Features

Input voltage range: 2.7V to 5.5V

four-channel LED drive:

-three-mode charge pump [ 123]

-Dori 20mA/channel

-S single interface, easy to control

-16 current level

-Four low-current settings, as low as 50 μA [ 123]

-The low IQ (50 μA) is suitable for low-current mode

- gt; 90%peak efficiency

Double 200MA LDO

# 8226; automatic soft start

overheating protection

provides 3x4mm TQFN34-20 packaging

-40 ° C to +85 ° C temperature range

Application

camera function power supply

White LED Backlight

General description

Aat2845A is a highly integrated power solution, which is suitable for the application of single battery lithium ion LCD display. It includes a four -channel LED backlit drive and two integrated 200mA LDOs, as an additional power supply for display and camera -related chipsets.

Backlight driver is a low noise, a constant -frequency charge pump DC/DC converter, which uses a three -mode load switch (1x), score (1.5X), and double (2x) conversion to maximize efficiency efficiency Essence Each of the four channels can drive 20mA current.

S2CWIRE #8482; (simple serial control #8482;) serial digital input for the current for enable, disable and set the current of each LED, and 16 available settings can be reduced to 50 μA. The low -current mode power current can be as low as 50 μA to save electricity and maintain high efficiency.

Each LED output is equipped with short -circuit and automatic disabled built -in protection device functions. Built-in-in the soft startup circuit, prevent excessive influx current during startup. The low -current shutdown function can disconnect the connection between the load and the vehicle identification number (VIN) and reduce the static current to below 1 μA.

AAT2845A is encapsulated with a lead -free heat enhancement type 20 needle 3X4mm TQFN.

Typical application

Typical features

CIN u003d CO1 u003d CO2 u003d 2.2 μF, C1 u003d C2 u003d 1.0 μF, CBP u003d 0.1 μF; TA u003d 25 ° C, unless otherwise explained. Typical values u200bu200bare TA u003d 25 ° C and vin u003d 3.6 V.

Figure Figure

Function description

T25A is a LCD display solution that integrates two LCD display power and LED backlit logic applications.

The backlight drive is a three -mode load switch (1x) and high -efficiency (1.5X or 2X) charge pump device. In order to maximize the power conversion efficiency, the internal sensing circuit monitor the voltage required for each constant current exchange input, and set the load switch and the charge pump mode according to the input battery voltage and current exchange input voltage. Over time, when the battery is pushed to discharge, when any of the four current exchange input is close to disconnection, the charge pump will be enabled. The charge pump was initially launched in 1.5 times. If the output voltage of the charge pump is reduced to the output of any current source, the charge pump will automatically convert to the 2X mode. The charge pump only requires four external components: two 1 μF ceramic capacitors for charge pump flight capacitors (C1 and C2), a 1 μF ceramic input capacitor (CIN), and a 0.33μF to 1 μF ceramic charge pump output capacitor (COUT).

Four constant current input (D1 to D4) can drive four independent LEDs, and the maximum current of each LED is 20mA. The unused Sink input must be connected to the OUT pin; otherwise the parts will run in only 2X charge pump mode. The S2CWIRE serial interface enables the charge pump and sets the current exchange volume.

Evergrande output level settings

The constant current absorption level from D1 to D4 via the S2CWIRE serial interface based on the pairing scale of the first 12 code and the separate low of the last 4 code. Settings of the current. Since the input D1 to D4 is a truly independent constant current, the voltage observed on any given input will be determined by the difference between the actual positive voltage (VF) of the VOUT and the actual positive voltage (VF) driven by VOUT.

Because the current is programmable, it does not require PWM (pulse width modulation) or additional control circuit to control LED brightness. This feature greatly reduces the burden of microcontroller or system IC management LED or display brightness, allowing users to ""set and forget"". Through its high -speed serial interface ( gt; 1MHz data rate), the LED current driver can be changed continuously, with smooth transitions (for example, fade) or suddenly brightening or darker LED, providing users with complete programming and LED brightnessReal -time control.

