LCD Panel Power, VCOM, and Gate Modulation ADD8754 FEATURES FUNCTIONAL BLOCK DIAGRAM COMP SS VIN_1 VIN_2 ADD8754 FB STEP-UP SWITCHING REGULATOR FREQ LX SHDN UNDER VOLTAGE LOCKOUT AND THERMAL PROTECTION LOGIC VOLTAGE REGULATOR LDO_OUT ADJ VDD_2 POS VCOM AMPLIFIER OUT NEG APPLICATIONS GATE PULSE MODULATION TFT LCD panels for monitors, TVs, and notebooks VGH VGH_M VDD_1 CE RE VFLK VDPM 05110-001 Step-up switching regulator with 2 A power switch 650 kHz or 1.2 MHz switching frequency Output adjustable to 20 V 350 mA logic voltage regulator Selectable output voltages: 2.5 V, 2.85 V, 3.3 V VCOM amplifier with 300 mA drive Gate pulse modulation circuitry Independently adjustable delay and falling slope General 3 V to 5.5 V input Undervoltage lockout Thermal shutdown 24-lead, Pb-free LFCSP package Figure 1. GENERAL DESCRIPTION The ADD8754 is optimized for use in TFT LCD applications, requiring only external charge pump components to provide all the requirements for panel power, VCOM, and gate modulation. Included in a single chip are a high frequency step-up dc-to-dc switching regulator, logic voltage regulator, VCOM amplifier, and gate pulse modulation circuitry. The step-up dc-to-dc converter provides up to 20 V output and includes a 2 A internal switch. Either a 650 kHz or 1.2 MHz stepup switching regulator frequency can be chosen, allowing easy filtering and low noise operation. It achieves 93% efficiency and features soft start to limit the inrush current at startup. The internal voltage regulator operates with an input voltage range of 3 V to 5.5 V and delivers a load current of up to 350 mA. Three selectable output voltages are available: 2.5 V, 2.85 V, and 3.3 V. The proprietary VCOM amplifier can deliver a peak output current of 300 mA and is specifically designed to drive TFT panel loads. The gate pulse modulator allows shaping of the TFT gate high voltage to improve image quality. The integrated switches provide the ability to independently control the delay and slope for the gate drive voltage. The ADD8754 is offered in a 24-lead, Pb-free LFCSP package and is specified over the industrial temperature range of −40 to +85°C. Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2005 Analog Devices, Inc. All rights reserved. ADD8754 TABLE OF CONTENTS Specifications..................................................................................... 3 Current-Mode, Step-Up Switching Regulator Operation..... 12 Step-Up Switching Regulator Specifications............................. 3 VCOM Amplifier ........................................................................... 16 LDO Regulator Specifications .................................................... 4 Gate Pulse Modulator Circuit................................................... 16 VCOM Amplifier Specifications .................................................... 5 Power-Up Sequence ................................................................... 17 Gate Pulse Modulator Specifications ......................................... 6 Shutdown..................................................................................... 17 General Specifications ................................................................. 6 UVLO........................................................................................... 17 Absolute Maximum Ratings............................................................ 7 Power Dissipation....................................................................... 18 ESD Caution.................................................................................. 7 Layout Guidelines....................................................................... 19 Pin Configuration and Function Descriptions............................. 8 Typical Application Circuits ......................................................... 20 Typical Performance Characteristics ............................................. 9 Outline Dimensions ....................................................................... 25 Theory of Operation ...................................................................... 12 Ordering Guide .......................................................................... 25 REVISION HISTORY 4/05—Revision 0: Initial Version Rev. 0 | Page 2 of 28 ADD8754 SPECIFICATIONS STEP-UP SWITCHING REGULATOR SPECIFICATIONS VIN_1 = VIN_2 = SHDN = 5 V, VOUT1 = VDD_1 = VDD_2 = 14 V, TA = 25°C, FREQ = GND, unless otherwise noted. Table 1. Parameter SUPPLY Input Voltage Range OUTPUT 1 Output Voltage Range Load Regulation Line Regulation Load Regulation Line Regulation Overall Regulation REFERENCE Feedback Voltage ERROR AMPLIFIER Transconductance Gain Input Bias Current SWITCH On Resistance Leakage Current Peak Current Limit OSCILLATOR Oscillator Frequency Maximum Duty Cycle SOFT START Peak Current 1 Symbol Conditions Min VIN Typ 3.0 VOUT1 10 mA ≤ ILOAD ≤ 150 mA, VOUT1 = 10 V ILOAD = 350 mA, 4.5 V ≤ VIN_1 ≤ 5.5 V 10 mA ≤ ILOAD ≤ 150 mA, VOUT1 = 10 V ILOAD = 150 mA, 3.0 V ≤ VIN_1 ≤ 5.5 V Line, load, temperature (−40°C ≤ TA ≤ +85°C) VFB RDS (ON) ILKG ICL FOSC DMAX Unit 5.5 V 20 +3 V μV/mA mV μV/mA mV % 1.220 V 200 200 −3 1.200 GMEA AV IB Max 1.211 100 1000 225 μA/V V/V nA VLX = 14 V, SHDN = GND 170 0.5 2.6 mΩ μA A FREQ = GND FREQ = VIN_1 VFB = 1 V 650 1.2 90 kHz MHz % SS = GND 2.5 Refer to the Figure 23. Rev. 0 | Page 3 of 28 95 μA ADD8754 LDO REGULATOR SPECIFICATIONS VIN_1 = VIN_2 = SHDN = 5 V, ADJ = LDO_OUT, 1 CLDO = 2.2 μF, TA = 25°C, unless otherwise noted. Table 2. Parameter Symbol Conditions Min INPUT Input Voltage Range VIN 2 ADJ = LDO_OUT1 ADJ = OPEN 3 ADJ = GND 4 Typ Max Unit 3.0 5.5 V 3.35 5.5 V 3.8 5.5 V OUTPUT Output Voltage LDO_OUT ILDO = 1 mA, ADJ = GND 3.31 V ILDO = 350 mA, ADJ = GND 3.29 V ILDO = 1 mA, ADJ = OPEN 2.86 V ILDO = 350 mA, ADJ = OPEN 2.84 V ILDO = 1 mA, ADJ = LDO_OUT 2.51 V ILDO = 350 mA, ADJ = LDO_OUT 2.49 V Voltage Accuracy ILDO = 1 mA to 350 mA, −40°C ≤ TA ≤ +85°C Line Regulation ILDO = 1 mA 3 mV/V Load Regulation ILDO = 1 mA to 350 mA 20 mV Dropout Voltage VDROP Current Limit ILDPK LDO_OUT = 98% of LDO_OUT(NOM), ILDO = 350 mA −3 +3 300 350 1 Sets LDO_OUT(NOM) to 2.5 V. VIN = VIN_1 = VIN_2. 