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December 2009 Rev. 1.0.0
Exar Corporation www.exar.com
48720 Kato Road, Fremont CA 94538, USA Tel. +1 510 668-7000 – Fax. +1 510 668-7001
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 I
2
C 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
• I
2
C 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
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© 2009 Exar Corporation 2/17 Rev. 1.0.0
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.
V
IN
, V
OUT
, LED
1
, LED
2
, LED
3
.......................... -0.3V to 6.0V
SCL, SDA, RDY, RESET_N, CAP ............ -0.3V to V
IN
+0.3V
C1P, C2P, C1N, C2N ........................... -0.3V to V
IN
+0.3V
Storage Temperature .............................. -65°C to 150°C
Power Dissipation ................... Internally Limited (Note 1)
Lead Temperature (Soldering, 10 sec) ................... 260°C
ESD Rating (HBM - Human Body Model) All Pins ......... 2KV
OPERATING RATINGS
Input Voltage Range V
IN
............................... 2.7V to 5.5V
Junction Temperature Range .................... -40°C to 125°C
Thermal Resistance θ
JA
................................... 30.8°C/W
ELECTRICAL SPECIFICATIONS
Specifications with standard type are for T
J
= 25°C only; limits in applying over the full Operating Junction Temperature (T
J
)
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 T
J
= 25°C, and are provided for reference purposes only. Unless
otherwise indicated, V
IN
= 3.4V, V
LED
= 0.8V, C
IN
= 47µF, C
F1
= C
F2
= 0.47µF, C
OUT1
(V
OUT
to CAP) = 47µF and C
OUT2
(CAP to
GND) = 47µF. T
A
= –40°C to 85°C, T
J
= –40°C to 125°C.
Parameter Min. Typ. Max. Units Conditions
Operating Input Voltage Range 2.7 5.5 V •
UVLO Turn-On Threshold 2.2 2.4 2.6 V •
V
IN
rising
UVLO Hysteresis 100 mV
V
IN
falling
Operating Input Current
Including In-rush Current 600 725 mA • 1x, 1.5x or 2x Mode
Torch Mode Input Current 202 228 mA
1x Mode, I
OUT
= 200mA
Torch Mode Input Current 302 340 mA
1.5x Mode, I
OUT
= 200mA
Standby Input Current 30 40 µA All LEDs are Off, T
J(max)
= 85
o
C
Shutdown Supply Current 1 3 µA R
ESET_N
= 0V
Shutdown I
LED
Current 0 mA
STATUS1 Register [B7 B6] =00
Measure LED1 – LED3
Torch Mode Incremental current
Step
20 mA
XRP6840A, Table 6, averaged from all
channels
30 mA
XRP6840B, Table 6, averaged from all
channels
Flash Mode Incremental current
Step
200 mA
XRP6840A, Table 5, averaged from all
channels
300 mA
XRP6840B, Table 5, averaged from all
channels
Maximum Current in Torch Mode
per Channel
300 mA
XRP6840A, Note 2, averaged from all
channels
440 mA
XRP6840B, Note 2, averaged from all
channels
Maximum Current in Flash Mode 4.3 A Flash Mode, Measured current into all LED
pins
Output Current DAC Resolution 3 Bit
Flash Mode
4 Bit
Torch Mode
DAC Current Accuracy
-10 10 % •
120mA < I
LED
< 1.6A for XRP6840A
180mA < I
LED
< 1.6A for XRP6840B
-12 12 mA •
I
LED
≤ 120mA, XRP6840A
-18 18 mA •
I
LED
≤ 180mA, XRP6840B
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© 2009 Exar Corporation 3/17 Rev. 1.0.0
Parameter Min. Typ. Max. Units Conditions
Channel to Channel Current
Matching -3 3 % • 0mA < I
LED
< 1.6A Per Channel, Note 3
Switching Frequency 2.0 2.4 2.8 MHz •
Equivalent Resistance, 1X Mode 0.5 Ω •
V
IN
= 3.7V, I
OUT
= 200mA
Equivalent Resistance, 1.5X
Mode 4 7 Ω •
V
IN
= 3.2V, V
OUT
< V
OUT_LIMIT
,
I
OUT
= 200mA, Equivalent resistance =
[(V
IN
x 1.5) - V
OUT
] / I
OUT
LEDx Pin Dropout Voltage 0.36 V •
Flash mode, V
IN
= 3.4V, I
LED
= 1A,
Measure LED current at 95% I
LEDX-NOMINAL
at V
LEDX
=0.8V
LEDx Pin Dropout Voltage 0.1 V •
Torch mode, V
IN
= 3.4V, I
LED
= 80mA,
Measure LED current at 95% I
LEDX-NOMINAL
at V
LEDX
=0.8V
LED Short Detect Threshold 0.1 0.2 0.4 V •
V
OUT
– V
LED
, LED = 0mA for all DAC code
Thermal Regulation 0.01 %/
o
C
Thermal Shutdown Temperature 150
o
C Driver turn OFF
Thermal Shutdown Hysteresis 10
o
C
Driver turn ON
Output Voltage Regulation (OVR)
5.2 5.3 5.4 V •
Flash Mode, I
LED
= 0mA, V
OUT
Rising
STATUS2 Register: [B7 B6 B5] = 101
OVR value is set by STATUS2 register
between 4.55V – 5.6V, all setting have
+/- 100mV tolerance
Output Voltage Regulation
Hysteresis 50 mV
Flash Mode, I
LED
= 0mA
RDY Pin Output Trip Threshold V
O
– 0.1
V
STATUS2 Register: [B7 B6 B5] = 101
100mV below actual OVR value.
