LINER LTC3230 5-led main/sub display driver with dual ldo Datasheet

LTC3230
5-LED Main/Sub Display
Driver with Dual LDO
FEATURES
DESCRIPTION
■
The LTC®3230 is a low noise charge pump DC/DC converter
designed to drive 4 Main LEDs and 1 Sub LED, plus two
200mA linear regulators to provide additional system
power. The LTC3230 charge pump requires only four small
ceramic capacitors and one current set resistor to form a
complete LED power supply and current controller.
■
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Low Noise Charge Pump Provides High Efficiency
with Automatic Mode Switching
Multimode Operation: 1x, 1.5x, 2x
Full-Scale Current Set Resistor
Up to 125mA Total LED Current
Single Wire Enable/Brightness Control for Main and
Sub Display LEDs
32:1 Linear LED Brightness Control
Dual 200mA Linear Regulators
Four 25mA Low Dropout Main LED Current Sources
One 25mA Low Dropout Sub LED Current Source
Low Noise Constant Frequency Operation
Low Shutdown Current: 3μA
Internal Soft-Start Limits Inrush Current During
Start-Up and Mode Switching
Open/Short LED Protection
No Inductors
20-Lead 3mm × 3mm QFN Package
Built-in soft-start circuitry prevents excessive inrush current during start-up and mode changes. High switching
frequency enables the use of small external capacitors.
Main and Sub full-scale current settings are programmed
by a single external resistor.
Charge pump efficiency is optimized based on the voltage
across the LED current sources. The part powers up in 1x
mode and automatically switches to the next higher mode,
1.5x and subsequently 2x, whenever any LED current
source approaches dropout.
Two 200mA linear regulators have independent enable
and output voltage select pins. Each regulator can be set
to one of three pre-selected output voltages with tri-level
input pins. The regulators may be enabled independently
of the charge pump.
APPLICATIONS
■
Multi-LED Driver and Dual LDO Supplies for Cell
Phone, PDA, Digital Camera and PND Applications
The LTC3230 is available in a low profile (0.75mm) 3mm
× 3mm 20-lead QFN package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents
including 6411531.
TYPICAL APPLICATION
C1
1mF
C2
1mF
Efficiency vs VIN Voltage
100
C3
2.2mF
ENM
ENS
RSET
17.4k
1%
LTC3230
C6
1mF D1
MLED1
MLED2
MLED3
MLED4
SLED
LDO1
ENM
ENS
ENLDO1
ENLDO2
V1
V2
RSET
90
MAIN
GND
D2
C4
1mF
LDO2
C5
1mF
1.5V
200mA
2.8V
200mA
D3
SUB
D4
D5
3230 TA01a
EFFICIENCY (PLED/PIN) (%)
VIN = 2.7V
TO 5.5V
C1P C1M C2P C2M 125mA
CPO
VIN
80
70
60
50
40
30
20
4 LEDs AT 9mA/LED
VF = 3V
TA = 25°C
10
0
3
ENM OR ENS
SET BRIGHTNESS LEVEL
ON
OFF
3.2
3.4
3.6 3.8
VIN (V)
4
4.2
4.4
3230 TA01b
3230fa
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LTC3230
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Notes 1-5)
VIN, CPO....................................................... –0.3V to 6V
ENM, ENS, ENLDO1, ENLDO2,
V1, V2, LDO1, LDO2 ......................–0.3V to (VIN + 0.3V)
ICPO (Note 2) ........................................................200mA
LD01, LD02 (Note 3)............................................200mA
MLED1-4, SLED, RSET.................................. –0.3V to 6V
Operating Ambient Temperature Range
(Note 4).................................................... –40°C to 85°C
Junction Temperature ........................................... 125°C
Storage Temperature Range................... –65°C to 150°C
C2M
C1M
VIN
C2P
C1P
TOP VIEW
20 19 18 17 16
15 LDO1
CPO 1
14 LDO2
ENLDO1 2
13 V1
21
ENLDO2 3
12 V2
RSET 4
11 ENM
7
8
9 10
SLED
MLED2
MLED3
MLED4
6
MLED1
ENS 5
UD PACKAGE
20-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 125°C, θJA = 68°C/W
EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3230EUD#PBF
LTC3230EUD#TRPBF
LCYB
20-Lead (3mm × 3mm) Plastic QFN
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, C1 = C2 = C4 = C5 = C6 = 1μF, RSET = 17.4k, ENM = ENS =
high, ENLDO1 = ENLDO2 = low, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
●
VIN Operating Voltage
IVIN Operating Current
ICPO = 0, 1x Mode
ICPO = 0, 1.5x Mode
ICPO = 0, 2x Mode
VIN Shutdown Current
ENM = ENS = ENLD02 = ENLD01 = Low
TYP
2.7
MAX
5.5
0.48
1.2
1.6
●
3
UNITS
V
mA
mA
mA
9
μA
MLED1, MLED2, MLED3, MLED4 and SLED Currents
LED Current Ratio (ILED/IRSET)
555
A/A
LED Dropout Voltage
Mode Switch Threshold, IMLED = 15mA
100
mV
LED Current Matching
Any Two MLED Outputs, IMLED = Full Scale
0.5
%
MLED/SLED Current, 5-Bit Linear DAC
1 ENM/ENS Strobe (FS)
31 ENM/ENS Strobes (FS/31)
25.5
0.860
mA
mA
Unused LED Detection
Threshold Voltage
VCPO – MLED
●
200
780
mV
Test Current
LED Tied to CPO
●
39
178
μA
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LTC3230
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, C1 = C2 = C4 = C5 = C6 = 1μF, RSET = 17.4k, ENM = ENS =
high, ENLDO1 = ENLDO2 = low, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
CPO Short Circuit Detection
●
Threshold Voltage
0.4
1.3
V
Charge Pump (CPO)
1x Mode Output Voltage
ICPO = 0mA
VIN
V
1.5x Mode Output Voltage
ICPO = 0mA
4.5
V
2x Mode Output Voltage
ICPO = 0mA
5.0
V
1.6
Ω
1.5x Mode Output Impedance
VIN = 3.4V, VCPO = 4.6V (Note 6)
7.9
Ω
2x Mode Output Impedance
VIN = 3.4V, VCPO = 5.1V (Note 6)
9.2
Ω
Clock Frequency
0.9
MHz
Mode Switching Delay
0.5
ms
1x Mode Output Impedance
tEN
Current Source Enable Time (ENM, ENS = High)
(Note 7)
●
250
μs
LDO1, LDO2
Bias per 1 LDO
ENM = ENS = Low
Additional DC Bias per LDO
Output Voltage Accuracy
IOUT = 100μA
Current Limit
●
–3
●
280
125
μA
60
μA
475
3
%
750
mA
VLDO = 1.8V, IOUT = 50mA
0.1
Load Regulation
VIN = 3.6V, 100μA < ILDO < 200mA
0.65
%
Dropout Voltage
LDO2, VLDO = 3.3V, VIN – VLDO at VLDO 3% Down
from VLDO Measureed at VIN = 4.3V
250
mV
Line Regulation
%/V
V1, V2
VIL
●
VIH
●
0.2
VIN – 0.2
V
V
Shutdown Input Current
ENLDO1 = ENLDO2 = Low
–1
1
μA
Active Input Current
ENLDO1 = ENLDO2 = High
–3
3
μA
0.4
V
ENM, ENS, ENLDO1, ENLDO2
VIL
●
VIH
●
1.4
IIH
VIH = 3.6V
IIL
VIL = 0V
●
–1
tPWH
High Pulse Width
●
0.2
tPWL
Low Pulse Width
tSD
Low Time to Shutdown (ENM, ENS = Low)
V
3
μA
1
μA
ENM, ENS Timing
μs
0.2
●
250
VRSET
●
768
IRSET
●
20
μs
μs
RSET
800
832
mV
70
μA
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LTC3230
ELECTRICAL CHARACTERISTICS
Note 4: The LTC3230 is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C ambient
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 5: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may result in device degradation or failure.
Note 6: 1.5x mode output impedance is defined as (1.5VIN – VCPO)/IOUT. 2x
mode output impedance is defined as (2VIN – VCPO)/IOUT.
Note 7: If the part has been shut down then the initial enable time is about
100μs longer due to the bandgap start-up and charge pump soft-start
times.
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Based on long-term current density limitations. Assumes an
operating duty cycle of ≤10% under absolute maximum conditions
for durations less than 10 seconds. Maximum current for continuous
operation is 125mA.
Note 3: Based on long-term current density limitations. LD01 and LD02
have short circuit protection which limits current to no more than 750mA.
Assumes an operating short circuit duty cycle less than 3% for durations
less than 10 seconds.
TYPICAL PERFORMANCE CHARACTERISTICS
Dropout Time from Enable
1.5x
Dropout Time when Enabled
2x
1.5x
CPO
2V/DIV
1x
CPO
2V/DIV
TA = 25°C unless otherwise noted.
1.5x CPO Ripple
2x
1x
VCPO
20mV/DIV
AC COUPLED
MODE RESET
ENM
2V/DIV
ENM
2V/DIV
ENS = LOW
400μs/DIV
ENS = HIGH
3230 G01
400μs/DIV
3230 G02
VIN = 3V
400ns/DIV
ICPO = 80mA
C1 = C2 = C6 = 1μF
1.5x Mode Charge Pump OpenLoop Output Resistance vs
Temperature (1.5VIN – VCPO)/ICPO
1x Mode Switch Resistance vs
Temperature
2x CPO Ripple
11
2.0
ICPO = 100mA
1.9 VIN = 3.6V
10
1.8
1.7
RESISTANCE (Ω)
RESISTANCE (Ω)
VCPO
20mV/DIV
AC COUPLED
1.6
1.5
1.4
1.3
VIN = 3.6V
400ns/DIV
ICPO = 80mA
C1 = C2 = C6 = 1μF
3230 G04
3230 G03
1.2
VIN = 3V
VCPO = 4.2V
C1 = C2 = C6 = 1μF
9
8
7
6
1.1
1.0
–40
–15
35
10
TEMPERATURE (°C)
60
85
3230 G05
5
–40
–15
10
35
TEMPERATURE (°C)
60
85
3230 G06
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LTC3230
TYPICAL PERFORMANCE CHARACTERISTICS
2x Mode Charge Pump Open-Loop
Output Resistance vs Temperature
(2VIN – VCPO)/ICPO
1.5x Mode CPO Voltage
vs Load Current
12
4.8
4.2
4.0
VIN = 3.2V
VIN = 3.1V
VIN = 3V
3.8
10
9
8
50
100
150
LOAD CURRENT (mA)
6
–40
200
–15
10
35
TEMPERATURE (°C)
5.0
4.5
960
4.0
60
40
20
VIN CURRENT (μA)
80
TA = 85°C
940
920
TA = 25°C
900
880
TA = –40°C
860
20
15
MLED/SLED PIN CURRENT (mA)
TA = –40°C
3.0
2.5
2.0
1.5
1.0
820
0.5
0
2.7
25
TA = 85°C
TA = 25°C
3.5
840
800
10
3.2
3.7
4.2
VIN (V)
4.7
5.2
2.7
4.7
3.7
VIN (V)
3230 G11
1x Mode No-Load VIN Current vs
VIN Voltage
3230 G12
1.5x Mode Supply Current vs ICPO
(IVIN – 1.5ICPO)
7
RSET = 17.4k
560
200
3230 G09
980
FREQUENCY (kHz)
MLED/SLED DROPOUT VOLTAGE (mV)
100
100
50
150
LOAD CURRENT (mA)
0
VIN Shutdown Current
vs VIN Voltage
3230 G10
2x Mode Supply Current vs ICPO
(IVIN – 2ICPO)
5
VIN = 3.6V
VIN = 3.6V
6
SUPPLY CURRENT (mA)
520
500
480
460
440
SUPPLY CURRENT (mA)
4
540
VIN CURRENT (μA)
4.2
85
60
1000
120
580
4.5
Oscillator Frequency
vs VIN Voltage
140
5
4.6
3230 G08
VIN = 3.6V
0
VIN = 3.5V
VIN = 3.4V
VIN = 3.3V
VIN = 3.2V
VIN = 3.1V
VIN = 3V
4.7
4.3
MLED/SLED Pin Dropout Voltage
vs MLED/SLED Pin Current
0
4.8
4.4
3230 G07
160
VIN = 3.6V
7
3.6
0
CPO VOLTAGE (V)
4.4
C1 = C2 = C6 = 1μF
5.0
4.9
RESISTANCE (Ω)
CPO VOLTAGE (V)
11
VIN = 3.3V
VIN = 3.4V
VIN = 3.5V
VIN = 3.6V
5.1
VIN = 3V
VCPO = 4.8V
C1 = C2 = C6 = 1μF
C1 = C2 = C6 = 1μF
4.6
2x Mode CPO Voltage
vs Load Current
5
4
3
2
3
2
1
1
420
0
400
2.8
3.2
3.6
4
4.4
4.8
5.2
VIN (V)
3230 G13
0
100
50
LOAD CURRENT (mA)
150
3230 G14
0
0
100
50
LOAD CURRENT (mA)
150
3230 G15
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LTC3230
TYPICAL PERFORMANCE CHARACTERISTICS
MLED/SLED Pin Current vs
MLED/SLED Pin Voltage
25
VIN = 3.6V
MLED/SLED CURRENT (mA)
MLED/SLED PIN CURRENT (mA)
25
20
15
10
5
Efficiency vs VIN Voltage
90
VIN = 3.6V
RSET = 17.7k
80
20
EFFICIENCY (PLED/PIN) (%)
30
MLED/SLED Current vs ENM/ENS
Strobe Pulses
15
10
5
70
60
50
40
30
20
10
0
0
0.04
0.08
0.12
0.16
MLED/SLED PIN VOLTAGE (V)
0
0.20
16
8
24
NUMBER OF STROBE PULSES
0
3230 G16
2.7
0.35
0
0.30
–0.1
0.25
0.20
0.15
0.10
0.05
4.3
4.7
LDO2
50mV/DIV
AC COUPLED
–0.2
LDO1
50mV/DIV
AC COUPLED
–0.3
–0.4
60mA
ILDO
50mA/DIV
–0.5
10mA
–0.6
–0.8
0
50
3.9
VIN (V)
LDO1 and LDO2 Load Transient
Response
CLDO = 1μF
–0.7
25
3.5
3.1
3230 G18
Output Voltage Accuracy
vs Load Current
% CHANGE FROM NO LOAD (%)
DROPOUT VOLTAGE (V)
0
32
3230 G17
LDO2 Dropout Voltage vs
Load Current
0
C1 = C2 = C6 = 1μF
5 LEDs AT 25mA/LED
VF = 3.45V
TA = 25°C
75 100 125 150 175 200 225
LOAD CURRENT (mA)
0
25
40μs/DIV
3230 G21
50 75 100 125 150 175 200
LOAD CURRENT (mA)
3230 G20
3230 G19
Output Voltage Accuracy
vs Temperature
LDO1 and LDO2 Current Limit vs
Temperature
0.05
500
475
–0.05
LDO CURRENT LIMIT (mA)
% CHANGE FROM 25°C (%)
0
–0.10
–0.15
–0.20
–0.25
–0.30
–0.35
450
425
400
375
–0.40
–0.45
–40
–20
0
40
20
TEMPERATURE (°C)
60
80
3230 G22
350
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
3230 G23
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LTC3230
PIN FUNCTIONS
CPO (Pin 1): Output of the Charge Pump Used to Power
All LEDs. This pin is enabled or disabled using the ENM
and ENS inputs. A 1μF X5R or X7R ceramic capacitor
should be connected to ground.
ENLDO1, ENLDO2 (Pins 2, 3): LDO1 and LDO2 Enables.
Logic-level high enables LDO1 or LDO2. Logic-level low
disables LDO1 or LDO2.
RSET (Pin 4): LED Current Programming Resistor Pin. The
RSET pin will servo to 0.8V. A resistor connected between
RSET and GND is used to set the MLED and SLED full-scale
current level. Connecting a resistor 10k or less will cause
the LTC3230 to enter overcurrent shutdown.
ENS, ENM (Pins 5, 11): SLED and MLED Enable and Output
Control. The ENS and ENM pins are used to program the
LED output currents. Pulse the ENS pin up to 31 times to
decrement the internal 5-bit DAC which controls the Sub
LED current from full scale to one LSB. Pulse the ENM pin
up to 31 times to decrement the internal 5-bit DAC which
controls the MLED1-4 LED currents from full scale to one
LSB. The counters will stop at 1LSB when the number of
strobes exceeds 31. The pin must be held high after the
desired positive strobe edge and the data is transferred
after a 150μs (typical) delay. Holding the ENS or ENM
pin low will clear the counter for the selected display and
reset the LED current to zero. If both inputs are held low
for longer than 150μs (typical), the charge pump and LED
current sources will go into shutdown. The charge pump
mode is reset to 1x whenever ENS or ENM is held low or
when the part is shut down.
SLED (Pin 6): SLED Current Driver. SLED is the Sub current source output. The LED is connected between CPO
(anode) and SLED (cathode). The current to the LED output
is set via the ENS input.
MLED1, MLED2, MLED3, MLED4 (Pins 7, 8, 9, 10):
MLED1-4 Current Drivers. MLED1 to MLED4 are the Main
current source outputs. The LEDs are connected between
CPO (anodes) and MLED1-4 (cathodes). The current to
the LED outputs are set via the ENM input. Any of the four
LED outputs can be disabled by connecting the output
directly to CPO. A 100μA current will flow through each
directly connected LED output.
V2, V1 (Pins 12, 13): LDO Output Voltage Select. V1 is
used to set LDO1’s output voltage. V2 is used to set LDO2’s
output voltage. Tie to VIN, GND or float. LDO Output voltages set by V1 and V2 are shown below.
V1
GND
FLOAT
VIN
LDO1 (V)
1.2
1.5
1.8
V2
GND
FLOAT
VIN
LDO2 (V)
1.8
2.8
3.3
LDO2, LDO1 (Pins 14, 15): LDO Outputs. Bypass LDO1 and
LDO2 with 1μF X5R or X7R ceramic capacitors to GND.
C2M, C1M, C2P, C1P (Pins 16, 17, 19, 20): Charge
Pump Flying Capacitor Pins. 1μF X5R or X7R ceramic
capacitors should be connected from C1P to C1M and
from C2P and C2M.
VIN (Pin 18): Supply Voltage. This pin should be bypassed
with a 2.2μF or greater low ESR ceramic capacitor.
Exposed Pad (Pin 21): Ground. This pad must be connected directly to a low impedance ground plane for proper
thermal and electrical performance.
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LTC3230
BLOCK DIAGRAM
20
17
C1P
19
C1M
16
C2M
C2P
GND
900kHz
OSCILLATOR
18
21
VIN
CPO
1
–
+
+
0.8V
–
4
RSET
TIMER
ENABLE MAIN
ENM
5-BIT
DOWN
COUNTER
MLED1
7
MLED2
11
50ns FILTER
5-BIT
LINEAR
DAC
MLED
CURRENT
SOURCES
8
MLED3
9
MLED4
10
TIMER
5
ENS
ENABLE SUB
5-BIT
DOWN
COUNTER
50ns FILTER
5-BIT
LINEAR
DAC
TIMER
3
SLED
CURRENT
SOURCES
SLED
6
VIN
SHUTDOWN
ENLDO2
+
–
2
+
LDO1
–
12
14
ENLDO1
0.8V
13
LDO2
V1
LDO1
VOUT
SELECT
V2
LDO2
VOUT
SELECT
15
GND
21
3230 BD
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LTC3230
OPERATION
Power Management
The LTC3230 uses a switched capacitor charge pump to
boost CPO to as much as 2 times the input voltage up to
5V. The part starts up in 1x mode. In this mode, VIN is
connected directly to CPO. 1x mode provides maximum
efficiency and minimum noise. The LTC3230 will remain in
1x mode until any LED current source drops out. Dropout
occurs when a current source voltage becomes too low
for the programmed current to be supplied. When dropout
is detected, the LTC3230 will switch into 1.5x mode. The
CPO voltage will then start to increase and will attempt to
reach 1.5x VIN up to 4.5V. Any subsequent dropout will
cause the part to enter 2x mode. The CPO voltage will
attempt to reach 2x VIN up to 5V. The part will be reset to
1x mode whenever the part is shut down or when either
ENM or ENS is driven low.
A 2-phase non-overlapping clock activates the charge pump
switches. In 2x mode the flying capacitors are charged on
alternate clock phases from VIN to minimize CPO voltage
ripple. In 1.5x mode the flying capacitors are charged in
series during the first clock phase and stacked in parallel
on VIN during the second phase. This sequence of charging and discharging the flying capacitors continues at a
constant frequency of 900kHz.
LED Current Control
The MLED and SLED currents are delivered by programmable current sources controlled by the ENM and ENS
tPWH ≥ 200ns
pins and by the value of the resistor on the RSET pin.
There are four MLED current sources controlled by the
ENM pin and one SLED current source controlled by the
ENS pin. Full-scale current in the MLED and SLED pins
are set by a resistor from the RSET pin to GND according
to the following formula:
MLED/SLED Full-Scale Output Current =
0.8
• 555
RSETT
Thirty two linear current settings are available by applying
up to 31 pulses when enabling the ENM and ENS pins.
Each strobe counts down a 5-bit DAC to set the LED
current. When the desired count is reached, leave the
enable strobe high and the output current will be set to
the programmed value after a typical delay of 150μs. If
more than 31 strobes are received the counter will stop
at one LSB. The output current will be set to zero if the
enable is set low only after the 150μs delay. If the enable
is toggled before the 150μs delay, the DAC counter will
continue to count down and the current output will not be
enabled until the start-up delay is finished.
When both ENM and ENS are held low for more than
250μs (minimum) the LED drivers and charge pump will
go into shutdown. See Figure 1 for timing information. If
the charge pump is in either 1.5x or 2x modes, the falling
edge of either ENM or ENS will reset the charge pump to
1x mode.
tEN ≥ 250μs
tSD ≥ 250μs
ENM OR ENS
200ns < tPWL < 20μs
PROGRAMMED
CURRENT
LED
CURRENT
SHUTDOWN
ENM = ENS = LOW
3230 F01
Figure 1. Current Programming Timing Diagram
3230fa
9
LTC3230
OPERATION
Charge Pump Soft-Start
In shutdown, CPO is disconnected from VIN and is pulled
down through a 14.3k resistor. When enabled, a weak switch
connects VIN to CPO. This allows VIN to slowly charge the
CPO output to prevent large charging currents.
The LTC3230 also employs a soft-start feature on its
charge pump to prevent excessive inrush current and
supply droop when switching into the step-up modes. The
current available to the CPO pin is increased linearly over
a typical period of 50μs. Soft-start occurs at the start of
both 1.5x and 2x modes.
1.5 • VIN – CPO for 1.5x mode and 2 • VIN – CPO for 2x
mode. 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 for
1.5x mode is 3.1V • 1.5 – 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 2, for 1.5x mode the available current is
given by:
IOUT =
Charge Pump Strength and Regulation
Regulation is achieved by sensing the voltage at the CPO
pin and modulating the charge pump strength based
on the error signal. The CPO regulation voltages are set
internally, and are dependent on the charge pump modes
as shown in Table 1.
Table 1. Charge Pump Output Regulation Voltages
CHARGE PUMP MODE
REGULATED VCPO
1.5x
4.5V
2x
5V
When the LTC3230 operates in either 1.5x mode or 2x
mode, the charge pump can be modeled as a Thevenin
equivalent circuit to determine the amount of current
available from the effective input voltage and effective
open-loop output resistance, ROL (Figure 2).
ROL
+
–
+
1.5VIN OR 2VIN
CPO
–
3230 F02
Figure 2. Charge Pump Thevenin Equivalent Open-Loop Circuit
ROL is dependent on a number of factors including the
switching term, 1/(2 • fOSC • CFLY), internal switch resistances and the non-overlap period of the switching circuit.
However, for a given ROL, the amount of current available
will be directly proportional to the advantage voltage of
1.5 • VIN – VCPO
ROL
For 2x mode, the available current is given by:
IOUT =
2 • VIN – VCPO
ROL
Notice that the advantage voltage in this case is 3.1V •
2 – 3.8V – 0.1V = 2.3V. ROL is higher in 2x mode but a
significant increase in available current is achieved.
Typical values of ROL as a function of temperature are
shown in Figures 3 and 4.
Mode Switching
The LTC3230 will automatically switch from 1x mode
to 1.5x mode and subsequently to 2x mode whenever
a dropout condition is detected at any LED pin. Dropout
occurs when a current source voltage becomes too low
for the programmed current to be supplied. The time from
dropout detection to mode switching is typically 0.5ms.
The charge pump mode is reset back to 1x when the LED
drivers are shut down (ENM = ENS = Low) or on the falling
edge of either ENM or ENS. An internal comparator will
not allow the main switches to connect VIN and CPO in
1x mode until the voltage at the CPO pin has decayed to
less than or equal to the voltage at the VIN pin.
LDO Operation
Two independent low drop-out linear regulators are in the
LTC3230. Each regulator may be independently enabled
(ENLDO1 and ENLDO2) from each other and from the
3230fa
10
LTC3230
OPERATION
charge pump function. Driving ENLDO1 and ENLDO2 high
enable LDO1 and LDO2 respectively. When the charge
pump is enabled, each LDO consumes an additional 60μA
(typical) from VIN. If the charge pump is not enabled, one
LDO consumes 125μA (typical) and the second uses 60μA
(typical) additional current.
The reference input to each LDO is ramped when enabled
to provide an output soft-start lasting typically 100μs.
When an LDO is disabled its output is pulled to ground
through an 11.5k resistor.
LDO output voltage is set using three-level input pins V1
and V2 as shown in Table 2.
In shutdown mode all the circuitry is turned off and the
LTC3230 draws a very low current from the VIN supply.
When in shutdown, CPO is disconnected from VIN and is
pulled to ground through a 14.3k resistor. The LTC3230
enters shutdown mode when both ENM and ENS pins
are brought low for 250μs (minimum) and ENLDO1 and
ENLDO2 are brought low. All enable pins ENM, ENS, ENLDO1 and ENLDO2 have internal pull-downs to define the
shutdown state whenever the inputs are floating.
Table 2. LDO1 and LDO2 Output Voltage Control
V1
GND
FLOAT
VIN
LDO1 (V)
1.2
1.5
1.8
V2
GND
FLOAT
VIN
LDO2 (V)
1.8
2.8
3.3
RESISTANCE (Ω)
10
12
VIN = 3V
VCPO = 4.2V
C1 = C2 = C6 = 1μF
11
RESISTANCE (Ω)
11
Shutdown Current
9
8
7
6
5
–40
VIN = 3V
VCPO = 4.8V
C1 = C2 = C6 = 1μF
10
9
8
7
–15
10
35
TEMPERATURE (°C)
60
85
3230 G06
Figure 3. Typical 1.5x ROL vs Temperature
6
–40
–15
10
35
TEMPERATURE (°C)
60
85
3230 G08
Figure 4. Typical 2x ROL vs Temperature
3230fa
11
LTC3230
APPLICATIONS INFORMATION
VIN and CPO Capacitor Selection
The style and value of the capacitors used with the LTC3230
determine several important parameters such as regulator
control loop stability, output ripple, charge pump strength
and minimum start-up time.
To reduce noise and ripple, it is recommended that low
equivalent series resistance (ESR) ceramic capacitors
are used on both VIN and CPO. Tantalum and aluminum
capacitors are not recommended due to high ESR.
times. Since the nonoverlapping time is small (~10ns),
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 cause a higher input
noise due to the higher ESR. Input noise can be further
reduced by powering the LTC3230 through a very small
series inductor as shown in Figure 5. A 10nH inductor will
reject the fast current notches, thereby presenting a nearly
constant current load to the input power supply.
The value of CCPO directly controls the amount of output
ripple for a given load current. Increasing the size of CCPO
will reduce the output ripple but will increase start-up
time. The peak-to-peak output ripple of the 1.5x mode is
approximately given by the expression:
IOUT
VRIPPLE(P-P) =
3 • fOSC • CCPO
where fOSC is the oscillator frequency, typically 900kHz,
and CCPO is the output storage capacitor.
The output ripple in 2x mode is very small due to the fact
that load current is supplied on both cycles of the clock.
Both style and value of the output capacitor can significantly affect the stability of the LTC3230. As shown in the
Block Diagram, the LTC3230 uses a control loop to adjust
the strength of the charge pump to match the required
output current. The error signal for the loop is stored
directly on the output capacitor. The output capacitor
also serves as 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.
In addition, excessive output capacitor ESR >100mΩ will
tend to degrade the loop stability. Multilayer ceramic chip
capacitors typically have exceptional ESR performance and
when combined with a tight board layout will result in very
good stability. As the value of CCPO controls the amount
of output ripple, the value of CVIN controls the amount of
ripple present at the input pin (VIN). The LTC3230’s input
current will be relatively constant while the charge pump
is either in the input charging phase or the output charging
phase but will drop to zero during the clock overlapping
VBAT
LTC3230
GND
3230 F05
Figure 5. 10nH Inductor Used for Input Noise Reduction
Flying Capacitor Selection
Warning: Polarized capacitors such as tantalum or
aluminum should never be used for the flying capacitors since their voltage can reverse upon start-up of the
LTC3230. Ceramic capacitors should always be used for
the flying capacitors.
The flying capacitors control the strength of the charge
pump. In order to achieve the rated output current it is
necessary to have at least 0.6μF 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
lose considerable capacitance over that range. Capacitors
may also have a very poor 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 case. The capacitor manufacturer’s
data sheet should be consulted to determine what value
3230fa
12
LTC3230
APPLICATIONS INFORMATION
of capacitor is needed to ensure minimum capacitances
at all temperatures and voltages.
• LED pads must be large and connected to the other
layers of metal to ensure proper heat sinking.
Table 3 shows a list of ceramic capacitor manufacturers
and how to contact them.
• The RSET pin is sensitive to noise and capacitance. The
resistor should be placed near the part with minimum
line width.
Table 3. Recommended Capacitor Vendors
AVX
xww.avxcrp.com
Kemet
www.kemet.com
Murata
www.murata.com
Taiyo Yuden
www.t-yuden.com
Vishay
www.vishay.com
Layout Considerations and Noise
Due to the high switching frequency and the transient
currents produced by the LTC3230, 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.
The flying capacitor pins C1P, C2P, C1M and C2M will have
high edge rate waveforms. The large dv/dt on these pins
can couple energy to adjacent PCB runs. Magnetic fields
can also be generated if the flying capacitors are not close
to the LTC3230 (i.e., the loop area is large). To decouple
capacitive energy transfer, a grounded PCB trace between
the sensitive node and the LTC3230 pins will shield the
sensitive node. For a high quality AC ground, the shield
trace should be returned to a solid ground plane that
extends all the way to the LTC3230.
The following guidelines should be followed when designing a PCB layout for the LTC3230:
• The Exposed Pad should be soldered to a large copper plane that is connected to a solid, low impedance
ground plane using plated through hole vias for proper
heat sinking and noise protection.
• Input and output capacitors must be placed close to
the part.
• The flying capacitors must be placed close to the part.
The traces from the pins to the capacitor pad should
be as wide as possible.
• VIN and CPO traces must be wide to minimize inductance
and handle high currents.
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 numbers
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
The efficiency of the LTC3230 depends upon the mode in
which it is operating. Recall that the LTC3230 operates
as a pass switch, connecting VIN to CPO, until dropout is
detected at a LED pin. 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
since the input current will be very close to the sum of
the LED currents.
At moderate to high output power, the quiescent current
of the LTC3230 is negligible and the expression above is
valid.
Once dropout is detected at any LED pin, the LTC3230
enables the charge pump in 1.5x mode.
In 1.5x 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
for a 1.5x charge pump is approximately 1.5 times the
load current. In an ideal 1.5x charge pump, the power
efficiency would be given by:
η=
PLED
V •I
V
= LED LED = LED
PIN
VIN • 1.5 • IIN 1.5 • VIN
3230fa
13
LTC3230
APPLICATIONS INFORMATION
In 2x boost mode as well, the efficiency is similar to that
of a linear regulator with an effective input voltage of 2
times the actual input voltage. In an ideal 2x charge pump,
the power efficiency would be given by:
η=
PLED VLED • ILED
V
=
= LED
PIN
VIN • 2 • IIN 2 • VIN
Thermal Management
For higher input voltages and maximum output current,
there can be substantial power dissipation in the LTC3230.
If the junction temperature increases above approximately
150°C the thermal shutdown circuitry will automatically
deactivate the output current sources, charge pump and
both LDOs. To reduce maximum junction temperature,
a good thermal connection to the PC board is recommended. Connecting the Exposed Pad to a ground plane
and maintaining a solid ground plane under the device
will reduce the thermal resistance of the package and PC
board considerably.
Its built-in thermal shutdown circuitry will protect the
LTC3230 from short term transient events. For continuous operation the maximum rated junction temperature
is 125°C. The power dissipated by the device is made up
of three components:
1. The LTC3230 IVIN operating current (found in the Electrical Characteristics table) multiplied by VIN.
Given a thermal resistance, θJA, for the LTC3230 QFN
package of 68°C/W, at an ambient temperature of 70°C
the total power in the LTC3230 should be kept to less than
815mW. Applications in which the LDO output voltages
are set to the lower range and which use a high VIN input
voltage may require limiting the total current output to
keep TJ less than 125°C at the upper ambient temperature
corners.
An example using the parameters in Table 4 shows an application that just meets the maximum junction temperature
limit. An increase in VIN, for example, will require reducing
the output current of the charge pump or LDO.
Table 4. TJ Calculation Example Parameters
VIN
3.6V
Mode
1.5x
VLED
3.3V
ILEDTOTAL
100mA (20mA/LED)
VLDO1
1.5V
VLDO2
2.8V
ILDO1
200mA
ILDO2
200mA
θJA
68°C/W
TA
70°C
Total Power Dissipation
799mW
Internal Junction Temperature
124°C
PQ = IQ • VIN
2. The sum of the LED currents multiplied by the difference between VIN • Mode and the LED forward voltage
where Mode is 1, 1.5 or 2 depending on the charge
pump mode.
PCP = (VIN • Mode – VLED) • ILEDTOTAL
3. For each LDO, the product of the LDO output current
and the difference between VIN and the LDO.
PLDO = (VIN – VLDO1) • ILDO1 + (VIN – VLDO2) • ILDO2
3230fa
14
LTC3230
PACKAGE DESCRIPTION
UD Package
20-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1720 Rev A)
0.70 ±0.05
3.50 ± 0.05
(4 SIDES)
1.65 ± 0.05
2.10 ± 0.05
PACKAGE
OUTLINE
0.20 ±0.05
0.40 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
3.00 ± 0.10
(4 SIDES)
BOTTOM VIEW—EXPOSED PAD
R = 0.115
TYP
0.75 ± 0.05
R = 0.05
TYP
PIN 1
TOP MARK
(NOTE 6)
PIN 1 NOTCH
R = 0.20 TYP
OR 0.25 × 45°
CHAMFER
19 20
0.40 ± 0.10
1
2
1.65 ± 0.10
(4-SIDES)
(UD20) QFN 0306 REV A
0.200 REF
0.00 – 0.05
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
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
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
0.20 ± 0.05
0.40 BSC
3230fa
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
LTC3230
TYPICAL APPLICATION
3-LED Main and One LED Sub at 20mA Full Scale
C1
1mF
VIN = 2.7V
TO 5.5V
C2
1mF
C1P C1M C2P C2M
CPO
VIN
C3
2.2mF
MAIN
C6
1mF D1
LTC3230
MLED1
MLED2
MLED3
MLED4
SLED
LDO1
LDO2
ENM
ENS
ENM
ENS
ENLDO1
ENLDO2
ENLDO1
ENLDO2
V1
V2
RSET
RSET
21.5k
D2
SUB
D3
D5
MLED4
DISABLED
1.2V
3.3V
C5
1mF
3230 TA02
C4
1mF
GND
ENM OR ENS
SET BRIGHTNESS LEVEL
ON
OFF
RELATED PARTS
PART
NUMBER
DESCRIPTION
COMMENTS
LT®3023
Dual 100mA, Low Noise Micropower, LDO
Dual Low Noise < 20μVRMS, Stable with 1μF Ceramic Capacitors, VIN: 1.8V to 20V,
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DFN Packages
LT3024
Dual 100mA/500mA, Low Noise Micropower, LDO Dual Low Noise < 20μVRMS, Stable with 1μF/3.3μF Ceramic Capacitors,
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LT3028
Dual 100mA/500mA, Low Noise Micropower, LDO Dual Low Noise < 20μVRMS, Stable with 1μF/3.3μF Ceramic Capacitors,
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95% Efficiency, VIN: 2.9V to 4.5V, 1A Output Current; Up to 17 LEDs for 5 Displays,
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LTC3209
600mA MAIN/Camera LED Controller
Up to 8 LEDs, 94% Efficiency, VIN: 2.9V to 4.5V, 1x/1.5x/2x Boost Modes, 4mm ×
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LTC3210/
LTC3210-1/
LTC3210-2/
LTC3210-3
500mA MAIN/Camera LED Controller
Up to 5 LEDs, 95% Efficiency, VIN: 2.9V to 4.5V, 1x/1.5x/2x Boost Modes, Exponential
Brightness Control, “-1” Version Has 64-Step Linear Brightness Control, 3mm × 3mm
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250mA Universal 9-Channel LED Driver
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3230fa
16 Linear Technology Corporation
LT 0108 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2007