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SP7680 Complete Backlight Solution
LED 2
13 12 11 10 9 5 6 7 8
LED 5
LED 4
15
FEATURES Complete Backlight Solution Separate control for 4 main, 2 sub, and keypad LEDs Built-in 6-bit DAC for precise current setting 2 I C serial interface Data is stored in shutdown 1x and 1.5x mode operation with automatic switchover Very low dropout: 200mV typ Very low 31A current (LSB) 2MHz switching frequency reduces external components Power-saving shutdown mode of 1A Built-in over-temperature protection Available in Lead Free, RoHS compliant package: Small 16-pin 3x3 QFN
16
14
LED 6 LED 7 SDA SCL
1 2 3 4
LED 3
LED 1 GND C2+ C2-
The SP7680 is a complete backlight display solution that is designed to independently control LEDs for 2 main and auxiliary displays as well as the keypad. A two line I C serial interface allows a simple way to adjust each current individually in order to provide ultimate flexibility in driving LEDs. The data is loaded into internal registers upon power up and stored while in shutdown. When the chip is enabled the stored values set the LED currents. Extra low 33A LSB allows trickle current through the LEDs for nonreflecting LCD displays. The SP7680 automatically detects 1x or 1.5x operation for optimal efficiency. TYPICAL APPLICATION CIRCUIT MAIN SUB AUX
VOUT
VIN
C1-
C1+ DESCRIPTION
VIN 2.2F SDA SCL VIN
SP7680
C1 C2
VOUT 1F
0.47F
0.47F
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ABSOLUTE MAXIMUM RATINGS
These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. VIN, SDA, SCL, LEDx, VOUT.....................................-0.3V to 6.0V Power Dissipation ....................................... Internally limited Storage Temperature......................................-65C to 150C Junction Temperature (TJ = TA + PD*33.3C/W)............................. 40C to +125C JA (1 square 1oz Cu)......................................33.3C/W
ELECTRICAL SPECIFICATIONS Unless otherwise specified: VIN= 2.7V-5.5V, CIN = 2.2F, COUT = 1F, CFL2 =0.47F, CFL2 = 0.47F, TA = -40C to +85C, Tj=-40C to +125C. Bold values apply over the full operating temperature range.
PARAMETER Operating Input Voltage Range Operating Input Current (4 MAIN LEDs operating at 33uA each, all other LEDs off, in 1X mode) Operating Input Current (Charge pump in 1.5X mode with all LEDs at 33uA each) MIN 2.7 TYP MAX 5.5 UNITS V VIN=4.0V, VLED = 3.3V Status = 11000000 CNTRL = 00011110 Main=Sub=Aux=00000000 VIN = 3.0V, VLED = 3.3V Status = 11000000 CNTRL = 11111110 Main=Sub=Aux=00000001 VIn=4.0V Status = 10000000 CNTRL = 00000000 Main=Sub=Aux=00000000 VIN = 3.4V, VLED = 3.3V ILED = 20mA ILED = 20mA CONDITIONS
300
400
A
5
8
mA
Standby mode Quiescent Current
200
300
A
Maximum Output Current (Note 1) LED Current accuracy LED Current matching Current DAC Resolution Current for DAC=000000 Current for DAC=000001 Current DAC LSB DAC=00010 Current DAC LSB DAC=00010 LED Dropout Voltage (Note 2) Maximum LED Current Maximum LED Current Switching Frequency Equivalent Resistance, 1x mode Equivalent Resistance, 1.5x mode Control Clock Frequency 1.6 5 -10 -3
200 10 +3 6 0 31 1 2 0.2 31.5 63 2 3 6 2.4 5 10 0.4 50
mA % % bits mA A mA mA V mA mA MHz
1x mode only MAIN and SUB LEDs AUX LED ILED =20mA for MAIN and SUB; ILED =40mA for AUX After 63 counts MAIN and SUB LEDs After 63 counts AUX LED VIN=3.4V VIN=3.4V
MHz
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ELECTRICAL SPECIFICATIONS continued
