General Instructions

The AAT3152 is a low noise, constant frequency charge pump DC/DC converter that utilizes tri-mode load switching (1X), division (1.5X) and frequency doubling (2X) conversion to maximize efficiency in white LED applications . The AAT3152 is capable of driving 4-channel LEDs from 2.7V to 5.5V input. The current sinks can be operated individually or in parallel to drive higher current LEDs. The low external part count (two 1µF flying capacitors and two small 1µF V and V capacitors) makes this part ideal for small battery powered applications.

Analog Technologies 8482 ; (Simple Serial Control™) Serial digital input for enabling, disabling, and setting current per LED, with eight settings (20mA to 50µA), including primary/secondary display group control . The AAT3152 consumes very low current (typically 80µA) internally at light loads for optimum efficiency.

Each output of the AAT3152 is equipped with built-in V short-circuit protection and automatic disabling in the event of a short-to-load condition. Built-in soft-start circuit prevents excessive inrush current during startup. A low-current shutdown feature disconnects the load from V and reduces quiescent current to less than 1 µA.

The AAT3152 is available in a space saving, enhanced 12-pin 3x3mm DFN package.

feature

• Voltage range: 2.7V to 5.5V

• Fully programmable single wire current

• Eight-step current: 20mA to 50µA

• Single primary subgroup control

• Low I (80µA) at light load

• Tri-mode 1X, 1.5X and 2X charge pumps for maximum efficiency and V coverage Type F

• Drive 1-4 LED channels

• Sensorless, low noise operation

• 1MHz constant switching frequency

• Small application circuit

• Built-in thermal protection

• Built-in short-circuit auto-disable function

• Automatic soft start

• I<1µA during shutdown

• Thermally enhanced 3x3mm 12-pin DFN package

application

• Color (RGB) lighting

• Programmable current sink

• White LED backlight

• White flash for DSC

typical application

Pin Description

Pin configuration

Absolute Maximum Ratings

notes:

1. Stresses in excess of the Absolute Maximum Ratings may cause permanent damage to the device. Functional operation under conditions other than specified operating conditions is not implied. Only one absolute maximum rating can be applied at a time.

2. Based on long-term current density limitations.

Hot information

notes:

1. Installed on the FR4 board.

2. Above 25°C, derate by 20 MW/°C.

Typical features

Functional block diagram

Function description

The AAT3152 is a three-mode load switch (1X) and high efficiency (1.5X or 2X) charge pump device for white LED backlight applications. To maximize power conversion efficiency, an internal sensing circuit monitors the voltage required at each constant current receiver input and sets the load switch and charge pump modes based on the input battery voltage and current receiver input voltage. As the battery discharges over time, the four current sink inputs approach dropout when the AAT3152 charge pump is enabled. The priming pump starts in 1.5X mode. If the charge pump output drops enough that any current source output is close to falling, the charge pump will automatically switch to 2X mode. The AAT3152 requires only four external components: two 1µF ceramic capacitors for the charge pump flight capacitors (C1 and C2), a 1µF ceramic input capacitor (C), and a 0.33µF to 1µF ceramic charge pump output capacitor (C).

Four constant current sink inputs (D1 to D4) can drive four individual LEDs, each with a maximum current of 20mA. Unused receiver inputs must be connected to V, otherwise the part will only work in 2X charge pump mode. The S2Cwire serial interface enables the AAT3152 and sets the current receive amplitude. S2Cwire addressing allows independent control of two sets of current sink inputs: D1-D3 and D4.

Constant current output level setting

The constant current receiver levels for D1 to D4 are set through the serial interface. No PWM (pulse width modulation) or additional control circuitry is required to control the LED brightness. This feature greatly relieves the microcontroller or system IC of managing LED or display brightness, allowing users to "set it and forget it." Through its high-speed serial interface (up to 1MHz data rate), the input receive current of the AAT3152 can be successfully changed to brighten or dim the LED, giving the user real-time control of the LED brightness. Since inputs D1 to D4 are truly independent constant current sinks, the voltage observed on any given input will be determined by the actual forward voltage (V) of the LED being driven.

S2Cwire serial interface

The amount of current sink input on the AAT3152 is controlled by AnalogicTech's S2Cwire serial digital input. It depends on the number of rising edges of the EN/SET pin to address and load registers. S2Cwire locks data or address after EN/SET pin is held high for time T. The interface records the rising edge of the EN/SET pin and decodes it into 16 different states, as shown in the current settings table. There are four brightness levels for the primary or secondary display groups, and each group can be turned on or off individually. To further optimize power efficiency, the AAT3152 also offers four low current levels for dim LED operation (Data 13-16). In this low current mode, the internal supply current is typically reduced to only 80µA. lat

The counter can clock up to 1 MHz so that intermediate states are not visible. The first rising edge of EN/SET enables the IC and the ini to set the output LED current to 20mA. Once the final clock cycle for the desired brightness level is entered, the EN/SET pin will be held high to keep the device output current at the programmed level. The device is disabled for 500 microseconds (T) after the EN/SET pin transitions to a logic low state.