3 Sets LDO_OUT(NOM) to 2.85 V. 4 Sets LDO_OUT(NOM) to 3.3 V. 2 Rev. 0 | Page 4 of 28 500 % mV mA ADD8754 VCOM AMPLIFIER SPECIFICATIONS VIN_1 = VIN_2 = SHDN = 5 V, VDD_2 = 14 V, POS = 4.0 V, NEG = OUT, TA = 25°C, unless otherwise noted. Table 3. Parameter INPUT CHARACTERISTICS Min Typ Max Unit 19 50 300 mV nA VOS IB Input Voltage Range Common-Mode Rejection Ratio CMRR VCM = 2 V to (VDD_2 − 3) V 60 V dB VOH IOUT (source) = 50 mA VDD_2 − 0.5 V VOL IOUT (sink) = 50 mA 50 mV ±300 mA Output Current 1 POWER SUPPLY Supply Voltage Power Supply Rejection Ratio Supply Current DYNAMIC PERFORMANCE Slew Rate 2 Gain Bandwidth 2 Conditions Offset Voltage Noninverting Input Bias Current OUTPUT CHARACTERISTICS Output Voltage Swing 1 Symbol 2 IOUT VDD_2 PSRR 7.5 V ≤ VDD_2 ≤ 18.5 V 70 V dB ISY No load, POS = VDD_2 /2 2 mA SR GBW RL = 10 kΩ, CL = 10 pF −3 dB, RL = 10 kΩ, CL = 10 pF 105 1.95 V/μs MHz Not short-circuit protected. Slew rate is the average of the rising and the falling slew rates. Rev. 0 | Page 5 of 28 8 65 VDD_2 − 3 18 ADD8754 GATE PULSE MODULATOR SPECIFICATIONS VIN_1 = VIN_2 = SHDN = 5 V, VGH = 20 V, VDD_1 = 14 V, TA = 25°C, unless otherwise noted. Table 4. Parameter Symbol Condition INPUT CHARACTERISTICS VGH Voltage VGH Input Current VDD_1 Voltage VGH IVGH VFLK = GND, VDPM = LDO_OUT VDD_1 Input Current IVDD_1 VFLK = VDPM = LDO_OUT 7 VLOWFLK VHIGHFLK IFLK VLOWDPM VHIGHDPM IVDPM SWITCHING CHARACTERISTICS VGH to VGH_M On Resistance VGH_M Discharge Current 1 DELAY CHARACTERISTICS Delay Time 2 2 Typ Max Unit 30 V μA V 95 7 CONTROL INPUT CHARACTERISTICS VFLK Voltage Low VFLK Voltage High VFLK Input Current VDPM Voltage Low VDPM Voltage High VDPM Input Current 1 Min VGH 0.02 μA 0.8 0.9 ≤ VFLK ≤ LDO_OUT 2.2 −1 0.9 ≤ VDPM ≤ LDO_OUT 2.2 −1 V V μA V V μA +1 0.8 +1 RVGH IVGH_M VDPM = VFLK = LDO_OUT VFLK < 0.8 V, RE = 33 kΩ 60 8.0 Ω mA TDELAY CE = 470 pF, RE = 33 kΩ 1.88 μs Discharge current = 302.5/(RE + 5000). Delay time = CE × 4200. GENERAL SPECIFICATIONS VIN_1 = VIN_2 = SHDN = 5 V, TA = 25°C, unless otherwise noted. Table 5. Parameter Symbol SHUTDOWN Input Voltage Low VIL Input Voltage High VIH Conditions GND ≤ SHDN ≤ 5.5 V Total Ground Current SHDN = GND SHDN = GND VUVLOR VUVLOF Typ Max Unit 0.8 V V +1 μA μA +1 μA 2.2 Shutdown Pin Input Current Total VIN Current (IVIN_1 + IVIN_2) UNDERVOLTAGE LOCKOUT UVLO Rising Threshold UVLO Falling Threshold QUIESCENT CURRENT Step-Up Regulator in Nonswitching State Step-Up Regulator in Switching State Min VIN_1 rising VIN_1 falling IQ IQSW −1 2.0 −1 2.8 2.6 300 2 Rev. 0 | Page 6 of 28 V V 500 3 μA mA ADD8754 ABSOLUTE MAXIMUM RATINGS TA= 25°C, unless otherwise noted. Table 6. Parameter RE, CE, FB, SHDN, VIN_2, FREQ, COMP, SS, VIN_1, LDO_OUT, ADJ, VDPM, VFLK to GND, PGND, and AGND OUT, NEG and POS to GND, PGND, and AGND LX to GND, PGND, and AGND VDD_2 and OUT to GND, PGND, and AGND Voltage Between GND and AGND, GND and PGND, and AGND and PGND VDD_1, VGH, and VGH_M to GND, PGND, and AGND Differential Voltage Between POS and NEG Package Power Dissipation Thermal Resistance Maximum Junction Temperature Operating Temperature Range Storage Temperature Range Reflow Peak Temperature (20 sec to 40 sec) Symbol Rating −0.5 V to +6.5 V −0.5 V to +16 V −0.5 V to +22 V −0.5 V to +18.5 V ±0.5 V Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Absolute maximum ratings apply individually only, not in combination. −0.5 V to +32 V ±5 V PD θJA TJ max TA TS (TJ max − TA)/θJA 38°C/W 125°C −40°C to +85°C −65°C to +150°C 250°C ESD CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. Rev. 0 | Page 7 of 28 ADD8754 VGH RE CE PGND FB SHDN PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 24 23 22 21 20 19 GND 1 18 LX VGH_M 2 17 VIN_2 COMP VDD_1 5 14 SS VDD_2 6 13 VIN_1 OUT 7 8 9 10 11 12 05110-002 15 LDO_OUT TOP VIEW (Not to Scale) VFLK ADJ FREQ VDPM 4 AGND 16 POS ADD8754 NEG 3 Figure 2. Pin Configuration Table 7. Pin Function Descriptions Pin 1 2 3 Mnemonic GND VGH_M VFLK 4 VDPM 5 6 7 8 9 10 11 12 13 14 VDD_1 VDD_2 OUT NEG POS AGND ADJ LDO_OUT VIN_1 SS 15 COMP 16 FREQ 17 VIN_2 18 LX 19 SHDN 20 21 22 23 24 FB PGND CE RE VGH Description Ground. Gate Pulse Modulator Output. This pin supplies the gate drive signal. Gate Pulse Modulator Control Input. Gate Pulse Modulator Enable. VGH_M is enabled when the voltage on this pin is more than 2.2 V. VGH_M goes to GND when this pin is connected to GND. Gate Pulse Modulator Low Voltage Input. VCOM Amplifier Supply. VCOM Amplifier Output. Inverting Input of VCOM Amplifier. Noninverting Input of VCOM Amplifier. Analog Ground. LDO Output Voltage Select. Refer to Table 13 for details. LDO Output. Supply Input. This pin supplies power to the LDO and step-up switching regulator. Typically connected to VIN_2. Soft Start. A capacitor must be connected between GND and this pin to set the soft start time. Compensation for the Step-Up Converter. A capacitor