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X RP 6 8 4 0
4.3A Supercapacitor Flash LED Driver with I2C
December 2009 Rev. 1.0.0
GENERAL DESCRIPTION
The XRP6840 is a controlled-current dual-cell supercapacitor charger and high power LED driver. Operating from a standard lithium-ion battery, the XRP6840 provides up to 4.3A of programmable Flash LED current and up to 600mA and 5.6V of programmable supercapacitor charging current and voltage. Architectured around a 2.4MHz tri-mode 1x, 1.5x and 2x charge pump, the XRP6840 charges the stacked supercapacitor to the programmed output voltage with no more than 600mA drawn from the battery. While charging, an internal active balance circuitry insures matching of the stacked capacitors' voltages. A standard 2-line I2C serial interface allows the dynamic programming of LED currents in torch and flash modes, flash timeout, channel enable, gain control, capacitor charge voltage, and enable. The XRP6840 comes in a 2 and 3 channel version supporting respectively 440mA/2.15A per channel and 300mA/1.45A in torch/flash modes. The flexibility designed into the XRP6840 can also allow it to reverse the power flow back to the input to prevent unintended system resets as the battery voltage drops. The XRP6840 is available in a lead-free, "green"/halogen free 20-pin TQFN package.
APPLICATIONS
* High Power Torch/Strobe/Flash LED * High Resolution Cameras * Generic High Power Lighting * High Power White LED Backlighting
FEATURES
* Programmable 4.3A Flash LED Driver - Torch and Flash Modes - 2 and 3 Channels Versions * Programmable Supercapacitor Charger - 600mA Adjustable Charging Current - Programmable Supercapacitor Voltage - In-rush Current Control - Active Voltage Balance Control * Tri-mode Charge Pump Architecture - 1x, 1.5x, 2x Operation Modes - 2.4MHz Switching Frequency * I2C Serial Interface * Thermal, Over Current and Output Short Protection * LED Short Detection * RoHS Compliant "Green"/Halogen Free 20-pin 4mmx4mm TQFN package
TYPICAL APPLICATION DIAGRAM
Fig. 1: XRP6840 - 3 Channels Application Diagram
Exar Corporation 48720 Kato Road, Fremont CA 94538, USA
www.exar.com Tel. +1 510 668-7000 - Fax. +1 510 668-7001
X RP 6 8 4 0
4.3A Supercapacitor Flash LED Driver with I2C
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, VOUT, LED1, LED2, LED3 .......................... -0.3V to 6.0V SCL, SDA, RDY, RESET_N, CAP ............ -0.3V to VIN +0.3V C1P, C2P, C1N, C2N ........................... -0.3V to VIN +0.3V Storage Temperature .............................. -65C to 150C Power Dissipation ................... Internally Limited (Note 1) Lead Temperature (Soldering, 10 sec) ................... 260C ESD Rating (HBM - Human Body Model) All Pins ......... 2KV
OPERATING RATINGS
Input Voltage Range VIN ............................... 2.7V to 5.5V Junction Temperature Range ....................-40C to 125C Thermal Resistance JA ................................... 30.8C/W
ELECTRICAL SPECIFICATIONS
Specifications with standard type are for TJ = 25C only; limits in applying over the full Operating Junction Temperature (TJ) range are denoted by a "*". Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25C, and are provided for reference purposes only. Unless otherwise indicated, VIN = 3.4V, VLED = 0.8V, CIN = 47F, CF1 = CF2 = 0.47F, COUT1 (VOUT to CAP) = 47F and COUT2 (CAP to GND) = 47F. TA= -40C to 85C, TJ = -40C to 125C.
