LINER LTC3210-2

LTC3210-2/LTC3210-3
MAIN/CAM LED Controllers
with 32-Step Brightness Control
in 3mm × 3mm QFN
DESCRIPTION
FEATURES
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Low Noise Charge Pump Provides High Efficiency
with Automatic Mode Switching
Multimode Operation: 1x, 1.5x, 2x
Individual Full-Scale Current Set Resistors
Up to 500mA Total Output Current
Single Wire EN/Brightness Control for MAIN and
CAM LEDs
32:1 Linear Brightness Control Range for
MAIN Display
Three or Four 25mA Low Dropout MAIN LED Outputs
One 400mA Low Dropout CAM LED Output
Low Noise Constant Frequency Operation*
Low Shutdown Current: 3μA
Internal Soft-Start Limits Inrush Current During
Startup and Mode Switching
Open/Short LED Protection
No Inductors
3mm × 3mm 16-Lead Plastic QFN Package
APPLICATIONS
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Multi-LED Light Supply for Cellphones/DSCs/PDAs
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Protected by US Patents including 6411531.
The LTC®3210-2/LTC3210-3 are low noise charge pump
DC/DC converters designed to drive three or four MAIN
LEDs and one high current CAM LED for camera lighting.
The LTC3210-2/LTC3210-3 require only four small ceramic
capacitors and two current set resistors to form a complete
LED power supply and current controller.
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.
Independent MAIN and CAM full-scale current settings
are programmed by two external resistors.
Shutdown mode and current output levels are selected
via two logic inputs. ENM and ENC are toggled to adjust
the LED currents via internal counters and DACs. A 5-bit
linear DAC (32 steps) provides high resolution brightness
control for the MAIN display.
The charge pump optimizes efficiency based on the voltage across the LED current sources. The part powers up
in 1x mode and will automatically switch to boost mode
whenever any enabled LED current source begins to enter
dropout. The LTC3210-2/LTC3210-3 are available in a
3mm × 3mm 16-lead QFN package.
TYPICAL APPLICATION
C2
2.2μF
4-LED MAIN Display
Efficiency vs VBAT Voltage
C3
2.2μF
100
VBAT
C1
2.2μF
C1M
C2P
C2M
MAIN
CPO
VBAT
C4
2.2μF
LTC3210-2
MLED1
MLED2
MLED3
ENM
ENM
MLED4
ENC
ENC
CLED
RM
30.1k
1%
RC
GND
24.3k
1%
90
CAM
EFFICIENCY (PLED/PIN) (%)
C1P
321023 TA01
80
70
60
50
40
30
20 4 LEDs AT 9mA/LED
10 (TYP VF AT 9mA = 3V, NICHIA NSCW100)
TA = 25°C
0
3.0 3.2 3.4 3.6 3.8 4.0 4.2
VBAT (V)
4.4
321023 TA01b
321023fa
1
LTC3210-2/LTC3210-3
ABSOLUTE MAXIMUM RATINGS (Note 1)
VBAT, CPO to GND ........................................ –0.3V to 6V
ENM, ENC ................................... –0.3V to (VBAT + 0.3V)
ICPO (Note 2) ........................................................600mA
IMLED1-4 .................................................................35mA
ICLED (Note 2) ......................................................500mA
CPO Short-Circuit Duration .............................. Indefinite
Operating Temperature Range (Note 3) ...–40°C to 85°C
Storage Temperature Range...................–65°C to 125°C
PIN CONFIGURATION
12 GND
C1P 1
CPO 2
11 CLED
CPO 2
10 ENC
ENM 3
7
8
MLED3
MLED4
RM
10 ENC
MLED1 4
UD PACKAGE
16-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 125°C, θJA = 68°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
9
5
6
7
8
RM
6
RC
NC
5
MLED2
9
11 CLED
17
MLED3
MLED1 4
12 GND
MLED2
17
C2M
16 15 14 13
C1P 1
ENM 3
C1M
C2P
16 15 14 13
VBAT
TOP VIEW
C2M
C1M
VBAT
C2P
TOP VIEW
RC
UD PACKAGE
16-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 125°C, θJA = 68°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3210EUD-2#PBF
LTC3210EUD-2#TRPBF
LCHX
16-Lead (3mm × 3mm) Plastic QFN
–40°C to 85°C
LTC3210EUD-3#PBF
LTC3210EUD-3#TRPBF
LCHY
16-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.VBAT = 3.6V, C1 = C2 = C3 = C4 = 2.2μF, RM = 30.1k, RC = 24.3k,
ENM = high, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
●
VBAT Operating Voltage
IVBAT Operating Current
ICPO = 0, 1x Mode, LSB Setting
ICPO = 0, 1.5x Mode
ICPO = 0, 2x Mode
VBAT Shutdown Current
ENM = ENC = Low
TYP
2.9
MAX
4.5
0.4
2.5
4.5
●
UNITS
V
mA
mA
mA
3
6
μA
525
589
A/A
MLED1, MLED2, MLED3 and MLED4 (LTC3210-2 Only) Current
●
LED Current Ratio (IMLED/IRM)
IMLED = Full Scale
481
LED Dropout Voltage
Mode Switch Threshold, IMLED = Full Scale
75
mV
LED Current Matching
Any Two Outputs
0.5
%
321023fa
2
LTC3210-2/LTC3210-3
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.VBAT = 3.6V, C1 = C2 = C3 = C4 = 2.2μF, RM = 30.1k, RC = 24.3k,
ENM = high, unless otherwise noted.
PARAMETER
CONDITIONS
MLED Current, 5-Bit Linear DAC
1 ENM Strobe (FS)
31 ENM Strobes (FS/31)
MIN
TYP
MAX
20
0.640
UNITS
mA
mA
CLED Current
●
LED Current Ratio (ICLED/IRC)
ICLED = Full Scale
6930
7700
8470
A/A
LED Dropout Voltage
Mode Switch Threshold, ICLED = Full Scale
500
mV
CLED Current, 3-Bit Linear DAC
1 ENC Strobe (FS)
7 ENC Strobes (FS/7)
380
54
mA
mA
1x Mode Output Voltage
ICPO = 0mA
VBAT
V
1.5x Mode Output Voltage
ICPO = 0mA
4.55
V
2x Mode Output Voltage
ICPO = 0mA
5.05
V
0.55
Ω
Charge Pump (CPO)
1x Mode Output Impedance
1.5x Mode Output Impedance
VBAT = 3.4V, VCPO = 4.6V (Note 4)
3.15
Ω
2x Mode Output Impedance
VBAT = 3.2V, VCPO = 5.1V (Note 4)
3.95
Ω
CLOCK Frequency
0.8
MHz
Mode Switching Delay
0.4
ms
CPO Short Circuit Detection
Threshold Voltage
Test Current
CPO = 0V, ENM = ENC = Low
●
0.4
1.3
V
●
10
30
mA
ENC, ENM
VIL
●
VIH
●
1.4
0.4
IIH
ENM = ENC = 3.6V
●
10
IIL
ENM = ENC = 0V
●
–1
tPW
Minimum Pulse Width
●
200
tSD
Low Time to Shutdown (ENC, ENM = Low)
●
50
tEN
Current Source Enable Time
(ENC, ENM = High) (Note 5)
●
VRM, VRC
●
IRM, IRC
●
V
V
15
20
μA
1
μA
150
250
μs
50
150
250
μs
1.16
1.20
1.24
V
80
μA
ENC, ENM Timing
ns
RM, RC
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 300mA.
Note 3: The LTC3210-2/LTC3210-3 are guaranteed to meet performance
specifications from 0°C to 70°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 4: 1.5x mode output impedance is defined as (1.5VBAT – VCPO)/IOUT.
2x mode output impedance is defined as (2VBAT – VCPO)/IOUT.
Note 5: If the part has been shut down then the initial enable time is about
100μs longer due to the bandgap enable time.
321023fa
3
LTC3210-2/LTC3210-3
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise stated.
Dropout Time from Shutdown
EN
2V/DIV
2X
5.1V
CPO
1V/DIV
Dropout Time When Enabled
1.5X
VBAT = 3.6V
ICPO = 200mA
CCPO = 2.2μF
2X
5.1V
CPO
1V/DIV
1X
1.5x CPO Ripple
1.5X
1X
ENC
2V/DIV
MODE
RESET
VCPO
50mV/DIV
AC
COUPLED
MODE
RESET
ENM = HIGH
321023 G01
321023 G02
250μs/DIV
500μs/DIV
1.5x Mode Charge Pump Open-Loop
Output Resistance vs Temperature
(1.5VBAT – VCPO)/ICPO
1x Mode Switch Resistance
vs Temperature
0.70
VBAT = 3.6V
ICPO = 200mA
CCPO = 2.2μF
3.8
ICPO = 200mA
OPEN-LOOP OUTPUT RESISTANCE (Ω)
2x CPO Ripple
SWITCH RESISTANCE (Ω)
0.65
VCPO
20mV/DIV
AC
COUPLED
VBAT = 3.3V
0.55
VBAT = 3.6V
VBAT = 3.9V
0.45
321023 G04
500ns/DIV
0.60
0.50
0.40
–40
–15
321023 G03
500ns/DIV
10
35
TEMPERATURE (°C)
60
VBAT = 3V
VCPO = 4.2V
3.6
C2 = C3 = C4 = 2.2μF
3.4
3.2
3.0
2.8
2.6
2.4
–40
85
–15
10
35
60
321023 G06
321023 G05
2x Mode Charge Pump Open-Loop
Output Resistance vs Temperature
(2VBAT – VCPO)/ICPO
1.5x Mode CPO Voltage
vs Load Current
VBAT = 3.3V
VBAT = 3.4V
4.4
VBAT = 3.5V
4.2
VBAT = 3.6V
4.0
VBAT = 3.2V
3.8
VBAT = 3.1V
VBAT = 3V
3.6
0
100
5.2
200
300
400
LOAD CURRENT (mA)
500
VBAT = 3V
VCPO = 4.8V
4.4 C2 = C3 = C4 = 2.2μF
5.0
4.2
4.0
3.8
3.6
VBAT = 3.6V
4.9
4.8
VBAT = 3.5V
4.7
VBAT = 3.4V
4.6
VBAT = 3.3V
4.5
VBAT = 3.2V
4.4
3.4
3.2
–40
VBAT = 3.1V
4.3
–15
10
35
60
85
TEMPERATURE (°C)
321023 G07
C2 = C3 = C4 = 2.2μF
5.1
CPO VOLTAGE (V)
CPO VOLTAGE (V)
4.6
2x Mode CPO Voltage
vs Load Current
4.6
C2 = C3 = C4 = 2.2μF
OPEN-LOOP OUTPUT RESISTANCE (Ω)
4.8
85
TEMPERATURE (°C)
321023 G08
4.2
VBAT = 3V
0
100
300
400
200
LOAD CURRENT (mA)
500
321023 G09
321023fa
4
LTC3210-2/LTC3210-3
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise stated.
CLED Pin Dropout Voltage
vs CLED Pin Current
200
100
0
150 200 250 300 350
CLED PIN CURRENT (mA)
TA = 25°C
830
80
60
40
800
TA = –40°C
790
770
2
0
4
760
6 8 10 12 14 16 18 20
MLED PIN CURRENT (mA)
2.7
5.0
800
780
4.5
20
3.0
2.5
TA = 85°C
VBAT = 3.6V
RM = 33.2k
RC = 24.3k
SUPPLY CURRENT (mA)
VBAT CURRENT (μA)
TA = –40°C
4.5
1.5x Mode Supply Current
vs ICPO (IVBAT – 1.5ICPO)
760
TA = 25°C
3.5
4.2
321023 G12
1x Mode No Load VBAT Current
vs VBAT Voltage
4.0
3.6
3.3
3.9
VBAT VOLTAGE (V)
3.0
321023 G11
VBAT Shutdown Current
vs VBAT Voltage
740
720
700
680
660
15
10
5
640
2.0
620
3.9
3.6
3.3
VBAT VOLTAGE (V)
4.2
4.5
0
600
3.0
2.7
3.6
3.9
3.3
VBAT VOLTAGE (V)
4.2
321023 G13
2x Mode Supply Current
vs ICPO (IVBAT – 2ICPO)
20
4.5
0
100
300
400
200
LOAD CURRENT (mA)
500
321023 G15
321023 G14
CLED Pin Current
vs CLED Pin Voltage
400
VBAT = 3.6V
VBAT = 3.6V
360
CLED PIN CURRENT (mA)
3.0
SUPPLY CURRENT (mA)
VBAT SHUTDOWN CURRENT (μA)
TA = 85°C
810
780
321023 G10
1.5
2.7
820
20
0
400
840
100
FREQUENCY (kHz)
300
100
850
VBAT = 3.6V
400
50
Oscillator Frequency
vs VBAT Voltage
120
VBAT = 3.6V
MLED PIN DROPOUT VOLTAGE (mV)
CLED PIN DROPOUT VOLTAGE (mV)
500
MLED Pin Dropout Voltage
vs MLED Pin Current
15
10
5
320
280
240
200
160
120
80
40
0
0
100
300
400
200
LOAD CURRENT (mA)
500
321023 G16
0
0
0.2
0.6
0.8
0.4
CLED PIN VOLTAGE (V)
1
321023 G17
321023fa
5
LTC3210-2/LTC3210-3
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise stated.
MLED Pin Current
vs MLED Pin Voltage
CLED Current
vs ENC Strobe Pulses
400
22
VBAT = 3.6V
RC = 24.3k
VBAT = 3.6V
20
350
16
CLED CURRENT (mA)
MLED PIN CURRENT (mA)
18
14
12
10
8
6
300
250
200
150
100
4
50
2
0
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20
MLED PIN VOLTAGE (V)
0
0
321023 G19
321023 G18
MLED Current
vs ENM Strobe Pulses
Efficiency vs VBAT Voltage
21
80
EFFICIENCY (PLED /PIN) (%)
MAIN LED CURRENT (mA)
90
VBAT = 3.6V
RM = 30.1k
18
15
12
9
6
70
60
50
40
30
20
3
10
0
0
28
1
4
5
6
3
2
7
NUMBER OF ENC STROBE PULSES
24 20 16 12
8
4
NUMBER OF ENM STROBE PULSES
1
321023 G20
300mA LED CURRENT
(TYP VF AT 300mA = 3.1V, AOT-2015HPW
0
2.9 3.05 3.2 3.35 3.5 3.65 3.8 3.95 4.1 4.25 4.4
VBAT (V)
321023 G21
321023fa
6
LTC3210-2/LTC3210-3
PIN FUNCTIONS
C1P, C2P, C1M, C2M (Pins 1, 16, 14, 13): Charge Pump
Flying Capacitor Pins. A 2.2μF X7R or X5R ceramic capacitor should be connected from C1P to C1M and C2P
to C2M.
CPO (Pin 2): Output of the Charge Pump Used to Power
All LEDs. This pin is enabled or disabled using the ENM
and ENC inputs. A 2.2μF X5R or X7R ceramic capacitor
should be connected to ground.
ENM, ENC (Pins 3, 10): Inputs. The ENM and ENC pins
are used to program the LED output currents. The ENC
pin is strobed up to 7 times to decrement the internal 3-bit
DAC’s from full-scale to 1LSB. The ENM pin is strobed 31
times to decrement the 5-bit DAC from full-scale to 1LSB.
The counters will stop at 1LSB if the strobing continues.
The pin must be held high after the final desired positive
strobe edge and the data is transferred after a 150μs (typ)
delay. Holding the ENM or ENC pin low will clear the counter for the selected display and reset the LED current to
0. If both inputs are held low for longer than 150μs (typ)
the part will go into shutdown. The charge pump mode
is reset to 1x whenever ENC goes low or when the part
is shut down.
MLED1, MLED2, MLED3 (Pins 4, 5, 6): Outputs. MLED1
to MLED3 are the MAIN current source outputs. The LEDs
are connected between CPO (anodes) and MLED1-3 (cathodes). The current to each LED output is set via the ENM
input, and the programming resistor connected between
RM and GND.
MLED4 (Pin 7, LTC3210-2 Only): Output. MLED4 is the
fourth main current source output available only on the
LTC3210-2 product. The LED is connected between CPO
(anode) and MLED4 (cathode). The current to MLED4
is set via the ENM input and the programming resistor
connected between RM and GND. MLED4 tracks the LED
currents of MLED1-3.
NC (Pin 7, LTC3210-3 Only): This pin is not connected
and can be left floating or connected to ground.
RM, RC (Pins 8,9): LED Current Programming Resistor
Pins. The RM and RC pins will servo to 1.22V. Resistors
connected between each of these pins and GND are used
to set the high and low LED current levels. Connecting a
resistor 15k or less will cause the LTC3210-2/LTC3210-3
to enter overcurrent shutdown.
CLED (Pin 11): Output. CLED is the CAM current source
output. The LED is connected between CPO (anode) and
CLED (cathode). The current to the LED output is set via
the ENC input, and the programming resistor connected
between RC and GND.
GND (Pin 12): Ground. This pin should be connected to
a low impedance ground plane.
VBAT (Pin 15): Supply voltage. This pin should be bypassed
with a 2.2μF, or greater low ESR ceramic capacitor.
Exposed Pad (Pin 17): This pad should be connected
directly to a low impedance ground plane for optimal
thermal and electrical performance.
321023fa
7
LTC3210-2/LTC3210-3
BLOCK DIAGRAM
C1P
C1M
C2P
C2M
1
14
16
13
800kHz
OSCILLATOR
12 GND
VBAT 15
2
CPO
4
MLED1
5
MLED2
6
MLED3
7
MLED4
(LTC3210-2 ONLY)
CHARGE PUMP
–
+
+
ENABLE CP
1.215V
–
TIMER
ENABLE MAIN
500Ω
RM
8
ENM
3
5-BIT
DOWN
COUNTER
50ns FILTER
250k
+
–
5-BIT
LINEAR
DAC
MLED
CURRENT
SOURCES
4
1.215V
TIMER
SHUTDOWN
TIMER
ENABLE CAM
500Ω
RC
9
ENC 10
50ns FILTER
250k
3-BIT
DOWN
COUNTER
3-BIT
LINEAR
DAC
CLED
CURRENT
SOURCE
11 CLED
321023 BD
321023fa
8
LTC3210-2/LTC3210-3
OPERATION
Power Management
The LTC3210-2/LTC3210-3 uses a switched capacitor
charge pump to boost CPO to as much as 2 times the
input voltage up to 5.1V. The part starts up in 1x mode. In
this mode, VBAT is connected directly to CPO. This mode
provides maximum efficiency and minimum noise. The
LTC3210-2/LTC3210-3 will remain in 1x mode until an 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
LTC3210-2/LTC3210-3 will switch into 1.5x mode. The
CPO voltage will then start to increase and will attempt
to reach 1.5x VBAT up to 4.6V. Any subsequent dropout
will cause the part to enter the 2x mode. The CPO voltage
will attempt to reach 2x VBAT up to 5.1V. The part will be
reset to 1x mode whenever the part is shut down or when
ENC goes low.
A two phase nonoverlapping clock activates the charge
pump switches. In the 2x mode the flying capacitors are
charged on alternate clock phases from VBAT to minimize
input current ripple and CPO voltage ripple. In 1.5x mode the
flying capacitors are charged in series during the first clock
phase and stacked in parallel on VBAT during the second
phase. This sequence of charging and discharging the flying
capacitors continues at a constant frequency of 800kHz.
counter which controls a 5-bit linear DAC. When the
desired current is achieved ENM is stopped high. The
output current then changes to the programmed value
after 150μs (typ). The counter will stop when the LSB
is reached. The output current is set to 0 when ENM is
toggled low after the output has been enabled. If strobing
is started within 150μs (typ), after ENM has been set low,
the counter will continue to count down. After 150μs (typ)
the counter is reset.
The CLED current is delivered by a programmable current
source. Eight linear current settings (0mA to 380mA, RC
= 24.3k) are available by strobing the ENC pin. Each positive strobe edge decrements a 3-bit down counter which
controls a 3-bit linear DAC. When the desired current is
reached, ENC is stopped high. The output current then
changes to the programmed value after 150μs (typ). The
counter will stop when the LSB is reached. The output
current is set to 0 when ENC is toggled low after the output
has been enabled. If strobing is started within 150μs (typ)
after ENC has been set low, the counter will continue to
count down. After 150μs (typ) the counter is reset.
The full-scale output current is calculated as follows:
MLED full-scale output current
= (1.215V/(RM + 500)) • 525
CLED full-scale output current
= (1.215V/(RC + 500)) • 7700
LED Current Control
The MLED currents are delivered by the four programmable current sources. 32 linear current settings (0mA
to 20mA, RM = 30.1k) are available by strobing the ENM
pin. Each positive strobe edge decrements a 5-bit down
tPW ³ 200ns
When both ENM and ENC are held low for more than
150μs (typ) the part will go into shutdown. See Figure 1
for timing information.
ENC resets the mode to 1x on a falling edge.
tEN 150ms (TYP)
tSD 150ms (TYP)
ENM
OR ENC
PROGRAMMED
CURRENT
LED
CURRENT
ENM = ENC = LOW
SHUTDOWN
321023 F01
Figure 1. Current Programming Timing Diagram
321023fa
9
LTC3210-2/LTC3210-3
OPERATION
Soft-Start
Initially, when the part is in shutdown, a weak switch connects VBAT to CPO. This allows VBAT to slowly charge the
CPO output capacitor to prevent large charging currents.
The LTC3210-2/LTC3210-3 also employ 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 150μs. Soft-start occurs at the
start of both 1.5x and 2x mode changes.
When the LTC3210-2/LTC3210-3 operate 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
+
–
1.5VBAT OR 2VBAT
+
CPO
–
321023 F02
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
4.55V
2x
5.05V
Figure 2. Charge Pump Thevenin Equivalent Open-Loop Circuit
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.
However, for a given ROL, the amount of current available
will be directly proportional to the advantage voltage of
1.5VBAT – CPO for 1.5x mode and 2VBAT – 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.
321023fa
10
LTC3210-2/LTC3210-3
OPERATION
From Figure 2, for 1.5x mode the available current is
given by:
IOUT
(1.5VBAT – VCPO )
=
ROL
For 2x mode, the available current is given by:
(2V
– VCPO )
IOUT = BAT
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 overall increase in available current is achieved.
Typical values of ROL as a function of temperature are
shown in Figure 3 and Figure 4.
Shutdown Current
In shutdown mode all the circuitry is turned off and the
LTC3210-2/LTC3210-3 draw a very low current from the
VBAT supply. Furthermore, CPO is weakly connected to VBAT.
The LTC3210-2/LTC3210-3 enter shutdown mode when
both the ENM and ENC pins are brought low at 150μs (typ).
ENM and ENC have 250k internal pull down resistors to define the shutdown state when the drivers are in a high impedance state.
Thermal Protection
The LTC3210-2/LTC3210-3 have built-in overtemperature
protection. At internal die temperatures of around 150°C
thermal shut down will occur. This will disable all of the
current sources and charge pump until the die has cooled
by about 15°C. This thermal cycling will continue until the
fault has been corrected.
Mode Switching
The LTC3210-2/LTC3210-3 will automatically switch from
1x mode to 1.5x mode and subsequently to 2x mode
whenever a dropout condition is detected at an LED pin.
Dropout occurs when a current source voltage becomes
too low for the programmed current to be supplied. The
time from drop-out detection to mode switching is typically 0.4ms.
The part is reset back to 1x mode when the part is shut
down (ENM = ENC = Low) or on the falling edge of ENC.
An internal comparator will not allow the main switches to
connect VBAT and CPO in 1x mode until the voltage at the
CPO pin has decayed to less than or equal to the voltage
at the VBAT pin.
4.6
VBAT = 3V
VCPO = 4.2V
3.6
C2 = C3 = C4 = 2.2μF
OPEN-LOOP OUTPUT RESISTANCE (Ω)
OPEN-LOOP OUTPUT RESISTANCE (Ω)
3.8
3.4
3.2
3.0
2.8
2.6
2.4
–40
–15
10
35
60
85
TEMPERATURE (°C)
VBAT = 3V
VCPO = 4.8V
4.4 C2 = C3 = C4 = 2.2μF
4.2
4.0
3.8
3.6
3.4
3.2
–40
–15
10
35
60
85
TEMPERATURE (°C)
321023 F03
Figure 3. Typical 1.5x ROL vs Temperature
321023 F04
Figure 4. Typical 2x ROL vs Temperature
321023fa
11
LTC3210-2/LTC3210-3
APPLICATIONS INFORMATION
VBAT, CPO Capacitor Selection
The style and value of the capacitors used with the
LTC3210-2/LTC3210-3 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 for both CVBAT and CCPO. Tantalum and aluminum
capacitors are not recommended due to high ESR.
The value of CCPO directly controls the amount of output
ripple for a given load current. Increasing the size of CCPO
will reduce output ripple at the expense of higher start-up
current. The peak-to-peak output ripple of the 1.5x mode
is approximately given by the expression:
VRIPPLE(P−P) =
IOUT
(3f0SC • CCPO )
(3)
where fOSC is the LTC3210-2/LTC3210-3 oscillator frequency or typically 800kHz 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 LTC3210-2/LTC3210-3. As shown
in the Block Diagram, the LTC3210-2/LTC3210-3 use a
control loop to adjust the strength of the charge pump to
match the required output current. The error signal of 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 1.3μF 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 CVBAT controls the amount
of ripple present at the input pin(VBAT). The LTC3210-2/
LTC3210-3’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 nonoverlap times. Since the nonoverlap time
is small (~35ns), 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 higher ESR. Therefore,
ceramic capacitors are recommended for low ESR. Input
noise can be further reduced by powering the LTC3210-2/
LTC3210-3 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. For economy, the 10nH
inductor can be fabricated on the PC board with about
1cm (0.4") of PC board trace.
VBAT
LTC3210-2
LTC3210-3
GND
321023 F05
Figure 5. 10nH Inductor Used for Input Noise
Reduction (Approximately 1cm of Board Trace)
321023fa
12
LTC3210-2/LTC3210-3
APPLICATIONS INFORMATION
Flying Capacitor Selection
Layout Considerations and Noise
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 LTC3210-2/LTC3210-3. Ceramic capacitors should
always be used for the flying capacitors.
Due to the high switching frequency and the transient
currents produced by the LTC3210-2/LTC3210-3, 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 capacitors control the strength of the charge
pump. In order to achieve the rated output current it is
necessary to have at least 1.6μF 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
of capacitor is needed to ensure minimum capacitances
at all temperatures and voltages.
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 capacitively to adjacent PCB runs.
Magnetic fields can also be generated if the flying capacitors
are not close to the LTC3210-2/LTC3210-3 (i.e., the loop
area is large). To decouple capacitive energy transfer, a
Faraday shield may be used. This is a grounded PCB trace
between the sensitive node and the LTC3210-2/LTC3210-3
pins. For a high quality AC ground, it should be returned
to a solid ground plane that extends all the way to the
LTC3210-2/LTC3210-3.
Table 2 shows a list of ceramic capacitor manufacturers
and how to contact them:
Table 2. 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
The following guidelines should be followed when designing a PCB layout for the LTC3210-2/LTC3210-3:
• 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.
• VBAT, CPO traces must be wide to minimize inductance
and handle high currents.
• LED pads must be large and connected to other layers
of metal to ensure proper heat sinking.
• RM and RC pins are sensitive to noise and capacitance.
The resistors should be placed near the part with minimum line width.
321023fa
13
LTC3210-2/LTC3210-3
APPLICATIONS INFORMATION
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=
P LED
PIN
The efficiency of the LTC3210-2/LTC3210-3 depends upon
the mode in which it is operating. Recall that the LTC3210-2/
LTC3210-3 operates as a pass switch, connecting VBAT to
CPO, until dropout is detected at the 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
PIN
=
(VLED • ILED ) VLED
=
(VBAT • IBAT ) VBAT
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 LTC3210-2/LTC3210-3 is negligible and the expression above is valid.
Once dropout is detected at any LED pin, the LTC3210-2/
LTC3210-3 enable 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:
ηIDEAL =
PLED
PIN
=
(VLED • ILED )
VLED
=
(VBAT • (1.5)• ILED ) (1.5 • VBAT )
Similarly, in 2x boost mode, 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:
ηIDEAL =
PLED
PIN
=
(VLED • ILED )
VLED
=
(VBAT • (2)• ILED ) (2 • VBAT )
Thermal Management
For higher input voltages and maximum output current, there can be substantial power dissipation in the
LTC3210-2/LTC3210-3. If the junction temperature
increases above approximately 150°C the thermal shut
down circuitry will automatically deactivate the output
current sources and charge pump. 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.
321023fa
14
LTC3210-2/LTC3210-3
PACKAGE DESCRIPTION
UD Package
16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691)
0.70 ±0.05
3.50 ± 0.05
1.45 ± 0.05
2.10 ± 0.05 (4 SIDES)
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 ± 0.10
(4 SIDES)
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.20 TYP
OR 0.25 × 45° CHAMFER
R = 0.115
TYP
0.75 ± 0.05
15
16
PIN 1
TOP MARK
(NOTE 6)
0.40 ± 0.10
1
1.45 ± 0.10
(4-SIDES)
2
(UD16) QFN 0904
0.200 REF
0.00 – 0.05
NOTE:
1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2)
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
0.25 ± 0.05
0.50 BSC
321023fa
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
LTC3210-2/LTC3210-3
TYPICAL APPLICATION
3-LED MAIN, One LED Camera
C2
2.2μF
C1P
VBAT
C1
2.2μF
C3
2.2μF
C1M
C2P
MAIN
C2M
CAM
CPO
VBAT
C4
2.2μF
LTC3210-3
MLED1
MLED2
ENM
ENM
MLED3
ENC
ENC
CLED
RM
RC
30.1k
1%
321023 TA02
GND
24.3k
1%
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321023fa
16 Linear Technology Corporation
LT 1207 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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