and resistor are connected in series between GND and this pin for stable operation. Frequency Select. Set the switching frequency with a logic level. The step-up switching regulator operates at 650 kHz when this pin is connected to GND and at 1.2 MHz when connected to VIN_1. Step-Up Switching Regulator Power Supply. This pin supplies power to the driver for the switch. Typically connected to VIN_1. Step-Up Switching Regulator Switch Node. Device Shutdown Pin. This pin allows users to shut the device off when connected to GND. The normal operating mode is to pull this pin to VIN_1. Feedback Voltage Sense to Set the Output Voltage of the Step-Up Switching Regulator. Step-Up Switching Regulator Power Ground. GPM Time Delay. A capacitor must be connected between GND and this pin to set the delay time. GPM Negative Ramp Rate. A resistor must be connected between GND and this pin to set the negative ramp rate. Gate Pulse Modulator High Voltage Input. Rev. 0 | Page 8 of 28 ADD8754 TYPICAL PERFORMANCE CHARACTERISTICS 100 2.90 FREQ = GND 90 2.85 ADJ = OPEN 80 70 OUTPUT VOLTAGE (V) 2.80 FREQ = VIN VIN = 5V VOUT = 10V 60 50 40 30 2.70 2.65 2.60 2.55 10 1 10 100 ADJ = LDO_OUT 2.50 2.45 1k ILOAD (mA) 0 50 100 150 05110-050 05110-049 20 0 2.75 200 250 300 350 400 LOAD CURRENT (mA) Figure 3. Efficiency vs. Load Current (mA) Figure 6. LDO Output Voltage vs. Load Current, VIN = 3.3 V 3.4 T 3.3 OUTPUT VOLTAGE (V) ADJ = GND 1 CH1 = VOUT 5V/DIV CH2 = IL 1A/DIV CH3 = SD 5V/DIV 3.2 3.1 3.0 2.9 05110-026 2 3 2.8 ADJ = OPEN 0 50 100 150 200 05110-051 VIN = 5V VOUT = 10V IOUT = 200mA CSS = 0F 250 300 350 400 LOAD CURRENT (mA) Figure 7. LDO Output Voltage vs. Load Current, VIN = 5 V Figure 4. Start-Up Response from Shutdown, CSS = 0 F 6 5 T SD PIN 4 CH1 = VOUT 5V/DIV CH2 = IL 1A/DIV CH3 = SD 5V/DIV VOLTS (V) 1 VIN = 5V VOUT = 10V IOUT = 200mA CSS = 10nF 3 2 2.2μF OUTPUT CAP 750nF OUTPUT CAP 10μF OUTPUT CAP 1 05110-027 3 –1 –80 05110-052 0 2 –40 0 40 80 120 160 200 240 TIME (μs) Figure 8. LDO Power-Up Response from Shutdown Figure 5. Start-Up Response from Shutdown, CSS = 10 F Rev. 0 | Page 9 of 28 280 ADD8754 6 3.32 5 ADJ = GND 3.28 750nF OUTPUT CAP 3 3.26 VOUT = 20mV/DIV 2 2.2μF OUTPUT CAP 0 10μF OUTPUT CAP –1 –80 –40 0 40 80 400 ILOAD (mA) 120 160 200 240 200 05110-056 1 05110-053 VOLTS (V) LOAD STEP FROM 30kΩ TO 10Ω 3.30 VOUT (V) SD PIN 4 T IOUT = 200mA/DIV 280 0 TIME (μs) Figure 9. LDO Power-Up Response from Shutdown Figure 12. LDO Load Transient Response, VOUT = 3.3 V 6 5 T 4 VIN (V) 3 VIN LOW = 3.8V 2 4V 3V VOUT (V) 0 10μF OUTPUT CAP –1 –80 –40 0 40 80 120 160 200 240 2V ADJ = GND 1V 280 05110-057 1 2.2μF OUTPUT CAP 750nF OUTPUT CAP 05110-054 VOLTS (V) VIN HIGH = 5.5V SD PIN TIME (μs) Figure 10. LDO Power-Up Response from Shutdown Figure 13. LDO Line Transient Response, VOUT = 3.3 V 2.52 ADJ = LDO_OUT 2.50 VOUT (V) T VIN HIGH = 5.5V 2.48 VIN (V) 2.46 VOUT = 20mV/DIV VIN LOW = 3.8V 4V 300 3V IOUT = 100mA/DIV 0 2.5V 2V VOUT (V) ADJ = LDO_OUT 1V 05110-058 100 05110-055 200 ILOAD (mA) 100μs Figure 11. LDO Load Transient Response, VOUT = 2.5 V Figure 14. LDO Line Transient Response, VOUT = 2.5 V Rev. 0 | Page 10 of 28 ADD8754 5.0 T Δ: 8.00V @: 5.04V 4.5 Δ: 102ns @: –83.2ns 4.0 DELAY TIME (μs) 3.5 0kΩ 3.0 2.5 5kΩ 2.0 10kΩ 1.5 50kΩ 0.5 05110-059 1 Ch1 2.00 V M 40.0ns A Ch1 0 12.0 V Δ: 8.08V @: 9.08V Δ: 60.8ns @: 1.88μs 05110-060 1 M 40.0ns A Ch1 100 200 300 400 500 600 Figure 17. GPM Delay Time vs. CE Capacitance T 2.00 V 0 CAPACITANCE CE (pF) Figure 15. VCOM Rising Slew Rate, VDD_2 = 14 V Ch1 25kΩ 05110-061 1.0 5.16 V Figure 16. VCOM Falling Slew Rate, VDD_2 = 14 V Rev. 0 | Page 11 of 28 700 ADD8754 THEORY OF OPERATION COMP SS VIN_1 VIN_2 A 20 nF soft start capacitor results in negligible input-current overshoot at startup, making it suitable for most applications. However, if an unusually large output capacitor is used, a longer soft start period is required to prevent large input inrush current. ADD8754 REF BIAS gm FB FREQ LX F/F R SLOPE COMP Q OSC Table 8. Typical Soft Start Period S VIN (V) 3.3 3.3 3.3 3.3 5 5 5 5 SHDN PGND UVLO AND THERMAL PROTECTION VIN_1 LDO_OUT VDD_2 ADJ REF AGND GND VDD_2 POS VOUT (V) 9 9 12 12 9 9 12 12 COUT (μF) 10 10 10 10 10 10 10 10 CSS (nF) 20 100 20 100 20 100 20 100 tSS (ms) 2.5 8.2 3.5 15 0.4 1.5 0.62 2 VCOM OUT NEG On/Off Control AGND VGH VGH_M VDD_1 CE RE VFLK VDPM 05110-048 GATE HIGH MOD. CIRCUIT Figure 18. Detailed Functional Block Diagram CURRENT-MODE, STEP-UP SWITCHING REGULATOR OPERATION The ADD8754 uses current mode to regulate the output voltage. This current-mode regulation system allows fast transient response while maintaining a stable output voltage. By selecting the proper resistor-capacitor network from COMP to GND, the regulator response can be optimized for a wide range of input voltages, output voltages, and load conditions. Frequency Selection The ADD8754’s frequency is user-selectable to operate either at 650 kHz to optimize the regulator for high efficiency or at 1.2 MHz for small external components. Connect FREQ to VIN_2 for 1.2 MHz operation, or connect FREQ to GND for 650 kHz operation. The SHDN input turns the ADD8754 on or off. When the stepup dc-to-dc converter is turned off, there is a dc path from the input to the output through the inductor and output diode. This causes the output voltage to remain slightly below the input voltage by the forward voltage of the diode, preventing the output voltage from dropping to zero when the regulator is shut down. See Figure 25 for the typical application