Features

● 4.5V to 16V working input voltage range

● Synchronous rectification: 100MΩ internal high -voltage side switch and 20MΩ internal low -voltage side switch

● High -efficiency: Gundam: Gundam: Gundam: Gundam: Gundam: Gundam: 95%

● Internal soft start

● Effective high power and good state output voltage can be adjusted to 0.8V

● 3A continuous output current fixed 500kHz pulse width modulation operation [123 123 ]

● Weekly current limitation starts

● Short-circuit protection

● Hot shutdown

● Small DFN 5X4 and EPAD SO-8 packaging

Application

● Load point DC-DC conversion

● PCIe graphics card

● Top box

● DVD drive and hard disk drive

● LCD panel

● Cable modem

● Telecom/network/data communication equipment

General description

aoz1022

It is a synchronous and efficient, simple use, 3A antihypertensive regulator. AOZ1022 works within the input voltage range of 4.5V to 16V, providing a continuous output current up to 3A, and the output voltage can be reduced to 0.8V.

AOZ1022 is encapsulated with DFN 5X4 and EPAD SO-8, and the rated ambient temperature range is between -40 ° C to+85 ° C.

Typical Application

Typical performance features

Figure in Figure 1 circuit. TA 25 ° C, vin Ven 12V, vout 3.3V, unless there are other regulations.

Thermal drop curve

Detailed description

AOZ1022 is a current mode antihypertensive regulator with integrated high -voltage side PMOS switch and low -voltage side NMOS switch. It works within the input voltage range of 4.5V to 16V and provides a load current of up to 3A. The duty cycle can be adjusted from 6%to 100%, and the output voltage range is wide. Functions include enabling control, power -on reset, input, under voltage lock, output overvoltage protection, good power and good power, good power, and fixed internal soft start and heat shutdown.

Enable and soft start

AOZ1022The internal soft startup function can limit the impact current and ensure that the output voltage rises smoothly to the adjustment voltage. When the input voltage rises to 4.1V and the voltage on the EN pin is high, the soft start process begins. During the soft startup process, the output voltage usually becomes a adjustable voltage within 4ms, and the 4ms soft start time is set internally.

The EN pin of AOZ1022 is in a high activation state. If the enlightenment function is not used, the EN pin is connected to V. Pull EN to the ground will be disabled aoz1022. Don't let it open. The voltage on the EN pin must be higher than 2V to enable AOZ1022. When the voltage on the EN pin is lower than 0.6V, AOZ1022 was disabled. If the application circuit is required to disable AOZ1022, the open path drain or the open circuit collector circuit should be connected to the EN pin.

Good power

The output with good power is a leakage N -channel MOSFET, which provides a good high -power high -power level. The pull -up resistor (R) should be connected to the DC power cord with a maximum voltage of 6V. AOZ1022 monitor FB voltage. When the FB voltage is 90%below the normal voltage, the N -channel MOSFET is turned on, and the power foot is pulled down. This indicates that the power supply is abnormal.

steady -state operation

Under steady -state conditions, the converter works in a fixed frequency and continuous transmission mode (CCM).

AOZ1022 integrates an internal P-MOSFET as a high-voltage side switch. The inductance current is detected by amplifying the voltage drop of the drain to the high -voltage side power MOSFET source. The output voltage is reduced by the external pressure dealer at the FB pin. The difference between the voltage of the FB pipe foot and reference voltage through the internal cross -guidance error amplification is amplified. The error voltage displayed on the COMP tube feet is compared with the current signal (that is, the sum of the inductive current signal and the slope compensation signal) at the PWM comparator input. If the current signal is less than an error voltage, the internal high -voltage side switch is connected. The inductive current from the input through the inductance flow to the output. When the current signal exceeds the error voltage, the high -voltage side switch is broken. The inductive current passes through the internal low-side N-MOSFET switch freely rotated to output. The internal adaptive FET driver guarantees that the high and low -side switches are not overlapped.

Compared with the regulator with a free rotation of the Schottky diodes, AOZ1022 uses free rotation NMOSFET to achieve synchronous rectification. It greatly improves the efficiency of the converter and reduces the power loss of the low -voltage side switch tube.

