicle converteruDi嘉泰姆
(Figure 6-1) In the 12V10A scheme, the voltage is divided by the FB pin resistance (formula:Vout=(1 R1/R2)*1.2V) Realize accurate voltage stabilization, and cooperate with synchronous MOS tube to efficiently reduce 48V/60V battery voltage to 12V system power supply.uDi嘉泰姆

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2. Industrial power systemuDi嘉泰姆

a. Suitable for telecommunication equipment, PoE power supply and industrial control:uDi嘉泰姆

B. VCC pin configuration 22μF storage capacitor to enhance short-circuit protectionuDi嘉泰姆

c.REF5V reference source (± 50mV adjustment rate) provides stable reference for sensing circuituDi嘉泰姆

3. Constant voltage and constant current schemeuDi嘉泰姆

(Figure 6-2) In the 5V output design, the CP pin is connected to a 200pF capacitor to achieve a 72KHz switching frequency, and the inductor selection formula is as follows:uDi嘉泰姆

L = Vout(Vin-Vout)/(Wine · Fs · Iripple)(Ripple current ≤ 30% full load current is recommended)uDi嘉泰姆

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3. Key Design Guide

1.PCB layout pointsuDi嘉泰姆

A. REF5V pin needs to be close to 1μF ceramic capacitor to filter noiseuDi嘉泰姆

B. power ground (COM) and signal ground (VSS) separate wiringuDi嘉泰姆

c. bootstrap circuit, inter-VB-VS withstand voltage 600VuDi嘉泰姆

2. Short circuit protection mechanism:When the output is short-circuited, the VCC capacitor discharges to 8V to turn off the PWM, and the voltage rises to 17V to automatically restart, forming an intermittent protection cycle (CXSD62679 exclusive function).uDi嘉泰姆

3. Component selectionuDi嘉泰姆

Summary of 4. technical advantages

CXSD62679 series throughFour-fold technological innovationSolve high pressure application pain points:uDi嘉泰姆

1.36 μA/720 μA constant current charge and dischargeAchieve precise frequency controluDi嘉泰姆

2.180mV Current DetectionImprove current limiting accuracyuDi嘉泰姆

3.VCC dual power mode(self-powered/externally powered)uDi嘉泰姆

4.-45 ℃ ~ 125 ℃ industrial temperature rangeuDi嘉泰姆

The chip has been successfully applied to scenarios such as electric bicycle converters and industrial inverters. Its SOP16 package (see section 9.1 for dimensions) is compatible with the standard mounting process, significantly reducing the threshold for high-voltage system design. Design documents and typical circuit diagrams can be obtained by visiting the official website.uDi嘉泰姆

VI. Component Parameters and Precautions in Application DesignuDi嘉泰姆

1 REF5V input capacitanceuDi嘉泰姆
Placing a high-frequency small-capacitance bypass capacitor at the REF5V pin end to the ground will reduce the high-frequency noise at the REF5V end, and the high-frequency bypass capacitor can be selecteduDi嘉泰姆
1uF ceramic capacitor, as close as possible to the chip pin REF5V input when the board is arranged.uDi嘉泰姆
2 VCC storage capacitoruDi嘉泰姆
CXSD62679 requires that a 22uF capacitor is placed at the VCC pin end to the ground, which is mainly used for energy storage, charging and normal operation of the VCC pin during startup.uDi嘉泰姆
At the same time, the capacitor has a certain effect on the output short-circuit protection. When the output is short-circuited, the VCC pin will dropuDi嘉泰姆
Electricity, the chip enters UVLO mode, the size of the capacitor will affect the time for the chip gap to turn on the power tube when the output is short-circuited, the larger the gapuDi嘉泰姆
The longer the time, the smaller the power tube heating, and the power tube heating will increase.uDi嘉泰姆
3 Start-up processuDi嘉泰姆
The CXSD62679 is that the input power supply starts to charge the external capacitor of the VCC pin through the external R1 resistor, and the chip will work at a low static current.uDi嘉泰姆
The mode consumes about 0.3mA of working current, only UVLO circuit is working inside, and other oscillators and PWM modules are in a closed state,uDi嘉泰姆
The output voltage is zero. When the capacitor voltage on the VDD pin is charged above 17V, the chip starts to work normally, and the oscillator and PWM module are turned on.uDi嘉泰姆
And feedback processing circuit, the output voltage regulator output, while the output voltage through the external diode to the VCC pin to provide VCC operating power, start.uDi嘉泰姆
End of process. The CXSD62680 is started by an external power supply.uDi嘉泰姆
4 Oscillator Cr Capacitor Switching Frequency CalculationuDi嘉泰姆
The CXSD62679/CXSD62680 only needs an external capacitor to set the PWM operating frequency, and the internal constant current source is used to charge and discharge the Cp capacitor.uDi嘉泰姆
As shown in figure 8.4a, the constant current source for current sinking provides about 36uA of current to charge Cp capacitor, and the constant current source for current drawing providesuDi嘉泰姆
A current of about 720uA discharges the CT capacitor. The approximate relationship between the operating frequency and the capacitor is determined by the formula f =(14.4 x 10⁶)/Cp OKuDi嘉泰姆
(The capacitance unit of this formula is pF), such as Cp = 200pF capacitance, the corresponding PWM operating frequency is about 72KHz.uDi嘉泰姆