RDY Pin Sink Current 1 mA •
SDA, SCL, RESET_N, FLASH
Input Logic Low Voltage 0.4 V •
SDA, SCL, RESET_N, FLASH
Input Logic High Voltage 1.6 V •
Turn-Off Time (T
OFF
) Into
Shutdown 50 µs
RDY goes low when RESET_N goes from
high top low
Flash Time Duration Before
Standby
0.09 0.11 0.13 s • STATUS1 register [B1 B0]=00
0.18 0.22 0.26 s •
STATUS1 register [B1 B0]=01
0.43 0.53 0.63 s •
STATUS1 register [B1 B0]=10
0.9 1.1 1.3 s • STATUS1 register [B1 B0]=11
I
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C SPECIFICATIONS
I
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C ADDRESSING FORMAT
S
XRP6840
Address R/W A
Status
Data A LED1 Data A LED2 Data A LED3 Data A SP
7-bit 1/0 8-bit 8-bit 8-bit 8-bit
Fig. 2: I
2
C Data Input Format
Start Condition
Acknowledgement
sent by the slave
Acknowledgement
- sent by the slave when R/
W
=0
- sent by master when R/
W
=1
Stop Condition
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© 2009 Exar Corporation 4/17 Rev. 1.0.0
Default I
2
C slave 7-bit address for XRP6840 is 0101000b
I
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C TIMING CHARACTERISTICS
V
IN
= 3.3V, T
A
= –40°C to 85°C, T
J
= –40°C to 125°C. Unless otherwise noted.
Parameter Symbol Min. Typ. Max. Units Conditions
Serial Clock Frequency f
SCL
400 KHz
Bus Free Time between a STOP
and a START t
BUF
1.3 µs
Hold Time, Repeated START
Condition t
HD_STA
0.6 µs
STOP Condition Setup Time t
SU,STO
0.6 ms
Data Hold Time t
HD,DAT(OUT)
225 900 ns
Input Data Hold Time t
HD,DAT(IN)
0 900 ns
Data Setup Time t
SU,DAT
100 ns
SCL Clock Low Period t
LOW
1.3 ms
SCL Clock High Period t
HIGH
0.6 ms
Rise Time of Both SDA and SCL
Signals, receiving t
R
20 +
0.1Cb 300 ns
Note 4,5
Fall Time of Both SDA and SCL
Signals, Receiving t
F
20 +
0.1Cb 300 ns
Note 4,5
Fall Time of SDA Transmitting t
F.TX
20 +
0.1Cb 250 ns
Note 4,5,6
Pulse Width of Spike Suppressed
t
SP
0 50 ns
Note 7
Capacitive Load for each Bus
Line Cb 400 pF Note 4
I
2
C Startup Time after UVLO
clears t
SRT
1 µs Note 4
Note 1: All parameter tested at T
A
= 25°C. 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 I
AVG
is the average current of all channels.
Note 4: Guaranteed by design.
Note 5: Cb = total capacitance of one bus line in pF. tR and tF measured between 0.3 x V
DD
and 0.7 x V
DD
.
