Features

Vehicle recognition number range: 2.7 volts to 5.5 volts

300 mia LDO current output

300 mAh 400 millico LDO output voltage

High output accuracy:? 1.5%

Quick LDO line/load transient response

400 mAh, 96%efficiency antihypertensive converter

#8226 : 25 Weian empty static current of the steps of the transformer

Turn off the current lt; 1 Wei'an

Low RDS (open) 0.4Ω integrated integrated Power switch

low dropout rate 100%duty cycle

1MHz switch frequency

123] overheating protection

Flowing protection

TDFN33-12 or STDFN33-12 packaging

- The temperature range of 40 ° C to+85 ° C

Application

Mobile phone

digital camera

#8226 Handheld instrument

microprocessor/DSP core/IO power supply

Palm -up computer and palm computer

Portable media playback Instrument

General description

AAT2500

is a member of the total power management chip of Analogictech #8482; (TPMIC) #8482;) product series. It is a low -voltage difference (LDO) linear regulator and an antihypertensive converter. The input voltage range is 2.7V to 5.5V, which is very suitable for single lithium ion/polymer batteries.

LDO has an independent input that can output a current with up to 300mA. Linear regulator is the performance of high -speed switches, fast transient response, and good power suppression ratio (PSRR). Other features include low static current and low voltage drops. The design of the 400 mAh antihypertensive converter is to minimize the size and cost of external components while maintaining a low -load static current.

Peak current mode control and internal compensation provides a stable converter with low equivalent series resistance (ESR) ceramic output capacitors very lowOutput ripples.

For the largest battery life, the increase in voltage converter increased to a 100%duty cycle, and at 400 mAh, it had a typical 180 millivolvoral voltage drop. The output voltage can be fixed, and it can also be adjusted by integrated P and N -channel MOSFET power grade and 1 MMS switch frequency.

AAT 2500 has 12 stitches TDFN33 or STDFN33 packaging, and the rated temperature range is -40 ° C to+85 ° C.

Typical application

Typical features

Unless otherwise explained, vehicle recognition number 5V, temperature index 25 ° C.

Unless otherwise explained, the vehicle identification number 5V, the temperature index 25 ° C, vehicle identification number vldo vcc vp.

Unless otherwise explained, the vehicle identification number 5V, the temperature index 25 ° C.

Figure Figure

Note: The internal resistor division includes ≥1.2V versions. For low -voltage versions, the feedback foot is directly connected to the error amplifier input terminal.

Functional description

AAT2500 is a high -performance power management chip, which consists of a buck converter and linear regulator. The BUCK converter is an high -efficiency converter that can output up to 400 mAh. The design frequency of the converter is 1.0 MM, only three external components (CIN, COUT, and LX) are required, and the stability of ceramic output capacitors. Linear regulator can output 300 mAh and stabilize with ceramic capacitors.

Linear regulator

The advanced circuit design of the linear regulator has been specially optimized to achieve very fast start and closing time. This proprietary CMOS LDO is also customized as a superior transient response characteristics. These characteristics are particularly important for applications that require fast power supply.

By rapidly starting the implementation of the control circuit, the basic control and feedback circuits in the LDO regulator are accelerated, thereby realizing the high -speed opening function. Quick shutdown time response is achieved through an activated output drop -down circuit. The circuit is enabled when the LDO regulator is in the turnover mode. This active and fast shutdown circuit has no adverse effects on the normal operation of the equipment. The output of the LDO regulator is specially optimized and can be used with low -cost, low ESR ceramic capacitors; however, this design will allowRun the type.

Provides a bypass pipe foot that allows an optional reference voltage bypass electrical container to reduce output self -noise and increase power supply ripple suppression. Adding a small ceramic capacitor to the foot can increase the self -noise and PSRR of the device. However, the increase in the CBYPASS value may slow the opening time of the LDO regulator. The regulator is equipped with complete short circuit and heat protection. The combination of these two internal protection circuits provides a comprehensive security system to prevent extremely harsh operating conditions.

