PRELIMINARY TECHNICAL DATA a Charge Pump Driver for LCD LED Backlights ADM8845/6 APPLICATIONS White LED Backlighting Micro TFT color displays Mobile phones DSC PDA's GENERAL DESCRIPTION The ADM8845 provides the power required to drive up to 6 white LEDs, using charge pump technology. The ADM8846 provides the power required to drive up to 5 white LEDs, using charge pump technology. The LEDs are used for backlighting a color LCD display. To maximize power efficiency, a charge pump that can operate in either of a 1x, 1.5x or 2x mode is used. The Charge Pump automatically switches between 1x/1.5x/2x modes based on the input voltage, to maintain correct output levels at a high power efficiency. Improved brightness matching of the LEDs is achieved by the use of a feedback pin to sense individual LED current with a maximum matching accuracy of 1% and LED to ISET maximum matching of 1%. The ADM8845/6 provides two digital input control pins, CTRL1 and CTRL2. Which control the operation and the brightness of the LEDs. C1 C2 1F VCC C4 ADM8845 Vout C1- Charge Pump 1x/1.5x/2x mode C4+ 4.7F C2+ 1F C1+ FEATURES ADM8845 drives 6 White LEDs from a 2.6 V to 5.5 V (li-ion) input supply ADM8846 drives 5 White LEDs from a 2.6 V to 5.5 V (li-ion) input supply 1x/1.5x/2x Fractional Charge Pump to maximise power efficiency 1% LED Current Matching Low power shutdown mode Package footprint only 9mm2 (3mm x 3mm) Package height only 0.9mm Shutdown Function Soft-start limiting inrush current C2- Preliminary Technical Data C4- C3+ + - Osc CTRL1 CTRL2 C3- Control Logic C3 2.2F FB1 FB2 FB3 Vref FB4 FB5 FB6 LED Current Control Rset Circuit Iset Current Control 1 Current Control 2 Current Control 3 Current Control 4 Current Control 5 Current Control 6 Current Controlled Sinks GND Figure 1. ADM8845 FUNCTIONAL BLOCK DIAGRAM The ADM8846 controls the operation and brightness of all 5 LEDs together. The ADM8846 provides 3 built-in brightness levels for brightness control of the 6 LEDs. The ADM8845/6 also allows the brightness of the LEDs to be controlled using a DC volatage, refer to page 8, Figure 10. The ADM8845/6 also has soft-start circuitry to limit inrush current flow at power up. The ADM8845/6 is fabricated using CMOS technology for minimal power consumption. The part is packaged in a 16pin LFCSP package. The ADM8845 is configured with a main and a sub display options, the main display refers to 4 of the 6 LEDs (FB1 FB4) and the sub display refers to the remaining 2 LEDs (FB5 - FB6), refer to Figure 2. The ADM8845 provides the option to control the brightness of the LEDs with a Digital PWM signal. The duty cycle of the PWM signal determines the brightness of the backlight LEDs. REV. PrE 06/03 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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 Analog Devices, Inc., 2003 PRELIMINARY TECHNICAL DATA ADM8845/6 C1 C2 1F C4 ADM8845 C4- main CTRL2 sub + - Osc CTRL1 Vout Charge Pump 1x/1.5x/2x mode C4+ 4.7F C2- C1- C1+ VCC C2+ 1F Control Logic C3+ C3 C3- 2.2F FB1 FB2 Vref FB3 FB4 FB5 FB6 Iset Rset LED Current Control Circuit Current Control 1 Current Control 2 Current Control 3 Current Control 4 Current Control 5 Current Control 6 Current Controlled Sinks GND Figure 2. ADM8845 FUNCTIONAL BLOCK DIAGRAM C1 C2 C4 4.7F ADM8846 