The last four codes of the current level marking adopt the static current mode to improve the efficiency of low current settings. This model is particularly useful for low -current applications. In this application, the state of continuous and low -current maintained for a long time.

S2CWIRE serial interface

The current exchange volume is controlled by the S2CWire serial digital input of Analogictech. The interface records of the rising edge of the EN/SET pin and decoded it into 16 different states. The 16 -current level settings are shown in Table 1.

S2CWire serial interface has flexible timing function. Data can be recorded at a speed higher than 1MHz or slower (such as 15kHz). After the application data, EN/SET keeps high to lock the data. Once EN/SET is maintained in TLAT (500 μs) in the logical high level, the programming current becomes activated, and the internal data register is reset to zero. For subsequent current level programming, the number of ascending edges corresponding to the required code must be applied on the EN/SET pin. When the EN/SET pin remained low time exceeding TOFF (500 μs), AAT2845A entered the shutdown mode and extracted a current of less than 1 μA from the input. During the closure, the internal data register is reset to zero.

Automatic disable function

The charge pump in AAT2845A is equipped with automatic disable function for each LED channel. After the IC is enabled and activated, the test current (typical value) of 100 μA will pass through each receiver channel. If the voltage of a specific DX pin does not drop to a certain threshold, the channel will be disabled. This function is very convenient for disabled unused channels or during the LED fault short event.

Low -voltage differential regulator

AAT2845A includes two LDO linear regulators. The input voltage of the regulator is the same as the charging pump, from 2.7V to 5.5V. The regulator uses a single/off control input ENLDO. The LDO output voltage is set to the feedback input terminal (FBA or FBB) from the output end (OUTA or OUTB) through the resistor division. The ratio of the resistance value determines the output voltage of LDO. The 200MV low voltage difference between the 200mA load current allows the regulator to keep the output voltage adjustment.

Each LDO regulator can provide continuous load current up to 200mA. Both LDOs include current limit and heat overload protection to prevent load or LDO damage.

Thermal protection

The charge pump has a built -in thermal protection circuit. When the temperature of the chip rises to the thermal limit, if the output pin is short, the circuit will turn off the charge pump and LDO.

Application information

LED selection

AAT2845A is specifically used to drive white LEDs. However, the design of the device will allow AAT2845A to drive most types of LEDs, with a positive voltage specification of 2.0V to 4.7V. LED applications may include the display backlight, color (RGB) LED, infrared (IR) diode, and any other loads that need to be generated by different input voltages. Because the voltage dependence of D1 to D4 constant streaming can be ignored, regardless of the specific LED forward voltage (VF) level, the constant flow channel will match.

The low -voltage differential current exchange of AAT2845A maximizes the performance and enables it to drive LEDs with high positive voltage. Multiple channels can be combined to obtain higher LED -drive current without complex problems.

The noise performance of the device switch

AAT2845A works at a fixed frequency of about 1MHz to control noise and restrict the harmonic waves that might interfere with honeycomb phones or other communication equipment radio frequency operations. The reverse injection noise on the charging pump input pin is 20mv peak value, usually 10 times less than the inductive DC/DC boost converter white LED backlight solution. The AAT2845A soft startup function prevents the noise transient effect of influxing current during the launch of the charge pump circuit.

Turn off

Since the Sink switch is the only power supply of all loads, when all Sink switches are disabled, there is no leakage current. To activate the shutdown mode, keep the EN/SET input at a low time exceeding TOFF (500 μs). In this state, AAT2845A usually extracts a current of less than 1 μA from the input. When closed, the data and address registers are reset to 0.

LDO output voltage programming

The output voltage of the LDOA and LDOB is programmed by the external resistance compressor network. As shown below, choosing R8 and R9 is a simple problem.

