EXTVCC connection

LTC1735 contains a switch connected between EXTVCC and INTVCC pins. When the ExtVCC pin is higher than 4.7V, the internal 5.2V regulator is turned off, the switch is closed, and the INTVCC power supply is powered by EXTVCC until ExtVCC drops below 4.5V and runs normally. When the output exceeds the adjustment range (start, short -circuit) power supply is internal regulator. The voltage applied to the EXTVCC pin must not exceed 7V and ensure EXTVCC ≤Vin. A significant efficiency can be achieved through power -on. As the VIN current generates the drive and the control current, the control current will pass through the coefficient (duty cycle)/(efficiency). For the 5V regulator, simply connect the EXTVCC foot to VOUT. However, for 3.3V and other low -voltage regulators, additional circuits are required to obtain INTVCC power from output. The following table summarizes the four possible connections of EXTVCC:

1.ExtVCC left (or ground). This will cause INTVCC to supply power from the internal 5.2V regulator at a high input voltage, and the efficiency loss is as high as 10%.

2.ExtVCC is directly connected to VOUT. This is a normal phenomenon connecting 5V output regulator and provides the highest efficiency. For output voltage higher than 5V, EXTVCC needs to be connected to VOUT in order to detect pins #39; not exceeding the absolute maximum rated value. Allow the MOSFET gate driver and control power supply

3.ExtVCC to connect to the output derived Boost network. For 3.3V and other low -voltage regulators, the efficiency can still be improved by connecting EXTVCC to an output voltage, which has been increased to greater than 4.7 volts. This can be used to achieve the winding of the winding as shown in Figure 3A or the capacitance charging pump as shown in Figure 3B. The charging pump has the advantages of simple magnetism.

4.ExtVCC is connected to the external power supply. If the external power supply can be available in the range of 5V to 7V (EXTVCC ≤Vin), if the laptop main 5V system power supply can be used, if EXTVCC and MOSFET gate driver requirements can be used. This is a typical case because the 5V power supply almost always exists, and is another high -efficiency regulator.

Output voltage programming

The output voltage is set by the external resistor division device according to the following formulas:

The resistor separator is connected to the output to the output As shown in Figure 4, the remote sensing voltage is allowed.

上部模块MOSFET驱动器电源（CB，DB）外部自举电容器CB连接到升压引脚为上部模块提供栅Polar drive voltage MOSFET. The capacitor CB in the function chart is charged. When the SW pin is charged, the external diode DB is very low through the INTVCC. Note that the voltage of CB is lower than INTVCC. When the upper MOSFET is opened, the driver places the CB voltage at the grid source of MOSFET. This enhances MOSFET to open the upper switch. The voltage SW of the access node rises to VIN, and the Boost Pin rises to VIN+INTVCC. The value of the voltage capacitor CB needs to be 100 times the total input capacitor MOSFET than the upper module. In most applications, 0.1 μF to 0.33 μF is equivalent. The reverse breakdown on DB must be greater than VIN (maximum value). When the grid driver is adjusted, the final arbiter is the total input current of the regulator. If you make a change in the input current, then you improve your efficiency. If the input current has not changed, the efficiency has not changed

Sense+/Sense - pin

The co -mode input range of the current comparator is from 0V to 1.1 (INTVCC). In the entire process, the continuous linear operation is allowed to allow the output voltage between 0.8V and 7V to the guarantee range of the antihypertensive application. Use the differential NPN input level and use an internal resistor with an internal 2.4V power supply, as shown in the function chart as shown in the figure. This causes the current from the inductive needle source or sink, depending on the output voltage. If the output voltage is lower than 2.4V current, it will flow from the two sensing tube feet to the main infusion end. This compulsory can be divided by the minimum load current resistor. The maximum current influenza in the outflow is: Isense ++ Isense - (2.4V – Vout)/24K. Due to the Vosense servo to 0.8V reference voltage, we can select the R1 in Figure 4 so that it has the maximum value to absorb this current:

adjust the output voltage 1.8V, the value of the maximum value R1 should be 32K. Note that the output voltage is higher than 2.4V without R1 to absorb the detection pin current; however, R1 is still a feedback current of Vosense.