PARAMETER MIN TYP MAX UNITS CONDITIONS VIN = 4.2V, VLED=3.3V Initial State: Status = 00000000 Final State: Status = 11000000 CNTRL = 11111110 1.5 2 ms Main=Sub=Aux=00000000 Time measured from stop bit of 2 final state I C command to point where VOUT = 4.1V VIN = 4.0V, VLED=3.3V Initial State: Status = 11000000 CNTRL = 11111110 Main=Sub=Aux=00000000 Final State: Status = 11000000 CNTRL = 11111110 5 s Main=Sub=Aux=11111100 Time measured from the raising edge of STATUS acknowledge bit of final state command to the point where all current is within 5% of its final value. VIN = 3.4V, VLED = 3.3V Initial State: Status = 11000000 CNTRL = 11111110 Main=Sub=Aux=00000000 Final State: Status = 11000000 CNTRL = 11111110 Main=Sub=Aux=11111100 Time measured from the raising edge of CNTRL acknowledge bit of final state command to the point where output voltage is within 5% of its final value. If both SDA and SCL are low for 50ms, the part goes into shutdown mode, set STATUS=00000000, VSUPPLY = 4.2V If both SDA and SCL are low for 50ms, part goes into shutdown mode set STATUS=00000000, VSUPPLY = 4.2V
Power-up time from Shutdown (Note 3)
Soft Start Interval (within 1X mode) (Note 4)
Soft Start Interval (transition 1X to 1.5X) (Note 5)
140
s
Shutdown Supply Current @ 25 C
0.01
2
A
Shutdown Supply Current @ 85 C VOUT - 0.5V 170 25 50 65
5 VOUT - 1V
A
Short LED threshold Thermal Shutdown Die Temperature Thermal Shutdown Hysteresis SDA, SCL low timeout SDA, SCL input logic low voltage SDL, SCA input logic high voltage 1.6
C C ms 0.4 V V
Regulator turns off Regulator turns on again @ 150C If both SDA and SCL are low for 50ms, part goes into shutdown mode set STATUS=00000000 Regulator shutdown Regulator enabled
Note 1: The maximum output current is a derived spec IOUTMAX = (VIN*1.5 - VLED - VDROPOUT)/(max Req 1.5X mode). Note 2: Dropout is defined when LED current goes 10% below nominal value as VIN is lowered.
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TIMING CHARACTERISTICS Note 3: Power-up time from Shutdown
I2C data input START ADDRESS A STATUS A CNTRL A MAIN A SUB A AUX A STOP
Power-up time (Softstart time)
1.5x mode VOUT 1x mode 1x mode
IOUT
5% Drivers ON
Note 4: Soft Start Interval (within 1x Mode)
Soft Start Interval within 1X mode I2C data input (Final state) START ADDRESS A STATUS A CNTRL A MAIN A SUB A AUX A STOP
Output Current within 5% of final value 5% ILED
The softstart interval within 1x mode: After mode changes from Standby to Active, the time from the rising edge of "STATUS" acknowledge bit to the point where the ILED is within 5% of its final value at full load. This softstart is tested with VIN = 4.0V to ensure 1x mode.
Note 5: Soft Start Interval (Transition 1x to 1.5x Mode)
Soft Start Interval within 1.5X mode I2C data input (Final state) START ADDRESS A STATUS A CNTRL A MAIN A SUB A AUX A STOP
Mode of charge pump changes from 1x mode to 1.5x mode at the full load.
5% VOUT 1x mode 1.5x mode
The softstart interval from 1x to 1.5x mode: After mode changing from 1x mode to 1.5x mode, the time from the rising edge of "CNTRL" acknowledge bit to the point where VOUT is within 5% of its final value at full load. This is the measurement to know the boosting time of the charge pump at full load current. In this case, it is easier to measure VOUT than IOUT. Softstart is tested with VIN = 3.4V to force a mode transition.