Choose R9 by considering the compromise between the feedback network bias current and the resistance value. Higher resistance values u200bu200bare allowed to become a major factor in the performance of the circuit, and the lower resistance value increases the bias current and reduces efficiency.

In order to choose the appropriate resistance value, the bias current of the feedback network was selected reasonably. Then, calculate R8 based on the required VOUT. The following is an example of calculation.

Select R9 to 120K, generate a small feedback network bias current with 1.2V/120K u003d 10μA. The expected output voltage is 1.8V. According to this information, R8 is calculated based on the following equal formula.

The result is R8 u003d 60K. Because 60K is not a standard 1%value, 60.4K is selected. Calculated according to this example, for VOUT u003d 1.8V, use R9 u003d 120K and R8 u003d 60.4K. Here are forms that provide a form output voltage and the corresponding resistance value.

Power efficiency and device assessment

The charge pump efficiency discussion in the following chapters only indicates the efficiency of the charge pump itself. Due to the unique circuit structure and design of AAT2845A, it is difficult to measure efficiency with the percentage value of input power and output power.

Because the output of AAT2845A is a purely constant current-rents decrease, usually drive a single load, it is difficult to measure the output voltage of a given output (D1 to D4), thereby obtaining the overall output power measurement value. For any given application, the white LED may be different in the voltage level, but the output drive current will remain constant.

This makes the quantitative output power become a difficult task when comparing the topology of other white LED drive circuit. The better way to quantify the total efficiency of the equipment is to observe the total input power of the device at a given LED current driver level. For a given application, the best white -light LED drive should be based on size, number of external components, reliability, scope of work, and total energy use, not just the percentage of efficiency.

The efficiency of AAT2845A can be quantified under very specific conditions, and depends on the output voltage seen by the load from the output D1 to D4 under the input voltage and the load of the output D1 to D4 under a given constant current settings. According to the combination of VIN and the voltage sensitive at the current exchange, the device will run in the load switch mode. When any voltage at the current exchange is close to a decrease, the device will work in 1.5 times or 2 times the charge pump mode. Each mode generates different efficiency values. For descriptions of each operation mode, see the following two parts.

1x mode efficiency

AAT2845A 1X mode can always be operated, and run alone when Vin is higher than the load voltage to improve the power conversion efficiency of the equipment. In the 1x mode, the voltage conversion efficiency is defined as the output power divided by input power:

Define the ideal efficiency (η) expression can be rewritten to:

]

-or-

1.5 times and 2x charge pump mode efficiency

AAT2845A contains a score charge pump, which contains a score charge pump,, a score charge pump, which contains a score charge pump. When the vehicle recognition number (VIN) is less than the voltage required for the output power supply, the charging pump will increase the input power voltage. Efficiency (可以) can be simply defined as a linear voltage toneThe effective output voltage is equal to 1.5 times or twice the input voltage. The efficiency (η) of the ideal 1.5 times charge pump can usually be represented as the output power divided by input power.

In addition, for the ideal 1.5 times charge pump, the output current can be represented as 2/3 of the input current. Defining ideal efficiency (表) expression can be rewritten to:

-or-

5V, the nominal input of 3.5V charge pump, the theoretical efficiency is 95%. Due to internal switching loss and IC static current consumption, the actual efficiency can be measured to 93%. These numbers are very consistent under the output load conditions of 1MA to 100mA. When the load current drops below 1mA or VIN is close to VOUT, the efficiency will decrease significantly.

The same calculation is suitable for 2X mode, that is, the output current becomes 1/2 of the input current.

Capacitor selection

Careful choosing four external capacitors CIN, C1, C2, and COUT is important because they will affect the opening time, output ripples and transient performance. When using low -equate series resistance (ESR) ceramic capacitors, the best performance will be obtained; usually, low ESR can be defined as less than 100MΩ. When choosing a capacitor, the value of all four capacitors is 1 μF is a good starting point. If Hengliuhui is only programmed for small current levels, the size of the capacitor may be reduced.