Parameter Operating Input Voltage Range UVLO Turn-On Threshold UVLO Hysteresis Operating Input Current Including In-rush Current Torch Mode Input Current Torch Mode Input Current Standby Input Current Shutdown Supply Current Shutdown ILED Current Torch Mode Incremental current Step
Min. 2.7 2.2
Typ. 2.4 100 600 202 302 30 1 0 20 30 200 300 300 440 4.3 3 4
Max. 5.5 2.6 725 228 340 40 3
Units V V mV mA mA mA A A mA mA mA mA mA mA mA A Bit Bit * * * VIN rising VIN falling
Conditions
1x, 1.5x or 2x Mode 1x Mode, IOUT = 200mA 1.5x Mode, IOUT = 200mA All LEDs are Off, TJ(max) = 85oC RESET_N = 0V STATUS1 Register [B7 B6] =00 Measure LED1 - LED3 XRP6840A, Table 6, averaged from all channels XRP6840B, Table 6, averaged from all channels XRP6840A, Table 5, averaged from all channels XRP6840B, Table 5, averaged from all channels XRP6840A, Note 2, averaged from all channels XRP6840B, Note 2, averaged from all channels Flash Mode, Measured current into all LED pins Flash Mode Torch Mode
Flash Mode Incremental current Step
Maximum Current in Torch Mode per Channel Maximum Current in Flash Mode Output Current DAC Resolution -10 DAC Current Accuracy -12 -18
10 12 18
% mA mA
* * *
120mA < ILED < 1.6A for XRP6840A 180mA < ILED < 1.6A for XRP6840B ILED 120mA, XRP6840A ILED 180mA, XRP6840B
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Parameter Channel to Channel Current Matching Switching Frequency Equivalent Resistance, 1X Mode Equivalent Resistance, 1.5X Mode LEDx Pin Dropout Voltage Min. -3 2.0 2.4 0.5 4 7 Typ. Max. 3 2.8 Units % MHz * * * * VIN = 3.7V, IOUT = 200mA VIN = 3.2V, VOUT < VOUT_LIMIT, IOUT = 200mA, Equivalent resistance = [(VIN x 1.5) - VOUT] / IOUT Flash mode, VIN = 3.4V, ILED = 1A, Measure LED current at 95% ILEDX-NOMINAL at VLEDX=0.8V Torch mode, VIN = 3.4V, ILED = 80mA, Measure LED current at 95% ILEDX-NOMINAL at VLEDX=0.8V VOUT - VLED, LED = 0mA for all DAC code Driver turn OFF Driver turn ON Flash Mode, ILED = 0mA, VOUT Rising STATUS2 Register: [B7 B6 B5] = 101 OVR value is set by STATUS2 register between 4.55V - 5.6V, all setting have +/- 100mV tolerance Flash Mode, ILED = 0mA STATUS2 Register: [B7 B6 B5] = 101 100mV below actual OVR value. * * * s * * * * RDY goes low when RESET_N goes from high top low STATUS1 register [B1 B0]=00 STATUS1 register [B1 B0]=01 STATUS1 register [B1 B0]=10 STATUS1 register [B1 B0]=11 Conditions 0mA < ILED < 1.6A Per Channel, Note 3
0.36
V
*
LEDx Pin Dropout Voltage LED Short Detect Threshold Thermal Regulation Thermal Shutdown Temperature Thermal Shutdown Hysteresis 150 10 0.1 0.2
0.1 0.4 0.01
V V %/oC
o o
* *
C C
Output Voltage Regulation (OVR)
5.2
5.3
5.4
V
*
Output Voltage Regulation Hysteresis RDY Pin Output Trip Threshold RDY Pin Sink Current SDA, SCL, RESET_N, FLASH Input Logic Low Voltage SDA, SCL, RESET_N, FLASH Input Logic High Voltage Turn-Off Time (TOFF) Into Shutdown 0.09 Flash Time Duration Before Standby 0.18 0.43 0.9 1.6 1
50 VO - 0.1
mV V mA 0.4 V V 50
0.11 0.22 0.53 1.1
0.13 0.26 0.63 1.3
s s s s
I2C SPECIFICATIONS I2C ADDRESSING FORMAT
S XRP6840 Address 7-bit R/W 1/0 A Status Data 8-bit A LED1 Data 8-bit A LED2 Data 8-bit A LED3 Data 8-bit A SP
Start Condition Acknowledgement Acknowledgement sent by the slave - sent by the slave when R/ W =0 - sent by master when R/ W =1 Fig. 2: I2C Data Input Format Stop Condition
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Default I2C slave 7-bit address for XRP6840 is 0101000b
I2C TIMING CHARACTERISTICS
VIN = 3.3V, TA = -40C to 85C, TJ = -40C to 125C. Unless otherwise noted. Parameter Serial Clock Frequency Bus Free Time between a STOP and a START Hold Time, Repeated START Condition 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 I2C Startup Time after UVLO clears Symbol fSCL tBUF tHD_STA tSU,STO tHD,DAT(OUT) tHD,DAT(IN) tSU,DAT tLOW tHIGH tR tF tF.TX tSP Cb tSRT 1.3 0.6 0.6 225 0 100 1.3 0.6 20 + 0.1Cb 20 + 0.1Cb 20 + 0.1Cb 0 300 300 250 50 400 1 900 900 Min. Typ. Max. 400 Units KHz s s ms ns ns ns ms ms ns ns ns ns pF s Note 4,5 Note 4,5 Note 4,5,6 Note 7 Note 4 Note 4 Conditions
Note 1: All parameter tested at TA = 25C. Specifications over temperature are guaranteed by design. Note 2: Current into all LED pins is up to 400mA continuously in Torch 1.5x mode. Note 3: LED current matching is calculated by this equation: 100% where IAVG is the average current of all channels. Note Note Note Note 4: 5: 6: 7: Guaranteed by design. Cb = total capacitance of one bus line in pF. tR and tF measured between 0.3 x VDD and 0.7 x VDD. ISINK 6mA. Cb =total capacitance of one bus line in pF. tR and tF measured between 0.3 x VDD and 0.7 VDD. Input filters on the SDA and SCL inputs suppress noise spikes less than 50ns.