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TIMING CHARACTERISTICS (Typical Operating Circuit, VIN =2.7V to 5.5 V, Tj =-40 to 125C, unless otherwise noted. Typical C Values are at VIN=3.3V, TA=+25 C) PARAMETER Serial Clock Frequency Bus Free Time Between a STOP and a START Hold Time, Repeated START Condition Repeated START Condition Setup Time STOP Condition Setup Time Data Hold Time Input Data Hold Time Data Setup Time SCL Clock Low Period SCL Clock High Period Rise Time of Both SDA and SCL Signals, receiving Fall Time of Both SDA and SCL Signals, Receiving Fall Time of SDA Transmitting Pulse Width of Spike Suppressed Capacitive Load for Each Bus Line IC startup time after UVLO clears SYMBOL fSCL tBUF t HD_STA TSU,STA tSU,STO tHD,DAT(OUT) tHD,DAT(IN) tSU,DAT tLOW tHIGH tR tF tF.TX tSP Cb Tsrt CONDITIONS MIN 1.3 0.6 0.6 0.6 225 0 100 1.3 0.6 20+ 0.1Cb 20+ 0.1Cb 20+ 0.1Cb 0 400 1 TYP 400 MAX UNITS kHz s s s s ns ns ns s s ns ns ns 250 50 ns pF s
900 900
(Notes2, 3) (Note2, 3) (Note2, 3, 4) (Note5) (Note 2) (Note 2)
300 300
Note 1: All parameters tested at TA=25 C. Specifications over temperature are guaranteed by design. Note 2: Guaranteed by design. Note 3: Cb = total capacitance of one bus line in pF. tR and tF measured between 0.3 x VDD and 0.7 x VDD. Note 4: ISINK 6mA. Cb =total capacitance of one bus line in pF. tR and tF measured between 0.3 x VDD and 0.7 VDD. Note 5: Input filters on the SDA and SCL inputs suppress noise spikes less than 50ns.
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PIN DESCRIPTION PIN # 6 PIN NAME VIN DESCRIPTION Input voltage for the regulator. Connect a 2.2F decoupling capacitor between this pin and ground. Connect an LED between each pin and VOUT. Current value is controlled by the serial interface. The current level through each pin is internally matched within 3%. This current value can be programmed to any level for MAIN or SUB LEDs with 0.5mA step (64 steps total). Voltage at these pins is internally monitored to control the switching between 1x and 1.5x mode in order to ensure the best possible efficiency. Output of the charge pump. Place a 1F decoupling capacitor from this pin to ground. This voltage is regulated by the 1x or 1.5x charge pump to create voltage sufficient to operate the current sources. Ground pin. 2 Clock and data inputs for I C interface. Connect a 100K pull-up to VIN or Vcc. Connect 0.47F ceramic capacitor between these pins. Connect 0.47F ceramic capacitor between these pins. Connect to GND.
12-16 1,2
LED1-LED 5 LED6,LED7
5 11 3,4 7,8 9,10 -
VOUT GND SDA,SCL C1-, C1+ C21, C2+ Thermal Pad
SP7680 FUNCTIONAL DIAGRAM
2.2uF
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THEORY OF OPERATION The SP7680 is a charge pump regulator designed for converting an input voltage of 2.7V to 5.5V to drive backlight white LEDs used in portable applications. It has a total of 7 LED driver outputs consisting of 4 Main, 2 Sub and one Auxiliary keypad output. The Main and Sub outputs can drive up to 31.5mA for each LED while the Aux output can drive up to 63mA. With 2 the I C serial interface, each LED can be turned on/off independently so any combination of 7 outputs is available. Three 6-bit DACs are included to provide precise current level setting. The drive current is set simultaneously for one group. The brightness integrity and good current matching among channels are assured by this control method. The SP7680 is a fractional charge pump and can multiply the input voltage by 1 or 1.5 times. The charge pump switches at a high fixed frequency of 2MHz which allows for reduced external component sizes. The internal mode selection circuit automatically switches the mode between 1x and 1.5x mode based on the input voltage, output voltage and load current. This mode switching maximizes the efficiency throughout the entire load range. When the battery voltage is high enough, the SP7680 operates in 1x mode to provide maximum efficiency. Dropout detection is provided on all four MAIN LED outputs and the two SUB LED outputs, to determine when the SP7680 needs to transition to 1.5X mode. If the battery voltage is too low to sustain the LED current, the 1.5x mode is automatically enabled. As the battery discharges and the voltage decays, the SP7680 automatically switches between modes to maintain a constant current to drive LEDs throughout the battery life. Overtemperature Protection When the temperature of the SP7680 Rises above 170C, the overtemperature protection circuitry turns off the output switches to prevent damage to the device. If the temperature drops back down below 145C, the SP7680 automatically recovers and executes a soft start cycle.