Capacitor characteristics

Ceramic composite capacitors are strongly recommended to all other types of capacitors used in Aat2845A. Compared with 钽 and aluminum electrolytic containers, ceramic capacitors have many advantages. Ceramic capacitors usually have very low ESRs, the lowest cost, small PCB occupied area, and is non -polarized. Low ESR ceramic capacitors help to maximize the charge pump transient response. Because ceramic capacitors are non -polarized, they are not prone to incorrect connection damage.

Equivalent series resistance

ESR is an important feature to consider when choosing a capacitor. ESR is the resistance inside the capacitor, which is caused by wire, internal connection, size or area, material composition and ambient temperature. The capacitance heavy molten melting is a typical-ceramic capacitor measurement unit is millometer, and the measurement range of 钽 or aluminum electrolytic capacitors can reach more than a few ohm.

Ceramic capacitor materials

Ceramic capacitors less than 0.1 μF are usually made of NPO or C0G material. NPO and C0G materials usually have strict tolerance and are very stable at ultra -temperature. Larger capacitors are usually composed of X7R, X5R, Z5U or Y5V media materials. Large ceramic capacitors (that is, greater than 2.2μF) can usually be used in low -cost Y5V and Z5U media, but the AAT2845A application usually does not require capacitors greater than 1 μF.

The area of u200bu200bthe capacitor is another factor in the heavy melting of electric slag. Compared with capacitors with smaller materials, larger capacitors have lower ESRs. Compared with equivalent capacitors with smaller packaging size, these larger devices can improve the transient response of the circuit.

Evaluation board layout

Evaluation board user interface

AAT2845A evaluation board's user interface is provided by three buttons and two connection terminals provided Essence The board of directors supply external power and press a single button or button combination. The following table shows the function of each button or button combination.

To connect the power supply of the evaluation board, connect the power or battery to DC-and DC+terminals. Place the J1 cross -connected line to the ON position and turn off the power connection of the circuit board. Red LED indicates that it is powered on.

The assessment board is flexible so that users can disconnect the enable and microcontroller and the external enable enabled signal. From jumping lines on J2 and/or J3, the external signal can be applied to the board of directors. The external enable signal must be applied to the ON pins of each J2 or J3 terminal.

When an external enable signal is enabled, the voltage level must be considered. The external voltage applies should not exceed the auxiliary voltage applied to the tolerance of the device (DC+).

LDO load can be directly connected to the evaluation board. In order to obtain sufficient performance, make sure to connect loads between Outa/OUTB and DC instead of other GNDs in the system.

Order information

Packaging information [

123]

[1]. The stress that exceeds the absolute maximum rated value may cause permanent damage to the device. Do not hint to perform functional operations under conditions other than prescribed operation conditions. Only one absolutely maximum rated value can be applied at a time.

[2]. Based on long -term current density restrictions.

[3]. The ambient temperature is 20mW/° C above 40 ° C.

[4]. Installed on the FR4 circuit board.

[5] .aat2845A guaranteed to meet performance specifications within the working temperature range of -40 ° C to+85 ° C, and was guaranteed by designing, characteristic, and controlling the correlation with statistical process control.

[6]. The current matching is defined as the average value of any exchange current departs from all activity channels.

[7] .aat2845A guaranteed from -40 ° C to+85 °C meets the performance specifications within the operating temperature range of C, and is guaranteed through design, characteristic and statistical control.

[8]. ""+"" Means pressing and release these buttons at the same time.

[9] .xyy u003d assembly and date code.

[10]. Sample inventory is usually based on the part number displayed by the thick body.

[11]. Lead -free packaging series include QFN, TQFN, DFN, TDFN, and STDFN. Due to the manufacturing process, there are naked copper (unsolved) at the end of the lead terminal.The welding angle of the exposed copper edge cannot be guaranteed, nor does it need to ensure that the bottom welding connection is correct.