AOZ1022 uses the P channel MOSFET as a high -voltage side switch. It saves the guidance capacitance usually seen in the circuit using NMOS switches. Allowing high -side switches to open 100%to achieve linear adjustment operation methods. The minimum voltage drop from V to V is the DC resistance of MOSFET's load current X DC resistance+BUCK inductance. Can be calculated through the following formula:

Among them: VO_MAX is the maximum output voltage, VIN is the input voltage between 4.5V and 16V, IO is the output current from 0A to 3A, and RDS (ON) is the internal MOSFETT The value of the drive resistance is between 97MΩ and 200MΩ, depending on the input voltage and knot temperature.

Switching frequency

AOZ1022 switching frequency is fixed and set by internal oscillator. Due to the changes in the device, the actual switching frequency can be from 350kHz to 600kHz.

Output voltage programming

The output voltage can be set up to the FB pins by using a resistor separation voltage network. See the application circuit shown in FIG. 1. The resistor network includes R1 and R2. Usually, the design starts with the selection of a fixed R1 value, and then uses the formula of the following page to calculate the required R2:

Table 1 lists some of R and R. Standard values and the most commonly used output voltage values.

The combination of R1 and R2 should be large enough to avoid drawing too much current from the output end, which causes power loss.

Since the switching ratio can be as high as 100%, the maximum output voltage can be set to the high -level input voltage minus the PMO and inductance voltage drop.

Protection feature

AOZ1022 has multiple protection functions to prevent damage to the system circuit under abnormal situations.

Over current protection (OCP)

The inductive induction current signal is also used for over -current protection. Because AOZ1022 is controlled by peak current mode, the COMP pin voltage is proportional to the peak inductor current. COMP PIN voltage is limited between 0.4V and 2.5V. The peak current of the inductance is the automatic restriction cycle.

When the output is short -circuited under the ground, due to V 0V, the inductor current is very slow during the switching cycle. In order to prevent catastrophic failure, secondary current restrictions were designed within AOZ1022. The measured inductance current is compared with the preset voltage of the representative current limit, and the voltage is between 3.5A and 5.0A. When the output current is greater than the current limit, the high -voltage side switch will be turned off. Once the flow situation is solved, the converter will start softly.

Powering reset (POR)

Monitoring input voltage of the power -up reset circuit. When the input voltage exceeds 4.1V, the inverter starts to work. When the input voltage is lower than 3.7V, the converter is closed.

Hot protection

Internal temperature sensor monitoring joint temperature. When the knot temperature exceeds 150 ° C, close the internal control circuit and high -voltage side PMOS. When the knot temperature drops to 100 °When C, the regulator will automatically restart under the control of the soft startup circuit.

Application information

The basic AOZ1022 application circuit is shown in Figure 1. The selection of parts is as follows.

Input a capacitor

The input capacitor must be connected to the V pins and PGND pins of AOZ1022 to maintain a stable input voltage and filter out the pulse input current. The rated voltage of the input capacitor must be greater than the maximum input voltage plus ripple voltage.

The input ripple voltage can be approximately similar to the following formula:

Because the input current of the BUCK converter is not continuous, when selecting a capacitor, the input capacitor is entered. The current stress is another question to be considered. For the antihypertensive circuit, the average root value of the input capacitance current can be calculated through the following formulas:

If we make M equal to the conversion ratio:

]

Calculate the relationship between the average cubic current and voltage conversion rate of the input capacitor, as shown in Figure 2 below. It can be seen that when V is half of V, C's current stress is the most. The worst current stress on C is 0.5x IO.

For reliable operation and best performance, the input capacitor must have a rated current higher than i under the worst working conditions. Ceramic capacitors are the preferred input capacitors because their low ESR and high -current rated values. Depending on the application circuit, other low ESR 钽 capacitors can also be used. When selecting ceramic capacitors, the X5R or X7R -type medium ceramic capacitor should be used to obtain better temperature and voltage characteristics.

