LTC3452EUF [Linear]
Synchronous Buck-Boost MAIN/CAMERA White LED Driver; 同步降压 - 升压型主/相机白光LED驱动器
| 型号： | LTC3452EUF |
| 厂家： | 
Linear |
| 描述： | Synchronous Buck-Boost MAIN/CAMERA White LED Driver |
| 文件： | 总16页 (文件大小：271K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3452
Synchronous Buck-Boost
MAIN/CAMERA White LED Driver
U
FEATURES
DESCRIPTIO
The LTC®3452 is a synchronous buck-boost DC/DC con-
verter optimized for driving two banks of white LEDs from
a single Li-Ion battery input. Five parallel LEDs can be
driven at up to 25mA each in the low power LED bank,
while two LEDs can be driven at up to 150mA each (or a
single LED at 300mA) in the high power LED bank. The
regulator operates in either synchronous buck, synchro-
nous boost or buck-boost mode, depending on input
voltage and LED maximum forward voltage. Optimum
efficiency is achieved by sensing which LED requires the
largest forward voltage drop at its programmed current,
andregulatingthecommonoutputrailforlowestdropout.
Efficiency of 85% can be achieved over the entire usable
range of a Li-Ion battery (2.7V to 4.2V).
■
High Efficiency:
≥
85% Over Entire Li-Ion Battery
Range
■
Wide VIN Range: 2.7V to 5.5V
Independent MAIN/CAMERA Current Control
Up to 425mA Continuous Output Current
Internal Soft-Start
Open/Shorted LED Protection
PWM Brightness Control
■
■
■
■
■
■
■
■
■
■
LED Current Matching Typically <2.5%
Constant Frequency 1MHz Operation
Low Shutdown Current: 6.5µA
Overtemperature Protection
Small Thermally Enhanced 20-Lead
(4mm × 4mm) QUFN Package
Maximum LED current for each LED display is program-
mable with a single external resistor. Dual enable pins
allow for PWM brightness control in the low power bank
and independent on/off control for the high current bank
(optimal for LED camera flash). In shutdown, the supply
current is only 6.5µA.
APPLICATIO S
■
Cell Phones
■
Digital Cameras
■
PDAs
Portable Devices
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
A high constant operating frequency of 1MHz allows the
use of a small external inductor. The LTC3452 is offered
in a low profile (0.75mm) thermally enhanced 20-lead
(4mm × 4mm) QFN package.
U
TYPICAL APPLICATIO
5 × 20mA White LED Display + 200mA Camera Light Driver
L
4.7µH
V
IN
Torch and Flash Mode Efficiency
SINGLE
Li-Ion CELL
2.7V TO 4.2V
+
4.7µF
2.2µF
D1
95
V
IN
PV
IN
SW1
SW2
V
OUT
CAM
T
= 25°C
A
(V
OUT
– V
) • I
LEDx LEDx
93
91
89
87
85
83
81
79
77
75
LED
EFFICIENCY = Σ
H1
H2
200mA
D2
EN
H
V
• I
IN IN
LED
I
SETH
6.19k
TORCH MODE AT 100mA
FLASH MODE AT 200mA
0mA TO
20mA
D3
LED
LED
LED
LED
LED
L1
L2
L3
L4
L5
D4
0mA TO
20mA
1MHz
V
C
D5
BUCK/BOOST
0mA TO
20mA
0.1µF
0mA TO
20mA
D6
EN
L
0mA TO
20mA
LTC3452
I
SETL
2.7
3.5 3.9 4.3 4.7 5.1 5.5
(V)
3.1
V
IN
10.2k
3452 TA01a
MAIN DISPLAY LED BACKLIGHT
3452 TA01b
GND
GND
PGND
EXPOSED PAD
D1: AOT 2015
D2 TO D6: NICHIA NSCW100
L: COILCRAFT DO3314-472
3452f
1
LTC3452
W W U W
U W
U
ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Note 1)
TOP VIEW
VIN, PVIN, SW1, SW2, VOUT Voltage ........... –0.3V to 6V
LEDL1 to LEDL5 Voltage ... –0.3V to (VOUT + 0.3V) or 6V
LEDH1, LEDH2 Voltage ..... –0.3V to (VOUT + 0.3V) or 6V
VC, ENL, ENH,
ISETL, ISETH Voltage............ –0.3V to (VIN + 0.3V) or 6V
LEDL1 to LEDL5 Current ....................................... 50mA
LEDH1, LEDH2 Current ....................................... 250mA
Operating Temperature Range (Note 2) .. –40°C to 85°C
Junction Temperature (Note 3)............................ 125°C
Storage Temperature Range ................ –65°C to 125°C
20 19 18 17 16
V
V
1
2
3
4
5
15
14
13
12
11
C
IN
EN
EN
H
L
I
I
21
8
SETH
LED
SETL
LED
H2
L1
L2
GND
LED
6
7
9 10
UF PACKAGE
20-LEAD (4mm × 4mm) PLASTIC QFN
TJMAX = 125°C, θJA = 40°C/W
EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LTC3452EUF
Order Options Tape and Reel: Add #TR
UF PART MARKING
3452
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
IN
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are T = 25°C.