Note 6: I
SINK
≤6mA. Cb =total capacitance of one bus line in pF. t
R
and t
F
measured between 0.3 x V
DD
and 0.7 V
DD
.
Note 7: Input filters on the SDA and SCL inputs suppress noise spikes less than 50ns.
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© 2009 Exar Corporation 5/17 Rev. 1.0.0
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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© 2009 Exar Corporation 6/17 Rev. 1.0.0
PIN DESCRIPTION
Name Pin Number Description
C
GND
1 Charge pump ground pin.
RDY 2
Active high push-pull output. RDY is high when V
OUT
reached to 100mV below its
V
OUT_LIMIT
voltage. The V
OUT_LIMIT
for Flash mode is determined by STATUS2 register [B7
B6 B5]. The V
OUT_LIMIT
for Torch mode is 4.50V.
SCL, SDA 3, 4 The SDA and SCL pins connect to the I
2
C bus. Multiple functions can be programmed
through his interface. They can also be used for read-back.
P
GND
5, 11 Power ground pin. The Source of internal NMOS is connected to this pin.
RESET_N 6
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.
LED
1
, LED
2
, LED
3
(XRP6840A) 7, 8, 9
LED
1
, LED
2
, LED
3
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 I
2
C to provide the Torch and Flash current for
the LEDs. LED
1
, LED
2
, LED
3
pins can be connected together to provide higher LED
current. If a pin is not used connect it to V
OUT
. The XRP6840 incorporates a short LED
protection circuit which shut-down LED current if LED voltage approaches to V
OUT_LIMIT
.
LED
1
, NC, LED
2
(XRP6840B) 7, 8, 9
FLASH 10
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].
NC 12
No connection. This pin can be connected to P
GND
pin for heat sink.
GND 13 Ground pin. This ground pin doesn’t carry high internal current.
CAP 14
This pin is the output of an internal Op-Amp. This internal Op-Amp is powered by V
OUT
.
The output voltage is half of V
OUT
, and output resistance is 470Ω. The sink and source
current is limited by 470Ω output resistance. This provides active balancing between
two internal sections of the super capacitor.
V
OUT
15
Output voltage. Connect positive terminal of SuperCap here. Connect the LEDs
between this pin and the corresponding internal current source. Decouple with 10µF
ceramic capacitor close to the pins of the IC.
C
2P
, C
2N
16, 17
Connect C
2
external flying capacitor between these pins.
C
1P
, C
2P
18, 19 Connect C
1
external flying capacitor between these pins.
V
IN
20 Power supply input. Decouple with 10µF ceramic capacitor close to the pins of the IC.
Thermal Pad - Connect thermal pad to P
GND
pins.
ORDERING INFORMATION
Part Number
Junction
Temperature
Range
Marking Package Packing
Quantity Note 1 Note 2
XRP6840AILB-F -40°C≤T
A
≤+125°C 6840AI
YYWWX 20-pin TQFN
Bulk RoHS Compliant/
Halogen Free 3 Channels
XRP6840AILBTR-F -40°C≤T
A
≤+125°C 6840AI
YYWWX 20-pin TQFN
3K/Tape & Reel RoHS Compliant/
Halogen Free 3 Channels
XRP6840BILB-F -40°C≤T
A
≤+125°C 6840BI
YYWWX 20-pin TQFN
Bulk RoHS Compliant/
Halogen Free 2 Channels
XRP6840BILBTR-F -40°C≤T
A
≤+125°C 6840BI
YYWWX 20-pin TQFN
3K/Tape & Reel RoHS Compliant/
Halogen Free 2 Channels
XRP6840EVB XRP6840 Evaluation Board – XRP6840A based.
“YY” = Year – “WW” = Work Week – “X” = Lot Number
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© 2009 Exar Corporation 7/17 Rev. 1.0.0
TYPICAL PERFORMANCE CHARACTERISTICS
All data taken at V
IN
= 2.7V to 5.5V, T
J
= T
A
= 25°C, unless otherwise specified - Schematic and BOM from Application
Information section of this datasheet.