Soft start/running function

Run/SS pin is a multi -function pin, providing a soft startup function and a method of turning off the LTC1735. Soft startup gradually reduces the current surge current increased controller current limit ITH (MAX). This pinch can also be used for power sorting. Pull the RUN/SS pin below 1.5V and put the LTC1735 in the shutdown. This pin can be directly driven by logic driver as shown in Figure 5. VIN static current is a function running voltage/SS voltage (refer to the typical performance characteristics of page 6). Remove Run/SS sales allow the internal 1.2 μA current source to start the CSS of the external soft startup capacitor. If RUN/SS has been dragged on the ground, there is a delay before starting:

When RUN/SSWhen the voltage reaches 1.5V, the LTC1735 is about 25 millivolves/second at the current limit. When the voltage on the RUN/SS pins increases from 1.5V to 3.0V, the internal current limit increases from 25mv/RSENSE to 75MV/RSENSE. The output current limit rises slowly, and an additional 1.25S/μF is required to reach the maximum current. Therefore, the output current rises slowly from the input power.

The diode D1 in FIG. 5 decreases the lax delay, and at the same time, the CSS is allowed to charging slowly for the soft startup function. If you do not need to start softly, you can delete the diode and CSS. RUN/SS pin has an internal 6V Zina pliers (see functional map).

Failure condition: over -current atresia RUN/SS pin also provides closed current conditions as detection. The RUN/SS capacitor CSS was originally used to turn on and limit the surge current of the controller. After that, the controller has been started and has enough time to charge the output capacitor and provide a full load current. The CSS is used as a short -circuit timer. If the output voltage drops to its nominal output voltage below 70%. After the CSS reaches 4.1V, assuming that the output is severely overcurrent and/or short -circuit conditions, the CSS starts discharge. If the situation continues according to the size of the CSS, SS/PIN will be turned off until the controller is recycled within a long enough time. It can be provided with a current gt; 5μA when providing a Run/SS pin component 5V as shown in Figure 6. This current shortens the soft starting cycle, but it can also prevent the net emissions of RUN/SS

severe over current and/or short circuit capacitor conditions. When the vehicle recognition number (VIN) obtains a 5μA current, as shown in Figure #9251; 6A, the current Latchoff has always failed. The diode is connected to INTVCC, as shown in Figure 6b to eliminate any additional power current during the controller's closure, and at the same time eliminate INTVCC loads to prevent the controller from starting. If the voltage on the CSS does not exceed 4.1V, the over -current lock is not enabled, and the function is disabled. In the design of the design, there may be problematic noise pickup or bad layouts lead to the protection circuit. Canceling this function can easily eliminate the circuit and PC layout. Internal short circuit and folding current limit are still effective, thereby protecting the power supply system without failure. After the design is completed, you can make a decision to enable the Latchoff function. The value of the soft startup capacitor CSS needs to be reduced according to the output current, output capacitance and load. The minimum soft startup capacity is given by the following formula: CSS GT; (COUT) (VOUT) (VOUT) (10–4) (RSENSE) The minimum soft startup capacitor CSS #9251; #9251; 0.1μF is enough to meet most applications.

Failure conditions: current limit and current return LTThe C1735 current comparator has a maximum induction of 75mv voltage 75 mv/second of 75mv voltage of the maximum MOSFET current. The LTC1735 includes the current folding to further help output the load current when the ground is short -circuited. Even in the case of overload, the folding circuit is in a state of activity. If the output drops more than half, and then the maximum sensing voltage gradually decreases from 75 millivolttilum to 30 millivolttil. In the short circuit with a very low cycle, the LTC1735 will start to skip the cycle to limit the short -circuit current. In this case, the bottom MOSFET will conduct peak current. Short -circuit -patterned wave current determines the ton (minimum value) of the LTC1735 (about 200NS), the input voltage and inductor value: #8710; IL (SC) ton (minimum) vin/l short circuit. The current is:

The current Foldback function is always in a state of activity, not affected by the current Latchoff function.