The regulator has enable/disable function. This pin (ENLDO) is high -level -based, compatible with CMOS logic. To ensure that the LDO regulator is opened, the control level of ENLDO must be greater than 1.5V. When the voltage on the EN pin is lower than 0.6V, the LDO regulator will enter the disabled closing mode. If you do not need to be enabled in a specific application, you can bind it to the vehicle recognition number to keep the LDO regulator continuously open.

When the regulator is in a close mode, an internal 1.5kΩ resistor is connected between the output and ground. This is to release the COUT when the LDO regulator is disabled. The internal 1.5kΩ resistor has no adverse effects on the power of the device.

Anti -pressure converter

AAT2500 Buck is a constant -frequency peak current PWM converter with internal compensation. Its design input voltage range is 2.7V to 5.5V. The output voltage range is 0.6V to the input voltage of the internal fixed version, and the input voltage from 2.5V to the external adjustable version. The 0.6V fixed model shown in FIG. 1 is also a adjustable model. External programming can be performed through a resistor division, as shown in Figure 2. The size of the converter MOSFET power level is 400 mAh's load capacity, up to 96%of the efficiency. Under the load of 500 Weian, light load efficiency exceeds 80%.

Soft starting

When the input power supply or enable input to be applied, the AAT 2500 soft start control can prevent the output voltage from adjusting and limit the surge current. When pulling down, the enable input force the converter into a low power, no switching state, and the bias current is less than 1 microan.

The operation of the low dropout rate

For the situation where the input voltage drops to the output voltage level, the converter's duty ratio increases to 100%. When nearly 100%duty occupy the duty ratio, the minimum off -cutting time was forced to force the high -pressure side to start over 1MHz clock cycle and reduce the effective switching frequency. Once the input drops below the level that can be adjusted, the high -voltage side P channel MOSFET will continue to open a 100%duty cycle. Under a 100%duty cycle, the output voltage tracking input voltage minus the IR drop of the high -voltage P channel MOSFET RDS (on).

Low supply

Impurous voltage lock (UVLO) guarantees that there are sufficient VIN bias and normal work before activating all the internal circuits.

Fault protection

For overload, the peak of the inductance current is limited. When the internal dissipation or the environmental temperature is too high, the heat protection will be disabled. The over -temperature threshold is 140 ° C, and the lag is 15 ° C.

Application information

Linear regulator

Input and output capacitors: The basic operation of the linear regulator does not require a capacitor. However, if the physical location of the AAT2500 is more than 3 cm input, the CIN capacitor is required to stabilize the work. Generally, in most applications, CIN is recommended to use 1 μF or larger capacitors. CIN should be as close to the device's VIN pin.

Input capacitors greater than 1 μF will provide superior input cable transient response and maximize the suppression of power ripples. Ceramics, pupa or aluminum electrolytic capacitors can be used for CIN. CIN does not have specific capacitors ESR requirements. However, for the output operation of the 300MA LDO regulator, ceramic capacitors can withstand the input current from low impedance sources (such as batteries in portable devices) due to its inherent abilities that are inherently capable of comparison capacitors.

In order to adjust and operate stability in appropriate load voltage, a capacitor is required between the output and ground. The COUT capacitors should be connected to the LDO regulator to the LDO regulator as much as possible to obtain the maximum equipment performance. Because the regulator is designed to use a very low ESR capacitor, it is recommended to use ceramic capacitors from 1.0 μF to 10 μF to obtain the best performance. Applications with extremely low output noise and best power ripples should be used with 2.2 μF or higher COUT. In the low output current application, when the output load is less than 10mA, the minimum value of the COUT can be as low as 0.47 μF.

Equivalent series resistance: When choosing a capacitor, ESR is a very important feature. ESR is an internal series resistance related to capacitors, including lead resistance, internal connection, size and area, material composition and ambient temperature. Generally, the capacitor ESR of ceramic capacitors is measured in the units of the mile, and the ESR of 钽 or aluminum electrolytic capacitors can exceed a few ohms.

Wingrser's container and low noise applications

In order to improve the low noise characteristics of LDO, a bypass tube foot was designed. Wingrser's container does not need to run; however, in order to obtain the best device performance, a small ceramic capacitor should be placed between 470pf to 10NF between the bypass (BYP) and the grounding pin (GND). In order to actively achieve the highest power ripple suppression and the lowest output noise performance, the capacitor connection between the ByP pin and the GND pin must be direct, and the PCB line should be as short as possible.