Overvoltage Protection The SP7680 has overvoltage protection. In normal operation if the current-sinks are all open-circuited, the output voltage will rise only to the regulation voltage of 4.2V. When the currentsinks are no longer open-circuited, the device resumes normal operation. Shorted LED Protection Shorted LED protection is provided. If the SP7680 detects a shorted LED the corresponding LED output will turn off (no current). IC interface The IC interface allows a simple way to adjust each bank of channel currents in order to provide ultimate flexibility in driving LEDs. The SP7680 has five data registers which can be programmed serially via the IC interface. The STATUS register is used to enable/disable the part as well as for fault mode readback. The CNTRL register contains information regarding the state of each of the 7 individual LEDs. The final three registers contain information regarding the current level for the MAIN, SUB and AUX channels.
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TYPICAL PERFORMANCE CHARACTERISTICS VIN = 3.6V, Typical Application Circuit, TA = 25C unless otherwise noted. For 7 LED curves, LED7 anode is connected to VOUT, not VIN.
Output Efficiency Vs VIN, 6 WLEDs 100 95 . 90 Efficiency (%) 85 80 75 70 65 60 3.0 3.3 3.6 3.9 4.2 ILED=15mA,Vf=3.4V ILED=20mA,Vf=3.6V ILED=25mA,Vf=3.8V Efficiency (%) . 100 95 90 85 80 75 70 65 60 3.0 ILED=15mA,Vf=3.4V ILED=20mA,Vf=3.6V ILED=25mA,Vf=3.8V 3.3 3.6 VIN (V) 3.9 4.2 Output Efficiency Vs VIN, 7 WLEDs
VIN (V)
Output Current Vs VIN, 6 WLEDs 200 ILED=25mA,Vf=3.4V ILED=20mA,Vf=3.6V ILED=15mA,Vf=3.8V
Output Current Vs VIN, 7 WLEDs 200
IOUT (mA) .
100
IOUT (mA) .
150
150
100
ILED=15mA,Vf=3.4V ILED=20mA,Vf=3.6V ILED=25mA,Vf=3.8V 3.0 3.3 3.6 VIN (V) 3.9 4.2
50 3.0 3.3 3.6 VIN(V) 3.9 4.2
50
LED Efficiency Vs VIN, 6 WLEDs 100 95 90 Efficiency (%) 85 80 75 70 65 60 3.0 3.3 3.6 VIN (V) 3.9 4.2
LED Efficiency Vs VIN, 7 WLEDs
100 95 90 Efficiency (%) 85 80 75 70 65 60 3.0 3.3 3.6 VIN (V) 3.9 4.2
ILED=15mA,Vf=3.4V ILED=20mA,Vf=3.6V ILED=25mA,Vf=3.8V
ILED=15mA,Vf=3.4V ILED=20mA,Vf=3.6V ILED=25mA,Vf=3.8V
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TYPICAL PERFORMANCE CHARACTERISTICS VIN = 3.6V, Typical Application Circuit, TA = 25C unless otherwise noted. Scope Photo #1 Startup from Shutdown Scope Photo #2 Soft start Interval (within 1X)
ch1=VOUT
ch1=VOUT ch2=SCL
ch4=IOUT 10mA/div ch4= IOUT 100mA/div
Scope Photo #3 Soft start Interval (1X to 1.5X)
Scope Photo #4 Voltage Ripple (1.5X Mode)
ch1=VOUT
VIN(AC)
ch2=SCL
VOUT(AC)
ch4= IOUT 100mA/div
Scope Photo #5 Startup in 1.5X Mode 6 LEDs at 20mA
Scope Photo #6 Startup in 1X Mode 6 LEDs at 20mA
Vout(AC) VOUT Vin(AC)
VOUT
IIN 0.2A/div
IIN 0.2A/div
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APPLICATIONS INFORMATION I C Specifications The I C protocol defines any device that sends data to the bus as a transmitter and any device that reads the data as a receiver. The device that controls the data transfer is known as the Data input format:
S SP7680 Address 7-bit R/W 1/0 A Data for Status 8-bit A Data for CNTRL 8-bit A Data for Main 8-bit A Data for Sub 8-bit A Data for Aux 8-bit A SP
2 2
master and the other device as the slave. The master will always initiate a data transfer and will provide the serial clock for synchronization.