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BLOCK DIAGRAM
Fig. 3: XRP6840 Block Diagram (XRP6840A Shown)
PIN ASSIGNEMENT
XRP6840A - 3 Channel Version
XRP6840B - 2 Channel Version
Fig. 4: XRP6840 Pin Assignment
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PIN DESCRIPTION
Name CGND RDY SCL, SDA PGND Pin Number 1 2 3, 4 5, 11 Charge pump ground pin. Active high push-pull output. RDY is high when VOUT reached to 100mV below its VOUT_LIMIT voltage. The VOUT_LIMIT for Flash mode is determined by STATUS2 register [B7 B6 B5]. The VOUT_LIMIT for Torch mode is 4.50V. The SDA and SCL pins connect to the I2C bus. Multiple functions can be programmed through his interface. They can also be used for read-back. Power ground pin. The Source of internal NMOS is connected to this pin. Active Low input pin. If RESET_N = 0, then XRP6840 is in Shut-down mode If RESET_N = 0 and STATUS1 register [B5] = 0, then reset all registers to logic low. If RESET_N = 0 and STATUS1 register [B5] = 1, then all bits of all registers will be saved. LED1, LED2, LED3 connect to the drain of the internal NMOS which are current sources for LED current. These current sources are controlled by LEDFLASH or LEDTORCH registers which is programmed through I2C to provide the Torch and Flash current for the LEDs. LED1, LED2, LED3 pins can be connected together to provide higher LED current. If a pin is not used connect it to VOUT. The XRP6840 incorporates a short LED protection circuit which shut-down LED current if LED voltage approaches to VOUT_LIMIT. Digital Input pin. Active high. If STATUS1 register [B7 B6] = 11 and FLASH = 1 then LEDs are ON for one Flash timeout duration. Flash Timeout duration is controlled by STATUS1 register [B1 B0]. No connection. This pin can be connected to PGND pin for heat sink. Ground pin. This ground pin doesn't carry high internal current. This pin is the output of an internal Op-Amp. This internal Op-Amp is powered by VOUT. The output voltage is half of VOUT, and output resistance is 470. The sink and source current is limited by 470 output resistance. This provides active balancing between two internal sections of the super capacitor. Output voltage. Connect positive terminal of SuperCap here. Connect the LEDs between this pin and the corresponding internal current source. Decouple with 10F ceramic capacitor close to the pins of the IC. Connect C2 external flying capacitor between these pins. Connect C1 external flying capacitor between these pins. Power supply input. Decouple with 10F ceramic capacitor close to the pins of the IC. Connect thermal pad to PGND pins. Description
RESET_N
6
LED1, LED2, LED3 (XRP6840A) LED1, NC, LED2 (XRP6840B) FLASH NC GND CAP 7, 8, 9 7, 8, 9
10 12 13 14
VOUT C2P, C2N C1P, C2P VIN Thermal Pad
15 16, 17 18, 19 20 -
ORDERING INFORMATION
Part Number XRP6840AILB-F XRP6840AILBTR-F XRP6840BILB-F XRP6840BILBTR-F XRP6840EVB Junction Temperature Range -40CTA+125C -40CTA+125C -40CTA+125C -40CTA+125C XRP6840 Evaluation Marking Package Packing Quantity Bulk 3K/Tape & Reel Bulk 3K/Tape & Reel Note 1 RoHS Compliant/ Halogen Free RoHS Compliant/ Halogen Free RoHS Compliant/ Halogen Free RoHS Compliant/ Halogen Free Note 2 3 Channels 3 Channels 2 Channels 2 Channels
6840AI 20-pin TQFN YYWWX 6840AI 20-pin TQFN YYWWX 6840BI 20-pin TQFN YYWWX 6840BI 20-pin TQFN YYWWX Board - XRP6840A based.