Note that the ripple current rated value of the capacitor manufacturer is based on a certain service life. The actual design may need to be further reduced.

sensor

The inductor is used to provide a constant current output, it is driven by a switch voltage. For the given input and output voltage, the inductance and switching frequency determine the current ripple current, that is,:

The peak of the inductor current is:

[ 123]

High inductor provides low -induced ripple current, but requires a larger dimension to avoid saturation. Low -line wave current reduces the inductive iron heart loss. It also reduces the balance of the square root of the inductance and switch, thereby reducing the conduction loss. Generally, the wire ripple current in the inductance is designed to be designed to 20%to 30%of the output current.

When selecting an inductor, make sure that the peak current can be processed even at the highest working temperature.

The highest current in the antihypertensive circuit. The conduction loss in the inductance needs to check whether it meets the heat efficiency requirements.

Coilcraft, Elytone, and Murata offers different shapes and styles of surface stickers. The volume of the shielded inductance and small radiation electromagnetic interference. But their price is higher than the shielding sensor. Selecting depends on electromagnetic interference requirements, prices and size.

Output capacitor

Select the output capacitor according to DC output voltage, output ripple voltage specifications, and ripple current rated values.

The rated voltage specifications of the selected output capacitor must be higher than the maximum expected output voltage (including ripples). Long -term reliability needs to be relegated.

Output ripple voltage specifications are another important factor in selecting output capacitors. In the BUCK converter circuit, the output ripple voltage is determined by inductance value, switching frequency, output capacitance value and ESR. Can be calculated through the following formula:

In the formula, the CO is the output capacitor value, and ESRCO is the equivalent series resistance of the output capacitor.

When a low ESR ceramic capacitor is used as the output capacitor, the impedance of the capacitor at the switch frequency is dominated. Output ripples are mainly caused by capacitor values and inductive ripples. The calculation of the output ripple voltage can be simplified to:

When the ESR impedance of the switch frequency dominates, the output ripple voltage is mainly determined by the capacitor ESR and inductive ripple current. The calculation of the output ripple voltage can be further simplified to:

In order to reduce the output ripple voltage within the entire working temperature range, it is recommended to use X5R or X7R medium -type ceramics or other low ESR器 As an output capacitor.

In the buck converter, the output capacitor current is continuous. The equity of the output capacitor is determined by an inductive peak ripple current. The calculation method is as follows:

Generally, due to the low current stress, the ripple current rated value of the output capacitor is a small problem. When the choice of voltage reduction inductance is small and the electromotive ripple current is large, the output capacitor will produce stress.

Circle compensation

AOZ1022 uses peak current mode control, easy to use, and fast transient response. The peak current mode control eliminates the bipolar effect of the output L AMP; C filter. Greatly simplified the design of the compensation circuit.

Using peak current mode control, the Buck power level can be simplified into a single pole and a zero system in a frequency domain. The pole is the leading point, which can be calculated through the following formula:

Due to the output capacitor and its ESR, the zero point is the zero point of ESR. The calculation method is as follows:

Among them; CO is output filteringThe capacitor, RL is a load resistance value, and ESRCO is an equivalent series resistance of the output capacitor.

The compensation design is actually to obtain the expected gain and phase by changing the transformation of the transformer control loop. AOZ1022 can use several different types of compensation networks. In most cases, the series capacitors and resistance network settings connected to the COMP tube foot are set up to achieve a stable high -bandwidth control loop.

In AOZ1022, the FB pin and COMP pin are the inverter input and output of the internal error amplifier. The series R and C compensation networks connected to the COMP provide one pole and 10. The pole is:

Among them; GEA is a cross-guidance of an error amplifier, 200 × 10-6a/v, GVEA is an error amplifier voltage; and C2 is compensation in Figure 1 in Figure 1 Capacitor.

The zero point given by external compensation network capacitor C and resistor R is located at:

In order to design the compensation circuit, the target cross frequency F must be selected as a closed loop. System cross -frequency is where the control loop has a unit gain. Cross is also called converter bandwidth. Generally, higher bandwidth means a faster response to the load transient. However, considering the stability of the system, the bandwidth should not be too high. When designing compensation circuits, the stability of the converter must be under all lines and load conditions.