Start Condition
Acknowledge, sent by slave
Acknowledge, sent by slave when R/W =0 Or, sent by master when R/W =1
Stop condition
SP7680 I2C Slave Address Map: (Default Address: 28H)
Fuses Fuse1 0 0 1 1 Fuse0 0 1 0 1 A7 0 0 0 0 A6 0 0 0 0 A5 1 1 1 1 Device Address A4 0 0 1 1 A3 1 0 1 0 A2 0 0 0 0 A1 0 0 0 0 A0 0 0 0 0
IC Serial Interface The SP7680 has five data registers which can be programmed serially via the IC interface. The STATUS register is used to enable/disable the part as well as for fault mode readback. The CNTRL register contains information regarding the state of each of the 7 individual LEDs. The final three registers contain information regarding the current level for the MAIN, SUB and AUX channels. The register bits are as follows:
Registers STATUS Register
In the STATUS register, b7 and b6 are used to enable/disable the SP7680. The following table defines the states for bits WZ and WP. These bits are used to put the SP7680 into shutdown, standby or active mode.
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APPLICATIONS INFORMATION
LED drivers Off For all three fault conditions: 0uA Off Under Voltage Lockout Over Temperature Detection Over Voltage Protection Upon entering any of these fault modes, the LED drivers should turn off but the register contents should remain unchanged with the exception of the fault mode readback bits of the status register. The WZ and WP bits of the status register should also remain unchanged. The microprocessor should not have to reset the SP7680 if it goes into fault mode. The chip should continuously monitor its fault indicators and when the fault condition is no longer present, normal operation can resume.
WZ 0
WP 0
State Shutdown and reset registers to 00000000 Shutdown - keep register contents Standby - keep register contents - bandgap and other analog circuits active, Vin shorted to Vout through internal switch Active
Iq 0uA
Fault Conditions
0
1
1
0
200uA
Off
1
1
Active Iq
On
*When WZ=0 and WP=0 all registers are set to zero. Bits B5, B4, B3, B2 and B1 are for read back only. Bit B5 is held high whenever any kind of fault condition exists on the SP7680. Bits B4, B3 and B2 indicate the specific fault condition, over-voltage (B4=1), over-temp (B3=1) or undervoltage lockout (B2=1). B1 communicates the state of the charge pump, (B1=1 for 1.5x mode or B1=0 for 1x mode). B0 of the STATUS register is used to select between automatic charge pump mode selection and forced charge pump mode selection. If B0 is low then the charge pump mode (1X or 1.5X) is automatically selected. If B0 is high then the charge pump is forced into either 1X mode or 1.5X mode depending upon B0 of the CNTRL register. CNTRL Register
In the CNTRL register B1, B2, B3 and B4 are used to control the four MAIN LEDs, bits B5 and B6 are used for the two SUB LEDs, and B7 is used for the AUX LED. To enable an individual LED the corresponding bit is active high. When B0 of the STATUS register is high, B0 of the CNTRL register is used to force the charge pump into 1X mode (CNTRL B0=low) or 1.5X mode (CNTRL B0=high). When B0 of the STATUS register is low then CNTRL B0 is ignored.