"YY" = Year - "WW" = Work Week - "X" = Lot Number
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TYPICAL PERFORMANCE CHARACTERISTICS
All data taken at VIN = 2.7V to 5.5V, TJ = TA = 25C, unless otherwise specified - Schematic and BOM from Application Information section of this datasheet.
Fig. 5: High Efficiency Torch Mode ILED at 200mA no supercap
Fig. 6: High Efficiency Torch Mode, LED Current versus VIN no supercap
Fig. 7: High Efficiency Torch Mode, Input Current versus VIN ILED at 200mA, no supercap
Fig. 8: VOUT RDY: 0.6F Supercap, CH1 = VIN, CH2 = VOUT, CH3 = RDY, CH4 = IVIN =0.5A/div
1100mA
680mA
Fig. 9: In-rush Current with Li-ion Battery 0.6F Supercap, CIN=10F CH1 = VIN, CH4 = IVIN =0.5A/div
Fig. 10: In-rush Current, 0.6F Supercap, CIN = 22F, CH1 = VIN, CH4 = IVIN =0.5A/div
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Fig. 11: 0.11s Flash Duration with 0.55F Supercap at 4.3A, LED VF < 3.8V, CH1 = FLASH, CH2 = RDY, CH3 =VOUT, CH4 = ILED =2A/div
Fig. 12: 0.22s Flash Duration with 0.9F Supercap at 4.3A, LED VF < 3.8V, CH1 = FLASH, CH2 = RDY, CH3 =VOUT, CH4 = ILED =2A/div
Fig. 13: 200mA High Efficiency Torch Mode with 0.55F Supercap, CH1=VIN, CH2=VOUT, CH3=LEDX, CH4=IVIN =0.5A/div
Fig. 14: 200mA Torch Mode with 0.55F Supercap, CH1=VIN, CH2=VOUT, CH3=LEDX, CH4=IVIN =0.5A/div
Fig. 15: LED Current Settling Time: 0mA to 100mA. CH1=SDA, CH2=SCL, CH4=ILED=0.1A/div
Fig. 16: LED Current Settling Time: 100mA to 200mA. CH1=SDA, CH2=SCL, CH4=ILED=0.1A/div
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Fig. 17: LED Current Settling Time: 200mA to 0mA. CH1=SDA, CH2=SCL, CH4=ILED=0.1A/div
Fig. 18: LED Current Settling Time 200mA to Shutdown. CH1=RESET_N, CH2=LEDx, CH4=ILED=0.2A/div
Fig. 19: LED Current Settling Time From Shutdown to 200mA. CH1=RESET_N, CH2=LEDx, CH4=ILED=0.2A/div
Fig. 20: Flash Mode Shutdown. CH1=RESET_N, CH2=RDY, CH3=VOUT
Fig. 21: Figure 21: Flash Mode Enable From Shutdown CH1=RESET_N, CH2=RDY, CH3=VOUT
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APPLICATION INFORMATION I2C SERIAL INTERFACE REGISTERS
The XRP6840 has five serially programmable data registers via the IC interface. These registers can be reset to `0' through power on reset or setting RESET_N, pin 6, to `0'. The first register is for Device Address as shown in Figure 3; it is activated by `28' HEX (7-bit format). The second register, STATUS1, contains the control word for programming operating modes, shutdown control, charge pump modes and flash timeout. The third register, STATUS2, contains the flash voltage level, read back of the Flash Ready, and fault conditions UVLO and over temperature. The fourth register, LEDFLASH, controls individual LED channels and current level in Flash Mode. The fifth register, LEDTORCH, controls individual LED channels and current level in Torch Mode.