C2+ C1- C1+ VCC C2- 1F 1F C4- + - Osc CTRL1 CTRL2 Vout Charge Pump 1x/1.5x/2x mode C4+ Control Logic C3+ C3 C3- 2.2F FB1 FB2 Vref FB3 FB4 FB5 NC Iset Rset LED Current Control Circuit Current Control 1 Current Control 2 Current Control 3 Current Control 4 Current Control 5 Current Controlled Sinks GND Figure 2. ADM8846 FUNCTIONAL BLOCK DIAGRAM -2- REV. PrE 06/03 PRELIMINARY TECHNICAL DATA (VCC =2.6V to 5.5V, TA=-40C to +85C unless otherwise noted ) F; C3 = 2.2 F; C1,C2 = 1.0 PARAMETER Input Voltage,V CC Min Typ 2.6 Shutdown Current mA V % V % mV V % V % mV 4 30 4.77 4 4.81 4 40 % % V ILED = 20mA, VFB =0.4V ILED = 20mA, VFB =0.4V 0.3 2.5 6 30 V Ohm's Ohm's mA Iset = 20mA 1.5x Mode 2x Mode 200 KHz 0.3Vcc 1 V V uA 1 1 1.18 120 LED Current 0.1 All 6 LEDs Disconnected, Vcc = 3.3V, RSET = 7.08kOhm ADM8845: CTRL1 = 1, CRTL2 = 1, ADM8846: CTRL1 = 0, CRTL2 = 1. MHz 3.36 0.2 Test Conditions uA 4 Min Compliance on FB pin Charge Pump Output Resistance Vout Ripple V 3.33 Iset Pin LED : LED Accuracy LED : ISET Accuracy Iset pin voltage ILED to ISET Ratio Charge Pump Power Efficiency 5.5 1.5 Charge Pump Mode Thresholds 1.5x to 2x Accuracy 2x to 1.5x Accuracy Hysteresis 1x to 1.5x Accuracy 1.5x to 1x Accuracy Hysteresis Inputs Hi Low Leakage Current Units 5 Charge-Pump Frequency Digital Input Input Input Max 2.6 Supply Current,ICC PWM ADM8845/6 - SPECIFICATIONS 0.7Vcc 75 % 30 mV ADM8845: CTRL1 = 1, CRTL2 = 1, ADM8846: CTRL1 = 0, CRTL2 = 1, Vcc = 3.3V, Iload = 120mA VfLED = 3.8V ILED = 20mA * Specifications are target values and are subject to change without notice. THERMAL CHARACTERISTICS 16-Lead LFCSP Package: JA = 50C/Watt Note: If ILED = 30mA per LED and all 6 LEDs are being used, then TA = -40C to 70C REV. PrE 06 /03 -3- PRELIMINARY TECHNICAL DATA ADM8845/6 PIN Pin ADM8845 ADM8846 1 4 FUNCTION DESCRIPTION Mnemonic Function VOUT Charge Pump Output. A 2.2F capacitor to ground is required on this pin. Bias current set input. The current flowing through the RSET resistor ISET is gained up by 120 to give the ILED curent. Connect a resistor RSET to GND to set the bias current as VSET/RSET. (Note: Vset = 1.18V) 4 5 FB1 LED1 Cathode connection and Charge Pump Feedback. The current flowing in LED1 is 120 times the current flowing through RSET, ISET. 5 6 FB2 LED2 Cathode connection and Charge Pump Feedback. The current flowing in LED2 is 120 times the current flowing through RSET, ISET. When using fewer than six LEDs this pin can be left unconnected. 6 7 FB3 LED3 Cathode connection and Charge Pump Feedback. The current flowing in LED3 is 120 times the current flowing through RSET, ISET. When using fewer than six LEDs this pin can be left unconnected. 7 8 FB4 LED4 Cathode connection and Charge Pump Feedback. The current flowing in LED4 is 120 times the current flowing through RSET, ISET. When using fewer than six LEDs this pin can be left unconnected. 8 9 FB5 LED5 Cathode connection and Charge Pump Feedback. The current flowing in LED5 is 120 times the current flowing through RSET, ISET. When using fewer than six LEDs this pin can be left unconnected. 9 11 FB6/NC LED6 Cathode connection and Charge Pump Feedback. The current flowing in LED6 is 120 times the current flowing through RSET, ISET. When using fewer than six LEDs this pin can be left unconnected. This Pin is No Conect in the ADM8846. 