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APPLICATIONS INFORMATION
MAIN, SUB and AUX registers B7...B2 010001 010010 010011 010100 010101 010110 010111 011000 011001 011010 011011 011100 011101 011110 011111 100000 100001 100010 100011 100100 100101 100110 100111 101000 101001 101010 101011 101100 101101 101110 101111 110000 110001 110010 110011 110100 110101 110110 110111 111000 111001 111010 111011 111100 111101 111110 111111 Main 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 15.5 16.0 16.5 17.0 17.5 18.0 18.5 19.0 19.5 20.0 20.5 21.0 21.5 22.0 22.5 23.0 23.5 24.0 24.5 25.0 25.5 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0 30.5 31.0 31.5 Sub 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 15.5 16.0 16.5 17.0 17.5 18.0 18.5 19.0 19.5 20.0 20.5 21.0 21.5 22.0 22.5 23.0 23.5 24.0 24.5 25.0 25.5 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0 30.5 31.0 31.5 Aux 17.0 18.0 19.0 20.0 21.0 22.0 23.0 24.0 25.0 26.0 27.0 28.0 29.0 30.0 31.0 32.0 33.0 34.0 35.0 36.0 37.0 38.0 39.0 40.0 41.0 42.0 43.0 44.0 45.0 46.0 47.0 48.0 49.0 50.0 51.0 52.0 53.0 54.0 55.0 56.0 57.0 58.0 59.0 60.0 61.0 62.0 63.0
In the MAIN, SUB and AUX registers bits B7, B6, B5, B4, B3 and B2 represent the DAC codes D5-D0 used to set the LED current in the MAIN, SUB and AUX channels. Bits B1 and B0 are don't care. The following table lists the DAC codes and the corresponding current for each channel in mA; the table appears below and continues on the right column.
Addressing and Writing Data to the SP7680 To write data to the SP7680 the following data cycle must be obeyed: [Slave Address with write bit][Data for STATUS][Data for CNTRL][Data for MAIN][Data for SUB][Data for AUX] Six bytes are communicated each data cycle. All the settings will take effect right after the acknowledgement bit of the current data byte.
B7...B2 000000 000001 000010 000011 000100 000101 000110 000111 001000 001001 001010 001011 001100 001101 001110 001111 010000
Main 0 0.031 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
Sub 0 0.031 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
Aux 0 0.031 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0
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APPLICATIONS INFORMATION
LED Selection The SP7680 is designed as a driver for backlight white LEDs, but is capable of driving other LED types with forward voltage specifications ranging from 2.0V to 3.8V. LED applications may include main and sub LCD display backlighting, camera photo-flash applications, color (RGB) LEDs, infrared (IR) diodes for remotes, and other loads benefiting from a controlled output current generated from a varying input voltage. Since the D1 to D6 output current-sinks are matched with negligible voltage dependence, the LED brightness will be matched regardless of the specific LED forward voltage (VF) levels. In flash applications, it may be necessary to drive highVF type LEDs. The low dropout current-sinks in the SP7680 make it capable of driving main LEDs with forward voltages as high as 4.0V at full current from an input supply as low as 3.2V. LED current-sink inputs can be paralleled to drive high-current LEDs without complication. Device Switching Noise Performance The SP7680 operates at a fixed frequency of approximately 2MHz to control noise and limit harmonics that can interfere with the RF operation of cellular telephone handsets or other communication 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 white LED backlight solutions. The SP7680 soft-start feature prevents noise transient effects associated with inrush currents during startup of the charge pump circuit. here for reference. The second case of LED power efficiency is included to show the user the true power delivered to the LEDs. As you can see in the curves, the LED efficiency is greatest when VIN is higher than the VF of the LEDs (and higher than the voltage required on the constant current-sink outputs of the LEDs) and that is when the SP7680 is in the 1x mode. When VIN is less than the VF (and less than the voltage required on the constant current-sink outputs of the LEDs) the SP7680 is in the 1.5x mode and in this mode the input current is 1.5 times the output current and therefore the efficiency will be reduced. VOUT efficiency = VOUT*IOUT/(VIN*IIN)*100% LED efficiency = (VOUT -VLED) *IOUt/(VIN*IIN)*100% Refer to the Typical Characteristics section of this document for measured plots of efficiency versus input voltage and output load current versus input voltage for given LED output current options. Capacitor Characteristics Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the SP7680. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor has very low ESR, is lower in cost, has a smaller PCB footprint, and is non-polarized. Low ESR ceramic capacitors help to maximize charge pump transient response. Since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage. Equivalent Series Resistance (ESR) ESR is an important characteristic to consider when selecting a capacitor. ESR is a resistance internal to a capacitor that is caused by the leads, internal connections, size or area, material composition, and ambient temperature. Capacitor ESR is typically measured in milliohms for ceramic capacitors and can range to more than several Ohms for tantalum or aluminum electrolytic capacitors.