EN/SET timing is designed to accommodate a wide range of data rates. After the first rising edge of EN/SET, the charge pump starts and reaches full capacity after the soft-start time (T). During the soft-start time, multiple clock pulses can be input on the EN/SET pin, and a single clock pulse can be used to set the final output current level. Alternatively, the EN/set clock pulses can be entered one at a time to gradually increase the LED brightness over any desired time period. The current output remains constant as long as EN/SET remains logic high. When EN/SET is held low for at least T timeout; then, the AAT3152 enters shutdown mode and extracts less than 1µA from V. During shutdown, the data is reset to 0.

S2Cwire serial interface timing

Auto-disable feature

The AAT3152 is equipped with an "auto-disable" function for each LED channel. After the IC is enabled and powered up, a test current of 150 µA (typical) is forced through each receiver channel. If the voltage on a particular current sink pin does not drop below a certain threshold, the channel will be disabled. This feature is handy for disabling unused channels (by connecting the DX pin to V) or during an LED fault short-circuit event.

Thermal Protection

The AAT3152 has a built-in thermal protection circuit that will shut down the charge pump when the die temperature rises above the thermal limit, as if the V pin was shorted.

application information

LED selection

Although the AAT3152 is specifically designed to drive white LEDs, the device can also be used to drive most types of LEDs with forward voltage specifications ranging from 2.0V to 4.7V. LED applications may include primary and secondary LCD display backlights, camera photo flash applications, color (RGB) LEDs, remote control infrared (IR) diodes, and other loads that benefit from controlled output currents generated by varying input voltages. Since the D1 to D4 input current sinks are matched with negligible voltage dependence, the LED brightness will match regardless of the specific LED forward voltage (V) level. In some cases (e.g. in high light output applications such as flash) it may be necessary to drive high V-type LEDs. The low leakage current receiver in the AAT3152 enables it to drive LEDs with forward voltages up to 4.7V at full current from an input supply as low as 3.0V. The outputs can be paralleled to drive high current LEDs without complexity.

Device Switching Noise Performance

The AAT3152 operates at a fixed frequency of approximately 1MHz to control noise and limit hardware monitoring that could interfere with the RF operation of cell phone handsets or other communication equipment. The reverse injection noise present at the input pin of the charge pump is 20 mV peak-to-peak, typically ten times less than an inductor-based DC/DC boost converter white LED backlight solution. The AAT3152 soft-start feature prevents the effects of noise transients associated with fast current flow during start-up of charge pump circuits.

Capacitor selection

Careful selection of the four external capacitors

C, C1, C2, and C are important because they affect turn-on time, output ripple, and transient performance. Best performance is obtained when using low equivalent series resistance (ESR) ceramic capacitors. In general, low ESR can be defined as less than 100mΩ. All four capacitors have a capacitance value of 1µF, which is a good starting point for capacitor selection. If the LED current source is only programmed for small current levels, the size of the capacitor may be reduced.

Capacitor Characteristics

Ceramic synthetic capacitors are highly recommended compared to all other types of capacitors used with the AAT3152. Ceramic capacitors offer many advantages over tantalum and aluminum electrolytic capacitors. Ceramic capacitors typically have very low ESR, lowest cost, small PCB footprint and non-polarization. Low ESR ceramic capacitors help maximize charge pump transient response. Because ceramic capacitors are non-polarized, they are less prone to damage from improper connections.

and ambient temperature. For ceramic capacitors, capacitor ESR is usually measured in milliohms, and for tantalum or aluminum electrolytic capacitors, ESR can be measured in the range of several ohms.

Ceramic Capacitor Materials

Ceramic capacitors smaller than 0.1µF are usually made of NPO or COG materials. NPO and COG materials typically have tight tolerances and are temperature stable. Larger capacitance values typically consist of X7R, X5R, Z5U or Y5V dielectric materials. Large ceramic capacitors typically larger than 2.2µF can be used for low-cost Y5V and Z5U dielectrics, but AAT3152 applications typically do not require capacitors larger than 1µF. Capacitive area is another contributor to ESR. Physically larger capacitors have lower ESR compared to smaller capacitors of the same material. These larger devices can improve the transient response of the circuit compared to equivalent capacitors in smaller package sizes.

Equivalent series resistance

ESR is an important characteristic to consider when choosing a capacitor. ESR is the resistance inside the capacitor, which consists of leads, internal connections, size or area, material,

Thermal Protection

The AAT3152 has a built-in thermal protection circuit that will shut down the charge pump when the die temperature rises above the thermal limit, as if the V pin was shorted.

Ordering Information

Package Information: All dimensions are in millimeters.