On this pinDC leakage affects the output noise and voltage regulatory performance of the LDO regulator. Therefore, it is strongly recommended to use low leakage, high -quality ceramics (NPO or C0G) or thin film capacitors.

Anti -pressure converter

Sensor selection: The antihypertensive converter uses the peak current mode control with slope compensation to maintain the stability of the duty cycle of more than 50%. The output inductance value must be selected to meet the inside slope compensation requirements for the decrease of the inductive current. The internal slope compensation of AAT2500's adjustable and low -voltage fixed version is 0.24A/microsecond. This is equivalent to the slope compensation of 1.5V output and 4.7 μH inductance, that is, 75%of the inductive current leaning down.

This is the internal slope compensation of the adjustable (0.6V) version or the low -voltage fixed version. When an external programming 0.6V version is 2.5V, the calculated inductance is 7.5 μH.

In this case, select the standard 10 μH value.

For high -voltage fixed type (2.5V and above), M 0.48A/microsecond. Table 1 shows the inductance value of AAT2500 fixed and adjustable options.

The manufacturer specification lists the rated value (thermal limit) and the peak current rated value (determined by the saturation characteristics). Under normal load conditions, the inductor should not have obvious saturation. Some inductors may meet the peak and average current rated values, but due to high DCR cause excessive loss. When selecting an inductance, we must consider the loss of DCR and its impact on the efficiency of the total converter.

The 4.7 μH CDRH3D16 series induction of Sumida has 105MΩDCR and 900mA DC rated current. At full load, the inductance DC loss is 17mW, with 400mA and 1.5V output, the efficiency loss is 2.8%.

Input a capacitor

Select a 4.7 to 10 micro F X7R or X5R ceramic capacitor as input. To estimate the required input capacitor size, determine the acceptable input ripple level (VPP) and solve C. The calculation value changes with the input voltage, and it is the maximum value when VIN is twice the output voltage.

When selecting the appropriate value, be sure to check the characteristics of the DC voltage coefficient of the ceramic capacitor. For example, the capacitors of 10 μF, 6.3V, and X5R ceramic capacitors for 5.0V DC are actually about 6μF.

The maximum input capacitor's average square current current is:

The input capacitor RMS ripple current changes with the input and output voltage, and it is always less than or equal to the total total. Half of the DC load current.

The term

appeared in the input voltage ripple and the input capacitor RMS current equation, and it was the maximum value when Vobuck was two VIN. This is why the input voltage ripple and the input capacitance RMS current ripples are the biggest reasons when the 50%duty occupation ratio. Apkobak · 1

Input a low impedance circuit for the edge of the pulse current generated by AAT2500. Low ESR/ESL X7R and X5R ceramic capacitors are ideal choices for this feature. In order to reduce the sensation, the capacitor should be close to the integrated circuit as much as possible. This will keep the high -frequency component of the input current maintained, minimize EMI and input voltage ripples.

The correct position of the input capacitor (C2) can be seen in the assessment board layout in Figure 3.

The laboratory testing device is usually composed of two long wires from the power supply of the workbench to the assessment board input voltage pins. The inductance of these wires, coupled with low ESR ceramic input capacitors, can create a high Q network, which may affect the performance of the converter. In the process of load transient, this problem often becomes obvious in the form of excessive output voltage. The error in the loop phase and the gain measurement will also occur.

Because the inductor input voltage of the short PCB tracking feed is significantly lower than the power cord of the workbench power, most applications do not exist in this problem.

In the application of the input power supply, the inductance inductance cannot be reduced to the level that does not affect the level of the flow device, high ESR 钽 or aluminum electrolytes and low ESR, ESL bypass ceramics Put in parallel. This will suppress high Q network and stabilize the system.

Output capacitor

The output capacitor limits the output ripple and provides a maintenance rate during the large load conversion period. 4.7 μF to 10 μF X5R or X7R ceramic capacitors usually provide sufficient volume capacitors to stabilize the output during the large load conversion period, and has the ESR and ESL characteristics required for low output ripples.