10 10 GND Device Ground Pin. 11 1 C2- Flying Capacitor 2 Negative Connection. 12 12 CTRL2 Digital Input. 3 V CMOS Logic. Used with CTRL1 to control the operation of the LEDs. 13 13 CTRL1 Digital Input. 3 V CMOS Logic. Used with CTRL2 to control the operation of the LEDs. 14 14 C1- Flying Capacitor 1 Negative Connection. 15 15 Vcc Positive Supply Voltage Input. Connect this pin to a 2.6 V to 5.5 V supply with a 4.7F decoupling capacitor. 16 16 C1+ Flying Capacitor 1 Positive Connection. 16 15 VOUT 1 C2+ 2 ISET 3 FB1 4 13 16 15 TOP VIEW (NOT TO SCALE) C2- 1 C2- C2+ 2 10 GND ISET 3 9 FB6 VOUT 4 12 (NOT TO SCALE) 6 7 8 FB3 5 FB4 Figure 3. ADM8845 PIN CONFIGURATION 13 TOP VIEW FB1 8 14 ADM8846 FB2 FB2 FB3 7 FB4 6 FB5 5 CTRL2 11 12 ADM8845 VCC 14 CTRL1 I SET C1- 3 C1+ 3 C1- Flying Capacitor 2 Positive Connection CTRL1 C2+ C1+ 2 VCC 2 CTRL2 11 NC 10 GND 9 FB5 Figure 4. ADM8846 PIN CONFIGURATION -4- REV. PrE 06/03 PRELIMINARY TECHNICAL DATA ADM8845/6 By holding CTRL1 high and applying a digital PWM signal to CTRL2, the sub display is turned on and the main display is on, the brightness of the main display is determined by the duty cycle off the applied digital PWM signal. The brightness of the sub display is set to the maximum (maximum is set by the RSET resistor) ADM8845 LED BRIGHTNESS CONTROL WITH A DIGITAL PWM SIGNAL PWM brightness control provides the widest brightness control by pulsing the LEDs on and off using the digital input control pins, CTRL1 and CTRL2. The LEDs operate at either zero or full current (set by the RSET resistor). The PWM signal turns the current control sinks on and off. The average current through the LEDs changes with the PWM signal duty cycle. C1 C2 1F 1F Vout ADM8845 PWM Input or High/Low PWM Input or High/Low When CTRL1 and CTRL2 go low the LED Current Control Sinks shutdown. Shutdown of the Charge Pump is delayed by 15mS. This timeout period allows the ADM8845 to determine if a PWM signal is present on CTRL1 and CTRL2 or if the user has selected a full chip shutdown. C3+ C3- C3 2.2F CTRL1 CTRL1 The minimum frequency of the PWM signal is 100Hz, if a PWM signal of frequency of less than 100Hz is used the part shuts down. The PWM signal is applied to digital input pins, CTRL1 and/or CTRL2. If digital PWM brightness control of the LEDs is not required then a constant logic level 1 or 0 must be applied, refer to Page 6, Figure 7. ADM8845 FB1 FB2 FB3 Iset FB4 FB5 FB6 Rset Digital Inputs Truth Table and also Page 5 Figure 4. ADM8845 PWM Brightness Control Application Diagram. Figure 4. ADM8845 Digital PWM Brightness Control Application Diagram By applying a PWM signal to the digital input control pins, CTRL1 and/or CTRL2 you can adjust the brightness of the sub and main displays. The ADM8845 six LEDs are organised into 2 groups, Main Display (FB1-FB4) and Sub Display (FB4 - FB6), refer to Figure 2, Page 2. Vout ADM8845/6 The ADM8845 main and sub display brightness can be controlled together or separately. By applying a digital PWM signal to both CTRL1 and CTRL2 pins. The Duty Cycle of the applied PWM determines the brightness of the main and sub displays together. By varying the duty cycle of the applied PWM signal you vary the brightness of the main and sub displays from 0% to 100%. CTRL1 