circuit to disconnect the output voltage from the input voltage at shutdown. Setting the Output Voltage The ADD8754 features an adjustable output voltage range of (VIN + 2 V) to 20 V. The output voltage is set by the resistive voltage divider from the output voltage (VOUT) to the 1.21 V feedback input at FB. Use the following formula to determine the output voltage: VOUT = 1.21 V × (1 + R1/R2) (1) Use an R2 resistance of 10 kΩ or less to prevent output voltage errors due to the 10 nA FB input bias current. Choose R1 based on the following formula: Soft Start Capacitor The voltage at SS ramps up slowly by charging the soft start capacitor (CSS) with an internal 2.5 μA current source. Table 8 lists the values for the soft start period based on maximum output current and maximum switching frequency. The soft start capacitor limits the rate of voltage rise on the COMP pin, which in turn limits the peak switch current at startup. Table 8 shows a typical soft start period, tSS, at the maximum output current, IOUT_MAX, for several conditions. ⎛V − 1.21 V R1 = R2 × ⎜ OUT ⎜ 1.21 V ⎝ ⎞ ⎟ ⎟ ⎠ For example, R1 = 75.8 kΩ with VOUT = 10 V and R2 = 10 kΩ Rev. 0 | Page 12 of 28 (2) ADD8754 The inductor ripple current (ΔIL) in steady state is Inductor Selection The inductor is an integral part of the step-up converter. It stores energy during the switch-on time and transfers that energy to the output through the output diode during the switch-off time. Use inductance in the range of 1 μH to 22 μH. In general, lower inductance values have higher saturation current and lower series resistance for a given physical size. However, lower inductance results in higher peak current, which can lead to reduced efficiency and greater input and/or output ripple and noise. Peak-to-peak inductor ripple current at close to 30% of the maximum dc input current typically yields an optimal compromise. For determining the inductor ripple current, the input (VIN) and output (VOUT) voltages determine the switch duty cycle (D) by the following equation: D= VOUT − V IN (3) VOUT ΔIL = D f SW (5) L Solving for the inductance value, L, L= V IN × t ON (6) ΔI L Make sure that the peak inductor current (the maximum input current plus half of the inductor ripple current) is less than the rated saturation current of the inductor. In addition, ensure that the maximum rated rms current of the inductor is greater than the maximum dc input current to the regulator. For duty cycles greater than 50% that occur with input voltages greater than half the output voltage, slope compensation is required to maintain stability of the current-mode regulator. For stable current-mode operation, ensure that the selected inductance is equal to or greater than LMIN: Using the duty cycle and switching frequency, fSW, determine the on time by using the following equation: tON = V IN × t ON L > L MIN = VOUT − V IN (7) 1.8 A × f SW (4) Table 9. Inductor Manufacturers Vendor Sumida www.sumida.com Coilcraft www.coilcraft.com Toko www.tokoam.com Part CMD4D11-2R2MC CMD4D11-4R7MC CDRH4D28-100 CDRH5D18-220 CR43-4R7 CR43-100 DS1608-472 DS1608-103 D52LC-4R7M D52LC-100M L (μH) 2.2 4.7 10 22 4.7 10 4.7 10 4.7 10 Rev. 0 | Page 13 of 28 Max DC Current 0.95 0.75 1.00 0.80 1.15 1.04 1.40 1.00 1.14 0.76 Max DCR (mΩ) 116 216 128 290 109 182 60 75 87 150 Height (mm) 1.2 1.2 3.0 2.0 3.5 3.5 2.9 2.9 2.0 2.0 ADD8754 Choosing the Input and Output Capacitors Diode Selection The ADD8754 requires input and output bypass capacitors to supply transient currents while maintaining a constant input and output voltage. Use a low effective series resistance (ESR) 10 μF or greater input capacitor to prevent noise at the ADD8754 input. Place the capacitors between VIN_1, VIN_2, and GND and as close as possible to the ADD8754. Ceramic capacitors are preferred because of their low ESR characteristics. Alternatively, use a high value, medium ESR capacitor in parallel with a 0.1 μF low ESR capacitor as close as possible to the ADD8754. The output diode conducts the inductor current to the output capacitor and load while the switch is off. For high efficiency, minimize the forward voltage drop of the diode. Schottky diodes are recommended. However, for high voltage, high temperature applications, where the Schottky diode reverse leakage current becomes significant and can degrade efficiency, use an ultrafast junction diode. The output capacitor maintains the output voltage and supplies current to the load while the ADD8754 switch is on. The value and characteristics of the output capacitor greatly affect the output voltage ripple and stability of the regulator. Use a low ESR output capacitor; ceramic dielectric capacitors are preferred. For very low ESR capacitors such as ceramic capacitors, the ripple current due to the capacitance is calculated as follows. Because the capacitor discharges during the on time, tON, the charge removed from the capacitor, QC, is the load current multiplied by the on time. Therefore, the output voltage ripple (ΔVOUT) is ΔVOUT = QC C OUT = I L × t ON C OUT where: COUT is the output capacitance. IL is the average inductor current. D t ON = f SW V − V IN D = OUT VOUT (8) I L × (VOUT − V IN ) f SW × VOUT × ΔVOUT D MIN = VOUT − V IN _ MAX (12) VOUT where VIN_MAX is the maximum input voltage. For example, DMIN = 0.45 when VOUT = 10 V and VIN_MAX = 5.5 V Table 11. Schottky Diode Manufacturers Vendor ON Semiconductor Web Address www.onsemi.com Diodes, Inc. www.diodes.com Central Semiconductor Corp. www.centralsemi.com