A
IN
V
= PV = V
OUT
= 3.6V unless otherwise specified. (Note 2)
CONDITIONS
PARAMETER
MIN
TYP
MAX
UNITS
Input Supply Voltage (V )
●
2.7
5.5
V
IN
Input DC Supply Current
Normal Operation
Shutdown
2.7V ≤ V ≤ 5.5V, R
= R
= 51.1k, I = 0 (Note 4)
LEDx
= 0V
0.6
6.5
3
1
18
5
mA
µA
µA
IN
ISETL
ISETH
2.7V ≤ V ≤ 5.5V, V
= V
IN
ENL
ENH
UVLO
V
< UVLO Threshold
IN
Undervoltage Lockout Threshold
V
V
Rising
Falling
●
2.0
1.87
2.3
V
V
IN
IN
1.6
0.2
EN DC Threshold for Normal Operation (V ) 2.7V ≤ V ≤ 5.5V, V
Rising
Falling
●
●
0.54
0.52
1.2
V
V
L,H
IH
IN
ENL,H
EN DC Threshold for Shutdown (I
= 0)
2.7V ≤ V ≤ 5.5V, V
IN
L,H
LEDx
ENL,H
(V )
IL
EN Input Current (I , I )
2.7V ≤ V ≤ 5.5V
●
●
–1
10
1
µA
kHz
L,H
IH IL
IN
EN PWM Frequency
L
2.7V ≤ V ≤ 5.5V (Note 5)
IN
I
Servo Voltage
R
= R = 20k
ISETH
788
780
800
800
812
812
mV
mV
SETL,H
ISETL
●
●
LED Output Current Ratio (I
/I
)
I
= 100mA, V = 300mV
LEDHx
730
714
768
768
806
806
mA/mA
mA/mA
Hx
LEDHx SETH
LEDHx
LED Output Current Matching
(Max – Min)/[(Max + Min)/2] • 100%, I
= 100mA,
1
6
%
Hx
LEDHx
V
= 300mV, 2.7V ≤ V ≤ 5.5V
LEDHx
IN
LED Pin Voltage
I
= 100mA
250
mV
Hx
LEDHx
3452f
2
LTC3452
ELECTRICAL CHARACTERISTICS
The
IN
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are T = 25°C.
A
IN
V
= PV = V
OUT
= 3.6V unless otherwise specified. (Note 2)
CONDITIONS
PARAMETER
MIN
TYP
MAX
UNITS
LED Output Current Ratio (I
(Note 6)
/I
)
I
= 20mA, V
= 300mV
LEDLx
Lx
LEDLx SETL
LEDLx|MAX
PWM Duty Cycle = 6%
PWM Duty Cycle = 19%
PWM Duty Cycle = 31%
PWM Duty Cycle = 44%
PWM Duty Cycle = 56%
PWM Duty Cycle = 69%
PWM Duty Cycle = 81%
PWM Duty Cycle = 94%
1.8
1.75
2
2
2.16
2.21
mA/mA
mA/mA
●
●
●
●
●
●
●
●
3.66
3.56
4
4
4.28
4.38
mA/mA
mA/mA
7.32
7.12
8
8
8.56
8.76
mA/mA
mA/mA
14.72
14.32
16
16
17.04
17.44
mA/mA
mA/mA
29.44
28.64
32
32
33.92
34.56
mA/mA
mA/mA
58.88
57.92
64
64
67.2
68.16
mA/mA
mA/mA
117.12
114.56
128
128
134.4
137.6
mA/mA
mA/mA
234.24
229.12
256
245
268.8
272.64
mA/mA
mA/mA
LED Output Current Matching
(Max – Min)/[(Max + Min)/2] • 100%, I
= 20mA,
2.5
8
%
Lx
LEDLx
V
= 300mV
LEDLx
LED Pin Voltage
I
= 20mA
130
4.5
mV
V
Lx
LEDLx
Regulated Maximum V
V
= V = 0V
LEDHy
●
4.35
4.75
OUT
LEDLx
PMOS Switch R
Switches A and D at 100mA
Switches B and C at 100mA
Switch A
210
205
1600
200
mΩ
mΩ
mA
mA
µA
µA
MHz
µs
ON
NMOS Switch R
ON
Forward Current Limit
Reverse Current Limit
PMOS Switch Leakage
NMOS Switch Leakage
Oscillator Frequency
Soft-Start Time
1000
2400
Switch D
Switches A and D
Switches B and C
–1
–1
1
1
0.9
1
1.1
650
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 3: T is calculated from the ambient temperature T and power
J A
dissipation P according to the following formula:
D
T = T + (P • θ °C/W).
J
A
D
JA
Note 4: Dynamic supply current is higher due to the gate charge being
Note 2: The LTC3452E is guaranteed to meet specifications from 0°C to
70°C. Specifications over the –40°C to 85°C operating temperature range
are assured by design, characterization and correlation with statistical
process controls.
delivered at the switching frequency.
Note 5: Do not exceed 50kHz PWM frequency in the application.
Note 6: This parameter is tested in a setup which forces conditions
equivalent to those programmed by the indicated duty cycle.
