Features

4.5 V to 18 V working input voltage range

Synchronous antihypertensive: 85MΩ internal high -voltage side switch and 50MΩ internal low -voltage side switch (12V 12V )

pulse energy mode (PEM) makes efficiency greater than 85%

IOUT 10 mia (vehicle identification number 12 volts, output voltage 5 volts ilcus )

350 Weian power supply current under typical applications

efficiency is as high as 95%

internal soft start

output voltage can be adjusted to 0.8V

3 A continuous output current

500 kHz pulse width modulation operation

] cycle -by -cycle current limit

Pre -definition startup

short circuit protection

hot turnover

exposed pad SO-8 packaging

Application

Load point DC/DC converter

LCD TV [ 123]

Top Box

DVD and Blu -ray player/recorder cable modem

General description

AOZ3015pi

is a highly efficient and easy -to -use 3A synchronous antihypertensive regulator. AOZ3015PI works within the input voltage range of 4.5V to 18V, providing a continuous output current of up to 3A, and the output voltage can be reduced to 0.8V. AOZ3015PI is encapsulated in SO-8 with exposed pads, and the temperature range of the rated working environment is between -40 ° C to+85 ° C.

Typical application

block diagram

Typical performance features [[[] 123] The circuit in FIG. 1. T 25 ° C, V V 12 V, V 3.3 V, unless there are other regulations.

Detailed description

AOZ3015PI is a current mode antihypertensive regulator with integrated high -side PMOS switch and low -side NMOS switch. AOZ3015PI from 4.5V to 18V input voltage rangeInternal work provides a load current of up to 3A. Functions include enabling control, power -on reset, input -under pressure lock, output overvoltage protection, internal soft start and heat shutdown.

AOZ3015PI can be used in an exposed pad SO-8 package.

Enable and soft start

AOZ3015PI has an internal soft startup function, which can limit the impact current and ensure that the output voltage rises smoothly to the adjustment voltage. When the input voltage rises to 4V and the voltage on the EN pins is high, the soft start process begins. During the soft startup process, the output voltage usually becomes a adjustable voltage within 5 milliseconds. 5 millisecond soft starting time is set internally.

The EN pin of AOZ3015PI is in a high activation state. If the connection is not used, enter it to the vehicle recognition number. Aoz3015pi will be disabled. Don't let the door open. The voltage on the EN pin must be higher than 2 V to enable AOZ3015PI. When the EN pin voltage is lower than 0.6 V, AOZ3015PI is disabled.

Light load and pulse width modulation operation

Under the setting of low output current, AOZ3015PI will work with pulse energy mode to obtain high efficiency. In the pulse energy mode, the PWM will be closed until the inductance current reaches 800mA and the current signal exceeds the error voltage.

Stable operation

Under large load steady -state conditions, the converter works in the fixed frequency continuous direction mode (CCM).

AOZ3015PI 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 and reference voltage of the FB tube foot through the internal cross -guidance error. 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 inductor 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. Internal adaptive FET drivers ensure that high and low -side switches will not open overlap.

Compared with the voltage regulator using the free rotation of the Schartki diodes, AOZ3015PI uses free rotation NMOSFET to achieve synchronous rectification. This greatly improves the efficiency of the converter and reduces the power loss of the low -voltage side switch.

AOZ3015PI uses P channel MOSFET as a high -voltage side switch. This saves the guidance capacitance that is usually seen in the circuit using NMOS switches.

Output voltage programming

The output voltage can be set up to the FB pins by using the resistance division of the resistor shown in Figure 1. The resistor network includes R and R. Usually, the design starts by selecting a fixed R value and using the following formula calculation:

Table 1 lists some of the most common output voltage standards for the most common output voltage. Value R and R.

The combination of R and R should be large enough to avoid excessive current from the output end, which will cause power loss. 12

Protection feature

AOZ3015PI has multiple protection functions to prevent system circuits from damaging system circuits.

Over current protection (OCP)

The inductive induction current signal is also used for over -current protection. Because AOZ3015PI 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 3.1V. The peak current of the inductance is the automatic restriction cycle.

When the output is short -circuited under the ground under failure, the inductor current is slowly attenuated during the switching cycle because the output voltage is 0V. In order to prevent catastrophic failure, secondary current restrictions were designed within AOZ3015PI. Compare the measured inductor current with the preset voltage of the current limit. 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 and resetting (POR)

Monitoring input voltage of the power -up reset circuit. When the input voltage exceeds 4V, the inverter starts to work. When the input voltage drops below 3.7V, the inverter will be closed.

Hot protection

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

Application information

The basic AOZ3015PI 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 AOZ3015PI 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. Anti -pressure reductionCircuit, the balance of the input capacitance current can be calculated through the following formulas:

If we let M equal to conversion ratio:

]

The relationship between the input capacitors and the voltage conversion rate of the capacitors is shown in Figure 2 below. It can be seen that when V is half of V, C's current stress is the most. CIN's maximum current stress is 0.5x IO.