Sanyo www.sanyovideo.com Loop Compensation (9) (10) Choose the output capacitor based on the following equation: C OUT ≥ The diode must be rated to handle the average output load current. Many diode manufacturers derate the current capability of the diode as a function of the duty cycle. Verify that the output diode is rated to handle the average output load current with the minimum duty cycle. The minimum duty cycle of the ADD8754 is Use of external components to compensate the regulator loop allows optimization of the loop dynamics for a given application. A step-up converter produces an undesirable right-half plane zero in the regulation feedback loop. This requires compensating the regulator such that the crossover frequency occurs well below the frequency of the right-half plane zero. The right-half plane zero is determined by the following equation: (11) ⎛ V FZ (RHP ) = ⎜⎜ IN ⎝ VOUT 2 ⎞ R ⎟ × LOAD ⎟ 2π × L ⎠ Table 10. Capacitor Manufacturers Vendor AVX Murata Sanyo Taiyo Yuden Web Address www.avxcorp.com www.murata.com www.sanyovideo.com www.t-yuden.com where: FZ(RHP) is the right-half plane zero. RLOAD is the equivalent load resistance, or the output voltage divided by the load current. Rev. 0 | Page 14 of 28 (13) ADD8754 The regulator loop gain is AVL V V = FB × IN × G MEA × Z COMP × G CS × Z OUT VOUT VOUT (14) where: AVL is the loop gain. VFB is the feedback regulation voltage, 1.210 V. VOUT is the regulated output voltage. VIN is the input voltage. GMEA is the error amplifier transconductance gain. ZCOMP is the impedance of the series RC network from COMP to GND. GCS is the current sense transconductance gain (the inductor current divided by the voltage at COMP), which is internally set by the ADD8754. ZOUT is the impedance of the load and output capacitor. To determine the crossover frequency, it is important to note that at that frequency the compensation impedance (ZCOMP) is dominated by the resistor and the output impedance (ZOUT) is dominated by the impedance of the output capacitor. Therefore, when solving for the crossover frequency, (by definition of the crossover frequency) the equation is simplified to AVL = V VFB 1 × IN × GMEA × RC × GCS × =1 VOUT VOUT 2π × f C × COUT (15) where: fC is the crossover frequency. RC is the compensation resistor. Solving for RC, RC = 2π × f C × C OUT × VOUT × VOUT For VFB = 1.21 V, GMEA = 100 μs, and GCS = 2 sec, RC = 2.55 × 10 4 × f C × C OUT × VOUT × VOUT V IN (17) Once the compensation resistor is known, set the zero formed by the compensation capacitor and resistor to one-fourth of the crossover frequency, or CC = 2 π × f C × RC (18) where CC is the compensation capacitor. ERROR AMP REF GMEA FB RC C2 CC 05110-007 To stabilize the regulator, make sure that the regulator crossover frequency is less than or equal to one-fifth of the right-half plane zero and less than or equal to one-fifteenth of the switching frequency. Figure 19. Compensation Components The capacitor C2 is chosen to cancel the zero introduced by output capacitance ESR. Solving for C2, C2 = ESR × C OUT (19) RC For low ESR output capacitance, such as with a ceramic capacitor, C2 is optional. For optimal transient performance, the RC and CC might need to be adjusted by observing the load transient response of the ADD8754. For most applications, the compensation resistor should be in the range of 30 kΩ to 400 kΩ, and the compensation capacitor should be in the range of 100 pF to 1.2 nF. Table 12 shows external component values for several applications. (16) V FB × V IN × G MEA × G CS Table 12. Recommended External Components for Various Input/Output Voltage Conditions VIN (V) 5 VOUT (V) 9 fSW 650 kHz L (μH) 10 COUT (μF) 10 CIN (μF) 10 R1 (kΩ) 63.4 R2 (kΩ) 10 RC (kΩ) 84.5 Cc (pF) 390 IOUT_MAX (mA) 450 5 5 9 12 1.2 MHz 650 kHz 4.7 10 10 10 10 10 63.4 88.7 10 10 178 140 100 220 450 350 5 12 1.2 MHz 4.7 10 10 88.7 10 300 100 350 3.3 3.3 3.3 9 9 12 650 kHz 1.2 MHz 650 kHz 10 4.7 10 10 10 10 10 10 10 63.4 63.4 88.7 10 10 10 71.5 150 130 820 180 420 350 350 250 3.3 12 1.2 MHz 4.7 10 10 88.7 10 280 100 250 Rev. 0 | Page 15 of 28 ADD8754 VCOM AMPLIFIER The output of the VCOM amplifier is designed to control the voltage on the VCOM plane of the LCD display. The VCOM amplifier is designed to source and sink the capacitive pulse current and ensure stable operation with high load capacitance. The delay capacitance in farad is calculated using the following equation: CE = (Delay Time) × 0.000238 The RE in ohms is calculated using the following equation: Input Overvoltage Protection Whenever the input exceeds the supply voltage, attention must be paid to the input overvoltage characteristics. When an overvoltage occurs, the amplifier can be damaged, depending on the voltage level and the magnitude of the fault current. When the input voltage exceeds the supply voltage by more than 0.6 V, the internal pin junctions allow current to flow from the input to the supplies. This input current is not inherently damaging to the device, provided it is 5 mA or less. RE = 302 (Slew Rate × Load Capacitance ) − 5000 When the voltage on the VDPM pin is less than the turn-on threshold value, the CE pin is internally connected to GND to discharge the delay capacitor. GATE HIGH MOD. CIRCUIT VIN_1 VGH Short-Circuit Output Conditions The VCOM amplifier does not have internal short-circuit protection circuitry. As a precaution, do not short the output directly to the positive power supply or to the ground. VDPM S1 L O G I C VFLK VGH_M S3 CL S2 