Fig. 5: High Efficiency Torch Mode I
LED
at 200mA
no supercap
Fig. 6: High Efficiency Torch Mode, LED Current versus V
IN
no supercap
Fig. 7: High Efficiency Torch Mode, Input Current versus V
IN
I
LED
at 200mA, no supercap
Fig. 8: VOUT RDY: 0.6F Supercap, CH1 = V
IN
,
CH2 = V
OUT
, CH3 = RDY, CH4 = I
VIN
=0.5A/div
Fig. 9: In-rush Current with Li-ion Battery
0.6F Supercap, C
IN
=10µF CH1 = V
IN
, CH4 = I
VIN
=0.5A/div
Fig. 10: In-rush Current, 0.6F Supercap, C
IN
= 22µF,
CH1 = V
IN
, CH4 = I
VIN
=0.5A/div
1100mA
680mA
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© 2009 Exar Corporation 8/17 Rev. 1.0.0
Fig. 11: 0.11s Flash Duration with 0.55F Supercap at 4.3A,
LED V
F
< 3.8V, CH1 = FLASH, CH2 = RDY, CH3 =V
OUT
,
CH4 = I
LED
=2A/div
Fig. 12: 0.22s Flash Duration with 0.9F Supercap at 4.3A,
LED V
F
< 3.8V, CH1 = FLASH, CH2 = RDY, CH3 =V
OUT
,
CH4 = I
LED
=2A/div
Fig. 13: 200mA High Efficiency Torch Mode with 0.55F
Supercap, CH1=V
IN
, CH2=V
OUT
, CH3=LED
X
,
CH4=I
VIN
=0.5A/div
Fig. 14: 200mA Torch Mode with 0.55F Supercap, CH1=V
IN
,
CH2=V
OUT
, CH3=LED
X
, CH4=I
VIN
=0.5A/div
Fig. 15: LED Current Settling Time: 0mA to 100mA.
CH1=SDA, CH2=SCL, CH4=I
LED
=0.1A/div
Fig. 16: LED Current Settling Time: 100mA to 200mA.
CH1=SDA, CH2=SCL, CH4=I
LED
=0.1A/div
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© 2009 Exar Corporation 9/17 Rev. 1.0.0
Fig. 17: LED Current Settling Time: 200mA to 0mA.
CH1=SDA, CH2=SCL, CH4=I
LED
=0.1A/div
Fig. 18: LED Current Settling Time 200mA to Shutdown.
CH1=RESET_N, CH2=LEDx, CH4=I
LED
=0.2A/div
Fig. 19: LED Current Settling Time From Shutdown to
200mA. CH1=RESET_N, CH2=LEDx, CH4=I
LED
=0.2A/div
Fig. 20: Flash Mode Shutdown. CH1=RESET_N,
CH2=RDY, CH3=V
OUT
Fig. 21: Figure 21: Flash Mode Enable From Shutdown
CH1=RESET_N, CH2=RDY, CH3=V
OUT
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© 2009 Exar Corporation 10/17 Rev. 1.0.0
APPLICATION INFORMATION
I
2
C SERIAL INTERFACE
REGISTERS
The XRP6840 has five serially programmable
data registers via the I²C 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 B7 B6 B5 B4 B3 B2 B1
B0
Address
0 1 0 1 0 0 0 R/W
STATUS1
Flash
Torch
Mode
Flash
Torch
Mode
Shut
Down
Control
Gain Gain - Flash
Timeout
Flash
Timeout
STATUS2
Flash
V
Flash
V
Flash
V
Flash
Ready
UVLO
Fault
Temp
Fault 0 0
LEDFLASH
LED1 LED2 LED3* D2 D1 D0 - -
LEDTORCH
LED1 LED2 LED3* D3 D2 D1 D0 -
Table 1: XRP6840 I
2
C Registers Bit Map
* Not used for XRP6840B
STATUS1 Register
STATUS1 Register Bits B7, B6, B4 and B3
B7 B6 B4 B3 Operation Mode
0 1 0 0 High Efficiency Torch Mode
0 1 0 1 1X Torch Mode
0 1 1 0 1.5X Torch Mode
0 1 1 1 2X Torch Mode
1 0 0 0 Auto Gain Torch Mode
1 0 0 1 1X Torch Mode
1 0 1 0 1.5X Torch Mode
1 0 1 1 2X Torch Mode
1 1 0 0 Auto Gain Flash Mode
1 1 0 1 1X Flash Mode
1 1 1 0 1.5X Flash Mode
1 1 1 1 2X Flash Mode
Table 2: STATUS1 Register Operation Modes
STATUS1 Register Bit B5
This bit is used to save or reset the contents
of STATUS1, STATUS2, LEDFLASH and
LEDTORCH registers for the next I
2
C 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 B0 Flash Duration
0 0 0.11s
0 1 0.22s
1 0 0.53s
1 1 1.10s
Table 3: Charge Pump Mode Selection
STATUS2 Register
Flash Mode Voltage Programming
V
OUT_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 B6 B5 Comment
0 0 0 4.55V
0 0 1 4.70V
0 1 0 4.85V
0 1 1 5.00V
1 0 0 5.15V
1 0 1 5.30V
1 1 0 5.45V
1 1 1 5.60V
Table 4: Flash Mode V
OUT_LIMIT
Settings
Bit B4
RDY bit is available for I
2
C read-back. This bit
is set to ‘1’ when V
OUT
> V
OUT_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 I