Register Address STATUS1 STATUS2 LEDFLASH LEDTORCH B7
0 Flash Torch Mode Flash V LED1 LED1
STATUS1 Register Bit B5 This bit is used to save or reset the contents of STATUS1, STATUS2, LEDFLASH and LEDTORCH registers for the next I2C command when RESET_N, pin 6, is `1'. If B5 is `1' then all bits in these registers will be saved. Otherwise if B5 is `0' then all bits will be reset to `0'. STATUS1 Register Bits B1 and B0 These two bits program the flash timeout duration as follows:
B1
0 0 1 1
B0
0 1 0 1
Flash Duration
0.11s 0.22s 0.53s 1.10s
Table 3: Charge Pump Mode Selection
STATUS2 Register Flash Mode Voltage Programming VOUT_LIMIT in Flash Mode is regulated with 50mV of hysteresis and is programmed through bits B7, B6 and B5 of STATUS2 register as follows:
B7
0 0 0 0 1 1 1 1
B6
1
B5
0
B4
1
B3
0 Gain UVLO Fault D1 D2
B2
0 Temp Fault D0 D1
B1
0
B0
R/W
Flash Shut Gain Torch Down Mode Control Flash Flash Flash V V Ready LED2 LED2 LED3* LED3* D2 D3
Flash Flash Timeout Timeout 0 D0 0 -
B6
0 0 1 1 0 0 1 1
B5
0 1 0 1 0 1 0 1
Comment
4.55V 4.70V 4.85V 5.00V 5.15V 5.30V 5.45V 5.60V
Table 1: XRP6840 I2C Registers Bit Map * Not used for XRP6840B
STATUS1 Register STATUS1 Register Bits B7, B6, B4 and B3
B7 0 0 0 0 1 1 1 1 1 1 1 1 B6 1 1 1 1 0 0 0 0 1 1 1 1 B4 0 0 1 1 0 0 1 1 0 0 1 1 B3 0 1 0 1 0 1 0 1 0 1 0 1 Operation Mode High Efficiency Torch Mode 1X Torch Mode 1.5X Torch Mode 2X Torch Mode Auto Gain Torch Mode 1X Torch Mode 1.5X Torch Mode 2X Torch Mode Auto Gain Flash Mode 1X Flash Mode 1.5X Flash Mode 2X Flash Mode
Table 4: Flash Mode VOUT_LIMIT Settings
Bit B4 RDY bit is available for I2C read-back. This bit is set to `1' when VOUT > VOUT_LIMIT, and set to `0' otherwise. Fault mode read-back bits B3, B2 These bits are designed for 2 Fault Mode flags and are also available for I2C read-back. Bits 3 and 2 are set to `1' when UVLO and over temperature conditions are detected, as shown in Table 1. LEDFLASH Register LEDFLASH register, bits B7, B6 and B5 are used to activate the LED outputs channels as summarized in Table 1; they correspond to LED1, LED2 and LED3. Bits B4, B3 and B2
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Table 2: STATUS1 Register Operation Modes
(c) 2009 Exar Corporation
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4.3A Supercapacitor Flash LED Driver with I2C
represent the DAC codes D2, D1, D0. They are used to set the flash LED current levels in each channel. Table 5 provides the DAC codes and the corresponding nominal current levels for each channel:
D2-D0 Code
0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1
Addressing and Writing Data To write data to the XRP6840 one of the following two sequences is required: Easy shutdown/startup sequence [Slave Address with write bit][Data for Status] Full shutdown/startup sequence [Slave Address with write bit][Data for Status] [Data for LEDFLASH][Data for LEDTORCH] Slave address is `28' Hex. Addressing and Reading Data To read data from the XRP6840 the following sequence is required: [Slave Address with read bit][Data for Status] [Data for LEDFLASH][Data for LEDTORCH]
XRP6840A IOUT/Ch. (mA)
0 400 586 770 948 1197 1291 1445
D2-D0 Code
0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1
XRP6840B IOUT/Ch. (mA)
0 597 875 1127 1400 1671 1910 2150
Table 5: Nominal Flash Mode Output Current
LEDTORCH Register LEDTORCH register bits B2 to B7, also summarized in Table 1; they correspond to LED1, LED2 and LED3. Bits B4, B3, B2, and B1 represent the DAC codes D3, D2, D1, D0. They are used to set the torch LED current levels in each channel. Table 6 provides the DAC codes and their corresponding nominal current levels for each channel. Remember that the total current that can be supported in torch mode is 600mA divided by the gain of the charge pump. If 2 channels are set to 440mA (a total of 880mA), even with a gain of 1X, the input current limit will clamp the total current to approximately 600mA.