GND GATE PULSE MODULATOR CIRCUIT VDD_1 The gate pulse modulator is used for LCD applications in which shaping of the gate high voltage signal improves image quality. A charge pump is used to generate the on voltage, VGH. A lower gate voltage level, VDD_1, is desired during the last portion of the gate’s on time and is provided by VOUT. The integrated gate pulse modulator circuit provides control over the slope and delay of the transition between these two TFT on-voltage levels. When the control voltage VFLK switches from logic low to logic high during normal operation with VDPM at logic high (see Figure 21), the output voltage VGH_M transitions from VDD_1 to VGH. When the control voltage VFK switches from logic high to logic low, the output voltage VGH_M transitions from VGH to VDD_1 after a time delay determined by the size of a capacitor from the CE pin to the GND and a slew rate determined by the size of resistor from the RE pin to the GND. GND CE RE RAMP RESISTOR 05110-008 DELAY CAPACITOR GND Figure 20. Gate Pulse Modulator Functional Block Diagram ENABLE – VDPM LOW SLOPE CONTROLLED BY RE CONTROL SIGNAL – VFLK LOW T1 T2 VGH OUTPUT SIGNAL – VGH_M WITH LOAD CAPACITANCE CL Rev. 0 | Page 16 of 28 VDD_1 LOW T1 T2 DELAY CONTROLLED BY CE Figure 21. Gate Pulse Modulator Timing Diagram 05110-009 The gate pulse modulator circuit has four input pins (VGH, VDD_1, VDPM, and VFLK) and one output pin (VGH_M). VFLK is a digital control signal, usually provided by the timing controller, whose high or low level determines which of the two input voltages, VGH or VDD_1, is passed through to VGH_M. The gate high modulator circuit becomes active when the voltage on pin VDPM exceeds the turn-on threshold value of 2.2 V. VOUT/VGH REF S4 ADD8754 POWER-UP SEQUENCE LDO Input Capacitor Selection Most LCD panels require that when VIN is applied, LDO_OUT, VGL, BOOST_OUT, VGH, and VGH_M are established sequentially, as indicated in Figure 22. ADD8754 provides this sequence with appropriate capacitors for the VGL and VGH charge pumps. For the input voltage of the ADD8754 LDO regulator (VIN_1), a local bypass capacitor is recommended. The input capacitor provides bypassing for the internal amplifier used in the voltage regulation loop. Use at least a 1 μF low ESR capacitor. Larger input capacitance and lower ESR provide better supply noise rejection. Multilayer ceramic chip (MLCC) capacitors provide the best combination of low ESR and small size. VIN LDO Output Capacitor Selection SHDN The output capacitor improves the regulator response to sudden load changes. The output capacitor helps determine the performance of any LDO. The ADD8754 LDO requires at least a 2.2 μF capacitor. Transient response is a function of output capacitance, in that larger values of output capacitance decrease peak deviations, providing improved transient response for large load current changes. SHDN THRESHOLD LEVEL VDPM VGH_M VGH LDO_OUT Choose the capacitors by comparing their lead inductance, ESR, and dissipation factor. Output capacitance affects stability, and a larger cap provides a greater phase margin for the ADD8754 LDO. MLCC capacitors provide the best combination of low ESR and small size. 05110-010 BOOST_OUT VGL Figure 22. Power-Up Sequence Timing Diagram LDO Regulator The ADD8754 low dropout (LDO) regulator has three preset output voltage settings. As shown in Table 13, by tying the ADJ pin low, a 3.3 V nominal output is selected. By tying ADJ to the output voltage, a 2.5 V nominal output is selected. By leaving ADJ as an open circuit, a nominal voltage of 2.85 V is selected. Table 13. LDO Output Voltage Selection LDO Output Voltage 2.5 V 2.85 V 3.3 V ADJ Pin LDO_OUT No connection GND Note that the capacitance of some capacitor types show wide variations over temperature. A good quality dielectric X7R or better capacitor is recommended. SHUTDOWN Applying a TTL high signal to the shutdown pin (tying it to the VIN_1) turns on all outputs. Pulling SHDN down to 0.4 V or below (tying it to GND) turns off all outputs. In shutdown mode, quiescent current is reduced to a typical value of 300 μA. UVLO An undervoltage lockout (UVLO) circuit is included with a built in hysteresis. ADD8754 turns on when VIN_1 rises above 2.8 V and shuts down when VIN_1 falls below 2.6 V. Rev. 0 | Page 17 of 28 ADD8754 POWER DISSIPATION VCOM Amplifier The ADD8754’s maximum power dissipation depends on the thermal resistance from the IC die to the ambient environment and the ambient temperature. The thermal resistance depends on the IC package, PC board copper area, other thermal mass, and airflow. The ADD8754, with the exposed backside pad soldered to a 2-layer PC board with nine 12 mil-diameter thermal vias, can dissipate about 1.5 W into 65°C still air before the die exceeds 125°C. More PC board copper, cooler ambient air, and more airflow increase the dissipation capability, whereas less copper or warmer air decreases the IC’s dissipation capability. The major contributors to the power dissipation are the LDO regulator and the VCOM amplifier. The power dissipated in the VCOM amplifier depends on the output current, the output voltage, and the supply voltage: Step-Up Converter The largest portions of power dissipation in the step-up converter are the internal MOSFET, the inductor, and the output diode. For a 90% efficiency step-up converter, about 3% to 5% of the power is lost in the internal MOSFET, about 3% to 4% in the inductor, and about 1% in the output diode. The rest of the 1% to 3% is