FB1 Voltage Regulator ILED Current Control 2 By holding CTRL1 low and applying a digital PWM signal to CTRL2, the sub display is turned off and the main display is on, the brightness of the main display is determined by the duty cycle off the applied digital PWM signal. Current Control 1 Figure 5. ADM8845/6 Current Control Sinks Also applying a digital PWM signal to CTRL1 and holding CTRL2 low ,the sub display is turned on and the main display is off, the brightness of the sub display is determined by the duty cycle off the applied digital PWM signal. Also applying a digital PWM signal to CTRL1 and holding CTRL2 high ,the sub display is turned on and the main display is on, the brightness of the sub display is determined by the duty cycle off the applied digital PWM signal. The brightness of the main display is set to the maximum (maximum is set by the RSET resistor). REV. PrE 06/03 CTRL2 -5- PRELIMINARY TECHNICAL DATA ADM8845/6 LED Config. Full On sub + main 50% D.C. main + sub Off main 80% D.C., sub off tcp CTRL1 CTRL2 Vout ILED (sub) ILED (main) ILED (sub) (Brightness) ILED (main) (Brightness) 37mS > tcp > 15mS Figure 6. ADM8845 Application Timing CTRL1 CTRL2 LED Operation Notes 0 0 1 1 0 1 0 1 Sub Display Off / Main Display Off (Full SHDN) Sub Display Off / Main Display On Sub Display On / Main Display Off Sub Display On / Main Display On (Full On) 1,4 1,3 1,4 1,3 0 PWM 1 PWM PWM PWM 0 PWM 1 PWM Sub Display Off / Digital PWM Brightness Control On Main Display Digital PWM Control On Sub Display / Main Display Off Sub Display On / Digital PWM Brightness Control On Main Display Digital PWM Brightness Control On Sub Display / Main Display On Digital PWM Brightness Control On Sub Display and Main Display 2,5 5,4 1,5 5,3 5,5 Figure 7. ADM8845 Digital Inputs Truth Table Becuase the ADM8845 has its 6 LEDs arranged into 2 gropus, sub and main. It is possible to configure the 6 LEDs as in Figure 7. ADM8845 Digital Inputs Truth Table, refer also to Figure 6. ADM8845 Application Timing. Note 3: Main Display on means the display is on with the maximum brightness set by the RSET resistor. CTRL2 = 1 means a constant logic level (Vcc) is applied to CTRL2. Note 4: Main Display off means the main display only is off. CTRL2 = 0 means a constant logic level (Gnd) is applied to CTRL2. Note 1: Sub Display on means the display is on with the maximum brightness set by the RSET resistor. CTRL1 = 1 means a constant logic level (Vcc) is applied to CTRL1. Note 5: PWM means a Digital PWM signal is applied to the CTRL pin with a frequency from 100Hz to 200kHz. Note 2: Sub Display off means the sub display only is off. CTRL1 = 0 means a constant logic level (Gnd) is applied to CTRL1. -6- REV. PrE 06/03 PRELIMINARY TECHNICAL DATA ADM8845/6 ADM8846 THREE LEVELS OF BRIGHTNESS CONTROL WITH CTRL1 AND CTRL2 PINS The ADM8846 only allows all 5 LEDs brightness to be controlled together. The ADM8846 has 3 levels of brightness. By applying a constant logic CTRL1 = 0 and CTRL2 = 0 to the digital control pins the 5 LEDs are turned off (Full SHDN). Applying a constant logic CTRL1 = 0 and CTRL2 = 1 to the digital control pins all 5 LEDs are set to maximum brightness (set by the RSET resistor). A constant logic CTRL1 = 1 and CTRL2 = 0 on digital control pins sets all 5 LEDs to