Features

Flexible power supply from 5 V to 12 V

Power conversion input as low as 1.5V

0.8 internal reference voltage

0.8 0.8 %Output voltage accuracy

Large current integrated drive

Good output

No sensor and programmable OCP

Low -end RDS (open)

OV/UV Protection

VSEN disconnecting protection

The internal fixation of the oscillator is fixed at 300 kHz

LSLESS management predetermined

output voltage Tune

Disable function

Internal soft start

dfn10 package

memory and terminal power supply

子系统电源（MCH、IOCH、PCI…）

CPU和DSP电源

分布式电源

通用DC-DC转换器

说明[ 123]

L6728 is a single-phase antihypertensive controller integrated large current driver, providing complete control logic and protecting a simple and easy-to-run DC-DC converter compact DFN10 package. Equipment flexibility allows management to transform the power supply input VIN as low as 1.5 V and the voltage range of the equipment power supply is 5V to 12V. L6728 provides a simple voltage control circuit mode EA. Integrated 0.8 V reference voltage allows the output voltage adjustment accuracy to be ± 0.8%online and temperature changes. The oscillator is 300 kHz inside. L6728 provides programmable dual -level current protection and over -current and under current voltage protection. The current information is to monitor (open) the sensory resistance (open) to save the sensor and occupy the sensor that takes up space. PGOD output is easy to provide real -time output voltage status information, and via VSEN dedicated output monitor.

电气特性

（VCCu003d5 V到12 V；TJu003d0到70°C，除非另有规定）

[123 ] Electric characteristics (continued)

(VCC u003d 5 v to 12 V; tj u003d 0 to 70 ° C, unless there are other regulations)

1 The design guarantees, without testing.

Device description

L6728 is a single -phase PWM controller, a built -in large current drive, providing complete control logic and protection, simpleEasy ways to implement a universal DC DC antihypertensive converter. The design is used to drive the N -channel MOSFET topology structure in the synchronous buck. Due to its high integration, the 10 -pin device allows the reduction of cost and scale power solution also provides a compact DFN10 3X3 mm real -time program. L6728 is designed to work under 5 volt or 12 volt power. The output voltage can be accurately adjusted to 0.8V. In the case of changes in the line and temperature, the accuracy is ± 0.8%. This switching frequency is set to 300 kHz inside. This device provides a simple control loop and a voltage mode error amplifier. The error amplifier has a 15 MHz gain bandwidth and 8V/μs conversion rate, which allows high -fast transient response regulator bandwidth. In order to avoid damage to the load, L6728 provides overcurrent protection and over pressure protection, under pressure and feedback disconnection protection. The over -current check threshold is programmed by a simple resistance connected from LGATE to GND. The output current is monitored by the low -side MOSFET RDS (on), saving the use of sensitive resistance to consuming and occupying space. The output voltage is monitored by a special VSEN pin. L6728 implemented a soft start in the closed -loop adjustment, adding internal benchmarks. The low -side non -function allows the device to execute the soft startup exceeding the premium output to avoid the high current return of the output sensor and the danger negative peak side of the load. L6728 is packaged in a compact DFN10 3X3 MM with an externally exposed pad.

The integrated large current driver allows the use of different types of power MOSFETs (also multiple MOSFETs to reduce equivalent RDS (on) to maintain fast switching conversion. The driver of the high -voltage side MOSFET uses a starting pin to power, and the phase pins are used to return. The driver of the low side MOSFET uses the VCC foot to power, and the GND tube foot is used for circuit. This controller contains a reflex wearing and adaptive dead zone control, which is low at the minimum side diode in the side diode. While maintaining good efficiency, it saves the use of the Schottky diode:

In order to check the high -voltage side MOSFET Pass Broken, detect phase pins. When the voltage on the MOSFET driver's side suddenly decreases;

In order to check the low -voltage side MOSFET closed, the LGATE pin was detected. When the voltage at LGATE drops, the high -voltage side MOSFET gate driver is suddenly applied. If the current in the inductors is negative, the voltage on the phase will never decrease. By the allowable MOSFET to be allowed, even in this case, the door dog controller is enabled: if the source of the high side MOSFET does not decrease, the low -side MOSFET is the negative current of the allowable sensor to be connected. This mechanism allows the system to adjust even if the current is negative.

Power conversion input is flexible: 5 V, 12 V bus or any bus that allows conversion (see the maximum duty cycle ratio) can be freely selected.