3452f
3
LTC3452
TYPICAL PERFOR A CE CHARACTERISTICS
U W
Undervoltage Lockout Threshold
vs Temperature
Shutdown Current vs Temperature
Shutdown Current vs V
IN
12
10
8
20
18
16
14
12
10
8
2.5
2.3
T
= 25°C
A
V
V
= 5.5V
= 4.2V
2.1
IN
V
IN
RISING
6
IN
1.9
1.7
1.5
4
V
IN
FALLING
6
4
V
= 3.6V
2
IN
V
= 2.7V
IN
2
0
0
4.3
(V)
5.1 5.5
2.7 3.1 3.5 3.9
V
4.7
–55 –35 –15
5
25 45 65
85 105
125
25 45
TEMPERATURE (°C)
–55 –35 –15
5
65 85 105 125
TEMPERATURE (°C)
IN
3452 G02
3452 G03
3452 G01
I
Servo Voltage
SETL,H
vs Temperature
Enable Thresholds vs Temperature
Enable Thresholds vs V
IN
1000
900
800
700
600
500
400
300
200
1200
1100
1000
900
800
700
600
500
400
300
200
812
808
804
800
796
792
788
784
780
T
= 25°C
V
R
R
= 3.6V
V
= 3.6V
A
IN
IN
= 10.2k
ISETL
ISETH
= 4.99k
V
IH
V
IL
V
IH
V
IL
2.7
3.5 3.9 4.3
(V)
4.7 5.1 5.5
3.1
25 45
5
TEMPERATURE (°C)
–55 –35 –15
5
25 45 65 85 105 125
TEMPERATURE (°C)
–55 –35 –15
65 85 105 125
V
IN
3452 G05
3452 G04
3452 G06
Maximum Regulated V
vs Temperature
OUT
I
Servo Voltage vs V
SETL,H
IN
4.60
4.58
4.56
4.54
4.52
4.50
4.48
4.46
4.44
4.42
4.40
812
T
= 25°C
V
= 3.6V
IN
A
808
804
800
796
792
788
784
780
3.1
3.5
4.3 4.7 5.1 5.5
(V)
–55 –35 –15
5
45
85 105 125
2.7
3.9
25
65
TEMPERATURE (°C)
V
IN
3452 G07
3452 G08
3452f
4
LTC3452
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
vs Temperature
PMOS R
vs Temperature
NMOS R
vs Temperature
DS(ON)
DS(ON)
1050
1040
1030
1020
1010
1000
990
325
300
275
250
225
200
175
150
125
325
300
275
250
225
200
175
150
125
V
= 3V
OUT
V
= 2.7V
IN
V
= 5.5V
IN
V
= 3.6V
V
= 2.7V
IN
IN
V
= 4.2V
IN
V
= 3.6V
IN
V
= 3.6V
IN
V
= 5.5V
IN
V
= 5.5V
IN
V
= 4.2V
IN
980
V
= 4.2V
IN
V
= 2.7V
IN
970
960
950
25 45
TEMPERATURE (°C)
85
105 125
25 45
TEMPERATURE (°C)
–55 –35 –15
5
65 85 105 125
–55 –35 –15
5
25 45 65
–55 –35 –15
5
65 85 105 125
TEMPERATURE (°C)
3452 G11
3452 G12
3452 G10
Output Voltage Ripple
(Front Page Application)
Start-Up Transient
CH1, VOUT
1V/DIV
CH2, ILED
300mA FINAL VALUE
CH3, ENH
1V/DIV
3452 G14
VIN = 3.6V
ILEDH = 300mA
3452 G13
VIN = 3V
V
OUT = 3.1V
ILED = 100mA
3452f
5
LTC3452
U
U
U
PI FU CTIO S
VIN (Pin 1): Signal Voltage Input Supply Pin (2.7V ≤ VIN ≤
5.5V). Recommended bypass capacitor to GND is 2.2µF
ceramic or larger. Connect to PVIN (Pin 20).
ISETH (Pin 13): High Power LED Bank Current Program-
ming Pin. A resistor to ground programs each high power
bank current source output to ILEDHx = 768(0.8V/RISETH).
Enabled by ENH (Pin 14).
ENL (Pin2):EnableInputPinandPWMBrightnessControl
for Low Power LED Bank. Active high. For constant IMAXL
operation, connect the ENL pin to VIN (or any voltage
>1.2V). For ENL voltage <0.2V, all low power bank LED
current source outputs are Hi-Z (if both ENL and ENH are
<0.2V, thepartisinshutdownandtheinputsupplycurrent
drops to ~6µA). For brightness control between zero
currentandIMAXL,drivetheENL pinwithaPWMwaveform
of frequency ≥10kHz. The low power LED bank currents
will be equal to a percentage of IMAXL as given in Table 1.
The ENL pin is high impedance and should not be floated.
ENH (Pin 14): Enable Input Pin for High Power LED Bank.
Activehigh. TheENH pinishighimpedanceandshouldnot
be floated.
VC (Pin 15): Compensation Point for the Internal Error
AmplifierOutput.Recommendedcompensationcapacitor
to GND is 0.1µF ceramic or larger.
VOUT (Pin 16): Buck-Boost Output Pin. Recommended
bypass capacitor to GND is 4.7µF ceramic.
SW2 (Pin 17): Switching Node Pin. Connected to internal
power switches C and D. External inductor connects
between SW1 and SW2. Recommended value is 4.7µH.
ISETL (Pin 3): Low Power LED Bank Current Programming
Pin. A resistor to ground programs each low power bank
current source output maximum to ILEDLx|MAX = 256 •
(0.8V/RISETL). Enabled by ENL (Pin 2). PWM brightness
control also via ENL.
PGND (Pin 18): Power Ground Pin. Connect to GND (Pins
9 and 11).
SW1 (Pin 19): Switching Node Pin. Connected to internal
power switches A and B. External inductor connects
between SW1 and SW2. Recommended value is 4.7µH.
LEDL1 to LEDL5 (Pins 4 to 8): Individual Low Dropout
Current Source Outputs for Low Power LED Bank Current
Biasing. Connect each low power LED between VOUT and
an individual LEDLx pin. Unused LEDLx outputs should be
PVIN (Pin20):PowerVoltageInputSupplyPin. Connectto
VIN (Pin 1).
connected to VOUT
.