Power Efficiency The charge pump efficiency shown in the typical characteristic curves is shown for two cases. The first case is called output efficiency which is the power efficiency to the output as a ratio of the output voltage power to the input voltage power and expressed as a percentage. The second case is called LED efficiency and is the power efficiency to the LED outputs and is expressed as a ratio of the power to the LEDs to the input voltage power. The expressions are shown at the end of this section in their formulas. The first case is what is generally shown in competitors' datasheets and is shown
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APPLICATIONS INFORMATION
Ceramic Capacitor Materials Capacitors with large output values are typically composed of X7R, X5R, Z5U, or Y5V dielectric materials, but Z5U and Y5V are not recommended since they have a large change in value with temperature. X5R and X7R capacitors are recommended since they are relatively low in cost and their output value changes with temperature are relatively small. Capacitor Selection Careful selection of the four external capacitors CIN, C1, C2, and COUT is important because they will affect turn-on time, output ripple, and transient performance. Optimum performance will be obtained when low equivalent series resistance (ESR) ceramic capacitors are used. In general, low ESR may be defined as less than 100m . A value of 2.2F for the input and 1F for the output capacitor is sufficient for most applications. The fly capacitors C1 and C2 can be 0.47F for most applications. For applications with all 7 LED drivers used and driven to 20mA or more, it is advisable to use a 2.2F input capacitor in order to reduce the input ripple as seen by the battery. In very noise sensitive applications, the input capacitor can even be increased to 4.7F. If the LED current-sinks are only programmed for low current levels, or if the application is not very noise sensitive, then a 1F input capacitor may be used. See table 1 for capacitor selection. Thermal Protection The SP7680 has a thermal protection circuit that will shut down the internal LDO and charge pump if the die temperature rises above the thermal limit, and will restart when the die temperature drops about 25C below the thermal limit.
Manufacturers/ Website TDK/www.tdk.com TDK/www.tdk.com TDK/www.tdk.com TDK/www.tdk.com Murata/www.murata.com Murata/www.murata.com Murata/www.murata.com Murata/www.murata.com
Part Number C1005X5R0J474K C1005X5R0J105K C1608X5R0J225K C1608X5R0J475K GRM155R60J474KE19 GRM155R60J105KE19 GRM185R60J225KE26 GRM188R60J475KE19
Capacitance/ Voltage 0.47uF/6.3V 1uF/6.3V 2.2uF/6.3V 4.7uF/6.3V 0.47uF/6.3V 1uF/6.3V 2.2uF/6.3V 4.7uF/6.3V
Capacitor Size/Type/Thickness 0402/X5R/0.55mm 0402/X5R/0.55mm 0603/X5R/0.9mm 0603/X5R/0.9mm 0402/X5R/0.55mm 0402/X5R/0.55mm 0603/X5R/0.55mm 0603/X5R/0.8mm
ESR at 100kHz 0.05 0.03 0.03 0.02 0.05 0.03 0.03 0.02
Table 1: SP7680 Capacitor Selection
June 21-07 revH
SP7680: Complete Backlight Solution
2007 Sipex Corporation
Page 14
PACKAGE: 3x3mm 16 pin QFN
June 21-07 revH
SP7680: Complete Backlight Solution
2007 Sipex Corporation
Page 15
ORDERING INFORMATION
Part Number SP7680ER1-L SP7680ER1-L/TR SP7680EB Status Active Active Active Min Max Theta JA RoHS Temp C Temp C C/W -40 -40 -40 85 85 85 Yes Yes 33.3 33.3 MSL Level L3 @ 260C L3 @ 260C Pack Type Canister Tape & Reel Quantity Package Any 3000 3x3 16 Pin QFN 3x3 16 Pin QFN Board
Not Applicable to Eval Board
For further assistance: Email: WWW Support page: Sipex Application Notes: Sipexsupport@sipex.com http://www.sipex.com/content.aspx?p=support http://www.sipex.com/applicationNotes.aspx
Solved by
Sipex Corporation
Headquarters and Sales Office 233 South Hillview Drive Milpitas, CA95035 tel: (408) 934-7500 FAX: (408) 935-7600
TM
Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others.
June 21-07 revH
SP7680: Complete Backlight Solution
2007 Sipex Corporation
Page 16

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