Generally, it is recommended to set the bandwidth to 1/10 of the equal or less than the switch frequency. AOZ1022 works within the frequency range of 350kHz to 600kHz. It is recommended to choose the cross frequency of less than or equal to 40kHz.

The strategy of selecting RC and CC is to set the cross frequency with RC and set the compensator zero with CC. Calculate RC with the selected cross frequency FC:

Among them; FC is the expected cross -frequency. In order to obtain the best performance, set the FC to about 1/10 of the switching frequency, VFB is 0.8V, GEA is a cross-guidance of error amplifier, 200 × 10-6A/V, and GCS is the cross-guided direction of the current detection circuit. 6.86A/V compensation capacitor C and resistance r together constitute zero. This zero point is placed near the main pole F, but below 1/5 of the selected cross -frequency. C can choose in the following ways:

The above equation can be simplified as:

You can find an easy to use on it. Application software, the software helps design and simulate compensation circuits.

Thermal management and layout considerations

In AOZ1022 antihypertensive regulator circuit, the high pulse current flows through two circuit circuits. The first loop from input powerThe capacity, V pins, LX pins, filtering inductances, output capacitors and loads start, and then return to the input capacitance by grounding. When the high -voltage side switch is turned on, the current flows in the first circuit. The second loop starts from the inductance, to the output capacitance and load, to the anode of the Schottky diode, to the cathode of the Schottky diode. When the low -voltage side diode is opened, the current flows in the second loop.

In the PCB territory, the area of the minimized two circuits can reduce the noise of the circuit and improve efficiency. It is strongly recommended to use the floor to connect the input capacitor, output capacitor and PGND pins of AOZ1022.

In the AOZ1022 antihypertensive voltage regulator circuit, the main power dissipation elements are AOZ1022 and output inductors. The total power consumption of the converter circuit can be measured by subtracting the output power by input power.

The power loss of the inductor can be calculated by the output current of the inductance and DCR.

The actual knot temperature can be calculated with the power consumption and the thermal impedance computing of the environment in AOZ1022.

The maximum knot temperature of AOZ1022 is 150 ° C, which limits the maximum load current capacity. At different ambient temperatures, the maximum load current of AOZ1022 is shown in the heating capacity curve.

The thermal performance of AOZ1022 is greatly affected by the PCB layout. During the design process, users should be careful to ensure that integrated circuits work under the recommended environmental conditions.

AOZ1022 is encapsulated with Epad SO-8. The layout of the best electrical and thermal performance is listed below. Figure 3 shows the PCB layout example of AOZ1022.

1. LX pins are connected to the internal PFET and NFET drainage pipes. They are the largest opening nodes with low -resistance heat conduction paths and noise. Connect a large copper plane to the LX pin to help heat dissipation.

2. Do not use the heat dissipation connection of the V and PGND pins. Pate the most copper area on PGND tube and V tube feet to help heat dissipation.

3. The input capacitor should be as close to the V pins and PGND pins as much as possible.

4. Preferred ground plane. If you do not use ground planes, separate PGND from agng and connect them at only one point to avoid couples of PGND pins noise to AGND pins.

5. Make the current from LX to L to CO to PGND's current trajectory as short as possible.

6. Pour copper plane in all unused circuit board areas and connect it to a stable DC node, such as V, GND or V.

7. Keep the sensitive signal track away from the LX tube.

Packaging size, dfn 5x4

Note:

1. Size and tolerance conform to Asme Y14.5M-1994.

2. All units are millimeters.

3. The position and terminal number of the terminal#1 in line with the JEDEC publication 95 SP-002.

4. Size B is suitable for metalized terminals, measured between 0.15mm and 0.30mm from the tip of the terminal.If the other end of the terminal has an optional radius, the size B should not be measured in the radius area.

5. The coexistence is suitable for terminals and all other bottom metal.

6. The drawings shown only for explanation.

7. The size with*is for reference only

8. pin 3 and pin 7 melting with DAP.