The output voltage caused by the load transient state is determined by the capacitor of the ceramic output capacitor. In the process of increasing load current, ceramic output capacitors provide load current separately until the circuit response. During two or three switching cycles, the circuit response and the increase in inductance current increased to match the load current requirements. During the three switching cycles, the relationship between the output voltage drop and the output capacitor can be estimated in the following ways:

Once the average inductor current increases to the DC load level, the output voltage will be recover. The above equation establishes a limitation of the minimum value of the output capacitor relative to the minimum value of the load transient.

The internal voltage loop compensation also limits the value of the minimum output capacitor to 4.7μF. This is due to its impact on the cross frequency (bandwidth), phase margin, and gain of gain. The increase in the increase of the output capacitance will reduce the cross frequency, and the phase of the increasing phase will increaseEssence

The maximum output capacitor RMS ripple current is given from the following formula:

Due to the loss of the losses in the ceramic output capacitance ESR, As a result, the hotspot temperature rose less than a few degrees.

Selection of adjustable output resistance

For applications that need adjustable output voltage, the 0.6V version can be programmed external. The resistance R1 and R2 in FIG. 5 to adjust the output to adjust at a voltage higher than 0.6V. In order to limit the bias current required for external feedback resistors, while maintaining good noise resistance, the recommended minimum is R2 to 59kΩ. Although the larger value will further reduce the static current, it will also increase the impedance of the feedback node, making it more sensitive to external noise and interference. Table 2 summarizes the resistance value under different output voltage. The R2 is set to 59kΩ (for good noise resistance) or 221kΩ (used to reduce the air load input current).

The adjustable version of AAT2500, combined with external front -feed capacitors (C8 in Figure 2 and Figure 5), provides enhanced transient response for extreme pulse load applications. Adding feed capacitors usually requires a larger output capacitor C1 to maintain stability.

One. For anti -pressure converters, enhanced transient configuration C8 100pf and C1 10UF.

Thermal calculation

AAT2500 Anti -pressure converter has three types of loss: switching loss, conduction loss, and static current loss. The conduction loss is related to the RDS (on) feature of the power output switching device. The switch loss is mainly determined by the grid charge of the power output switch device. At full load, assuming the simplified form of continuous pitching mode (CCM), antihypertensive converter and LDO loss are as follows:

IQBuck is the static current of the antihypertensive converter , IQLDO is the static current of LDO. The term TSW is used to estimate the switch loss of the full -load antihypertensive converter.

For the exit state when the buck converter is in a 100%duty ratio, the total device loss is reduced to:

due to RDS (on) The static current and switching loss are changed with the input voltage, so the total loss should be studied within the entire input voltage range.

Considering total loss, the maximum knot temperature of TDFN/STDFN33-12 can be exported by θ and θ is 50 ° C/W.

Print circuit board layout

The following guidelines should be used to ensure the correct layout.

1. Input capacitor C2 should be connected with VP and PGND as much as possible, as shown in the figure as shown in the figure4.

2. The output capacitance and inductance should be connected as close as possible. The connection between the sensor and the LX pin should also be as short as possible.

3. The feedback tracking should be separated from any power tracking, and connected to the load point as closely as possible. The sensing trajectory along the large current load will reduce the DC load adjustment. If an external feedback resistor is used, it should be placed at the position near the FB pin as much as possible. This prevents noise coupling to high impedance feedback nodes.

4. The trajectory resistance returned from the load should be kept at the minimum value. This will help reduce the DC regulatory error caused by the differences between the internal signal grounding and the power of the power supply level.

5. In order to obtain good thermal coupling, you need to get the PCB pores from the TDFN/STDFN lever to the PCB hole on the ground plane. The diameter of the pores should be 0.3mm to 0.33mm and is located on the 1.2mm grid.

6. LDO bypass electrical container (C5) should be directly connected between pin 7 (BYP) and pin 8 (GND)

Design examples of antihypertensive converter

[ 123] Specification

1.8V Anti -voltage output inductance

l1 3a #8901; v 3a #8901 ; 1.8V 5.4 μH (see Table 1),

1.8V output capacitor

Input a capacitor

] Enter the ripple rod VPP 25mv

AAT 2500 loss

[ 123] Pack information