Features

4.5 V to 18 V working input voltage range

Synchronous antihypertensive: 70 mΩ internal high -voltage side switch and 40 mΩ internal low -voltage side switch (12 v)

efficiency as much as 95%

outer soft start

output voltage can be adjusted to 0.8 v [123 123 ]

3 A continuous output current

500 kHz pulse width modulation operation

weekly current limit

Start of the pre-partial pressure

short circuit protection

heat shutdown

exposed cushion SO-8 packaging

Application

Load point DC/DC converter

LCD TV

Top box

DVD and Blu -ray player/recorder

Wired modem

General description

aoz1051pi

is an efficient, easy, easy Use 3 A synchronous antihypertensive regulator. AOZ1051PI works within the input voltage range of 4.5V to 18V, and provides continuous output current and output voltage up to 3A to 0.8 V.

AOZ1051PI is encapsulated with exposed pads SO-8, and the rated working environment temperature range is between -40 ° C to+85 ° C.

Typical Application

Typical performance features

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

Efficiency

Detail There are integrated high -voltage side PMOS switches and low -voltage side NMOS switches. AOZ1051PI works within the input voltage range of 4.5 V to 18 V, and provides a load current of up to 3 A. Functions include enabling control, power -on reset, input -under pressure lock, output overvoltage protection, external soft start and heat shutdown.

AOZ1051PI has one outsideThe exposed gasket SO-8 package.

Enable and soft start

AOZ1051PI has an external 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 4.1V and the voltage on the EN pin is high, the soft start process begins. During the soft startup process, the FB voltage gradually increased to follow the voltage of the soft starting pin until it reached 0.8V. The voltage of the soft starting pin is charged from the internal 5 μA current.

The EN pin of AOZ1051PI is in a high activation state. If the enlightenment function is not used, the EN pin is connected to the vehicle identification number. Aoz1051pi will be disabled by EN. Don't let the door open. The voltage on the EN pin must be higher than 2 V to enable AOZ1051PI. When the EN pin voltage is lower than 0.6 V, AOZ1051PI is disabled.

Stable operation

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

AOZ1051PI 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 removed from the external pressure device 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 pin is compared with the current signal (the sum of the inductance current signal and the slope compensation signal) input with the PWM comparator. 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. 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, AOZ1051PI 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.

AOZ1051PI 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. It also allows 100%to turn on the high -voltage side switch to achieve a linear adjustment operation mode. The minimum voltage drop from V to V is the DC resistance of the load current by MOSFET, plus the DC resistance of the BUCK inductor. Its calculation formula is as follows:

Among them: VO_MAX is the maximum output voltage, VIN is from 4.5 to 18 volt input voltage, IO is output from 0 a to 3 a output The current, and RDS (ON) is the internal MOSFET drive resistance.

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 R1 and R2.

The combination of R1 and R2 should be large enough to avoid excessive current from the output end, which will cause power loss.

Because the switching ratio can be as high as 100%, the maximum output voltage can be set to the high -level input voltage to reduce the voltage drop on the PMOS and inductance.

Protection feature

AOZ1051PI has multiple protection functions to prevent the system circuit from damaging in abnormal conditions.

Over current protection (OCP)

The inductive induction current signal is also used for over -current protection. Because AOZ1051PI 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 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 AOZ1051PI. Compare the measured inductance current with the preset voltage (between 3.5 A and 5.0 A) of the current limit of the current. 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 converter starts working. When the input voltage is lower than 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 AOZ1051PI 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 AOZ1051PI 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.

Input ripple voltage can be approximately similar to the following formula:

Since the input current of the BUCK converter is discontinuous, when choosing a capacitor, the current stress on the input capacitor is another problem that needs 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:

]

The relationship between the input capacitor's average cubes and voltage conversion rates is 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 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 selectedAnother important factor in the capacitor. 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 an equivalent connected resistance capacitor output.

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

AOZ1051PI 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 a single pole and a zero system in a 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. AOZ1051PI 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 AOZ1051PI, FB and COMP are the reverse 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 an error amplifier cross-guided, 200 X 10-6 A/V, GVEA is the voltage gain of the error amplifier, 500V/v, CC is the compensation capacitor in Figure 1 in Figure 1 Essence

The zero point given by external compensation network capacitors CC and resistor RC 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 C. Calculate RC with the selected cross frequency F:

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-guided by an error amplifier, that is, 200 x 10-6 A/V, and GCS is the cross-guided by the current detection circuit. It It is 8 volts.

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 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 AOZ1051PI antihypertensive regulator circuit, the high pulse current flows through the 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 capacitors, output capacitors, and PGND pins of AOZ1051PI.

In AOZ1051PI antihypertensive regulator circuit, the main power consumption elements are AOZ1051PI and output inductors. The total power consumption of the converter circuit can be reduced with input powerDrop output power to measure:

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

]

Actual knot temperature can be calculated through the power consumption and thermal impedance computing of the environment in AOZ1051PI:

The maximum knot temperature of AOZ1051PI is 150 ° C. This limit is limited Maximum load current capacity.

AOZ1051PI'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

AOZ1051PI is an exposed pad SO-8 package. Here are some of the best electrical and thermal properties.

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

2. Do not use the heat dissipation connection of the vehicle recognition number pin or the PGND password. Pour the maximum copper area into the PGND pin and VIN pin that helps heat dissipation.

3. The connection of the input capacitor should be as close as possible to the vehicle recognition code (VIN) and the vehicle identification code (PGND).

4. Preferred ground plane. If the ground plane is not used, separate PGND from agng, and only connect them to a point of noise to AGND sales at a point at one point.

5. The current trajectory from LX pad to L to CO is as short as possible as possible.

6. In all unused board areas and connecting 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 bag does not include mold flying edges and pouring bonded burrs. Essence

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