ExposedPad (Pin21):HeatSinkGround.ConnecttoGND
(Pins 9 and 11) and solder to PCB ground for electrical
contact and rated thermal performance.
GND (Pins 9 and 11): Signal Ground Pins. Connect
together and to PGND (Pin 18) and Exposed Pad ground
(Pin 21).
LEDH1, LEDH2 (Pins 10, 12): Individual Low Dropout
Current Source Outputs for High Power LED Bank Current
Biasing. Connect each high power LED between VOUT and
an individual LEDHx pin. Unused LEDHx outputs should be
connected to VOUT
.
3452f
6
LTC3452
W
BLOCK DIAGRA
V
IN
V
OUT
2.7V TO 5.5V
V
IN
PV
IN
SW1
19
SW2
17
V
OUT
1
20
16
4
5
6
7
8
UNDERVOLTAGE
LOCKOUT
UV
SWITCH
A
SWITCH
LED
LED
LED
LED
L1
L2
L3
L4
LED
D
DETECT
SWITCH
B
SWITCH
C
OVERTEMPERATURE
PROTECTION
OT
GATE
DRIVERS
AND
LED
DETECT
LOW
ANTI-CROSS-
CONDUCTION
FORWARD
CURRENT
LIMIT
REVERSE
CURRENT
LIMIT
BANDGAP
REFERENCE
POWER
LED
1.23V
+
–
+
–
BANK
LED
DETECT
200mA
1600mA
AB PWM
COMPARATOR
CD PWM
COMPARATOR
LOGIC
LED
DETECT
+
–
+
–
OT
UV
LED
L5
LED
DETECT
1MHz
OSCILLATOR
V
C
15
1.23V
MAIN
ERROR AMP
SAFETY
ERROR AMP
V
BIAS
V
OUT
–
+
–
+
327k
V
FB
123k
SOFT-START
CLAMP
1.23V
LOW POWER
LED CURRENT
SETTING AMP
I
MAXL
256
800mV
+
8 LEVELS
I
SETL
EXPONENTIAL
BRIGHTNESS
CONTROL
3
–
10
12
R
ISETL
SDL
HIGH
POWER
LED
LED
LED
SDL
SDH
H1
LED
DETECT
EN
2
L
SHUTDOWN
CIRCUIT
BANK
SHUTDOWN
EN
H
14
HIGH POWER
LED CURRENT
SETTING AMP
LED
DETECT
H2
800mV
+
I
MAXH
768
I
SETH
13
–
R
ISETH
SDH
9
11
18
21
3452 BD
GND
GND
PGND
EXPOSED
PAD
3452f
7
LTC3452
U
OPERATIO
Buck-Boost DC-DC Converter
Buck Mode (VIN > VOUT)
The LTC3452 employs an LTC proprietary buck-boost
DC/DC converter to generate the output voltage required
to drive the LEDs. This architecture permits high-effi-
ciency, low noise operation at input voltages above, below
or equal to the output voltage by properly phasing four
internal power switches. The error amp output voltage on
theVC pindeterminesthedutycycleoftheswitches. Since
the VC pin is a filtered signal, it provides rejection of
frequencies well below the factory trimmed switching
frequency of 1MHz. The low RDS(ON), low gate charge
synchronousswitchesprovidehighfrequencypulsewidth
modulation control at high efficiency. Schottky diodes
across synchronous rectifier switch B and synchronous
rectifier switch D are not required, but if used, do provide
a lower voltage drop during the break-before-make time
(typically 20ns), which improves peak efficiency by typi-
cally 1% to 2% at higher loads.
Inbuckmode,switchDisalwaysonandswitchCisalways
off. Referring to Figure 2, when the control voltage VC is
above voltage V1, switch A begins to turn on each cycle.
During the off time of switch A, synchronous rectifier
switch B turns on for the remainder of the cycle. Switches
A and B will alternate conducting similar to a typical
synchronous buck regulator. As the control voltage in-
creases, the duty cycle of switch A increases until the
maximum duty cycle of the converter in buck mode
reaches DCBUCK|max given by:
DCBUCK|max = 100% – DC4SW
where DC4SW equals the duty cycle in % of the “four
switch” range.
DC4SW = (150ns • f) • 100%
where f is the operating frequency in Hz.
Beyond this point the “four switch” or buck-boost region
is reached.
Figure 1 shows a simplified diagram of how the four
internal power switches are connected to the inductor, VIN
= PVIN, VOUT and GND. Figure 2 shows the regions of
operation of the buck-boost as a function of the control
voltage VC. The output switches are properly phased so
transitions between regions of operation are continuous,
filtered and transparent to the user. When VIN approaches
VOUT, thebuck-boostregionisreachedwheretheconduc-
tion time of the four switch region is typically 150ns.
Referring to Figures 1 and 2, the various regions of
operation encountered as VC increases will now be
described.
Buck-Boost or Four-Switch Mode (VIN ≈ VOUT
)
Referring to Figure 2, when the control voltage VC is above
voltage V2, switch pair AD continue to operate for duty
cycle DCBUCK|max, and the switch pair AC begins to phase
in. As switch pair AC phases in, switch pair BD phases out
accordingly. When the VC voltage reaches the edge of the
buck-boostrangeatvoltageV3, switchpairACcompletely
phases out switch pair BD and the boost region begins at
75%
D
MAX
BOOST
V4 (≈2.1V)
A ON, B OFF
PV
V
IN
OUT
BOOST REGION
PWM CD SWITCHES
20
16
D
MIN
BOOST
V3 (≈1.65V)
V2 (≈1.55V)
BUCK/BOOST REGION
FOUR SWITCH PWM
PMOS A
PMOS D
NMOS C
D
MAX
BUCK
SW1
19
SW2
17
D ON, C OFF
PWM AB SWITCHES
BUCK REGION
V1 (≈0.9V)
0%
NMOS B
DUTY
CYCLE
CONTROL
VOLTAGE, V
3452 F02
3452 F01
C
Figure 1. Simplified Diagram of Internal Power Switches
Figure 2. Switch Control vs Control Voltage, V
C
3452f
8
LTC3452
U
OPERATIO
duty cycle DC4SW. The input voltage VIN where the four
Overtemperature Protection
switch region begins is given by:
If the junction temperature of the LTC3452 exceeds 130°C
for any reason, all four switches are shut off immediately.
