LTC3205
Multidisplay
LED Controller
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FEATURES
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DESCRIPTIO
Step-Up/Step-Down Fractional Charge Pump for Up
to 92% Efficiency
Independent Current and Dimming Control for
1-4 LED Main, 1-2 LED Sub and RGB LED Displays
LED Currents Programmable Using 3-Wire Serial
Interface
Up to 250mA of Continuous LED Current
0.7% LED Current Matching
Low Noise Constant Frequency Operation*
Minimal Component Count
Automatic Soft-Start Limits Inrush Current
Four Programmable Dimming States for Main and
Sub Displays
Up to 4096 Color Combinations for RGB Display
Low Shutdown Current: ICC < 1µA
Tiny 24-Lead (4mm × 4mm) QFN Package
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APPLICATIO S
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Cellular Phones
Wireless PDAs
Multidisplay Handheld Devices
The LTC®3205 is a highly integrated multidisplay LED controller. The part contains a high efficiency, low noise fractional step-up/step-down charge pump to provide power
for both main and sub white LED displays plus an RGB
color LED display. The LTC3205 requires only four small
ceramic capacitors plus two resistors to form a complete
3-display LED power supply and current controller.
Maximum currents for the main/sub and RGB displays are
set independently with a single resistor. Current for each
LED is controlled with an internal current source. Dimming and ON/OFF control for all displays are achieved via
a 3-wire serial interface. Four dimming states exist for the
main and sub displays and 16 dimming states are available
via internal PWM for the red, green and blue LEDs resulting in up to 4096 color combinations.
The LTC3205 charge pump optimizes efficiency based on
VIN and LED forward voltage conditions. The part powers
up in step-down mode and automatically switches to stepup mode once any enabled LED current source begins to
enter dropout. Internal circuitry prevents inrush current and
excess input noise during start-up and mode switching.
The LTC3205 is available in a low profile 24-lead
(4mm × 4mm × 0.8mm) QFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
* U.S. Patent 6,411,531
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TYPICAL APPLICATIO
4-LED Main Panel Efficiency
vs Input Voltage
1µF
1µF
100
90
MAIN DISPLAY
VIN
SUB DISPLAY
RGB ILLUMINATOR
CPO
1µF
1µF
LTC3205
MAIN1-4
SUB1-2
SERIAL
INTERFACE
3
RGB
SERIAL PORT
IMS
IRGB
4
RED
GREEN BLUE
2
3
3205 TA01a
EFFICIENCY (PLED/PIN) (%)
VIN
2.8V TO
4.5V
80
70
60
50
40
30
20
10
FOUR LEDs AT 15mA/LED
(TYP VF AT 15mA = 3.2V)
TA = 25°C
0
3.0
3.3
3.6
3.9
INPUT VOLTAGE (V)
4.2
3205 TA01b
3205f
1
LTC3205
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
ORDER PART
NUMBER
GREEN
BLUE
SUB2
SUB1
MAIN4
MAIN3
TOP VIEW
24 23 22 21 20 19
MAIN2 1
18 RED
MAIN1 2
17 SGND
C2– 3
15 CPO
13 IRGB
9 10 11 12
UF PART
MARKING
DVCC
8
STEPUP
7
LD
14 IMS
C2+ 6
DIN
C1+ 5
ENRGB
LTC3205EUF
16 VIN
25
C1– 4
SCLK
VIN, DVCC, CPO to GND............................. – 0.3V TO 6V
DIN, SCLK, LD, STEPUP,
ENRGB ...................................... – 0.3V to (DVCC + 0.3V)
ICPO (Note 4)...................................................... 250mA
IMAIN1-4, ISUB1,2 (Note 4) ..................................... 50mA
IRED,GREEN,BLUE (Note 4) ..................................... 100mA
IMS, IRGB (Note 4) .................................................. 1mA
CPO Short-Circuit Duration ............................ Indefinite
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
3205
UF PACKAGE
24-LEAD (4mm × 4mm) PLASTIC QFN
TJMAX = 150°C, θJA = 37°C/W, θJC = 2°C/W
EXPOSED PAD IS PGND (PIN 25)
MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, DVCC = 1.8V unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
4.5
V
Input Power Supply
VIN Operating Voltage
DVCC Operating Voltage
IVIN Operating Current
ICPO, IMS, IIRGB = 0µA, Step-Down Mode
ICPO = 0µA, Step-Up Mode
IDVCC Operating Current
Serial Port Idle
●
2.8
●
1.5
5.5
V
µA
mA
70
4.2
1
µA
VIN Shutdown Current
1
µA
DVCC Shutdown Current
1
µA
V
V
White LED Current (MAIN1-MAIN4, SUB1, SUB2)
IMS Servo Voltage
25µA < IMS < 75µA
●
1.193
1.175
1.223
1.223
1.253
1.271
Full-Scale LED Current Ratio (ILED/IMS)
MAIN1-MAIN4, SUB1, SUB2 Voltage = 1V
●
368
400
432
mA/mA
Half-Scale LED Current Ratio (ILED/IMS)
MAIN1-MAIN4, SUB1, SUB2 Voltage = 1V
●
184
200
216
mA/mA
Quarter-Scale LED Current Ratio (ILED/IMS) MAIN1-MAIN4, SUB1, SUB2 Voltage = 1V
●
92
100
108
mA/mA
LED Current Matching
Any Two MAIN or SUB Outputs
0.7
%
RGB LED Current (RED, GREEN, BLUE)
IRGB Servo Voltage
25µA < IRGB < 75µA
●
LED Current Ratio (ILED/IRGB)
RED, GREEN, BLUE Voltage = 1V
1.193
1.175
1.223
1.223
1.253
1.271
360
400
440
V
V
mA/mA
RGB PWM Frequency
RGB LED Switching Frequency
RGB PWM (Duty Factor) Range
3.5
0/15
kHz
15/15
%
3205f
2
LTC3205
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, DVCC = 1.8V unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Charge Pump (CPO)
1:1 Mode Output Impedance
2:3 Mode Output Impedance
VIN = 3V, VCPO = 4.2V (Note 3)
CPO Regulation Voltage
ICPO = 20mA, 2:3 Mode
0.8
Ω
2.5
Ω
4.7
CLK Frequency
0.6
V
0.8
1.1
MHz
DIN, SCLK, LD, STEPUP, ENRGB
VIL
Low Level Input Voltage
VIH
High Level Input Voltage
IIH
Input Current
DIN, SCLK, LD, STEPUP, ENRGB = DVCC
●
IIL
Input Current
DIN, SCLK, LD, STEPUP, ENRGB = 0V
●
0.15 • DVCC
V
–1
1
µA
–1
1
µA
●
● 0.85 • DVCC
V
Serial Port Timing
tDS
DIN Valid to SCLK Setup
35
ns
tDH
DIN Valid to SCLK Hold
35
ns
tL
SCLK Low Time
35
ns
tH
SCLK High Time
35
ns
tLW
LD Pulse Width
35
ns
tCL
SCLK to LD
35
ns
tLC
LD to SCLK
0
ns
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC3205E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: 2:3 mode output impedance is defined as (1.5VIN – VCPO)/ICPO.
Note 4: Based on long term current density limitations.
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TYPICAL PERFOR A CE CHARACTERISTICS
LED Pin Sink Current
vs LED Pin Voltage
Input and Output
Charge Pump Noise
4-LED Main Panel Efficiency
vs Input Voltage
100
90
ILED
3mA/DIV
(100%
SETTING)
EFFICIENCY (PLED/PIN) (%)
VIN
AC COUPLED
(20mV/DIV)
VOUT
AC COUPLED
(50mV/DIV)
0mA
200mV/DIV
3205 G01
ICPO = 150mA
500ns/DIV
VIN = 3.6V
CIN = CCPO = 0.7µF
80
70
60
50
40
30
20
3205 G02
10
FOUR LEDs AT 15mA/LED
(TYP VF AT 15mA = 3.2V)
TA = 25°C
0
3.0
3.3
3.6
3.9
INPUT VOLTAGE (V)
4.2
3205 TA01b
3205f
3
LTC3205
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TYPICAL PERFOR A CE CHARACTERISTICS
2:3 Mode Charge Pump OpenLoop Output Resistance vs
Temperature (3/2VIN – VCPO)/ICPO
1:1 Mode Switch Resistance
vs Temperature
3.2
1.0
OUTPUT RESISTANCE (Ω)
SWITCH RESISTANCE (Ω)
VIN = 3.6V
VIN = 3.9V
0.8
0.7
TA = 25°C
4.7
VIN = 3.6V VIN = 3.5V
4.6
CPO VOLTAGE (V)
3.0
VIN = 3.3V
4.8
VIN = 3V
VCPO = 4.2V
CIN = CCPO = CFLY1 = CFLY2 = 1µF
ICPO = 100mA
0.9
2:3 Mode CPO Voltage
vs Load Current
2.8
2.6
2.4
4.5
4.4
4.3
VIN = 3.1V
4.2
VIN = 3.2V
4.1
VIN = 3.3V
4.0
2.2
VIN = 3.4V
3.9
0.6
–40
–15
35
10
TEMPERATURE (°C)
60
2.0
–40
85
–15
10
35
TEMPERATURE (°C)
60
2:3 Mode CPO Voltage in
Current Limit
0.5
1000
VIN = DVCC
3.0
2.5
2.0
1.5
DVCC SHUTDOWN CURRENT (µA)
TA = 25°C
900
FREQUENCY (kHz)
CPO VOLTAGE (V)
4.0
TA = –40°C
800
TA = 85°C
700
1.0
VIN = 4.2V
TA = 25°C
0.5
0
0
200
400
300
LOAD CURRENT (mA)
100
500
0.4
0.3
2.7
3.0
3.3
3.6
3.9
VIN VOLTAGE (V)
4.2
3205 G13
TA = –40°C
TA = 85°C
0.1
4.5
90
DVCC = VIN
SUPPLY CURRENT (µA)
0.8
TA = 85°C
4.2
4.5
2:3 Mode Supply Current
vs ICPO (IIN – 3/2ICPO)
10
VIN = 3.6V
9 TA = 25°C
TA = 25°C
IMS = IRGB = 0µA
8
80
SUPPLY CURRENT (mA)
1.0
0.4
3.3
3.6
3.9
DVCC VOLTAGE (V)
3.0
3205 G08
1:1 Mode No Load Supply Current
vs VIN
0.6
2.7
3205 G07
VIN Shutdown Current
vs Input Voltage
TA = 25°C
TA = –40°C
TA = 25°C
0.2
0
600
600
250
DVCC Shutdown Current
vs DVCC
4.5
3.5
150
200
100
LOAD CURRENT (mA)
3205 G06
Oscillator Frequency
vs VIN Voltage
5.0
VIN = 3.0V
50
0
3205 G05
3205 G04
VIN SHUTDOWN CURRENT (µA)
3.8
85
70
60
7
6
5
4
3
2
0.2
1
0
2.7
3.0
4.2
3.3
3.6
3.9
VIN INPUT VOLTAGE (V)
4.5
3205 G09
50
2.7
3
3.3
3.6
3.9
INPUT VOLTAGE (V)
4.2
4.5
3205 G12
0
0
100
50
150
LOAD CURRRENT (mA)
200
3205 G10
3205f
4
LTC3205
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TYPICAL PERFOR A CE CHARACTERISTICS
Input Supply Voltage Required for
Higher LED Currents
3.9
120
TA = 25°C
VIN = 3.6V
TA = 25°C
100
IMS
LED CURRENT (mA)
INPUT VOLTAGE (V)
3.7
3.5
3.3
3.1
IRGB
2.9
IRGB = 250µA
IRGB = 200µA
80
ILED
3mA/DIV
IRGB = 150µA
60
IRGB = 100µA
40
0mA
IRGB = 50µA
20
2.7
RGB LED Turn On and Off
Characteristics
Compliance Voltage for Higher
LED Currents
5µs/DIV
3205 G011
0
2.5
25
50
75
100 125 175 200 225 250
IMS OR IRGB CURRENT (µA)
0
0.2
0.4
0.6
0.8
LED PIN VOLTAGE (V)
3205 G14
1.0
3205 G15
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PI FU CTIO S
MAIN1-MAIN4 (Pins 2, 1, 24, 23): Current Source
Outputs for the Main Display White LEDs. The current for
the main display is controlled by the resistor on the IMS
pin. The LEDs on the main display can be set to 100%,
50%, 25% or 0% of full-scale programmed current under
software control. See Tables 1 and 2.
C1+, C1–, C2+, C2– (Pins 5, 4, 6, 3): Charge Pump Flying
Capacitor Pins. A 1µF X7R or X5R ceramic capacitor should be
connected from C1+ to C1– and another from C2+ to C2–.
DIN (Pin 7): Input Data for the 16-Bit Serial Port. Serial data
is shifted in one bit per clock to control the LTC3205 (see
Table 1). The logic level for DIN is referenced to DVCC.
SCLK (Pin 8): Clock Input for the 16-Bit Serial Port (see
Figure 3). The logic level for SCLK is referenced to DVCC.
LD (Pin 9): Load Input for the 16-Bit Serial Port. Command
data is loaded into the command latch on the falling edge
of LD (see Figure 3). The logic level for LD is referenced to
DVCC.
ENRGB (Pin 10): This pin is used to enable and disable the
red, green and blue current sources. Once ENRGB is brought
high, the LTC3205 illuminates the RGB display with the color
combination that was previously programmed via the serial
port. When the main and sub displays are off and ENRGB is
low, the LTC3205 will be in shutdown. The logic level for
ENRGB is referenced to DVCC.
STEPUP (Pin 11): A logic high on this pin forces the
LTC3205’s charge pump to operate in 2:3 step-up mode,
thereby eliminating any possibility of the device switching
from 1:1 mode to 2:3 mode during critical communication
periods. The logic level for STEPUP is referenced to DVCC.
DVCC (Pin 12): This pin sets the logic reference level of the
LTC3205.
IRGB (Pin 13): This pin controls the amount of LED current
at the RED, GREEN and BLUE LED pins. The IRGB pin
servos to 1.223V when there is a resistor to ground. The
current in the RED, GREEN and BLUE LEDs will be 400
times the current at the IRGB pin when programmed to full
scale (see Tables 1 and 3).
IMS (Pin 14): This pin controls the maximum amount of
LED current in both the main and sub LED displays. The
IMS pin servos to 1.223V when there is a resistor to
ground. The currents in the main and sub display LEDs will
be 100, 200 or 400 times the current at the IMS pin
depending on which setting is chosen from the serial port.
CPO (Pin 15): Output of the Charge Pump. This output
should be used to power white, blue and “true” green
LEDs. Red LEDs can be powered from VIN or CPO. An X5R
or X7R low impedance (ceramic) 1µF charge storage
capacitor is required on CPO.
3205f
5
LTC3205
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PI FU CTIO S
VIN (Pin 16): Supply Voltage for the Charge Pump. The VIN
pin should be connected directly to the battery and bypassed with a 1µF X5R or X7R ceramic capacitor.
colors for the illuminator. See Tables 1 and 3. The RGB
LEDs are modulated at 1/240 the speed of the charge
pump oscillator.
SGND (Pin 17): Ground for the Control Logic. This pin
should be connected directly to a low impedance ground
plane.
SUB1, SUB2 (Pins 22, 21): Current Source Outputs for
the Sub Display White LEDs. The current for the sub
display is controlled by the resistor on the IMS pin. The
LEDs on the sub display can be set to 100%, 50%, 25% or
0% of full scale under software control. See Tables 1
and␣ 2.
RED, GREEN, BLUE (Pins 18, 19, 20): Current Source
Outputs for the RGB Illuminator LEDs. The currents for
the RGB LEDs are controlled by the resistor on the IRGB
pin. The RGB LEDs can independently be set to any duty
cycle from 0/15 through 15/15 under software control
giving a total of 16 shades per LED and a total of 4096
PGND (Pin 25, Exposed Pad): Power Ground for the
Charge Pump. The exposed pad should be connected
directly to a low impedance ground plane.
W
BLOCK DIAGRA
C1+
C1–
C2+
C2–
5
4
6
3
800kHz
OSCILLATOR
25 PGND
15 CPO
VIN 16
1:1 AND 2:3 CHARGE PUMP
–
+
ENABLECP
+
2 MAIN1
–
1 MAIN2
24 MAIN3
IMS 14
23 MAIN4
+
–
22 SUB1
2
21 SUB2
2
IRGB 13
SGND 17
18 RED
DVCC 12
STEPUP 11
ENRGB 10
LD 9
19 GREEN
CONTROL
LOGIC
2
PWM
2
4
4
20 BLUE
4
COMMAND LATCH
16
DIN 7
SCLK 8
SHIFT REGISTER
3205 BD
3205f
6
LTC3205
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OPERATIO
Power Management
To optimize efficiency, the power management section of
the LTC3205 provides two methods of supplying power to
the CPO pin: 1:1 direct connect mode or 2:3 boost mode.
When either the main or sub displays of the LTC3205 are
enabled, the power management system connects the CPO
pin directly to VIN with a low impedance switch. If the voltage
supplied at VIN is high enough to power all of the LEDs with
the programmed current, the system will remain in this
“direct connect” mode providing maximum efficiency.
Internal circuits monitor all MAIN and SUB current sources
for the onset of “dropout,” the point at which the current
sources can no longer supply programmed current. As the
battery voltage falls, the LED with the largest forward voltage will reach the “drop out” threshold first. When any of
the four main or two sub display LEDs reach the dropout
threshold, the LTC3205 will switch to boost mode and automatically soft-start the 2:3 boost charge pump. The constant frequency charge pump is designed to minimize the
amount of noise generated at the VIN supply.
However, for a given ROL, the amount of current available
will be directly proportional to the advantage voltage 1.5VIN
– VCPO. Consider the example of driving white LEDs from
a 3.1V supply. If the LED forward voltage is 3.8V and the
current sources require 100mV, the advantage voltage is
3.1V • 1.5V – 3.8V – 0.1V or 750mV. Notice that if the input
voltage is raised to 3.2V, the advantage voltage jumps to
900mV—a 20% improvement in available strength.
From Figure 1, the available current is given by:
IOUT =
Typical values of ROL as a function of temperature are
shown in Figure 2.
ROL
+
–
To prevent excessive inrush current and supply droop
when switching into step-up mode, the LTC3205 employs
a soft-start feature on its charge pump. The current
available to the CPO pin is increased linearly over a period
of 1.2ms.
Figure 1. Equivalent Open-Loop Circuit
3.2
3.0
VIN = 3V
VCPO = 4.2V
CIN = CCPO = CFLY1 = CFLY2 = 1µF
2.8
2.6
2.4
2.2
2.0
–40
–15
10
35
TEMPERATURE (°C)
Charge Pump Strength
When the LTC3205 operates in 2:3 boost mode, the
charge pump can be modeled as a Thevenin-equivalent
circuit to determine the amount of current available from
the effective input voltage, 1.5VIN and the effective openloop output resistance, ROL (Figure 1).
ROL is dependent on a number of factors including the
switching term, 1/(2fOSC • CFLY), internal switch resistances and the nonoverlap period of the switching circuit.
1.5VIN
–
OUTPUT RESISTANCE (Ω)
Soft-Start
+
CPO
3205 F01
The 2:3 step-up charge pump uses a patented constant
frequency architecture to combine the best efficiency with
the maximum available power at the lowest noise level.
If the red, green or blue LEDs are programmed to be on at
any duty cycle, the charge pump runs continuously.
1.5VIN – VCPO
ROL
60
85
3205 F02
Figure 2. Typical ROL vs Temperature
Zero Shutdown Current
Although the LTC3205 is designed to have very low shutdown current, it will draw about 400nA on VIN when in
shutdown. For applications that require zero shutdown
current, the DVCC pin can be grounded. This will reduce the
VIN current to very near zero. Internal logic ensures that the
3205f
7
LTC3205
U
OPERATIO
LTC3205 is in shutdown when DVCC is grounded. Note,
however, that all of the logic signals that are referenced to
DVCC (DIN, SCLK, LD, ENRGB and STEPUP) will need to be
at DVCC or below (i.e., ground) to keep from violating the
absolute maximum specifications on these pins.
The current levels of both the main and sub displays are
controlled by precisely mirroring a multiple of the current
at the IMS pin.
The main and sub display LED currents will follow the
relationship:
Serial Port
The microcontroller compatible serial port provides all of
the command and control inputs for the LTC3205. Data on
the DIN input is loaded on the rising edge of SCLK. D15 is
loaded first and D0 last. Once all bits have been clocked into
the shift register, the command data is loaded into the
command register by bringing LD low. At this time, the
command register is latched and the LTC3205 will begin
to act upon the new command set. The serial port uses static
logic registers so there is no minimum speed at which it can
be operated. Figure 3 shows the operation of the serial port.
Table 1 shows the mapping of the serial port bits to the
operation of the various displays. Bits D15 and D14
control the brightness of the four LEDs in the main display.
Bits D13 and D12 control the brightness of the two LEDs
in the sub display. The red, green and blue LEDs each have
four bits assigned giving a linear range of 16 brightness
levels to each of the LEDs.
IMAIN/SUB = N
where N is equal to 400, 200, 100 or 0 depending on which
current setting is selected. RMAIN/SUB is the value of the
resistor on the IMS pin. The scale factors are spaced pseudo
exponentially to compensate for the vision perception of
the human eye (zero is a special case needed for
shutdown).
The LTC3205 can power up to six white LEDs (four for the
main display, two for the sub display), however, it is not
necessary to have all six in each application. Any of the four
main or two sub LED outputs can be disabled by connecting the unused output to CPO.
Table 2. Main and Sub Display Current Levels
D15
D13
0
0
1
1
Programming the MAIN and SUB LED Currents
Table 2 indicates the decoding of the Main and Sub display
control bits.
tLC
tDS
1.223V
RMAIN/SUB
tDH
tH
FRACTION OF
FULL-SCALE
CURRENT (%)
0
25
50
100
D14
D12
0
1
0
1
tL
tCL
tLW
SCLK
DIN
X
D15
D14
D2
D1
D0
X
LD
3205 F03
Figure 3. Serial Port Timing Diagram
Table 1. Serial Port Mapping
D15
D14
MAIN1MAIN4
Current
Level
(Table 2)
D13
D12
SUB1SUB2
Current
Level
(Table 2)
D11
D10
D9
Blue LED Duty Cycle
(Table 3)
D8
D7
D6
D5
D4
Green LED Duty Cycle
(Table 3)
D3
D2
D1
D0
Red LED Duty Cycle
(Table 3)
3205f
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LTC3205
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OPERATIO
Table 3. RGB Duty Cycles
Unused MAIN or SUB Display LED Pins
Any of the six white LED pins (MAIN1-MAIN4, SUB1 and
SUB2) can cause the LTC3205 to switch from 1:1 mode to
2:3 charge pump mode if they drop out. If an unused LED
pin is left unconnected or grounded, it will automatically
drop out and force the LTC3205 into charge pump mode.
To avoid this problem, unused LED pins on the MAIN and
SUB displays should be connected to CPO. However, power
is not wasted in this configuration. When the LED pin voltage
is within approximately 1V of CPO, its LED current is
switched off and only a small 10µA test current remains.
Figure 4 shows a block diagram of each of the MAIN and
SUB LED pins. The RED, GREEN and BLUE pins do not affect
the state of the charge pump so they can be left floating or
grounded if unused.
CPO
~1V
+
–+
D10
D6
D2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
D9
D5
D1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
D8
D4
D0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
HEX
CODE
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
DUTY
CYCLE (%)
0/15
1/15
2/15
3/15
4/15
5/15
6/15
7/15
8/15
9/15
10/15
11/15
12/15
13/15
14/15
15/15
MAIN1-MAIN4
SUB1, SUB2
–
ENABLE
D11
D7
D3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
total of 4096 colors. Table 3 indicates the decoding of the
red, green and blue LEDs.
10µA
ILED
3205 F04
Figure 4. Internal MAIN and SUB Panel LED Disable Circuit
RGB Illuminator Drivers
The red, green and blue LEDs can be individually set to
have a duty cycle ranging from 0/15 (off) to 15/15 (full on)
with 1/15 increments in between. The combination of 16
possible brightness levels gives the RGB indicator LED a
The full-scale currents in the red, green and blue LEDs are
controlled by the current at the IRGB pin in a similar manner
to those in the main and sub panels. The IRGB pin is
regulated at 1.223V and the LED current is a precise
multiple of the IRGB current.
The RGB display LED currents will follow the relationship:
1.223V
RRGB
where RRGB is the value of the resistor on the IRGB pin.
IRED,GREENBLUE
= 400
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Interfacing to a Microcontroller
The serial port of the LTC3205 can be connected directly
to an MC68HC11 style microcontroller’s serial port. The
microcontroller should be configured as the master device
and its clock’s idle state should be set to high (MSTR = 1,
CPOL = 1 and CPHA = 1 for the MC68HC11 family).
Figure␣ 5 shows the recommended configuration and
directon of data flow. Note that an additional I/O line is
µCONTROLLER
MOSI
SCK
GPIO
LTC3205
DIN
SCLK
LD
3205 F05
Figure 5. Microcontroller Interface
3205f
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necessary for LD to load the data once it has shifted into
the device. Command data is latched into the command
register on the falling edge of the LD signal. The LTC3205
will begin to act on new command data as soon as LD goes
low. Any general purpose microcontroller I/O line can be
configured to control the LD pin if the microcontroller
doesn’t provide this feature automatically.
VIN, CPO Capacitor Selection
The style and value of capacitors used with the LTC3205
determine several important parameters such as regulator
control-loop stability, output ripple and charge pump
strength. To reduce noise and ripple, it is recommended
that low equivalent series resistance (ESR) multilayer
ceramic capacitors be used on both VIN and CPO. Tantalum and aluminum capacitors are not recommended because of their high ESR. The value of the capacitor on CPO
directly controls the amount of output ripple for a given
load current. Increasing the size of this capacitor will
reduce the output ripple. The peak-to-peak output ripple is
approximately given by the expression:
VRIPPLEP-P ≅
IOUT
3fOSC • COUT
where fOSC is the LTC3205’s oscillator frequency (typically
800kHz) and COUT is the output charge storage capacitor
on CPO. Both the style and value of the output capacitor
can significantly affect the stability of the LTC3205. The
LTC3205 uses a linear control loop to adjust the strength
of the charge pump to match the current required at the
output. The error signal of this loop is stored directly on
the output charge storage capacitor. The charge storage
capacitor also serves to form the dominant pole for the
control loop. To prevent ringing or instability, it is important for the output capacitor to maintain at least 0.6µF of
capacitance over all conditions. Likewise, excessive ESR
on the output capacitor will tend to degrade the loop
stability of the LTC3205. The closed-loop output resistance of the LTC3205 is designed to be 0.6Ω. For a 100mA
load current change, the error signal will change by about
60mV. If the output capacitor has 0.6Ω or more of ESR,
the closed-loop frequency response will cease to roll off in
a simple one-pole fashion and poor load transient response or instability could result. Multilayer ceramic chip
capacitors typically have exceptional ESR performance.
MLCCs combined with a tight board layout will yield very
good stability. As the value of COUT controls the amount of
output ripple, the value of CIN controls the amount of ripple
present at the input pin (VIN). The input current to the
LTC3205 will be relatively constant while the charge pump
is on either the input charging phase or the output charging phase but will drop to zero during the clock nonoverlap
times. Since the nonoverlap time is small (~25ns), these
missing “notches” will result in only a small perturbation
on the input power supply line. Note that a higher ESR
capacitor such as tantalum will have higher input noise
due to the input current change times the ESR. Therefore,
ceramic capacitors are again recommended for their exceptional ESR performance. Input noise can be further
reduced by powering the LTC3205 through a very small
series inductor as shown in Figure 6. A 10nH inductor will
reject the fast current notches, thereby presenting a nearly
constant current load to the input power supply. For
economy, the 10nH inductor can be fabricated on the PC
board with about 1cm (0.4") of PC board trace.
10nH
VIN
VIN
0.1µF
1µF
LTC3205
GND
3205 F06
Figure 6. 10nH Inductor Used for Input Noise
Reduction (Approximately 1cm of Wire)
Flying Capacitor Selection
Warning: A polarized capacitor such as tantalum or aluminum should never be used for the flying capacitors since
their voltage can reverse upon start-up of the LTC3205.
Ceramic capacitors should always be used for the flying
capacitors.
The flying capacitor controls the strength of the charge
pump. In order to achieve the rated output current it is
necessary to have at least 0.7µF of capacitance for each of
the flying capacitors. Capacitors of different materials lose
their capacitance with higher temperature and voltage at
different rates. For example, a ceramic capacitor made of
X7R material will retain most of its capacitance from
–40°C to 85°C whereas a Z5U or Y5V style capacitor will
3205f
10
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lose considerable capacitance over that range. Z5U and Y5V
capacitors may also have a very strong voltage coefficient
causing them to lose 60% or more of their capacitance when
the rated voltage is applied. Therefore, when comparing different capacitors, it is often more appropriate to compare
the amount of achievable capacitance for a given case size
rather than comparing the specified capacitance value. For
example, over rated voltage and temperature conditions,
a 1µF, 10V, Y5V ceramic capacitor in a 0603 case may not
provide any more capacitance than a 0.22µF, 10V, X7R
available in the same 0603 case. The capacitor
manufacturer’s data sheet should be consulted to determine
what value of capacitor is needed to ensure minimum
capacitances at all temperatures and voltages.
Table 4 shows a list of ceramic capacitor manufacturers
and how to contact them:
Table 4. Recommended Capacitor Vendors
AVX
www.avxcorp.com
Kemet
www.kemet.com
Murata
www.murata.com
Taiyo Yuden
www.t-yuden.com
Vishay
www.vishay.com
For very light load applications, the flying capacitors may
be reduced to save space or cost. The theoretical minimum output resistance of a 2:3 fractional charge pump is
given by:
ROL(MIN) ≡
1.5VIN – VOUT
1
=
IOUT
2fOSCCFLY
where fOSC is the switching frequency (800kHz typ) and
CFLY is the value of the flying capacitors. Note that the
charge pump will typically be weaker than the theoretical
limit due to additional switch resistance, however for very
light load applications, the above expression can be used
as a guideline in determining a starting capacitor value.
Layout Considerations and Noise
Due to its high switching frequency and the transient
currents produced by the LTC3205, careful board layout is
necessary. A true ground plane and short connections to
all capacitors will improve performance and ensure proper
regulation under all conditions. Figure 7 shows the recommended layout configuration.
The flying capacitor pins C1+, C2+, C1– and C2– will have
very high edge rate waveforms. The large dv/dt on these pins
can couple energy capacitively to adjacent printed circuit
board runs. Magnetic fields can also be generated if the
flying capacitors are not close to the LTC3205 (i.e., the loop
area is large). To decouple capacitive energy transfer, a
Faraday shield may be used. This is a grounded PC trace
between the sensitive node and the LTC3205 pins. For a high
quality AC ground, it should be returned to a solid ground
plane that extends all the way to the LTC3205
Power Efficiency
To calculate the power efficiency (η) of a white LED driver
chip, the LED power should be compared to the input
power. The difference between these two number represents lost power whether it is in the charge pump or the
current sources. Stated mathematically, the power efficiency is given by:
η≡
PLED
PIN
GND
PIN 1
VIN
CPO
3205 F07
Figure 7. Optimum Single Layer PCB Layout
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The efficiency of the LTC3205 depends upon the mode in
which it is operating. Recall that the LTC3205 operates as
a pass switch, connecting VIN to CPO until one of the LEDs
on the main or sub displays drops out. This feature
provides the optimum efficiency available for a given input
voltage and LED forward voltage. When it is operating as
a switch, the efficiency is approximated by:
η≡
PLED VLED • ILED VLED
=
≅
PIN
VIN • IIN
VIN
At moderate to high output power, the quiescent current
of the LTC3205 is negligible and the expression above is
valid. For example, with VIN = 3.9V, IOUT = 20mA • 6 LEDs
and VLED equal to 3.6V, the measured efficiency is 92.2%,
which is very close to the theoretical 92.3% calculation.
Once an LED drops out, the LTC3205 switches into stepup mode. Employing the fractional ratio 2:3 charge pump,
the LTC3205 provides more efficiency than would be
achieved with a voltage doubling charge pump.
In 2:3 boost mode, the efficiency is similar to that of a
linear regulator with an effective input voltage of 1.5 times
the actual input voltage. This is because the input current
VIN = 3.6V
TA = 25°C
IRGB = 250µA
TA = 25°C
3.7
IRGB = 200µA
IRGB = 150µA
IRGB = 100µA
40
Programming the IMS or IRGB pins for more than 75µA
requires a higher supply voltage to support the extra
current. Figure 9 shows the minimum input supply voltage
required to support various levels of current on the IMS and
IRGB pins.
3.9
80
60
PLED VLED • ILED
V
=
≅ LED
PIN V • 3 I
1.5VIN
IN
LED
2
The RED, GREEN and BLUE current source pins can be
used at higher current levels to provide features such as a
flash or camera light. Given that the output impedance of
the currrent source is approximately 3.3Ω when in saturation, more compliance voltage will be necessary to
operate the device at higher LED currents. Figure 8 shows
the current source accuracy of the RED, GREEN and BLUE
pins as a function of the pin voltage for various high
current settings.
INPUT VOLTAGE (V)
LED CURRENT (mA)
100
ηIDEAL ≡
Using the RED, GREEN and BLUE Pins with Higher
Currents
since the input current will be very close to the LED
current.
120
for a 2:3 fractional charge pump is approximately 1.5
times the load current. In an ideal 2:3 charge pump, the
power efficiency would be given by:
IMS
3.5
3.3
3.1
IRGB
2.9
IRGB = 50µA
20
2.7
0
2.5
0
0.2
0.4
0.6
0.8
LED PIN VOLTAGE (V)
1.0
3205 F08
Figure 8. Compliance Voltage Required to get Higher
LED Currents
25
50
75 100 125 175 200 225 250
IMS OR IRGB CURRENT (µA)
3205 F09
Figure 9. Input Supply Voltage Required to Support
Higher Currents
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If the desired input voltage range is below the data shown
in Figure 9, and a precise control of the LED current is
desired, then a precision current source may be added to
either the IMS or IRGB pins as shown in Figure 10.
LTC3205
IMS
1.8V
IRGB
14
13
80k
+
24.3k
Thermal Management
For higher input voltages and maximum output current,
there can be substantial power dissipation in the LTC3205.
If the junction temperature increases above approximately
160°C the thermal shutdown circuitry will automatically
deactivate the output. To reduce the maximum junction
temperature, a good thermal connection to the PC board
is recommended. Connecting the PGND pin (exposed
center pad) to a ground plane and maintaining a solid
ground plane under the device can reduce the thermal
resistance of the package and PC board considerably.
–
(
10k
V
ILED = 400 1.223V – CNTRL
R2
R1||R2
800Ω
LTC3205
IMS
)
R2
14
VCNTRL
3205 F10
IRGB
13
Figure 10. Precision Reference Current
R1
24.9k
3205 F11
Brightness Control
Although the LTC3205 has three exponentially spaced
brightness settings for the main and sub displays, it is
possible to control the brightness by alternative means.
Figure 11 shows an example of how an external voltage
source can be use to inject a current into the IMS or IRGB
pins to control brightness. For example, if R1 and R2 are
50k, then the LED current would range from 20mA to 0mA
as VCNTRL is swept from 0V to 2.5V.
Alternatively, if only digital outputs are available, the
number of settings can be doubled from 3 to 6 by simply
connecting VCNTRL to a digital signal. With a 1.8V logic
supply, the circuit shown in Figure 12 has LED current
settings of 2.5mA, 5mA, 7.5mA, 10mA, 15mA and 20mA.
This topology can be extended to any number of bits and
can also be applied to the RGB panel.
Figure 11. Alternative Linear Brightness Control
LTC3205
IMS
IRGB
71.5k
14
13
VDIG
0V TO 1.3V
OR HIGHER
38.3k
24.9k
3205 F12
Figure 12. Alternative Digital Brightness Control
LTC3205
IMS
IRGB
14 24.9k
13 24.9k
PWM SIGNAL
0V TO 1.3V OR HIGHER
BRIGHTNESS = 1 – D
3205 F13
Finally, PWM brightness control can be achieved by
applying a PWM signal to the IMS programming resistor as
shown in Figure 13. The signal should range from 0V (full
on) to any voltage above 1.3V (full off).
Figure 13. PWM Brightness Control of the MAIN and SUB Displays
3205f
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LTC3205
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TYPICAL APPLICATIO S
Ultralow Brightness MAIN and SUB Displays
LTC3205
PWM SIGNAL
0V TO 1.3V OR HIGHER
50Hz TO 15kHz
BRIGHTNESS = 1 – D
487k
14
IMS
13
IRGB
24.9k
24.9k
BRIGHT DIM
3205 TA08
All Charge Pump Main, Sub, RGB and Camera Light Controller
SUB DISPLAY
(DUTY CYCLE = 50%)
CAMERA LIGHT
CPO
ILLUMINATOR
15
1µF
LTC3205
MAIN1
MAIN2
MAIN3
MAIN4
SUB1
SUB2
RED
GREEN
BLUE
IMS
IRGB
2
1
24
23
22
21
18
19
20
13
14
24.9k
12.4k
WHITE
WHITE
WHITE
WHITE
WHITE
WHITE
ILED = 40mA
1µF
8
4
10
1
GREEN
BLUE
ILED = 20mA
1µF
7 9
6
MAIN DISPLAY
C1+ C1– C2+ C2–
3
VIN
VOUT
1µF
RED
1µF
LTC3202
D0
FB
D1
GND
2
WHITE
WHITE
WHITE
30Ω
30Ω
30Ω
5, 11
WHITE
30Ω
3205 TA02
Main, Sub and Keypad Illumination
MAIN DISPLAY
CPO
SUB DISPLAY
KEYPAD
15
1µF
LTC3205
IRGB
MAIN1
MAIN2
MAIN3
MAIN4
SUB1
SUB2
RED
GREEN
BLUE
IMS
2
1
24
23
22
21
18
19
20
13
14
16.6k
24.9k
WHITE
WHITE
WHITE
WHITE
WHITE
WHITE
BLUE
BLUE
BLUE
BLUE
BLUE
BLUE
39Ω
39Ω
39Ω
39Ω
39Ω
39Ω
3205 TA03
3205f
14
LTC3205
U
TYPICAL APPLICATIO S
4-LED Main Display Plus 160mA 4-LED Camera Light
MAIN DISPLAY
CPO
CAMERA LIGHT
15
1µF
LTC3205
MAIN1
MAIN2
MAIN3
MAIN4
SUB1
SUB2
RED
GREEN
BLUE
2
1
24
23
22
21
18
19
20
WHITE
WHITE
WHITE
WHITE
WHITE
ILED = 20mA
WHITE
WHITE
WHITE
ILED = 40mA
3205 TA05
IMS
IRGB
13
14
12.4k
24.9k
Main, Sub, RGB and Camera Light Controller
MAIN DISPLAY
CPO
SUB DISPLAY
CAMERA LIGHT
RGB
15
1µF
LTC3205
FLASH
11
STEPUP
IRGB
MAIN1
MAIN2
MAIN3
MAIN4
SUB1
SUB2
RED
GREEN
BLUE
IMS
2
1
24
23
22
21
18
19
20
13
14
24.9k
24.9k
WHITE
WHITE
WHITE
WHITE
WHITE
WHITE
RED
GREEN
BLUE
WHITE
WHITE
39Ω
39Ω
3205 TA06
U
PACKAGE DESCRIPTIO
UF Package
24-Lead Plastic QFN (4mm × 4mm)
(Reference LTC DWG # 05-08-1697)
4.00 ± 0.10
(4 SIDES)
0.70 ±0.05
BOTTOM VIEW—EXPOSED PAD
0.23 TYP
(4 SIDES)
0.75 ± 0.05
R = 0.115
TYP
23 24
0.38 ± 0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
4.50 ± 0.05
2.45 ± 0.05
(4 SIDES)
2.45 ± 0.10
(4-SIDES)
3.10 ± 0.05
PACKAGE OUTLINE
(UF24) QFN 1103
0.25 ±0.05
0.50 BSC
0.200 REF
0.00 – 0.05
0.25 ± 0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE
MO-220 VARIATION (WGGD-X)—TO BE APPROVED
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE, IF PRESENT
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
3205f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC3205
U
TYPICAL APPLICATIO
Using the RGB Display as a Camera Light
L1
2.2µH
Li-Ion
4
1µF
1µF
2.2µF
5
1
VIN
SW
SHDN
LT1930A
VRGB = 6V
IRGB = 300mA TOTAL
D1
38.3k
FB
3
10k
GND
5
6
4
C1+ C1–
3
1µF
16
C2 + C2 –
VIN
CPO
10µF
2
15
1µF
10
12
FROM
MICROCONTROLLER
7
8
9
MAIN1
ENRGB
MAIN2
DVCC
DIN
MAIN3
MAIN4
LTC3205
SCLK
SUB1
LD
SUB2
RED
GREEN
BLUE
2
WHITE
WHITE
WHITE
WHITE
1
WHITE
WHITE
RED
GREEN
BLUE
ILED = 20mA
24
23
22
21
18
19
20
3205 TA07
SGND STEPUP IMS
17
11
IRGB
14
13
24.9k
24.9k
6.2k
Si1406DH
IFLASH = 100mA PER R, G, B, LED
FLASH
RELATED PARTS
PART NUMBER
LT®1618
LTC1911-1.5
LT1932
LT1937
LTC3200-5
LTC3201
LTC3202
LTC3251
LTC3405/LTC3405A
LTC3406/LTC3406B
LTC3440
LT3465/LT3465A
DESCRIPTION
Constant Current, Constant Voltage, 1.4MHz
High Efficiency Boost Regulator
250mA (IOUT), 1.5MHz High Efficiency
Step-Down Charge Pump
Constant Current, 1.2MHz High Efficiency White
LED Boost Regulator
Constant Current, 1.2MHz High Efficiency White
LED Boost Regulator
Low Noise, 2MHz Regulated Charge Pump
White LED Driver
Low Noise, 1.7MHz Regulated Charge Pump
White LED Driver
Low Noise, 1.5MHz Regulated Charge Pump
White LED Driver
500mA (IOUT), 1MHz to 1.6MHz Spread Spectrum
Step-Down Charge Pump
300mA (IOUT), 1.5MHz Synchronous Step-Down
DC/DC Converter
600mA (IOUT), 1.5MHz Synchronous Step-Down
DC/DC Converter
600mA (IOUT), 2MHz Synchronous Buck-Boost
DC/DC Converter
1.2MHz/2.7MHz with Internal Schottky
COMMENTS
Up to 16 White LEDs, VIN: 1.6V to 18V, VOUT(MAX): 34V, IQ: 1.8mA, ISD: ≤1µA,
10-Lead MS
75% Efficiency, VIN: 2.7V to 5.5V, VOUT(MIN): 1.5V/1.8V, IQ: 180µA,
ISD: ≤10µA, MS8
Up to 8 White LEDs, VIN: 1V to 10V, VOUT(MAX): 34V, IQ: 1.2mA, ISD: ≤1µA,
ThinSOTTM
Up to 4 White LEDs, VIN: 2.5V to 10V, VOUT(MAX): 34V, IQ: 1.9mA, ISD: ≤1µA,
ThinSOT, SC70
Up to 6 White LEDs, VIN: 2.7V to 4.5V, VOUT(MAX): 5V, IQ: 8mA, ISD: ≤1µA,
ThinSOT
Up to 6 White LEDs, VIN: 2.7V to 4.5V, VOUT(MAX): 5V, IQ: 6.5mA, ISD: ≤1µA,
10-Lead MS
Up to 8 White LEDs, VIN: 2.7V to 4.5V, VOUT(MAX): 5V, IQ: 5mA, ISD: ≤1µA,
10-Lead MS
85% Efficiency, VIN: 3.1V to 5.5V, VOUT(MIN): 0.9V to 1.6V, IQ: 9µA, ISD: ≤1µA,
10-Lead MS
95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN): 0.8V, IQ: 20µA, ISD: ≤1µA,
ThinSOT
95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.6V, IQ: 20µA, ISD: ≤1µA,
ThinSOT
95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 2.5V, IQ: 25µA, ISD: ≤1µA,
10-Lead MS
Up to 6 White LEDs, VIN: 12.7V to 16V, VOUT(MAX): 34V, IQ: 1.9mA, ISD:
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