2
C 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
LED
1
, LED
2
and LED
3
. Bits B4, B3 and B2
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© 2009 Exar Corporation 11/17 Rev. 1.0.0
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
XRP6840A
I
OUT
/Ch. (mA)
D2-D0
Code
XRP6840B
I
OUT
/Ch. (mA)
0 0 0 0 0 0 0 0
0 0 1 400 0 0 1 597
0 1 0 586 0 1 0 875
0 1 1 770 0 1 1 1127
1 0 0 948 1 0 0 1400
1 0 1 1197 1 0 1 1671
1 1 0 1291 1 1 0 1910
1 1 1 1445 1 1 1 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
XRP6840A
I
OUT
/Ch. (mA)
D3-D0
Code
XRP6840B
I
OUT
/Ch. (mA)
0 0 0 0 0 0 0 0 0 0
0 0 0 1 23 0 0 0 1 34
0 0 1 0 46 0 0 1 0 66
0 0 1 1 66 0 0 1 1 97
0 1 0 0 86 0 1 0 0 127
0 1 0 1 105 0 1 0 1 155
0 1 1 0 125 0 1 1 0 185
0 1 1 1 145 0 1 1 1 215
1 0 0 0 165 1 0 0 0 245
1 0 0 1 185 1 0 0 1 275
1 0 1 0 205 1 0 1 0 305
1 0 1 1 225 1 0 1 1 330
1 1 0 0 245 1 1 0 0 360
1 1 0 1 260 1 1 0 1 385
1 1 1 0 280 1 1 1 0 415
1 1 1 1 300 1 1 1 1 440
Table 6: Torch Mode Output Current
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]
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© 2009 Exar Corporation 12/17 Rev. 1.0.0
THEORY OF OPERATION
When V
IN
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.
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 V
OUT_LIMIT
,
the charge pump will turn off.
In 1x mode, the input is simply connected to
the output through an internal 0.5Ω 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, C
1
and C
2
, are series
connected between V
IN
and ground, charging
each capacitor to ½ V
IN
. In the second clock
phase, the flying capacitors are parallel
connected and placed in series with V
IN
,
producing 1.5xV
IN
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 V
IN
. In the
second clock phase, this capacitor is placed in
series with V
IN
, producing 2xV
IN
to be
discharged across the output capacitor. Note
the maximum total output current is now
600mA÷2 or 300mA.
CHARGE PUMP CONTROLLER
The charge pump controller regulates the
output by turning the charge pump off once
the output reaches V
OUT_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 V
LEDX
is
below the drop out voltage of approximately
0.36V. Once the charge pump turns on again,
it will then monitor both V
OUT
and V
LEDX
voltages. This operation will be explained
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 V
OUT
>
VOUT_LIMIT
then the charge pump is
OFF.
2. If V
OUT
< V
IN
– 1V then the charge pump
can only operate in 1x mode.
3. If V
IN
– 1V < V
OUT
< V
IN
then the charge
pump is allowed to operate in either 1x or
1.5x mode but not in 2x mode.
4. If V
OUT
> V
IN
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 0.5Ω bypass MOSFET).
5. If V
OUT
> V
OUT_LIMIT
, and all LEDs are
deactivated then XRP6840 will operate in
standby mode with 30µA supply current.
V
OUT_LIMIT
is 4.5V for Torch Mode and High
Efficiency Torch Mode; for Flash mode
V
OUT_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.
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 B6 B4 B3 Operation Mode
0 1 0 0 High Efficiency Torch Mode
1 0 0 0 Auto Gain Start Torch Mode
1 1 0 0 Auto Gain Start Flash Mode
Table 7: Auto Start Mode from STATUS1 Register
When in Auto Gain Start Mode, the XRP6840
will charge up V
OUT
to V
OUT_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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© 2009 Exar Corporation 13/17 Rev. 1.0.0
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 V
OUT
reaches V
OUT_LIMIT
.