one-third (1/3) the maximum brightness. AUTOMATIC GAIN CONTROL The Automatic Gain Control block controls the operation of the Charge Pump, by selecting the apporipate Gain for the Charge Pump to maintain the correct outputs at a high power efficiency. The Charge Pump Switching thresholds are: From 1.5x to 2x : 3.33V From 2x to 1.5x : 3.36V From 1x to 1.5x : 4.77V From 1.5x to 1x : 4.81V Refer to ADM8845/6 Specification Page 3 for more details. A constant logic CTRL1 = 1 and CTRL2 = 1 on digital control pins sets all 5 LEDs to two-thirds (2/3) the maximum brightness. Refer to Page 6, Figure 8. ADM8846 Digital Inputs Truth Table. ADM8846 Digital Input Control Pins CTRL1 0 0 1 1 CTRL2 LED Operation 0 1 0 1 Full SHDN (All 6 LEDs) Max Brightness (1/1) One-Third Brightness (1/3) Two-Thirds Brightness (2/3) Figure 8. ADM8846 Digital Inputs Truth Table ADM8845/6 LED BRIGHTNESS CONTROL USING A PWM SIGNAL APPLIED TO VPWM By adding 2 external resistors and a capacitor as shown on figure 9, this configuration can also be used to achieve PWM brightness control. This PWM brightness control can be used instead of CTRL1 and/or CTRL2 PWM brightness control. With this configuration CTRL1 and CTRL2 digital logic pins can be used to control the LEDs operation while VPWM can be used to control the brightness of the LEDs. By applying a high-frequency PWM signal (0V to 2.5V) to drive an R-CR filter on the ISET pin of the ADM8845/6 (See Figure 4). A 0% PWM duty cycle corresponds to 20mA/LED, while a 100% PWM duty cycle corresponds to a 0mA/LED. At PWM frequencies above 5kHz, C5 may be reduced. Refer to Figure 9. ADM8845/6 PWM Brightness Control Using FilteredPWM Signal. The amplitude of the PWM signal must be 0 V and 2.5 V only, inorder to have 20mA flowing in each L E D. ILED = ISET_Voltage * 120 * (1 - Duty Cycle) RSET * 2R 100 RSET + 2R REV. PrE 06/03 -7- ADM8845/6 ISET VPWM 0V - 2.5V R = 7.5K R = 7.5K C5 = 1F RSET = 13.4K 100% = ILED = 0mA 0% = ILED = 20mA Figure 9. ADM8845/6 PWM Brightness Control Using Filtered-PWM Signal PRELIMINARY TECHNICAL DATA ADM8845/6 ADM8845/6 LED BRIGHTNESS CONTROL USING A DC VOLTAGE APPLIED TO VBRIGHT By adding 1 resistor as shown in figure 10 , this configuration can also be used to achieve brightness control of the LEDs. Figure 11 shows an application example of LED Brightness control using a DC Voltage applied to VBRIGHT. ADM8845/6 ISET VBRIGHT R = 15K 0V - 2.5V RSET = 13.4K Figure 10. ADM8845/6 PWM Brightness Control Using a DC Voltage applied to V BRIGHT The equation for ILED is: ISET = (1/RSET + 1/R)(VSET ) - (1/R)(VBRIGHT) ILED = 120*Iset Where R = 15k Ohm, VSET = voltage at Iset pin (1.18V) 2.5V VBRIGHT 1.6V 0.8V 0V 20mA 13.6mA ILED 7.2mA 0mA Figure 11. ADM8845/6 PWM Brightness Control Application Diagram Using a DC Voltage applied to V BRIGHT -8- REV. PrE 06/03 PRELIMINARY TECHNICAL DATA ADM8845/6 OUTLINE DIMENSIONS Dimensions Shown in mm. 16-Lead 3mm x 3mm Chip Scale Package (CP-16) (3.0) BSC SQ PIN 1 INDICATOR 0.80 MAX 0.65 NOM 12 o MAX 0.90 MAX 0.85 NOM SEATING PLANE 3.0 BSC SQ TOP VIEW 0.5 BSC 0.20 REF 0.60 0.42 0.24 0.60 0.42 0.24 0.30) 0.23) 0.18) 0.50) 0.40) 0.30) 0.010 (0.25) MIN 13 12 16 1 9 5 8 1.50 REF 0.05 0.01 0.00 CONTROLLING DIMENSIONS ARE IN MILLIMETERS REV. PrE 06/03 -9- 1.45 1.30 SQ 1.15 BOTTOM VIEW 4