Power Consumption

L6728 is an embedded MOSFET driver in high and low -side MOSFET: Yes, and then it is important to consider the energy consumed by the device in the process of driving them to avoid the energy consumed to avoid the energy consumed to avoid Overcoming the highest knot temperature. There are two main factors affecting the power consumption of the device: bias power and driver power.

Equipment bias power (PDC) depends on the assumption that HS can provide pins and can provide device drivers with the same VCC):

The driver's power supply refers to the driver's continuous opening and turning off the external MOSFET; it is the MOSFET selected by the function of the switch and the function of the total grid charge. Considering that the total power PSW can quantitatively dissipate the switch MOSFET (easy to calculate) by three main dissipation factors: external grid resistors (if existence), MOSFET resistance, and inherent drive resistance. The last semester is an important period of computing equipment power consumption for our determination to do. Total power consumption MOSFETS Result:

The external gate resistance helps the device to dissipate the switch power, because the power PSW will be shared between the internal drive impedance and the external resistor will be shared. The equipment is generally cool.

Soft start

L6728 realizes soft startup to charge the output filter smoothly to avoid the current required by highly input power supply. The device is gradually increased in the closed loop adjustment, from the internal reference voltage of 0 V to 0.8 V within 4.5 ms (typical values), and the output capacitor is charged to the final adjustment voltage linearly. If the current is triggered during soft startup, the overcover soft start sequence will be turned off and the PWM logic and high -voltage side door will be turned off. This situation is locked and the cycle is recovered. Only when the VCC power supply is higher than that of the UVLO threshold, the device begins to start the soft start -up phase of the current threshold setting stage.

There is no startup (LSLESS)

In order to avoid any dangerous return to start when the negative load occurs, the L6728 executes a special order At the stage, the LS driver will cause disable (ls u003d turn off) until HS start switching. This avoids dangerous negative peaks on the output voltage, if the output at a pre -defined voltage. If the output voltage is premedated to a voltage higher than the final voltage, HS will never start switching. In this case, at the end of the soft start time, enable LS and release the output to the final adjustment value. This special feature of the device only shields LS from the control loop point to open the point of view: In the case of need, protect the bypass to open the LS MOSFET.

Over current protection

Or through overload insuranceThe short -circuit of the transformer output is detected the output current information through the low -side MOSFET leakage source drive RDS (ON). This method reduces the cost and improves the efficiency of the converter to avoid the use of expensive and occupying the space resistance. The low -voltage side RDS (ON) current detection is held internally when the LS MOSFET is opened with a programming OCP threshold voltage. If the monitoring voltage is greater than these thresholds, the event is detected. In order to achieve the maximum security and load protection, L6728 realizes dual -level overcurrent

Protection system:

First -level threshold: the threshold of the user's external settings. If the monitored voltage phase exceeds this threshold, the level 1 over current is detected. If the four -level OC detects the incident within the four continuous switching cycles, over -current protection will be triggered.

Secondary threshold: Internal threshold is equal to the first -level threshold threshold multiplied by the coefficient 1.5. If the monitored phase voltage exceeds the threshold of this value, the over -current protection will be triggered immediately. When the current is triggered, the device will close the LS and HS MOSFET locking status at the same time. The VCC power supply must be opened from overcurrent protection trigger state.

Over -current threshold settings

L6728 allowed to easily program level 1 over -current threshold with a range of 50 mv to 550mv, just add a resistance (RocSet) between LGATE and GND. The secondary threshold will be automatically set accordingly. In the short time (about 5 milliseconds) after VCC exceeded the UVLO threshold, an internal 10 μA current (IOCSET) comes from the LGATE pin to determine the voltage reduction through Losseart. The voltage drop will be sampled and the internal internal is kept to the 1 -level exceeding the current threshold. The total length of the OC setting program is about 5 milliseconds. A ROCSET resistor is connected between LGATE and GND. The first -level threshold of programming is:

The range of the RocSet value is 5 k u0026#8486; to 55 k u0026#8486 ;. If there is no connection ROCSET, the device will set the OCP threshold to the maximum value: Once the LGATE voltage is reached, the internal security clip 600 MV on the LGATE will be triggered, the maximum threshold is set, and the OC setting phase is suddenly ended.