Failure conditions: Output overvoltage protection (crowbar) Output over -voltage prying rod design is used for system fuses to increase by regulatory agencies when the system fuse is inferior. This situation will lead to huge current flow, far greater than normal operations. This function aims to protect the top MOSFET short circuit at the top; it cannot protect the controller itself. The comparative (OV in the function diagram) detection is higher than the excess voltage failure output voltage with a nominal value of 7.5%. When you feel this situation, the top MOSFET is closed, and the bottom MOSFET is forced to open. The bottom MOSFET continues to open AS as long as 0V conditions continue; if Vout returns the level of the safe, the normal operation will automatically recover. Note that the dynamic change output voltage may instantly reduce the output voltage of over -voltage protection action. This will will not cause permanent atresia, nor will it damage the expected voltage change. With a soft -lock lock overvoltage protection, it allows dynamic changes to the output voltage of the output voltage over voltage and the new programming output voltage, and the load is always protected.

minimum precautions

The minimum connection time TON (min) is the minimum amount LTC1735 can open the top MOSFET and go away. It is delayed from the inside and the grid charge required for the top MOSFET. The low occupation ratio application may be close to the minimum working time limit. Pay attention to ensure:

If the duty cycle is lower than the minimum connection time, the LTC1735 will start to skip the cycle. The output voltage will continue to be adjusted, but the ripple current and voltage will increase. LTC1735 is generally less than 200NS in appropriate configuration applications. However, when the peak sensing voltage is reduced, the minimum value is shown in Figure 7, and the time of time gradually increases. This is particularly worthy of a low -ripple current in the mandatory continuous application. If the duty cycle decreases in this case, it is lower than the mostLow connection time limit corresponding to the ground, larger current and voltage ripples will cause a large number of cycle to jump. If the application can run without the minimum limit, you must choose a sufficiently low electrical sensor to provide sufficient ripple amplitude to meet the minimum on time requirements. Generally speaking, the iOut (maximum value) when the electrical sensor ripple current is equal to or greater than 30%VIN (maximum)

FCB pin operation

] When the FCB pin dropped to its 0.8V threshold, forced continuous mode operation. In this case, the top and bottom MOSFET continues to simultaneously drive the load on the main output. The emergency mode operation is disabled and allows the sensor. In addition to providing logic input to force continuous synchronous operation and external synchronous FCB pins, it provides a method output of regulating anti -fixing winding (see Figure 3A). In continuous mode, the current continues to flow in the main transformer. The second winding is only at the bottom, and the switch is opened simultaneously. When a load is low, the current and/or VIN/VOUT ratio is low, and the synchronous switch may not have enough turnover from the output capacitor to the second load. Forced continuous operation will support the second winding, provided that there is sufficient synchronous switch to occupy the duty cycle. Therefore, the FCB input pin removal must be extracted from the primary inductor to assist the winding winding. When the cycle is in a continuous mode, the auxiliary output can load the output load without consideration. The secondary output voltage vSEC is usually set to shown in Figure #9251; 3A. Small and stop switching, and then VSEC will decrease. VSEC setting minimum voltage VSEC (min) from the external resistor division to the FCB pin:

If the VSEC drops below this level, the FCB voltage is forced to switch operation until VSEC is higher than it again than it again. The minimum value. In order to prevent abnormal operations without external connection without the external connection of the FCB pin, the current of the FCB pins is 0.17 μA internal current source. Remember to choose the current and R4, including the current and R4. The internal LTC1735 oscillator can be used as an external frequency when the signal of A.V above the application and the clock FCB pin is prohibited when the signal above A.V is synchronized with A.V.1, and the emergency mode operation is banned, but under the low load current, the current is prohibited from reversing. The bottom door at the bottom every 10 clock cycles to ensure that the guidance cap is kept fresh. The rise of the external clock is used in the FCB pin to start a new cycle. Do not drive the FCB sales device when the device is shut down (RUN/SS is low). Synchronous range from 0.9fo to 1.3fo, where the FO set by COSC. Try to synchronize a higher frequency exceeding 1.3fo will lead to insufficient slope compensation, and under high occupation ratio leads to the circular unstable (occupy the duty ratio gt; 50%; 50%To. If you are synchronized, additional slope compensation can be obtained by simply reducing COSC. The following table summarizes the possible status available on the FCB pin:

Efficiency considerations

The efficiency percentage of the switching regulator is equal to the output power division by input power. Multiply 100%. Analyze a single loss to determine what limit is efficiency and which changes will produce the greatest improvement. The efficiency percentage can be expressed as:%efficiency 100% - (L1+L2+L3+...) formula, L1, L2, etc. are a percentage input power of a single loss.