distributed among the input and output capacitors and the PC board traces. For an input power of about 3 W, the power lost in the internal MOSFET is about 90 mW to 150 mW. LDO The power dissipated in the LDO depends on the output current, the output voltage, and the supply voltage: PDSOURCE = IOUT (source) × (VDD_2 − VOUT) PDSINK = IOUT (sink) × VOUT where: IOUT (source) is the output current sourced by the VCOM amplifier. IOUT (sink) is the output current that the VCOM amplifier sinks to AGND. In a typical case where the supply voltage is 12 V and the output voltage is 6 V with an output source current of 20 mA, the power dissipated is 120 mW. Thermal Overload Protection Thermal overload protection prevents excessive power dissipation from overheating the ADD8754. When the junction temperature exceeds TJ = 145°C, a thermal sensor immediately activates the fault protection, which shuts down the device, allowing the IC to cool. The device self-starts once the die temperature falls below TJ = 105°C. Thermal overload protection protects the controller in the event of fault conditions. For continuous operation, do not exceed the absolute maximum junction temperature rating of TJ = 125°C. PDLDO = (VIN_1 − LDO_OUT) × ILDO_OUT Rev. 0 | Page 18 of 28 ADD8754 LAYOUT GUIDELINES Layout Procedure When designing a high frequency, switching, regulated power supply, layout is very important. Using a good layout can solve many problems associated with these types of supplies. Some of the main problems are loss of regulation at high output current and/or large input-to-output voltage differentials, excessive noise on the output and switch waveforms, and instability. Using the following guidelines can help minimize these problems. To achieve high efficiency, good regulation, and stability, a good PCB layout is required. It is recommended that the reference board layout be followed as closely as possible because it is already optimized for high efficiency and low noise. Make all power (high current) traces as short, direct, and thick as possible. It is good practice on a standard PCB board to make the traces an absolute minimum of 15 mil (0.381 mm) per Ampere. The inductor, output capacitors, and output diode should be as close to each other as possible. This helps reduce the EMI radiated by the power traces that is due to the high switching currents through them. This also reduces lead inductance and resistance, which in turn reduce noise spikes, ringing, and resistive losses that produce voltage errors. The grounds of the IC, input capacitors, output capacitors, and output diode (if applicable), should be connected close together, directly to a ground plane. It is also a good idea to have a ground plane on both sides of the printed circuit board (PCB). This reduces noise by reducing ground-loop errors and absorbing more of the EMI radiated by the inductor. For multilayer boards of more than two layers, a ground plane can be used to separate the power plane (power traces and components) and the signal plane (feedback, compensation, and components) for improved performance. On multilayer boards, the use of vias is required to connect traces and different planes. If a trace needs to conduct a significant amount of current from one plane to the other, it is good practice to use one standard via per 200 mA of current. Arrange the components so that the switching current loops curl in the same direction. Use the following general guidelines when designing PCBs: 1. Keep CIN close to the IN and GND leads of the ADD8754. 2. Keep the high current path from CIN (through L1) to the SW and PGND leads as short as possible. 3. Keep the high current path from CIN (through L1), D1, and COUT as short as possible. 4. Keep high current traces as short and wide as possible. 5. Keep nodes connected to SW away from sensitive traces such as FB or COMP to prevent coupling of the traces. If these traces need to be run near each other, place a ground trace between the two as a shield. 6. Place the feedback resistors as close as possible to the FB pin to prevent noise pickup. 7. Place the compensation components as close as possible to the COMP pin. 8. Avoid routing noise-sensitive traces near the high current traces and components. 9. Use a thermal pad size that is the same as the dimension of the exposed pad on the bottom of the package. Heat Sinking When using a surface-mount power IC or external power switches, the PCB can often be used as the heat sink. This is done by simply using the copper area of the PCB to transfer heat from the device. Due to the how switching regulators operate, there are two power states: one state when the switch is on, and one when the switch is off. During each state, there is a current loop made by the power components currently conducting. Place the power components so that the current loop is conducting in the same direction during each of the two states. This prevents magnetic field reversal caused by the traces between the two half cycles and reduces radiated EMI. Rev. 0 | Page 19 of 28 ADD8754 TYPICAL APPLICATION CIRCUITS BAV99 R5 1kΩ D5 C7 1μF VZ2 BZX84C28 C3 1μF D3 C2 0.1μF C6 0.1μF R9 10Ω R2 9.5kΩ C8 0.1μF 5 6 SHDN FB PGND RE ADD8754 VDPM COMP VDD_1 SS VDD_2 VIN_1 +14V FROM VOUT 7 8 9 VCOM +4.0V C9 1μF 10 11 R3 100kΩ R4 250kΩ 18 17 VIN +5V 16 15 RC 180kΩ 14 CSS 10nF 13 CC 470pF CIN 10μF 12 VLOGIC +3.3V CLDO 4.7μF +14V FROM VOUT Figure 23. 