The output voltage is fixed and protected

L6728 can accurately adjust the output voltage benchmark as low as 0.8V with a fixed 0.8V internal benchmark to ensure that the output adjustment voltage line and temperature change ± 0.8 ± 0.8 Alert tolerance range (excluding the output resistor division of the pressure division (if there is). The output voltage is higher than 0.8V, which can easily increase the FB pins and ground between the resistance ROS. For:

Among them, VREF is 0.8V.

L6728 monitor the voltage at the VSEN pin, and compares the internal reference voltage of it to compare the under voltage and overvoltage protection and PGOOD signals.

According to the level of VSEN, the controller performs different operations:

Good

If the voltage monitored by VSEN exceeds the PGOOD window limit, the device de asserted that the PGOOD signal is still Continue to switch and adjust. The good thing is to assert at the end of the soft start phase.

Impurd voltage protection

If the voltage on the VSEN pin drops below the UV threshold, the device will turn off HS and Moss Fitz at the same time, locking status. The circular VCC is restored.

Overvoltage protection

If the voltage at the VSEN pins increases more than the OV threshold (1 V typical value), the overvoltage protection closed HS-MOSFET and open the LS-MOSFET. The LS MOSFET will be closed as once VSEN is lower than VREF/2 (0.4 V). Conditions are locked, circulating VCC to recovery. Please note that even if the device is locked, the device still controls the LSMOSFET. When the VSEN rises to the OV threshold, it can be opened.

Feedback disconnection protection

In order to provide load protection without connecting the VSEN pin, the 100 NA bias current always comes from the pin. If the VSEN pin is not connected, the current will permanently pull it up, so that the device detects OV: Therefore, LS will be locked to prevent the output voltage from rising out of control.

Application details

Compensation network

The control loop shown in FIG. 5 is the voltage mode control loop. The output voltage is adjusted to the internal benchmark (when the existence is existed, the offset resistance between the FB node and the GND can be ignored in the control loop calculation). Error amplifier output is compared with the oscillator sawtooth wave to provide PWM signals to the cab. Then PWM signal is transmitted to the access node amplitude through VIN. The waveform is filtered by the output filter. The transmission function of the converter is the small signal transmission function EA and VOUT between the output. This function has a bipolar at the frequency FLC, depending on the resonance of L-Cout at the FESR and zero point depends on the output capacitance ESR. The DC gain modulation is the input voltage VIN except the peak to the peak oscillator voltage u0026#8710; Vosc.

The compensation network is ideally equal to-ZF/ZFB through the transmission of the connection connection VOUT and EA output.

The target of compensation is to close the control circuit to ensure that the accuracy of DC regulation is high, good performance and stability. To achieve this, the entire ring requires a high DC gain, High -bandwidth and good phase margin. To achieve high DC gains, the compensation network transmission has the shape of the integral device. The ring bandwidth (F0DB) can be fixed by selecting the appropriate RF/RFB ratio, but the stability should not exceed FSW/2π. In order to obtain a good phase margin, the control circuit gain must be passed through the 0 DB axis at the -20 DB/decimal slope. As an example, FIG. 6 shows the closer BODE diagram of type III compensation.

In order to determine the pole and zero point of the compensation network, the following suggestions can follow:

A) Set the gain RF/RFB to obtain the required closed -loop regulator Bandwidth according to the approximity formula (RFB's suggestion value within the range of K u0026#8486;):

E) Check whether the compensation network gain Below the opening of the EA gain F0DB;

f) Check the obtained phase margin (should be greater than 45 °). And large current integrated drive to achieve a large current antihypertensive DC-DC converter. In this application, a good layout is very important and important. The first priority when placing components for these applications must be retained to the power supply part to minimize the length of each connection and circuit. To connect the noise and voltage peak (EMI and loss) power supply (highlighting the display graph 7) must be part of the power supply plane, and it must be tracked with wide and thick copper anyway: the cycle must be minimized. Key components, that is, power MOSFET, must approach each other. It is recommended to use a multi -layer printing circuit board. Input a capacitor (CIN), or a part of the total capacitance at least, must be placed near the power segment to eliminate traces of copper. Low ESR and ESL capacitors are the first choice. MLCC is recommended to connect near HS drainage pipes. When the power trace line must be to reduce the parasitic resistance and inductance of PCB. Furthermore, copying the same high -current trajectory on multiple PCB layers will reduce parasitic resistance related to that connection. Connect the output large -capacity capacitor (COUT) to the position closer to the load as much as possible, minimize the inductance and resistance related to the parasitic and copper traces, and increase the additional off -coupled electric container to the load. Bulk capacitors.