Although all dispersion components in the circuit will cause losses, 4 main sources usually occupy the loss in the LTC1735 circuit: 1) VIN current, 2) #9251; intVCC current, 3) I2R loss, 4 ) The transition loss of the upper module MOSFET.

(1) The VIN current is the DC power supply current given not includes the electrical characteristics of the MOSFET drive of the MOSFET drive. VIN current leads to a small ( lt; 0.1%) losses with the increase in vehicle recognition number (VIN).

(2) INTVCC current is MOSFET drive and control current. The current is derived from the grid capacitance of the MOSFET switch power MOSFET. Each time the MOSFET gate is switched from low to high to low, the charge package DQ moves from INTVCC to ground. The generated DQ/DT is usually much larger than the control circuit current from INTVCC. In the continuous mode, igatechg f (qt+qb), where QT and QB are the upper and bottom Moss Fitz. Extvcc switch input provides an INTVCC power supply from an output or other high -efficiency sources to zoom in the coefficient of the VIN current circuit required by the driver and control of the control of the driver and control. For example, in the application of 20V to 5V, the 10mA INTVCC current causes a VIN current of about 3 mA. This reduces from 10%or higher intermediate current loss (if the driver is directly from the vehicle identification number (VIN) to only a few percent.

(3) I2R loss is divided by MOSFET, inductance and current. In the continuous mode, the average output current flows over L and RSense, but in the upper main MOSFET and synchronous MOSFET. If two MOSFET, the resistance on RDS can roughly use the resistance and obtain I2R loss with the same mosFet. For example If each RDS (on) 0.03 #8486;, RL 0.05 #8486;, RSENSE 0.01 #8486;, then the total resistance is 0.09 #8486;. Increase to 5V output to 5A, 3.3V output is 3%to 14%loss. The change in efficiency depends on the same ones.External components and output power levels. Under high output current, the loss of loss will lead to a decline in efficiency.

(4) Transitional loss is only applicable to the upper module MOSFET only becomes an important voltage when running at high input (usually 12V or higher). The transitional loss can be estimated: transitional loss (1.7) VIN2 IO (maximum) CRSS F other ""hidden"" losses, such as copper tracking and internal efficiency of the portable system by 10%. It is very important to include these ""system"" -level losses in the system design. Internal batteries and fuse resistance loss can ensure that the CIN is sufficiently storage and ESR at the extremely low switching frequency. The 25W power supply usually requires a minimum of 20 μF to 40 μF capacitors, and the maximum ESR is 0.01 #8486; to 0.02 #8486; Other losses include Schottky conduction loss and inductive iron core loss in the dead zone usually account for less than 2%of the total loss.

Check the transient response

The response of the regulator loop can be viewed by viewing the load current transient response. The switching regulator response to a step of the load current several cycles. When the loading step occurs, the VOUT movement is equal to #8710; ILOAD (ESR), where ESR is an effective series resistance of COUT. #8710; ILOAD also starts charging or discharging feedback error signal regulators to adapt to changes in current and return voltage. Its steady state value. It can be monitored for excessive rushing or ringing during this recovery time, which shows that there is a problem with the stability. OPTI-LOOP compensation makes the transient response obtains optimized values u200bu200bin a large-scale output capacitor and ESR range. The availability of the i -i pin not only allows optimization of the control circuit behavior, but also provides DC coupling AC filter closed -loop response test points. At this stable point, the rise really reflects the closed -loop response. Assume that the second -order system is dominated by the phase, and/or the damping coefficient of phase can be used on this needle. Bandwidth can also be estimated by checking the rise of marketing. The external component circuit shown in Figure 1 will provide most applications with an appropriate starting point