1.2 MHz Application Circuit for TFT LCD Panel with Charge Pumps for VGH and VGL Rev. 0 | Page 20 of 28 RSD 180kΩ L 10μH 05110-003 R8 100kΩ FREQ LDO_ OUT R7 250kΩ VFLK ADJ 4 VOUT +14V CSD 10μF VIN_2 OUT +14V FROM VOUT COUT 20μF D1 1N5818 19 VGH_M AGND 3 20 LX POS 2 21 GND NEG 1 22 CE 23 VGH 24 R1 100kΩ CE 390pF RE 33kΩ VFLK C5 0.1μF D6 D7 C10 0.47μF VZ1 BZX84C5V1 TO GATE DRIVER D2 C1 0.1μF C4 0.47μF BAV99 R6 300Ω VGL –5V BAV99 D4 ADD8754 +30V VGH VZ2 1N7451A CVGH 10μF R2 10kΩ 5 6 SHDN FB PGND RE ADD8754 VDPM COMP VDD_1 SS VDD_2 VIN_1 +12V FROM VOUT 7 8 9 10 11 VZ1 BZX84C5V1 VGL –5V CVGL 0.1μF 17 16 VIN +5V 15 RC 180kΩ 14 CSS 10nF 13 CC 470pF T = TRANSTEK MAGNETICS TMS60059CS 12 VCOM +4.0V C9 1μF 18 D2 1N914 CIN 10μF LDO_ OUT C8 0.1μF FREQ VFLK ADJ R7 250kΩ R8 100kΩ VIN_2 AGND 4 COUT 20μF RVGL 50Ω VGH_M OUT +12V FROM VOUT T 19 LX POS 3 VFLK 20 VOUT +12V D1 1N5818 GND NEG 2 TO GATE DRIVER 21 RVGH 75Ω VLOGIC +3.3V +12V FROM VOUT CLDO 4.7μF R4 R12 R3 7.5kΩ 1kΩ 4.7kΩ Figure 24. 1.2 MHz Application Circuit for TFT LCD Display with Transformer for VGH and VGL Rev. 0 | Page 21 of 28 05110-004 1 22 CE 23 VGH 24 R1 91kΩ CE 390pF RE 33kΩ D3 1N914 ADD8754 VGH +28V BAV99 R5 1kΩ D5 C7 1μF VZ2 BZX84C28 C3 1μF D3 C2 0.01μF D2 C1 0.01μF C4 0.47μF C5 0.01μF BAV99 R6 300Ω VGL –5V BAV99 D4 D6 D7 C10 0.47μF VZ1 BZX84C5V1 C6 0.1μF R9 10Ω R2 9.5kΩ 1 VOUT +14V COUT 20μF SHDN 19 FB 20 PGND 21 CE 22 RE VGH 23 D1 1N5818 CE 390pF RE 33kΩ 24 R1 100kΩ LX GND 18 L 10μH CSD 10μF RSD 180kΩ FDC6331 6 VDD_1 SS VDD_2 VIN_1 +14V FROM VOUT 7 8 9 VCOM +4.0V C9 1μF 10 11 17 R10 10kΩ 16 VIN +5V 15 RC 180kΩ 14 13 CSS 10nF CC 470pF CIN 10μF ENABLE 12 R3 100kΩ R4 250kΩ VLOGIC +3.3V CLDO 4.7μF +14V FROM VOUT Figure 25. 1.2 MHz Application Circuit for TFT LCD Display with Charge Pumps with Input Power Disconnect Switch Rev. 0 | Page 22 of 28 05110-005 5 LDO_ OUT C8 0.1μF COMP ADJ R8 100kΩ ADD8754 VDPM AGND 4 R7 250kΩ FREQ VFLK OUT +14V FROM VOUT 3 POS VFLK VIN_2 VGH_M NEG 2 TO GATE DRIVER ADD8754 VGH +28V BAV99 R5 1kΩ D5 C7 1μF VZ2 BZX84C28 C3 1μF D3 C2 0.01μF C6 0.1μF R9 10Ω R2 9.5kΩ 6 SHDN FB PGND RE ADD8754 VDPM COMP VDD_1 SS VIN_1 VDD_2 +14V FROM VOUT 7 8 9 VCOM +4.0V C9 1μF 10 11 R3 100kΩ R4 250kΩ 18 L 10μH 17 VIN +5V 16 15 14 13 CSS 10nF CIN 10μF RC 180kΩ CC 470pF BOOST AND CHARGE PUMP ENABLE R10 10kΩ 12 VLOGIC +3.3V CLDO 4.7μF +14V FROM VOUT Figure 26. 1.2 MHz Application Circuit for TFT LCD Display with LDO_ALWAYS_ ON Rev. 0 | Page 23 of 28 Q1 2N7000 05110-047 5 FREQ LDO_ OUT C8 0.1μF VFLK OUT R8 100kΩ VIN_2 ADJ 4 D1 1N5818 VGH_M AGND 3 VFLK VOUT +14V COUT 20μF 19 20 LX POS 2 TO GATE DRIVER 21 GND NEG 1 22 CE 23 VGH 24 R1 100kΩ CE 390pF RE 33kΩ R7 250kΩ C5 0.01μF D6 D7 C10 0.47μF VZ1 BZX84C5V1 +14V FROM VOUT D2 C1 0.01μF C4 0.47μF BAV99 R6 300Ω VGL –5V BAV99 D4 ADD8754 ADJUSTABLE FROM 3V TO 5V WITH 15mV PER STEP ADJUSTMENT LDO_ OUT ADJ AGND VOUT 14V C10 2.2pF VCOM 4.0V POS OUT NEG ADD8754 R4 315kΩ RB 6kΩ VDD AD5259BRMZ10 RA 1kΩ VLOGIC W B SCL SDA C9 0.1μF R10 2.2kΩ R11 2.2kΩ SIGNAL FROM FACTORY PC, SOFTWARE PROVIDED BY ADI GND AD0 AD1 05110-006 R3 10kΩ A Figure 27. ADD8754 with Programmable VCOM The VCOM calibration for flicker reduction is one of the essential steps in the panel manufacturing process. In a typical panel production environment, such a process can take additional time to complete and, therefore, impacts production throughput. One additional concern is that a potentiometer typically used only for calibration offers limited resolution. The resistance can drift over time and can be noticeable after a few years of operation. The production throughput, image quality, and panel reliability concerns can all be solved by using a digital potentiometer. As shown in Figure 27, AD5259, a low cost 256-step digital potentiometer with nonvolatile memory, can calibrate the ADD8754 VCOM voltage precisely, reliably, and time efficiently. In the worst case, where the temperature, aging effect, and resistance tolerance of the AD5259 are all accounted for, the circuit in Figure 27 makes the VCOM voltage adjustable from 3.0 V to 5.0 V with 15 mV per step adjustment. A micro- controller or I2C programmer can be used to provide the control signal for the AD5259, but ADI provides programming software that simplifies the calibration process. The software can be installed in the factory computer, and two tester probes can be connected to the computer’s parallel port to implement the VCOM programming. The VCOM voltage can be calculated as VCOM D × R AB + R 3 256 = × 7 × VOUT R 4 + R AB + R 3 where: D is the decimal code of the AD5259 programmable resistance between the W-to-B terminals. RAB is the AD5259 nominal resistance. Rev. 0 | Page 24 of 28 ADD8754 OUTLINE DIMENSIONS 0.60 MAX 4.00 BSC SQ PIN 1 INDICATOR 0.60 MAX TOP VIEW 0.50 BSC 3.75 BSC SQ 1.00 0.85 0.80 12° MAX 0.30 0.23 0.18 SEATING PLANE 24 1 19 18 2.25 2.10 SQ 1.95 EXPOSED PAD 0.50 0.40 0.30 0.80 MAX 0.65 TYP PIN 1 INDICATOR (BOTTOM VIEW) 13 12 7 6 0.25 MIN 2.50 REF 0.05 MAX 0.02 NOM 0.20 REF COPLANARITY 0.08 COMPLIANT TO JEDEC STANDARDS MO-220-VGGD-2 Figure 28. 24-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 4 × 4 mm Body, Very Thin Quad (CP-24-1) Dimensions shown in millimeters ORDERING GUIDE Model ADD8754ACPZ-Reel 1 ADD8754ACPZ-Reel71 1 Temperature Range −40°C to +85°C −40°C to +85°C Package Description 24-Lead LFCSP_VQ 24-Lead LFCSP_VQ Z = Pb-free part. Rev. 0 | Page 25 of 28 Package Option CP-24-1 CP-24-1 Quantity 5,000 1,500 ADD8754 NOTES Rev. 0 | Page 26 of 28 ADD8754 NOTES Rev. 0 | Page 27 of 28 ADD8754 NOTES ©2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05110–0–4/05(0) Rev. 0 | Page 28 of 28