For reliable operation and best performance, the rated current of the input capacitor must be higher than 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 be used. When selecting ceramic capacitors, the X5R or X7R -type medium ceramic capacitor should be used to obtain better temperature and voltage characteristics. Please note that the ripple current rated value of the capacitor manufacturer is based on a certain working life. Long -term reliability may need to consider further reduction.

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 40%of the output current.

When selecting an inductor, it is confirmed that it can process the peak current at the highest working temperature and not saturate.

The highest current in the antihypertensive circuit. The conduction loss on the inductor needs to check whether it meets the heat and 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. However, they are more expensive than non -shielded inductors. 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 measured by the following formulaCount:

Among them, 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电 Capacitors are used as output capacitors.

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

AOZ3015PI is controlled by peak current mode, which is easy to use and fast transient response. The peak current mode control eliminates the bipolar effect of the output L AMP; C filter. It also greatly simplifies the design of the compensation circuit.

Using peak current mode control, the buck power level can be simplified into one pole 10 system in the frequency domain. The pole is the main 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 the output filter capacitor, RL is a load resistance value, and ESRCO is an equivalent series resistance for output capacitors.

Compensation design makes the transform control loop transfer function to the expected gain and phase. AOZ3015PI 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 AOZ3015PI, FB and COMP are the inverter input and output of internal error amplifiers. 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 x 10-6 A/V.500V/V, CC is the compensation capacitor in Figure 1.

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

In order to design the compensation circuit, the target cross frequency F must be closed to close the ring ring road. 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.

The strategy of selecting R and C is to set the cross frequency with R 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, the FC is set to about 1/10 of the switch frequency; VFB is 0.8V, GEA is a cross-guidance of error amplifier, 200 × 10-6A/V, and GCS is the cross-guided by the current detection circuit. It It is 8 A/V compensation capacitor C and resistance R together to form zero.

This zero point is placed near the main polar point F, but below 1/5 of the selected cross frequency. C can choose in the following ways:

The above equation can be simplified to:

A easy -to -use application software, It can be found to help design and simulation compensation circuits.

Precautions for thermal management and layout

In AOZ3015PI antihypertensive regulator circuit, high pulse current flows through two circuits. The first loop starts from the input capacitor, to the vehicle recognition code pins, to LX pad, to the filtering inductance, to the output capacitor and load, and then return to the input capacitor by grounding. When the high -voltage side switch is turned on, the current flows in the first circuit. The second loop starts from electrical sensors, to output capacitors and loads, and then to low -end NMOSFET. When the low -pressure NMOSFET is opened, the current flows in the second loop.

In the design of the PCB layout, the area of the minimized two circuits can reduce the noise of the circuit and improve efficiency. It is strongly recommended to use the ground plane connection input capacitor, output capacitor, and PGND pins of AOZ3015PI.

In AOZ3015PI antihypertensive regulator circuit, the main power consumption elements are AOZ3015PI and output inductors. The total power consumption of the converter circuit can be measured by input power to subtract the output power:

The power consumption of the inductor can be calculated by the output current of the inductor and the DCR value of the DCR value. :

The actual knot temperature can be calculated through the power consumption and the thermal impedance of the paired environment in AOZ3015PI:

aoz3015pi The maximum knot temperature is 150 ° C, which limits the maximum load current capacity.

AOZ3015PI's thermal performance is greatly affected by the PCB layout. During the design process, pay attention to ensure that the integrated circuit works under the recommended environmental conditions.

Precautions for layout

AOZ3015PI is an exposed Pad So-8 package. In order to obtain the best electrical and thermal performance, some layout tips are listed.

1. The exposed pad (LX) is connected to the internal PFET and NFET drain pipes. Connect a large copper plane to the LX pin to help heat dissipation.

2. Do not use the cooling connection of the vehicle recognition number (VIN) pin or PGND pin. Pour the largest copper area into the PGND pin and vehicle recognition code pin to help heat dissipation.

3. Input a capacitor should be as close to the vehicle identification number pins and PGND pins.

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

5. Make the current from LX pad to L to CO to PGND.

6. Pour copper planes on all unused circuit board areas and connect it to a stable DC node, such as VIN, GND or you.

7. Keep a sensitive signal tracking away from LX pads.

Packaging size, SO-8 EP1

Note:

1, the size of the package body does not include mold flying edges and the size Pour the burrs.

2. Size L measurement in the instrument plane.

3. Unless there are other regulations, the tolerance is 0.10 mm.

4. The control size is millimeter, and the inch size after conversion is not necessarily accurate.

5. The size of the mold pad is designed according to the lead framework.

6. Connect from Jedec MS-012.

Tape and roll size, so-8 EP1

Parts

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