The overtemperature protection circuit has a typical hys-
teresis of 11°C.
VOUT
1– 150ns • f
V =
IN
(
)
and the input voltage VIN where the four switch region
ends is given by:
Soft-Start
The LTC3452 includes an internally fixed soft-start which
is active when powering up or coming out of shutdown.
The soft-start works by clamping the voltage on the VC
node and gradually releasing it such that it requires 650µs
to linearly slew from 0.9V to 2.1V. This has the effect of
limiting the rate of duty cycle change as VC transitions
from the buck region through the buck-boost region into
the boost region. Once the soft-start times out, it can only
be reset by entering shutdown, or by an undervoltage or
overtemperature condition.
V
IN = VOUT • 1– 150ns • f
(
)
]
[
Boost Mode (VIN < VOUT
)
In boost mode, switch A is always on and switch B is
always off. Referring to Figure 2, when the control voltage
VC is above voltage V3, switches C and D will alternate
conducting similar to a typical synchronous boost regula-
tor. The maximum duty cycle of the converter is limited to
88% typical and is reached when VC is above V4.
Main Error Amp
Forward Current Limit
The main error amplifier is a transconductance amplifier
with source and sink capability. The output of the main
erroramplifierdrivesacapacitortoGNDattheVC pin. This
capacitor sets the dominant pole for the regulation loop.
(SeetheApplicationsInformationsectionforselectingthe
capacitor value.) The error amp gets its feedback signal
fromaproprietarycircuitwhichmonitorsall7LEDcurrent
sources to determine which LED to close the regulation
loop on.
If the current delivered from VIN through PMOS switch A
exceeds 1600mA (typical), switch A is shut off immedi-
ately. Switches B and D are turned on for the remainder of
the cycle in order to safely discharge the forward inductor
current at the maximum rate possible.
Reverse Current Limit
If the current delivered from VOUT backwards through
PMOS switch D exceeds 200mA (typical), switch D is shut
off immediately. Switches A and C are turned on for the
remainder of the cycle in order to safely discharge the
reverse inductor current at the maximum rate possible.
Safety Error Amp
The safety error amplifier is a transconductance amplifier
with sink only capability. In normal operation, it has no
effect on the loop regulation. However, if any of the LED
pins open-circuits, the output voltage will keep rising, and
safety error amp will eventually take over control of the
regulationlooptopreventVOUTrunaway.TheVOUT thresh-
old at which this occurs is approximately 4.5V.
Undervoltage Lockout
TopreventoperationofthepowerswitchesathighRDS(ON)
,
an undervoltage lockout is incorporated on the LTC3452.
Whentheinputsupplyvoltagedropsbelowapproximately
1.9V, the four power switches and all control circuitry are
turned off except for the undervoltage block, which draws
only a few microamperes.
3452f
9
LTC3452
U
OPERATIO
LED Current Setting Amps
implemented results in “smoother” brightness and dim-
ming control as perceived by the human eye, which is
logarithmic in nature.
The maximum forward current per LED for all LEDs in a
given bank is programmed by a single external resistor to
ground at the corresponding ISETL,H pin according to the
following formulas:
Table 1. Low Power Bank Brightness Control
EN DUTY CYCLE (% LOGIC HIGH)
L
LED CURRENT
Lx
0% (Logic Low)
0 (Shutdown)
⎛ 0.8 ⎞
IMAXL = 256
⎛ 0.8 ⎞
= 768
0% < Duty Cycle < 12.5%
12.5% < Duty Cycle < 25%
25% < Duty Cycle < 37.5%
37.5% < Duty Cycle < 50%
50% < Duty Cycle < 62.5%
62.5% < Duty Cycle < 75%
75% < Duty Cycle < 87.5%
87.5% < Duty Cycle ≤ 100%
1/128 • I
1/64 • I
MAXL
, I
MAXH
⎜
⎟
⎜
⎟
⎝RISETL
⎠
⎝RISETH⎠
MAXL
1/32 • I
1/16 • I
MAXL
MAXL
For operation at currents below IMAXL in the low power
bank, refer to the Exponential Brightness Control section
and also to external circuit options given in the Applica-
tions Section. For operation at currents below IMAXH in the
high power bank, refer only to the external circuit options
given in the Applications Section.
1/8 • I
1/4 • I
1/2 • I
MAXL
MAXL
MAXL
I
MAXL
Shutdown Circuit
LED Current Sources
The shutdown circuit monitors the voltages at the ENL,H
pins. Logic high on either/both inputs enables the part and
logic low on both puts the part in shutdown. Since the ENL
pindoublesasaPWMinputforLEDbrightnesscontrol, an
outputfilterintheshutdowncircuitisemployedtoprevent
the part from toggling in and out of shutdown for normal
PWMing of the ENL input when ENH is low. If ENH is low,
the LTC3452 is enabled immediately after a rising edge at
the ENL pin, but waits 200µs (typical) after a falling edge
to enter shutdown. Consequently, a minimum PWM fre-
quency is required for smooth brightness control at cur-
rents below IMAXL. The recommended PWM frequency is
10kHz to 50kHz.
Each LED pin is driven by a current source specifically
designedforlowdropout. TheLTC3452employsapropri-
etary architecture that determines which of the seven
LEDs requires the largest forward voltage drop at its
programmed current, and then generates a feedback
voltage based on this one for closing the buck-boost
regulation loop. This results in the lowest output voltage
required for regulating all of the LEDs and thus the highest
LED power efficiency. The voltage present at the LED pin
of the “controlling LED” will be typically 130mV at 20mA
(low power bank) or 250mA at 100mA (high power bank)
of current.
LED Detect Circuit
Exponential Brightness Control
(Low Power LED Bank Only)
If fewer than five LED outputs in the low power bank and/
or fewer than two LED outputs in the high power bank are
TheLTC3452implementsanexponentialbrightnesscon-
trol function for the low power LED bank only in which the
LEDLx current is a function of the PWM duty cycle at the
ENL pin. The LED current will be equal to a fraction of
IMAXL as given in Table 1. As the duty cycle (that the PWM
waveform is logic high) increases linearly, the LED cur-
rent will increase exponentially from 1/128th IMAXL to
128/128ths IMAXL in seven binary steps. The function
required, unused outputs should be connected to VOUT
.
Each LED pin has an internal LED detect circuit that
disables the output current source to save power if an
outputisnotneeded.Asmallcurrentisemployedtodetect
the presence of an LED at startup. This current is typically
10µA for the low power bank and 30µA for the high power
bank.
3452f
10
LTC3452
W U U
APPLICATIO S I FOR ATIO
U
COMPONENT SELECTION
Input Capacitor Selection
Since the VIN pin is the supply voltage for the IC it is
recommended to place at least a 2.2µF, low ESR bypass
capacitor to ground. See Table 3 for a list of component
suppliers.
Inductor Selection
The high frequency operation of the LTC3452 allows the
use of small surface mount inductors. The inductor cur-
rent ripple is typically set to 20% to 40% of the maximum
averageinductorcurrent. Foragivenrippletheinductance
term in boost mode is:
Table 3. Capacitor Vendor Information
SUPPLIER
AVX
WEB SITE
www.avxcorp.com
www.sanyovideo.com
www.t-yuden.com
www.component.tdk.com
V
2 • VOUT – V
•100%
Sanyo
(
)
IN(MIN)
IN(MIN)
L >
Taiyo Yuden
TDK
2
f •IOUT(MAX) •%Ripple• VOUT
and in buck mode is:
Output Capacitor Selection
VOUT • VIN(MAX) – VOUT •100%
(
)
L >
The bulk value of the capacitor is set to reduce the ripple
due to charge into the capacitor each cycle. The steady
state ripple due to charge is given by:
f •IOUT(MAX) •%Ripple• V
IN(MAX)
where:
f = operating frequency, Hz
IOUT(MAX) • VOUT – V
•100
(
)
%Ripple = allowable inductor current ripple, %
VIN(MIN) = minimum input voltage, V
VIN(MAX) = maximum input voltage, V
VOUT = output voltage, V
IN(MIN)
%Ripple_Boost =
%Ripple_Buck =
%
COUT • VOUT2 • f
V
IN(MAX) – VOUT •100
(
)
%
8• VIN(MAX) • f2 •L •COUT
IOUT(MAX) = maximum output load current
For high efficiency, choose an inductor with a high fre-
quencycorematerial, suchasferrite, toreducecoreloses.
The inductor should have low ESR (equivalent series
resistance) to reduce the I2R losses, and must be able to
handlethepeakinductorcurrentwithoutsaturating.Molded
chokes or chip inductors usually do not have enough core
to support peak inductor currents >1A. To minimize radi-
ated noise, use a toroid, pot core or shielded bobbin
inductor. For the white LED application, a 4.7µH inductor
valueisrecommended. SeeTable2foralistofcomponent
suppliers.
where COUT = output filter capacitor, F
The output capacitance is usually many times larger in
order to handle the transient response of the converter.
For a rule of thumb, the ratio of the operating frequency to
the unity-gain bandwidth of the converter is the amount
the output capacitance will have to increase from the
above calculations in order to maintain the desired tran-
sient response.
The other component of ripple is due to the ESR (equiva-
lent series resistance) of the output capacitor. Low ESR
capacitors should be used to minimize output voltage
ripple. For surface mount applications, Taiyo Yuden, TDK,
AVX ceramic capacitors, AVX TPS series tantalum capaci-
tors or Sanyo POSCAP are recommended. For the white
LED application, a 4.7µF capacitor value is recommended.
See Table 3 for a list of component suppliers.
Table 2. Inductor Vendor Information
SUPPLIER
Coilcraft
WEB SITE
www.coilcraft.com
www.cooperet.com
www.murata.com
www.japanlink.com/sumida
www.vishay.com
Cooper/Coiltronics
Murata
Sumida
Vishay-Dale
3452f
11
LTC3452
W U U
U
APPLICATIO S I FOR ATIO
The unity-gain frequency of the error amplifier with the
Type I compensation is given by:
Optional Schottky Diodes
Schottky diodes across the synchronous switches B and
D are not required, but provide a lower drop during the
break-before-make time (typically 20ns) of the NMOS to
PMOS transition, improving efficiency. Use a Schottky
diode such as an MBRM120T3 or equivalent. Do not use
ordinary rectifier diodes, since the slow recovery times
will compromise efficiency.
gm
2 • π •CVC
fUG
=
where gm is the error amp transconductance (typically
1/5.2k) and CVC is the external capacitor to GND at the
VC pin. For the white LED application, a 0.1µF or greater
capacitor value is recommended.
Closing the Feedback Loop
Paralleling LED Outputs for Higher Current
The LTC3452 incorporates voltage mode PWM control.
The control to output gain varies with operation region
(Buck, Boost, Buck/Boost), but is usually no greater than
15. The output filter exhibits a double pole response
given by:
Two or more LED output pins can be connected together
in parallel to achieve higher output current in fewer than 7
LEDs. For a very high power LED such as a LumiLED, all
7 outputs can be connected in parallel for maximum total
output current, as shown in the back page application of
this data sheet.
1
fFILTER_POLE
=
Hz
2 • π • L •COUT
Maximum LED Current
where COUT is the output filter capacitor.
The output filter zero is given by:
As described in the Operation section, the maximum
output LED currents are equal to:
1
⎛ 0.8V ⎞
fFILTER_ZERO
=
Hz
IMAXL = 256
⎜
⎟
2 • π •RESR •COUT
⎝RISETL
⎠
and
where RESR is the capacitor equivalent series resistance.
⎛ 0.8V ⎞
IMAXH = 768
A troublesome feature in Boost mode is the right-half
plane zero (RHP), and is given by:
⎜
⎟
⎝RISETH
⎠
Since the maximum LED current for the low power bank is
25mA, this sets a minimum limit on RISETL of:
2
V
IN
fRHPZ
=
Hz
2• π •IOUT •L•VOUT
0.8V
25mA
⎛
⎞
RMINL = 256
= 8192Ω
⎜
⎝
⎟
⎠
The loop gain is typically rolled off before the RHP zero
frequency.
Similarly, for the high power bank:
A simple Type I compensation network can be incorpo-
rated to stabilize the loop but at a cost of reduced band-
width and slower transient response. To ensure proper
phase margin, the loop is required to be crossed over a
decade before the LC double pole.
0.8V
150mA
⎛
⎞
RMINH = 768
= 4096Ω
⎜
⎝
⎟
⎠
Inaddition,sincethemaximumcontinuousoutputcurrent
for the buck-boost is limited to 425mA, this may impose
higher resistor value minimums if all outputs are used.
3452f
12
LTC3452
W U U
APPLICATIO S I FOR ATIO
U
Although the LTC3452 can safely provide this current
continuously, theexternalLED(s)maynotberatedforthis
high a level of continuous current. Higher current levels in
a single LED are generally reserved for pulsed applica-
tions, such as LED camera flash. This is accomplished by
programming a high current with one or both of the RISET
resistors and pulsing the appropriate enable pin or pins as
shown in the back page application.
Varying LED Brightness Linearly
Continuously variable LED brightness control can be
achieved by interfacing directly to one or both of the ISET
pins. Figure 3 shows four such methods employing a
voltage DAC, a current DAC, a simple potentiometer or a
PWM input applied to the ISETL pin for controlling the low
power bank LED currents. These four techniques can be
similarly applied to the ISETH pin for controlling the high
power bank LED currents.
V
IN
V
OUT
V
IN
V
OUT
EN
L
LED
EN
L
LED
L1
L1
LTC3452
LTC3452
I
I
SETL
SETL
LED
LED
L5
L5
0.8V – V
DAC
I
= 256
I
= 256 • IDAC
LED
LED
0.8V
R
SET
≥ R
MINL
R
SET
IDAC ≤
R
MINL
VOLTAGE
DAC
CURRENT
DAC
V
DAC
(3a)
(3b)
V
IN
V
OUT
V
IN
V
OUT
EN
L
LED
EN
L
LED
L1
L1
LTC3452
LTC3452
I
I
SETL
LED
SETL
LED
L5
L5
0.8V
+ R
0.8V – V
PWM
R
100
R
R
SET
MINL
I
= 256
I
= 256
= 256
R
≥ R
LED
LED
SET
MINL
R
R
SET
MINL
POT
V
PWM
0.8V – (DC% • V
)
DVCC
POT
1µF
R
SET
DV
CC
f
≥ 10kHz
PWM
(3c)
(3d)
3452 F03
Figure 3. Additional Brightness Control Methods: (3a) Using Voltage DAC,
(3b) Using Current DAC, (3c) Using Potentiometer, (3d) Using PWM Input
3452f
13
LTC3452
W U U
U
APPLICATIO S I FOR ATIO
Unused Outputs
initially designated unused at power-up by connecting its
LEDx pin to VOUT). Efficiency is not materially affected.
If fewer than 7 LED pins are to be used, unused LEDx pins
should be connected to VOUT. The LTC3452 senses which
current source outputs are not being used and shuts off
the corresponding output currents to save power. A small
trickle current (10µA: low power bank, 30µA: high power
bank) is still applied to unused outputs to detect if a white
LED is later switched in and also to distinguish unused
outputs from used outputs during start-up.
IfanindividualLEDfailsasanopencircuit,thecontrolloop
will initially attempt to regulate off of its current source
feedback signal, since it will appear to be the one requiring
the largest forward voltage drop to run at its programmed
current. This will drive VOUT higher. As the open circuited
LED will never accept its programmed current, VOUT must
be voltage-limited by means of a secondary control loop.
The LTC3452 limits VOUT to 4.5V in this failure mode. The
other LEDs will still remain biased at the correct pro-
grammed current but the overall circuit efficiency will
decrease.
LED Failure Modes
If an individual LED fails as a short circuit, the current
sourcebiasingitisshutofftosavepower. Thisisthesame
operation as described previously (if the output were
3452f
14
LTC3452
U
PACKAGE DESCRIPTIO
UF Package
20-Lead Plastic QFN (4mm × 4mm)
(Reference LTC DWG # 05-08-1710)
0.70 ±0.05
4.50 ± 0.05
3.10 ± 0.05
2.45 ± 0.05
(4 SIDES)
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
BOTTOM VIEW—EXPOSED PAD
R = 0.115
PIN 1 NOTCH
R = 0.30 TYP
0.75 ± 0.05
4.00 ± 0.10
(4 SIDES)
TYP
19 20
0.38 ± 0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
2.45 ± 0.10
(4-SIDES)
(UF20) QFN 10-04
0.200 REF
0.25 ± 0.05
0.50 BSC
0.00 – 0.05
NOTE:
1. DRAWING IS PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220
VARIATION (WGGD-1)—TO BE APPROVED
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
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
3452f
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 represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
15
LTC3452
U
TYPICAL APPLICATIO
4 × 20mA White LED Display + 2 × 150mA Camera Light Driver
L
4.7µH
V
IN
3V TO 5.5V
4.7µF
2.2µF
150mA
D1
150mA
D2
V
PV
SW1
SW2
V
OUT
IN
IN
EN
H
EN
H
I
SETH
LED
LED
H1
4.02k
H2
D3
LOW
LED , 20mA
L1
POWER
LED
D4
1MHz
BUCK/BOOST
V
C
LED , 20mA
L2
BANK
0.1µF
EN
D5
LED , 20mA
L3
L
LED , 20mA
L4
EN
LTC3452
D6
L
LED , UNUSED
L5
I
SETL
D1, D2: AOT 2015
D3-D6: NICHIA NSCW100
L: COILCRAFT D03314-472
10.2k
GND
GND
PGND
EXPOSED PAD
3452 TA02a
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
V : 1.6V to 18V, V
LT1618
Constant Current, Constant Voltage 1.4MHz, High Efficiency
Boost Regulator
= 34V, I = 1.8mA, I = <1µA,
OUT(MAX) Q SD
IN
MS10 Package/EDD Package
LT1930/LT1930A 1A (I ), 1.2MHz/2.2MHz, High Efficiency Step-Up
V : 2.6V to 16V, V
= 34V, I = 4.2mA/5.5mA, I = <1µA,
OUT(MAX) Q SD
SW
IN
DC/DC Converter
ThinSOT Package
LT1932
Constant Current, 1.2MHz, High Efficiency White LED
Boost Regulator
V : 1V to 10V, V
= 34V, I = 1.2mA, I = <1µA,
OUT(MAX) Q SD
IN
ThinSOT Package
LT1937
Constant Current, 1.2MHz, High Efficiency White LED
Boost Regulator
V : 2.5V to 10V, V
= 34V, I = 1.9mA, I = <1µA,
OUT(MAX) Q SD
IN
ThinSOT Package/SC70 Package
LTC3205
LTC3215
LTC3216
High Efficiency, Multi-Display LED Controller
V : 2.8V to 4.5V, V
= 6V, I = 50µA, I = <1µA,
Q SD
IN
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
QFN-24 Package
700mA Low Noise High Current LED Charge Pump
V : 2.9V to 4.4V, V
= 5.5V, I = 300µA, I = <2.5µA,
Q SD
IN
DFN Package
1A Low Noise High Current LED Charge Pump with
Independent Flash/Torch Current
V : 2.9V to 4.4V, V
= 5.5V, I = 300µA, I = <2.5µA,
Q SD
IN
DFN Package
LTC3440/
LTC3441
600mA/1.2A I , 2MHz/1MHz, Synchronous Buck-Boost
V : 2.4V to 5.5V, V
= 5.25V, I = 25µA/50µA, I = <1µA,
Q SD
OUT
IN
DC/DC Converter
MS-10 Package/DFN Package
LTC3443
LTC3453
LTC3454
600mA/1.2A I , 600kHz, Synchronous Buck-Boost
V : 2.4V to 5.5V, V
= 5.25V, I = 28µA, I = <1µA,
Q SD
OUT
IN
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
DC/DC Converter
DFN Package
500mA Synchronous Buck-Boost High Power White
LED Driver
V : 2.7V to 5.5V, V
= 4.5V, I = 600µA, I = 6µA,
Q SD
IN
QFN-16 Package
1A Synchronous Buck-Boost High Power White
LED Driver
V : 2.7V to 5.5V, V
= 5.15V, I = 825µA, I = 0µA,
Q SD
IN
DFN Package
LT3465/LT3465A Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED V : 2.7V to 16V, V
= 34V, I = 1.9mA, I = <1µA,
Q SD
IN
Boost Regulator with Integrated Schottky Diode
ThinSOT Package
LT3466
LT3479
Dual Constant Current, 2MHz, High Efficiency White LED
Boost Regulator with Integrated Schottky Diode
V : 2.7V to 24V, V
= 40V, I = 5mA, I = <16µA,
Q SD
IN
DFN Package
3A, Full Featured DC/DC Converter with Soft-Start and
Inrush Current Protection
V : 2.5V to 24V, V
= 40V, I = 6.5mA, I = <1µA,
Q SD
IN
DFN Package/TSOPP Package
3452f
LT 0406 • PRINTED IN THE USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2006
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