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AAT3103IJQ-1-T1 Datasheet(PDF) 11 Page - Advanced Analog Technology, Inc. |
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AAT3103IJQ-1-T1 Datasheet(HTML) 11 Page - Advanced Analog Technology, Inc. |
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11 / 17 page  AAT3103 3-Channel Charge-Pump LED Driver ChargePumpTM PRODUCT DATASHEET 3103.2008.03.1.0 11 www .analogictech.com Applications Information LED Selection The AAT3103 is specifically intended for driving WLEDs. However, the device design will allow the AAT3103 to drive most types of LEDs with forward voltage specifica- tions ranging from 2.2V to 4.7V. LED applications may include mixed arrangements for display backlighting, keypad display, and any other application needing a con- stant current sink generated from a varying input volt- age. Since the D1 to D3 constant current sources are matched with negligible supply voltage dependence, the constant current channels will be matched regardless of the specific LED forward voltage (VF) levels. The internal charge pump and low dropout current sources in the AAT3103 maximize performance and make it capable of driving LEDs with high forward volt- ages. Multiple channels can be combined to obtain a higher LED drive current without complication. Constant Current Setting The LED full scale current is controlled by the RSET resis- tor. The following formula can be used to calculate the AAT3103-1/2/4 full scale LED current: I LED_FS = · 4 · 60 1.2 R SET Table 4 shows the RSET resistor value for the AAT3103-1/2/4 for various LED full-scale current levels. For maximum accuracy, a 1% tolerance resistor is recommended. ILED_FS (mA) RSET (kΩ) 30.2 9.53 20.1 14.3 15.1 19.1 10.0 28.7 Table 4: Maximum LED Current and RSET Resistor Values (1% Resistor Tolerance) for the AAT3103. The S2C interface rising edges control the LED current from full scale to the LSB. For the AAT3103-1, 16 steps are employed. Figure 5 shows the LED current of the AAT3103-1 at different RSET values. S2C Wire Interface Data Code 0 5 10 15 20 25 30 35 1 2 34 56 7 8 9 10 11 12 13 14 15 16 RSET = 9.53k RSET = 14.3k RSET = 19.1k RSET = 28.7k Figure 5: AAT3103-1 LED Current Control Profile at Different RSET Values. Use the following formula to calculate the AAT3103-3 full scale LED current: I LED_FS = · 4 · 48 1.2 R SET For example, an 11.5kΩ 1% resistor is used to achieve 20mA full scale LED current operation. Device Switching Noise Performance The AAT3103 operates at a fixed frequency of approxi- mately 0.9MHz to control noise and limit harmonics that can interfere with the RF operation of mobile communi- cation devices. Back-injected noise appearing on the input pin of the charge pump is 20mV peak-to-peak, typically ten times less than inductor-based DC/DC boost converter WLED backlight solutions. The AAT3103's soft- start feature prevents noise transient effects associated with inrush currents during start-up of the charge pump circuit. Shutdown To activate the shutdown operation, the EN/SET input for the AAT3103-1/-2 should be pulsed low for longer than tOFF (500μs). For the 3103-4 PWM options, shutdown operation is enabled when the EN/PWM input is pulsed low longer than 500μs. In this state, the AAT3103 typi- cally draws less than 1μA from the input. Registers are reset to 0 in shutdown. |
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