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5 Output peak current limituDi嘉泰姆
The peak current limit of the high-end output of the CXSD62679/CXSD62680 chip is determined by the external current limiting resistor of the high-end MOS tube.uDi嘉泰姆
The system type is IPK = 180mV/(external current limiting resistor R37); The peak current limit of the low-end output current of the chip is determined by the internal resistance of the low-end MOS tube, and the peak currentuDi嘉泰姆
The relationship is IPK = 180mV/(low-end MOS tube internal resistance).uDi嘉泰姆
6 Output short circuit protectionuDi嘉泰姆
When the output is short-circuited, the CXSD62679 will work at the maximum peak current limiting output, and the voltage of VCC will lose power because the output voltage cannotuDi嘉泰姆
Then through the diode to provide power supply for the VCC pin, CXSD62679 the static working current of the chip quickly discharge the voltage of the capacitor on the VCC pin, when VCCuDi嘉泰姆
When the voltage of the pin is lower than 8V, the CXSD62679 chip will completely shut down the PWM output, and at the same time, the input power supply will lead VCC again through the external starting resistor.uDi嘉泰姆
The capacitor of the pin starts to charge. When the voltage of the VCC pin is higher than 17V, the chip restarts PWM. If the output has been in a short-circuit state, the chip willuDi嘉泰姆
Gap to open the power tube, at this time the CXSD62679 chip will be in current limiting and short circuit protection mode. CXSD62680 external power supply, the output is short-circuited.uDi嘉泰姆
Has a hiccup function.uDi嘉泰姆
7 Output inductanceuDi嘉泰姆
CXSD62679/CXSD62680 has two working modes: continuous working mode and discontinuous working mode. The value of inductance will affect the dropuDi嘉泰姆
The working mode of the voltage regulator, the CXSD62679/CXSD62680 works in discontinuous working mode at light load, and the inductance value will affect the inductance.uDi嘉泰姆
The selection of current ripple and inductance can be based on the following formula:where Vin is the input voltage, Vout is the output voltage, FsuDi嘉泰姆
is the PWM operating frequency, and the Iripple is the peak-to-peak value of the current ripple in the inductor. The Iripple is usually selected not to exceed 30% of the maximum output current.uDi嘉泰姆
8 Synchronous Rectification MOS TubeuDi嘉泰姆
The synchronous rectifier MOSFET is used to replace the freewheeling diode of the traditional asynchronous converter, thus greatly improving the power conversion efficiency;uDi嘉泰姆
MOSFET selection of low internal resistance, low junction capacitance, can give CXSD62679/CXSD62680 buck to provide good performance.uDi嘉泰姆
9 Output CapacitoruDi嘉泰姆
The output capacitor Co is used to filter the output voltage, so that the DC-DC voltage reducer outputs a relatively stable DC current to the load, and selectsuDi嘉泰姆
When selecting a capacitor with low ESR as much as possible, the size of the selected capacitor value is mainly determined by the ripple requirement of the output voltage, which can be determined by the following formula.uDi嘉泰姆
where & Delta;Vo is output voltage ripple, & Delta;IL is inductor current ripple, Fs is PWM operating frequency, ESRuDi嘉泰姆
is the equivalent series resistance of the output capacitor.uDi嘉泰姆
10 Output voltage regulation settinguDi嘉泰姆
The output voltage of the CXSD62679/CXSD62680 is set by the two divider resistors on the FB pin, and the internal error amplifier reference voltage is 1.2V,uDi嘉泰姆
As shown in fig. 8.10a, the output voltage Vout =(1 R1/R2)* 1.2V. if you need to set the output voltage to 12.12V, you can set R1 to 9.1K and R2uDi嘉泰姆
1K, output voltage Vout =(1 9.1/1)* 1.2V = 12.12V.uDi嘉泰姆
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Technical Specification (Product PDF): If you need detailed PDF specifications, please scan WeChat and contact us. You can also get free samples and technical support.!uDi嘉泰姆

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   Product packaging diagram uDi嘉泰姆

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   Circuit schematicuDi嘉泰姆

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  Related Chip Selection GuideMore related products......uDi嘉泰姆

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