The Auto Start Mode begins in 1x mode or
1.5x mode if V
OUT
> V
IN
. 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 V
OUT
has
not reached V
OUT_LIMIT
and when the input
current is below 300mA. After switching to 2x
mode, the charge pump continues to operate
until V
OUT_LIMIT
is reached.
If V
OUT_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 I
2
C,
RESET_N to ‘0’ or power down.
There are probably 2 main causes for the
XRP6840 to remain in 2x mode: V
OUT
overloaded or V
IN
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 V
IN
is too
low then it is advisable to power down the
system and change the battery.
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
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 V
OUT_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 V
OUT
to
V
OUT_LIMIT
then turn off. Then when the LEDs
are enabled, the control loop will adjust V
OUT
to the minimum value required to maintain
current regulation. It does this by monitoring
and regulating the V
LEDX
voltage with respect
to an adaptive drop out voltage, V
DO
.
The adaptive V
DO
algorithm will allow V
LEDX
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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© 2009 Exar Corporation 14/17 Rev. 1.0.0
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
V
IN
levels. Due to the XRP6840’s low drop out
voltage design, good current regulation can
still be achieved at extremely low V
LED
voltage
levels.
When V
LEDX
drops below V
DO
, and V
OUT
is also
below V
OUT_LIMIT
, the XRP6840 charge pump
will turn on to charge the V
OUT
and V
LEDX
. If
V
LEDX
is still below V
DO
after 64 clock cycles or
27µs (at 2.4MHz), the XRP6840 will jump to
the next higher gain. If at any time, V
OUT_LIMIT
is reached, then charge pump will turn off.
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 V
OUT
pin. Should an
open occur on the V
OUT
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 150°C,
the part is disabled. Once the temperature
drops below 140°C the part is re-enabled.
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
V
OUT
to V
LEDX
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.
COMPONENT SELECTION
The XRP6840 charge pump circuit requires the
following capacitors:
1. Input Cap: 22µF
2. Output Cap: 10μF
3. Charge Pump Flying caps: 2x0.47μF
4. Supercapacitor: 0.6F (0.3F to 0.9F).
Input capacitances higher than 10μF 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 V
IN
and V
OUT
pins as
possible to obtain best bypassing. Their
returns paths should be connected directly to
the P
GND
pin or to the thermal pad ground
located under the XRP6840. The flying
capacitors should be located as close to the
C
1P
, C
1N
and C
2P
, C
2N
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:
_
_
I
OUT
is the target flash current, T
FLASH
is the
flash duration, V
OUT_LIMIT
is the initial Super
Capacitor voltage programmed by STATUS2
register bits [B7 B6 B5], V
F
is the LED forward
voltage and V
LED
is the maximum LED pin
voltage before dropout (360mV at 125°C).
For example, for a 4.3A flash with 110ms
duration, LED V
F
of 3.5V and V
OUT_LIMIT
voltage
of 5.3V, the minimum capacitance is:
4.8 0.11
5.3 3.5 0.36 4.8 0.05Ω 0.44
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© 2009 Exar Corporation 15/17 Rev. 1.0.0
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 50mΩ of ESR, or the 0.6F HS206F
Super Capacitor from CAP-XX with a voltage
rating of 5.5V and 80mΩ of ESR.
TYPICAL APPLICATION SCHEMATICS
Fig. 22: XRP6840A - 3 Channel - 4.3A Total LED Flash Current
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© 2009 Exar Corporation 16/17 Rev. 1.0.0
PACKAGE SPECIFICATION
20-PIN TQFN
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© 2009 Exar Corporation 17/17 Rev. 1.0.0
REVISION HISTORY
Revision Date Description
1.0.0 12/05/2009 Initial Release of Data Sheet
FOR FURTHER ASSISTANCE
Email: customersupport@exar.com
Exar Technical Documentation: http://www.exar.com/TechDoc/default.aspx?
E
XAR CORPORATION
HEADQUARTERS AND SALES OFFICES
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Fremont, CA 94538 – USA
Tel.: +1 (510) 668-7000
Fax: +1 (510) 668-7030
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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 or
malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its
safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in
writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all
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.