D3-D0 Code
0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
XRP6840A IOUT/Ch. (mA)
0 23 46 66 86 105 125 145 165 185 205 225 245 260 280 300
D3-D0 Code
0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
XRP6840B IOUT/Ch. (mA)
0 34 66 97 127 155 185 215 245 275 305 330 360 385 415 440
Table 6: Torch Mode Output Current
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THEORY OF OPERATION
When VIN reaches 2.7V during initial power up, a power on reset signal will be issued to reset all the registers and the internal logic, and the system will be ready for operation. To be in operation the XRP6840 must be enabled through RESET_N, pin 6. The LEDs can be activated through LEDFLASH or LEDTORCH registers. further in the High Efficiency Torch Mode section. The XRP6840 can operate in either "Auto Gain Mode" or "Programmable Gain Mode". However, either mode will be overridden during start-up based on the following internal control algorithm: 1. If VOUT > VOUT_LIMIT then the charge pump is OFF. 2. If VOUT < VIN - 1V then the charge pump can only operate in 1x mode. 3. If VIN - 1V < VOUT < VIN then the charge pump is allowed to operate in either 1x or 1.5x mode but not in 2x mode. 4. If VOUT > VIN then the charge pump can operate either in 1.5x or 2x mode but not in 1x mode (there is no reverse current limit on the 0.5 bypass MOSFET). 5. If VOUT > VOUT_LIMIT, and all LEDs are deactivated then XRP6840 will operate in standby mode with 30A supply current. VOUT_LIMIT is 4.5V for Torch Mode and High Efficiency Torch Mode; for Flash mode VOUT_LIMIT is shown in Table 4. Standby mode is set by either LEDFLASH or LEDTORCH registers [B7 B6 B5] to [0 0 0]. This will deactivate all the LED channels.
CHARGE PUMP MODES 1X, 1.5X AND 2X
The XRP6840 charge pump can operate in 1x, 1.5x and 2x modes to ensure desired current regulation. Once the output reaches VOUT_LIMIT, the charge pump will turn off. In 1x mode, the input is simply connected to the output through an internal 0.5 MOSFET. An internal in-rush current limit will keep the charging current controlled to a maximum of 600mA. In 1.5x mode, during the first clock phase the 2 flying capacitors, C1 and C2, are series connected between VIN and ground, charging each capacitor to 1/2 VIN. In the second clock phase, the flying capacitors are parallel connected and placed in series with VIN, producing 1.5xVIN to be discharged across the output capacitor. Note the maximum total output current is now 600mA/1.5 or 400mA. In 2x mode, during the first clock phase, one flying capacitors is charged to VIN. In the second clock phase, this capacitor is placed in series with VIN, producing 2xVIN to be discharged across the output capacitor. Note the maximum total output current is now 600mA/2 or 300mA.
AUTO GAIN START-UP
The Auto Gain Start mode is the fastest way to charge the output toward VOUT_LIMIT. It is initiated with the following conditions; as shown in Table 7 (a sub-set of Table 2), in STATUS1 Register.
B7 0 1 1 B6 1 0 1 B4 0 0 0 B3 0 0 0 Operation Mode High Efficiency Torch Mode Auto Gain Start Torch Mode Auto Gain Start Flash Mode
CHARGE PUMP CONTROLLER
The charge pump controller regulates the output by turning the charge pump off once the output reaches VOUT_LIMIT. For both Torch and Flash Modes, there is 50mV of output voltage hysteresis before the charge pump is re-enabled. However, in High Efficiency Torch mode, it will only turn on again when VLEDX is below the drop out voltage of approximately 0.36V. Once the charge pump turns on again, it will then monitor both VOUT and VLEDX voltages. This operation will be explained
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Table 7: Auto Start Mode from STATUS1 Register
When in Auto Gain Start Mode, the XRP6840 will charge up VOUT to VOUT_LIMIT with maximum available current within the constraints defined above for start-up. In this mode the XRP6840 will initialize the system as follows: 1. Turn off all the LEDs that were programmed through LEDTORCH or LEDFLASH registers.
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2. Determine if VOUT_LIMIT is reached. If this condition is met anytime, the charge pump will turn off, release the control of the LEDTORCH or LEDFLASH registers, and will be ready for turning on the LEDs. After system initialization, the XRP6840 will automatically switch between 1x, 1.5x, or 2x mode modes to try and keep input current to a maximum without exceeding 600mA. Auto Start Mode ends when VOUT reaches VOUT_LIMIT. The Auto Start Mode begins in 1x mode or 1.5x mode if VOUT > VIN. When the input current drops to approximately 400mA the XRP6840 is able to switch from 1x to 1.5x mode without exceeding 600mA. The switch from 1.5x mode to 2x mode occurs if VOUT has not reached VOUT_LIMIT and when the input current is below 300mA. After switching to 2x mode, the charge pump continues to operate until VOUT_LIMIT is reached. If VOUT_LIMIT could not be reached, then the XRP6840 will continuously run the charge pump in 2x mode. At this point, it is recommended to shut down through I2C, RESET_N to `0' or power down. There are probably 2 main causes for the XRP6840 to remain in 2x mode: VOUT overloaded or VIN too low. If the output were shorted, the current in 1x mode would never drop below 600mA and the XRP6840 would never move to the higher gains. Removing the short or overload will allow the XRP6840 to recover back to normal operation. If VIN is too low then it is advisable to power down the system and change the battery. protection in 1x mode. Reverse current is possible in 1.5x or 2x modes and that leads to interesting applications possibilities.
REVERSING THE POWER FLOW
By forcing the charge pump into 1.5x mode once the output voltage is charged in Flash Mode, it is possible to reverse the current back to the input if the input voltage is <3.6V. This gives one the possibility of using the XRP6840 Flash system to provide power back to the input when other parts of the system require unusually high loads. A couple of examples are; a high power burst transmit, or HDD spin up. In Flash Mode, charge the output capacitor to 5.45V (STATUS2 Register B7-B5 = 110) using Auto Start Mode. When power is required back at the input, force to 1.5x mode (STATUS1 Register B4-B3 = 10) and change VOUT_LIMIT to 5.60V (STATUS2 Register B7-B5 = 111). This will have the effect of instantly turning on the charge pump in 1.5x mode. If the input voltage is 3V, then approximately 300mA will flow from the output super capacitor to the input for 650ms. The current will drop as the super capacitor discharges, but as much as 150mA is available after 1.5seconds. A more complete application note will be forthcoming on this topic.
HIGH EFFICIENCY TORCH MODE
High Efficiency Torch Mode is a special XRP6840 feature designed to achieve the highest torch mode power efficiency. This mode is activated only when STATUS1 [B7 B6 B4 B3] are [0 1 0 0]. LEDTORCH [B7 B6 B5] can be set according to the number of desired LED channels. First, the charge pump will charge VOUT to VOUT_LIMIT then turn off. Then when the LEDs are enabled, the control loop will adjust VOUT to the minimum value required to maintain current regulation. It does this by monitoring and regulating the VLEDX voltage with respect to an adaptive drop out voltage, VDO. The adaptive VDO algorithm will allow VLEDX to drop down to 220mV for 1x mode and 180mV for both 1.5x and 2x modes. This will ensure the XRP6840 stays in the lowest charge pump
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PROGRAMMABLE START MODE
Programmable start mode allows the flexibility to select the maximum gain. Start-up gains are based strictly on input and output voltage differences. The 600mA input current limit is still imposed, but typically is not triggered. This is why Auto Start Mode is recommended because it charges the output capacitor the fastest. Even though the maximum gain is programmed, the 5 stage internal control algorithm on the previous page will still override the programmed gain to ensure optimum operation and reverse current
(c) 2009 Exar Corporation
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4.3A Supercapacitor Flash LED Driver with I2C
mode to maintain good current regulation. As Figure 5 shows, very high efficiency can be obtained if the system can operate at the lowest available charge pump gain at very low VIN levels. Due to the XRP6840's low drop out voltage design, good current regulation can still be achieved at extremely low VLED voltage levels. When VLEDX drops below VDO, and VOUT is also below VOUT_LIMIT, the XRP6840 charge pump will turn on to charge the VOUT and VLEDX. If VLEDX is still below VDO after 64 clock cycles or 27s (at 2.4MHz), the XRP6840 will jump to the next higher gain. If at any time, VOUT_LIMIT is reached, then charge pump will turn off.
COMPONENT SELECTION
The XRP6840 charge pump circuit requires the following capacitors: 1. 2. 3. 4. Input Cap: 22F Output Cap: 10F Charge Pump Flying caps: 2x0.47F Supercapacitor: 0.6F (0.3F to 0.9F).
Input capacitances higher than 10F will help reduce input voltage ripple and in-rush current. Refer to Figures 9 and 10 for comparison. The input and output capacitors should be located as close to the VIN and VOUT pins as possible to obtain best bypassing. Their returns paths should be connected directly to the PGND pin or to the thermal pad ground located under the XRP6840. The flying capacitors should be located as close to the C1P, C1N and C2P, C2N pins as possible. All the capacitors should be surface mount ceramic types for low ESR and for low lead inductances. These capacitors can also improve bypassing. X5R or X7R temperature grades are recommended for this application. The supercapacitor selection depends on LED current, flash duration, and LED forward voltage. The minimum super capacitor is determined as follows:
FAULT PROTECTION
Although most of these modes of operation have already been previously described, they are repeated here to emphasize the robustness of the XRP6840. The output voltage is directly monitored and controlled through the VOUT pin. Should an open occur on the VOUT pin, the output is disconnected from the input and no damaging voltages will be applied to the output super capacitor due to an open loop condition. The XRP6840 also has a built-in over current protection because when the output is shorted, the XRP6840 will force the part to be in 1x mode and its output current is always limited to 600mA regardless of whether or not the part is in Auto or Programmed Start Modes. The XRP6840 also has thermal protection. If the junction temperature rises above 150C, the part is disabled. Once the temperature drops below 140C the part is re-enabled.
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OPEN AND SHORT LED PROTECTION
An open LED has no real effect on the operation of the XRP6840. If an LED fails short, that channel will be disabled. The short condition is asserted when VOUT to VLEDX is less than 200mV. Only the driver of the shorted LED will be turned off and no current will flow. However, the other channels will continue to operate as intended, independently of the shorted channel.
(c) 2009 Exar Corporation 14/17
IOUT is the target flash current, TFLASH is the flash duration, VOUT_LIMIT is the initial Super Capacitor voltage programmed by STATUS2 register bits [B7 B6 B5], VF is the LED forward voltage and VLED is the maximum LED pin voltage before dropout (360mV at 125C). For example, for a 4.3A flash with 110ms duration, LED VF of 3.5V and VOUT_LIMIT voltage of 5.3V, the minimum capacitance is: 4.8 0.11 0.36 4.8
5.3
3.5
0.05
0.44
Rev. 1.0.0
X RP 6 8 4 0
4.3A Supercapacitor Flash LED Driver with I2C
To achieve 4.3A flash pulses, we recommend using 0.55F Super Capacitor from TDK EDLC2720-501-2F-50 with voltage rating of 5.5V and 50m of ESR, or the 0.6F HS206F Super Capacitor from CAP-XX with a voltage rating of 5.5V and 80m of ESR.
TYPICAL APPLICATION SCHEMATICS
Fig. 22: XRP6840A - 3 Channel - 4.3A Total LED Flash Current
(c) 2009 Exar Corporation
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Rev. 1.0.0
X RP 6 8 4 0
4.3A Supercapacitor Flash LED Driver with I2C
PACKAGE SPECIFICATION 20-PIN TQFN
(c) 2009 Exar Corporation
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Rev. 1.0.0
X RP 6 8 4 0
4.3A Supercapacitor Flash LED Driver with I2C
REVISION HISTORY
Revision 1.0.0 Date 12/05/2009 Initial Release of Data Sheet Description
FOR FURTHER ASSISTANCE
Email: Exar Technical Documentation: customersupport@exar.com http://www.exar.com/TechDoc/default.aspx?
EXAR CORPORATION HEADQUARTERS AND SALES OFFICES
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NOTICE
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user's specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. or its in all
(c) 2009 Exar Corporation
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Rev. 1.0.0

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