The i -series RC -CC filter sets the main pole point zero point compensation. These values u200bu200bcan be modified slightly (0.5 to 2 times the recommended value) to optimize once the final PC layout and specific output capacitor types and values u200bu200bare determined. You need to choose the output capacitor because different types and values u200bu200bdetermine the gain and phase of the cycle feedback factor. The output current pulse of 20%to 100%full load current, the rise time of 1 μs to 10 μs will generate the output voltage and the i -i PIN waveform. This will give a feeling of a sense of overall ring stability to break the feedback circuit. The initial output voltage level jump may not be in the bandwidth of the feedback circuit, so the standard second -order over -built/DC ratio cannot be used to determine the phase margin. The gain of the ring circuit will increase by increasing RC and cycle. If the RC increases the same factors by reducing the CC, the zero frequency will be maintainedHolding unchanged, thereby keeping the phase unchanged in the most critical frequency range of the feedback loop. The overall supply performance of the stability of the output voltage and the actual supply of the closed -loop system. Detailed explanations on optimizing compensation components, including reviewing the theory of controlling circuit, see Application Comment 76.

The second more severe transient is providing bypass electrical containers caused by large ( gt; 1μF) loads caused by connection. This discharge side electric container is effective parallel with COUT, causing VOUT to decrease rapidly. No regulator can quickly change the conveying of the current to prevent the output voltage of the output voltage suddenly changing the resistance and the driving speed when the load switch is caused by the load switch. If CLOAD to COUT is greater than 1:50, the switch rising time should control the rising time of the load (25) (CLOAD). Therefore, the 10μF capacitor requires a 250 microsecond to rise, restricting the charging current to about 200 mAh.

Improve the transient response, reduce the output source voltage positioning capacitor fast load transient response, limited board space and low cost are the requirements of the power of microprocessor power supply. A The output capacitor required for power supply, the typical load level jumping is 15A or 100NS within 0.2A100ns, 15A to 0.2A. The microprocessor must keep about ± 0.1V of the nominal voltage, although there are these load current steps. Because the control loop cannot respond so quickly, the output capacitor must provide a load current until the control loop can respond. Capacitors ESR and ESL mainly determine the output voltage drop or overwhelming. Usually, several capacitors need to be connected to meet the transient requirements of microprocessors. A source of voltage positioning is a form of relaxation control. It sets a high output voltage when light load, and the output voltage is low load during heavy load. When the load current suddenly increases, the output voltage starts at a level higher than the nominal value, so the output voltage can be reduced more and keeps within the specified voltage range. When the load current suddenly reduces, the output voltage starts from the level below the nominal value. The output voltage can be excessive and kept within the specified voltage range. When using voltage positioning, a smaller output capacity is required because more voltage variable capacitors are allowed on the output.

The active voltage positioning can be connected to the i-i pin using the OPTI-LOOP architecture of LTC1735 and the two resistors. When the error placed must drive the resistor load, the input voltage offset is introduced. When the error input is input, the offset is limited to ± 30mv amplifier. The changes in the output voltage are the volume ratio of the input offset and the feedback pressure division. Figure 8 shows a CPU core voltage regulator voltage positioning. Resistors R1 and R4 forced input voltage offset, according to the load current level. To select the values u200bu200bof R1 and R4, first determine the allowable output relaxation. The actual specifications of this typical microprocessor allow the output change to ± 0.112V. The reference accuracy of the LTC1735 is ± 1%. Use 1%tolerance resistance, totalThe accuracy of the feedback scorer is about 1%, because the feedback resistance of the two is close to the same value. Results The setting point accuracy was ± 2%, so the output transient

The voltage cannot exceed ± 0.082V. When VOUT 1.5V, the maximum output voltage control of the I pin control will be:

Under the optimal resistance value of the i -i pin, the output voltage From 1.55V to 1.44V at the minimum load. Under the output voltage, the active voltage position provides additional ± 56mV for the allowable transmission voltage on the output capacitor, which is increased by 68%than the ± 82MV allowed when there is no source voltage. The next step is to calculate the first pins voltage of the proportion factor of the VITH. The eighth proportional factor reflects the voltage required for the load current given the load. Vitamin controls peak sensing resistance voltage, which represents DC output current plus half of the peak inductance current. The air load to the full load range is 0.3V to 2.4V, and the sensing resistance voltage is controlled from 0V to 75 millival #8710; vSense (maximum) voltage. The calculated vitamin with 0.003 #8486; the proportional factor of the inductive resistor is: