LTC3210 [Linear]
MAIN/CAM LED Controller in 3mm × 3mm QFN; MAIN / CAM LED控制器采用3mm × 3mm QFN封装型号: | LTC3210 |
厂家: | Linear |
描述: | MAIN/CAM LED Controller in 3mm × 3mm QFN |
文件: | 总16页 (文件大小:238K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LTC3210
MAIN/CAM LED Controller
in 3mm × 3mm QFN
U
DESCRIPTIO
FEATURES
TheLTC®3210isalownoisechargepumpDC/DCconverter
designed to drive four MAIN LEDs and one high current
CAM LED for camera lighting. The LTC3210 requires only
four small ceramic capacitors and two current set resis-
tors to form a complete LED power supply and current
controller.
■
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 (8 Brightness Steps)
Built-in soft-start circuitry prevents excessive inrush cur-
rent 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.
■
■
■
■
■
■
64:1 Brightness Control Range for MAIN Display
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
The full-scale current through the LEDs is programmed
via external resistors. ENM and ENC are toggled to adjust
the LED currents via internal counters and DACs. The
part is shut down when both ENM and ENC are low for
150µs (typ).
■
■
■
U
APPLICATIO S
The charge pump optimizes efficiency based on the volt-
age 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 en-
ter dropout. The LTC3210 is available in a 3mm × 3mm
16-lead QFN package.
■
Multi-LED Light Supply for Cellphones/DSCs/PDAs
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Protected by U.S. Patents, including 6411531.
U
TYPICAL APPLICATIO
4-LED MAIN Display
Efficiency vs V Voltage
C2
C3
BAT
2.2µF
2.2µF
100
90
80
C1P C1M
V
BAT
C2P
C2M
MAIN
CAM
70
60
50
40
30
CPO
V
BAT
C1
2.2µF
C4
2.2µF
LTC3210
MLED1
MLED2
MLED3
MLED4
CLED
ENM
ENC
ENM
ENC
20
4 LEDs AT 9mA/LED
(TYP V AT 9mA = 3V, NICHIA NSCW100)
3210 TA01
F
10
T
A
= 25°C
RM
RC
GND
0
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4
(V)
30.1k
1%
24.3k
1%
V
BAT
3210 TA01b
3210f
1
LTC3210
U
W
U
W W U W
PACKAGE/ORDER I FOR ATIO
ABSOLUTE AXI U RATI GS
(Note 1)
TOP VIEW
V
, CPO to GND ........................................–0.3V to 6V
BAT
ENM, ENC ................................... –0.3V to (V + 0.3V)
BAT
16 15 14 13
I
I
I
(Note 2)........................................................600mA
CPO
MLED1-4
CLED
C1P
CPO
1
2
3
4
12 GND
11 CLED
.................................................................30mA
(Note 2) ......................................................450mA
17
ENM
ENC
RC
10
9
CPO Short-Circuit Duration.............................. Indefinite
Operating Temperature Range (Note 3) ...–40°C to 85°C
Storage Temperature Range...................–65°C to 125°C
MLED1
5
6
7
8
UD PACKAGE
16-LEAD (3mm × 3mm) PLASTIC QFN
= 125°C, θ = 68°C/W
T
JMAX
JA
EXPOSED PAD IS GND (PIN 17)
MUST BE SOLDERED TO PCB
ORDER PART NUMBER
UD PART MARKING
LBXH
LTC3210EUD
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS The
ENM = high, unless otherwise noted.
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25°C.V = 3.6V, C1 = C2 = C3 = C4 = 2.2µF, RM = 30.1k, RC = 24.3k,
A
BAT
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
●
V
Operating Voltage
Operating Current
2.9
4.5
V
BAT
I
I
I
I
= 0, 1x Mode, MLED LSB Setting
= 0, 1.5x Mode
= 0, 2x Mode
0.375
2.5
4.5
mA
mA
mA
VBAT
CPO
CPO
CPO
●
●
V
Shutdown Current
ENM = ENC = LOW
3
6
µA
BAT
MLED1, MLED2, MLED3, MLED4 Current
LED Current Ratio (I /I
)
I
= Full Scale
463
515
100
1
567
A/A
mV
%
MLED RM
MLED
LED Dropout Voltage
LED Current Matching
Mode Switch Threshold, I
= Full Scale
MLED
Any Two Outputs, I
= Full Scale
MLED
MLED Current, 3-Bit Exponential DAC
1 ENM Strobe (FS)
2 ENM Strobes
3 ENM Strobes
4 ENM Strobes
5 ENM Strobes
6 ENM Strobes
20
10
mA
mA
mA
mA
mA
mA
mA
5
2.5
1.25
0.625
0.312
7 ENM Strobes (FS/64)
3210f
2
LTC3210
ELECTRICAL CHARACTERISTICS
ENM = high, unless otherwise noted.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25°C.V = 3.6V, C1 = C2 = C3 = C4 = 2.2µF, RM = 30.1k, RC = 24.3k,
A
BAT
PARAMETER
CLED Current
CONDITIONS
MIN
TYP
MAX
UNITS
●
LED Current Ratio (I
/I
)
I
= Full Scale
6750
7500
500
8250
A/A
mV
CLED RC
CLED
LED Dropout Voltage
Mode Switch Threshold, I
= Full Scale
CLED
CLED Current, 3-Bit Linear DAC
1 ENC Strobe (FS)
7 ENC Strobes (FS/7)
380
54
mA
mA
Charge Pump (CPO)
1x Mode Output Voltage
1.5x Mode Output Voltage
2x Mode Output Voltage
1x Mode Output Impedance
1.5x Mode Output Impedance
2x Mode Output Impedance
CLOCK Frequency
I
I
I
= 0mA
= 0mA
= 0mA
V
V
V
CPO
CPO
CPO
BAT
4.55
5.05
0.5
V
Ω
Ω
V
V
= 3.4V, V
= 3.2V, V
= 4.6V (Note 4)
= 5.1V (Note 4)
3.15
3.95
0.8
BAT
BAT
CPO
Ω
CPO
MHz
ms
Mode Switching Delay
ENC, ENM
0.4
●
●
●
●
V
0.4
V
V
IL
V
1.4
10
–1
IH
I
IH
I
IL
ENM = ENC = 3.6V
ENM = ENC = 0V
15
20
1
µA
µA
ENC, ENM Timing
●
●
t
t
t
Minimum Pulse Width
60
50
ns
µs
PW
SD
EN
Low Time to Shutdown (ENC and ENM = Low)
150
150
250
250
Current Source Enable Time
(ENC or ENM = High) (Note 5)
50
µs
●
RM, RC
, V
●
●
V
1.16
1.20
1.24
70
V
RM RC
I
, I
RM RC
µA
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may become impaired.
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
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 4: 1.5x mode output impedance is defined as (1.5V – V )/I
.
BAT
CPO OUT
2x mode output impedance is defined as (2V – V )/I
.
BAT
CPO OUT
Note 5: If the part has been shut down then the initial enable time is about
100µs longer due to the bandgap enable time.
Note 3: The LTC3210E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C ambient
3210f
3
LTC3210
U W
TYPICAL PERFOR A CE CHARACTERISTICS
T = 25°C unless otherwise stated.
A
Dropout Time from Shutdown
Dropout Time When Enabled
1.5x CPO Ripple
V
= 3.6V
= 200mA
= 2.2µF
BAT
CPO
CPO
I
2X
2X
CPO
1V/DIV
CPO
1V/DIV
C
1.5X
1.5X
1X
1X
V
CPO
50mV/DIV
AC
COUPLED
EN
2V/DIV
ENC
2V/DIV
MODE
RESET
MODE
RESET
ENM = HIGH
500µs/DIV
250µs/DIV
500ns/DIV
3210 G01
3210 G02
3210 G03
1.5x Mode Charge Pump Open-Loop
Output Resistance vs Temperature
1x Mode Switch Resistance
vs Temperature
2x CPO Ripple
(1.5V – V )/I
BAT CPO CPO
0.70
0.65
3.8
3.6
I
= 200mA
CPO
V
= 3.6V
= 200mA
= 2.2µF
V
V
= 3V
= 4.2V
BAT
CPO
CPO
BAT
CPO
I
C
C2 = C3 = C4 = 2.2µF
3.4
3.2
3.0
2.8
2.6
2.4
V
CPO
0.60
0.55
20mV/DIV
AC
V
= 3.3V
BAT
COUPLED
V
= 3.6V
BAT
0.50
0.45
0.40
V
= 3.9V
10
BAT
500ns/DIV
3210 G04
–15
10
35
85
–40
–15
35
60
85
–40
60
TEMPERATURE (°C)
TEMPERATURE (˚C)
3210 G05
3210 G06
2x Mode Charge Pump Open-Loop
Output Resistance vs Temperature
2x Mode CPO Voltage
vs Load Current
1.5x Mode CPO Voltage
vs Load Current
(2V – V )/I
BAT
CPO CPO
5.2
5.1
5.0
4.9
4.8
4.7
4.6
4.5
4.4
4.3
4.2
4.6
4.4
4.8
4.6
C2 = C3 = C4 = 2.2µF
C2 = C3 = C4 = 2.2µF
V
V
= 3V
BAT
CPO
= 4.8V
C2 = C3 = C4 = 2.2µF
V
= 3.3V
V
BAT
V
= 3.6V
= 3.4V
BAT
BAT
BAT
4.2
4.0
3.8
3.6
3.4
3.2
V
= 3.5V
= 3.6V
4.4
4.2
V
= 3.5V
BAT
V
BAT
V
= 3.4V
BAT
V
= 3.3V
BAT
4.0
3.8
3.6
V
= 3.2V
BAT
V
= 3.2V
BAT
V
= 3.1V
BAT
V
= 3.1V
V
BAT
= 3V
200
V
= 3V
400
BAT
BAT
0
100
200
300
500
–15
10
35
85
–40
60
0
100
300
400
500
LOAD CURRENT (mA)
LOAD CURRENT (mA)
TEMPERATURE (˚C)
3210 G09
3210 G08
3210 G07
3210f
4
LTC3210
U W
TYPICAL PERFOR A CE CHARACTERISTICS
T = 25°C unless otherwise stated.
A
CLED Pin Dropout Voltage
vs CLED Pin Current
MLED Pin Dropout Voltage
vs MLED Pin Current
Oscillator Frequency
vs V Voltage
BAT
500
400
300
200
100
0
100
90
80
70
60
50
40
30
20
10
0
850
840
830
820
810
800
790
780
770
V
= 3.6V
BAT
V
= 3.6V
BAT
T
= 25°C
A
T
= 85°C
A
T
= –40°C
A
760
50 100 150 200 250 300 350 400
CLED PIN CURRENT (mA)
0
2
4
6
8
10 12 14 16 18 20
2.7
3.0
3.3
3.6
VOLTAGE (V)
4.5
3.9
4.2
MLED PIN CURRENT (mA)
V
BAT
3210 G10
3210 G11
3210 G12
V
Shutdown Current
BAT
1x Mode No Load V Current
1.5x Mode Supply Current vs I
CPO
BAT
BAT
vs V Voltage
vs V Voltage
(IV – 1.5I
)
BAT
BAT
CPO
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
20
15
10
5
800
780
760
740
720
700
680
660
640
620
600
V
= 3.6V
BAT
RM = 33.2k
RC = 24.3k
T
= 25°C
A
T
= –40°C
A
T
= 85°C
A
0
3.9
3.6
VOLTAGE (V)
4.5
2.7
3.0
3.3
V
4.2
2.7
3.0
3.6
3.9
4.2
4.5
0
100
200
300
400
500
3.3
V
VOLTAGE (V)
LOAD CURRENT (mA)
BAT
BAT
3210 G13
3210 G14
3210 G15
2x Mode Supply Current vs I
CLED Pin Current
vs CLED Pin Voltage
CPO
(IV – 2I
)
CPO
BAT
20
400
V
= 3.6V
V
= 3.6V
BAT
BAT
360
320
280
240
200
160
120
80
15
10
5
40
0
0
0
100
200
300
400
500
0
0.2
0.4
0.6
0.8
1
LOAD CURRENT (mA)
CLED PIN VOLTAGE (V)
3210 G16
3210 G17
3210f
5
LTC3210
U W
TYPICAL PERFOR A CE CHARACTERISTICS
T = 25°C unless otherwise stated.
A
MLED Pin Current
vs MLED Pin Voltage
CLED Current
vs ENC Strobe Pulses
22
20
18
16
14
12
10
8
400
V = 3.6V
BAT
RC = 24.3k
V
= 3.6V
BAT
350
300
250
200
150
100
50
6
4
2
0
0.00
0
0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20
MLED PIN VOLTAGE (V)
7
6
4
3
2
1
0.02
0
5
NUMBER OF ENC STROBE PULSES
3210 G18
3210 G19
MLED Current
vs ENM Strobe Pulses
Efficiency vs V Voltage
BAT
20
18
16
14
12
10
8
90
80
70
60
50
40
30
20
10
0
V
= 3.6V
BAT
RM = 33.2k
6
4
300mA LED CURRENT
(TYP V AT 300mA = 3.1V, AOT-2015HPW
F
2
T
A
= 25°C
0
0
6
5
4
3
2
1
7
2.9 3.05 3.2 3.35 3.5 3.65
4.4
3.8 3.95 4.1 4.25
NUMBER OF ENM STROBE PULSES
V
(V)
BAT
3210 G20
3210 G21
3210f
6
LTC3210
U
U
U
PI FU CTIO S
C1P, C2P, C1M, C2M (Pins 1, 16, 14, 13): Charge Pump
Flying Capacitor Pins. A 2.2µF X7R or X5R ceramic ca-
pacitor should be connected from C1P to C1M and C2P
to C2M.
is set via the ENM input, and the programming resistor
connected between RM and GND. Each of the four LED
outputs can be disabled by connecting the output directly
to CPO. A 10µA current will flow through each directly
connected LED output.
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.
RM, RC (Pins 8, 9): LED Current Programming Resistor
Pins. The RM and RC pins will servo to 1.2V. Resistors
connected between each of these pins and GND are used
to set the CLED and MLED current levels. Connecting
a resistor 12k or less will cause the LTC3210 to enter
overcurrent shutdown.
ENM, ENC (Pins 3, 10): Inputs. The ENM and ENC pins
are used to program the LED output currents. Each input
is strobed up to 7 times to decrement the internal 3-bit
DACs from full-scale to 1LSB. The counter will stop at
1 LSB if the strobing continues. The pin must be held
high after the final desired positive strobe edge. The data
is transferred after a 150µs (typ) delay. Holding the ENM
or ENC pin low will set the LED current to 0 and will reset
the counter after 150µs (typ). 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 in shutdown mode.
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.
V
(Pin15):Supplyvoltage.Thispinshouldbebypassed
BAT
with a 2.2µF, or greater low ESR ceramic capacitor.
MLED1, MLED2, MLED3, MLED4 (Pins 4, 5, 6, 7):
Outputs. MLED1 to MLED4 are the MAIN current source
outputs. The LEDs are connected between CPO (anodes)
and MLED1-4 (cathodes). The current to each LED output
Exposed Pad (Pin 17): This pad should be connected
directly to a low impedance ground plane for optimal
thermal and electrical performance.
3210f
7
LTC3210
W
BLOCK DIAGRA
C1P
1
C1M
14
C2P
16
C2M
13
800kHz
OSCILLATOR
12 GND
15
V
2
CPO
BAT
CHARGE PUMP
–
+
ENABLE CP
+
–
1.215V
4
5
6
7
MLED1
MLED2
MLED3
MLED4
TIMER
ENABLE MAIN
500Ω
8
3
RM
3-BIT
DOWN
COUNTER
3-BIT
EXPONENTIAL
DAC
MLED
CURRENT
SOURCES
4
ENM
250k
+
–
1.215V
TIMER
TIMER
SHUTDOWN
ENABLE CAM
3-BIT
500Ω
RC
9
3-BIT
DOWN
COUNTER
CLED
CURRENT
SOURCE
10
11 CLED
LINEAR
DAC
ENC
250k
3210 BD
3210f
8
LTC3210
U
OPERATIO
Power Management
current is achieved ENM is stopped high. The output cur-
rent 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 LTC3210 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, V is
BAT
connected directly to CPO. This mode provides maximum
efficiencyandminimumnoise. TheLTC3210willremainin
1x mode until an LED current source drops out. Dropout
occurs when a current source voltage becomes too low
fortheprogrammedcurrenttobesupplied. Whendropout
is detected, the LTC3210 will switch into 1.5x mode. The
CPO voltage will then start to increase and will attempt
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 posi-
tive 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
currentissetto0whenENCistoggledlowaftertheoutput
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.
to reach 1.5x V
up to 4.6V. Any subsequent dropout
BAT
will cause the part to enter the 2x mode. The CPO voltage
will attempt to reach 2x V up to 5.1V. The part will be
BAT
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 V to minimize
inputcurrentrippleandCPOvoltageripple.In1.5xmodethe
flyingcapacitorsarechargedinseriesduringthefirstclock
phase and stacked in parallel on V
BAT
The full-scale output current is calculated as follows:
MLED full-scale output current
during the second
BAT
phase.Thissequenceofcharginganddischargingtheflying
capacitors continues at a constant frequency of 800kHz.
=
(
1.215V/(RM + 500)
CLED full-scale output current
1.215V/(RC + 500) • 7500
) • 515
LED Current Control
=
(
)
TheMLEDcurrentsaredeliveredbythefourprogrammable
current sources. Eight current settings (0mA to 20mA,
RM = 30.1k) are available by strobing the ENM pin. Each
positive strobe edge decrements a 3-bit down counter
which controls an exponential DAC. When the desired
When both ENM and ENC are held low for 150µs (typ)
the part will go into shutdown. See Figure 1 for timing
information.
ENC resets the mode to 1x on a falling edge.
t
≥
t
t
SD 150µs (TYP)
PW 60ns
EN 150µs (TYP)
ENM
OR ENC
PROGRAMMED
CURRENT
LED
CURRENT
ENM = ENC = LOW
SHUTDOWN
3210 F01
Figure 1. Current Programming and Shutdown Timing Diagram
3210f
9
LTC3210
U
OPERATIO
Soft-Start
However, for a given R , the amount of current available
OL
will be directly proportional to the advantage voltage of
Initially, when the part is in shutdown, a weak switch
1.5V
– CPO for 1.5x mode and 2V
– CPO for 2x
BAT
BAT
connects V to CPO. This allows V to slowly charge
BAT
BAT
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 avail-
able strength.
the CPO output capacitor to prevent large charging
currents.
The LTC3210 also employs a soft-start feature on its
charge pump to prevent excessive inrush current and
supplydroopwhenswitchingintothestep-upmodes. 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.
FromFigure2,for1.5xmodetheavailablecurrentisgivenby:
(1.5VBAT – VCPO
ROL
)
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.
For 2x mode, the available current is given by:
(2VBAT – VCPO
ROL
)
IOUT
=
Notice that the advantage voltage in this case is 3.1V • 2
– 3.8V – 0.1V = 2.3V. R is higher in 2x mode but a sig-
OL
Table 1. Charge Pump Output Regulation Voltages
nificant overall increase in available current is achieved.
Charge Pump Mode
Regulated V
4.55V
CPO
Typical values of R as a function of temperature are
OL
1.5x
2x
shown in Figure 3 and Figure 4.
5.05V
Shutdown Current
WhentheLTC3210operatesineither1.5xmodeor2xmode,
thechargepumpcanbemodeledasaThevenin-equivalent
circuit to determine the amount of current available from
the effective input voltage and effective open-loop output
In shutdown mode all the circuitry is turned off and the
LTC3210 draws a very low current from the V supply.
BAT
Furthermore, CPO is weakly connected to V . The
BAT
LTC3210 enters shutdown mode when both the ENM
and ENC pins are brought low for 150µs (typ). ENM and
ENC have 250k internal pull down resistors to define
the shutdown state when the drivers are in a high imped-
ance state.
resistance, R (Figure 2).
OL
R
is dependent on a number of factors including the
OL
switching term, 1/(2f
• C ), internal switch resis-
OSC
FLY
tances and the nonoverlap period of the switching circuit.
R
OL
+
+
CPO
1.5V
OR 2V
BAT
BAT
–
–
Figure 2. Charge Pump Thevenin-Equivalent Circuit
3210f
10
LTC3210
U
OPERATIO
Thermal Protection
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 LTC3210 has built-in overtemperature protection.
At internal die temperatures of around 150°C thermal
shutdown 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.
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
Mode Switching
connect V and CPO in 1x mode until the voltage at the
BAT
CPO pin has decayed to less than or equal to the voltage
The LTC3210 will automatically switch from 1x mode
to 1.5x mode and subsequently to 2x mode whenever
at the V pin.
BAT
3.8
4.6
4.4
V
V
= 3V
V
V
= 3V
BAT
CPO
BAT
CPO
= 4.2V
= 4.8V
3.6
C2 = C3 = C4 = 2.2µF
C2 = C3 = C4 = 2.2µF
3.4
3.2
3.0
2.8
2.6
2.4
4.2
4.0
3.8
3.6
3.4
3.2
–15
10
35
85
–15
10
35
85
–40
60
–40
60
TEMPERATURE (˚C)
TEMPERATURE (˚C)
3210 F03
3210 F04
Figure 3. Typical 1.5x R vs Temperature
Figure 4. Typical 2x R vs Temperature
OL
OL
3210f
11
LTC3210
U
W U U
APPLICATIO S I FOR ATIO
V
, CPO Capacitor Selection
In addition, excessive output capacitor ESR >100mΩ will
tend to degrade the loop stability. Multilayer ceramic chip
capacitorstypicallyhaveexceptionalESRperformanceand
when combined with a tight board layout will result in very
BAT
ThestyleandvalueofthecapacitorsusedwiththeLTC3210
determineseveralimportantparameterssuchasregulator
controlloopstability,outputripple,chargepumpstrength
and minimum start-up time.
good stability. As the value of C
controls the amount of
controls the amount of
CPO
output ripple, the value of CV
BAT
To reduce noise and ripple, it is recommended that low
equivalentseriesresistance(ESR)ceramiccapacitorsare
used for both CV
capacitors are not recommended due to high ESR.
ripple present at the input pin(V ). The LTC3210’s input
BAT
currentwillberelativelyconstantwhilethechargepumpis
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 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.
and C . Tantalum and aluminum
BAT
CPO
The value of C directly controls the amount of output
ripple for a given load current. Increasing the size of C
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:
CPO
CPO
IOUT
(3f0SC •CCPO
VRIPPLE(P−P)
=
)
(3)
Wheref istheLTC3210oscillatorfrequencyortypically
800kHz and C
OSC
is the output storage capacitor.
CPO
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 signifi-
cantly affect the stability of the LTC3210. As shown in the
Block Diagram, the LTC3210 uses 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.
V
BAT
LTC3210
GND
3210 F05
Figure 5. 10nH Inductor Used for Input Noise
Reduction (Approximately 1cm of Board Trace)
3210f
12
LTC3210
U
W U U
APPLICATIO S I FOR ATIO
Flying Capacitor Selection
Layout Considerations and Noise
Warning: Polarized capacitors such as tantalum or
aluminum should never be used for the flying capaci-
tors since their voltage can reverse upon start-up of the
LTC3210. Ceramic capacitors should always be used for
the flying capacitors.
Due to the high switching frequency and the transient
currents produced by the LTC3210, 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
losetheircapacitancewithhighertemperatureandvoltage
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
mayalsohaveaverypoorvoltagecoefficientcausingthem
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
ratherthancomparingthespecifiedcapacitancevalue.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.
Magneticfieldscanalsobegeneratediftheflyingcapacitors
are not close to the LTC3210 (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 pins. For a high quality
AC ground, it should be returned to a solid ground plane
that extends all the way to the LTC3210.
The following guidelines should be followed when design-
ing a PCB layout for the LTC3210:
• The exposed pad should be soldered to a large copper
planethatisconnectedtoasolid,lowimpedanceground
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.
Table 2 shows a list of ceramic capacitor manufacturers
and how to contact them:
• V , CPO traces must be wide to minimize inductance
BAT
and handle high currents.
Table 2. Recommended Capacitor Vendors
• LED pads must be large and connected to other layers
of metal to ensure proper heat sinking.
AVX
www.avxcorp.com
www.kemet.com
www.murata.com
www.t-yuden.com
www.vishay.com
Kemet
• RM and RC pins are sensitive to noise and capacitance.
The resistors should be placed near the part with mini-
mum line width.
Murata
Taiyo Yuden
Vishay
3210f
13
LTC3210
U
W U U
APPLICATIO S I FOR ATIO
Power Efficiency
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:
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:
PLED
(VLED •ILED
(VBAT •(1.5)•ILED) (1.5•VBAT
)
VLED
η
IDEAL
=
=
=
PIN
)
PLED
η =
PIN
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:
The efficiency of the LTC3210 depends upon the mode in
which it is operating. Recall that the LTC3210 operates
as a pass switch, connecting V
is detected at the LED pin. This feature provides the op-
timum efficiency available for a given input voltage and
LED forward voltage. When it is operating as a switch, the
efficiency is approximated by:
to CPO, until dropout
BAT
PLED
(VLED •ILED
)
VLED
η
IDEAL
=
=
=
PIN (VBAT •(2)•ILED) (2•VBAT
Thermal Management
)
For higher input voltages and maximum output current,
therecanbesubstantialpowerdissipationintheLTC3210.
Ifthejunctiontemperatureincreasesaboveapproximately
150°C the thermal shut down circuitry will automatically
deactivate the output current sources and charge pump.
Toreducemaximumjunctiontemperature,agoodthermal
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.
PLED
PIN
(VLED •ILED
(VBAT •IBAT ) VBAT
)
VLED
η =
=
=
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 is negligible and the expression above is
valid.
Once dropout is detected at any LED pin, the LTC3210
enables the charge pump in 1.5x mode.
3210f
14
LTC3210
U
PACKAGE DESCRIPTIO
UD Package
16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691)
0.70 0.05
3.50 0.05
2.10 0.05
1.45 0.05
(4 SIDES)
PACKAGE OUTLINE
0.25 0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.20 TYP
OR 0.25 × 45° CHAMFER
R = 0.115
TYP
0.75 0.05
3.00 0.10
(4 SIDES)
15 16
PIN 1
TOP MARK
(NOTE 6)
0.40 0.10
1
2
1.45 0.10
(4-SIDES)
(UD16) QFN 0904
0.200 REF
0.25 0.05
0.50 BSC
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
3210f
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC3210
U
TYPICAL APPLICATIO
3-LED MAIN, One LED Camera
C2
2.2µF
C3
2.2µF
MAIN
CAM
C1P C1M
V
BAT
C2P
C2M
CPO
V
BAT
C4
2.2µF
C1
2.2µF
LTC3210
MLED1
MLED2
MLED3
MLED4
CLED
MLED4 DISABLED
ENM
ENC
ENM
ENC
3210 TA02
RM
RC
GND
30.1k
1%
24.3k
1%
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3210f
LT 0106 • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
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