LINER LT3498 20ma led driver and oled driver with integrated schottky Datasheet

LT3498
20mA LED Driver and
OLED Driver with Integrated
Schottky in 3mm x 2mm DFN
DESCRIPTION
FEATURES
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Dual Output Boost for Dual Display Devices
Drives Up to Six White LEDs and OLED/LCD Bias
Internal Power Switches and Schottky Diodes
Independent Dimming and Shutdown
200mV High Side Sense on LED Driver Allows
“One-Wire Current Source”
Wide Input Voltage Range: 2.5V to 12V
Wide Output Voltage Range: Up to 32V
2.3MHz PWM Frequency for LED Driver
PFM for OLED Driver is Non-Audible Over Entire
Load Range
Open LED Protection (27V Maximum on CAP1 Pin)
OLED Output Disconnect
Available in 12-Pin DFN Package
1mm Tall Solution Height
APPLICATIONS
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Cellular Phones
PDAs, Handheld Computers
Digital Cameras
MP3 Players
GPS Receivers
The LT®3498 is a dual output boost converter featuring a
2.3MHz PWM LED Driver and PFM OLED Driver. It includes
an internal power switch and Schottky diode for each
driver. Both converters can be independently shut down
and modulated. This highly integrated power solution is
ideal for dual display electronic devices.
The 2.3MHz step-up converter is designed to drive up to six
white LEDs in series from a Li-Ion cell. The device features
a unique high side LED current sense that enables the part
to function as a “one-wire” current source—one side of the
LED string can be returned to ground anywhere. Traditional
LED drivers use a grounded resistor to sense LED current,
requiring a 2-wire connection to the LED string.
The PFM OLED driver is a low noise boost converter that
features a novel control technique.* The converter controls
power delivery by varying both the peak inductor current
and switch off time. This technique results in low output
voltage ripple, as well as, high efficiency over a wide load
range. The off time of the switch is not allowed to exceed a
fixed level, guaranteeing a switching frequency that stays
above the audio band.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Patent Pending
TYPICAL APPLICATION
Li-Ion to Six White LEDs and OLED/LCD Bias
OLED Efficiency
80
4.7μF
75
70
15μH
16V
24mA
1μF
CAP1 SW1
10Ω
SW2 CAP2 VOUT2
VIN
10μF
LT3498
LED1
20mA
CTRL1
GND1
OFF ON
SHUTDOWN
AND
DIMMING
CONTROL
GND2
CTRL2
OFF ON
SHUTDOWN
AND
CONTROL
FB2
2.21MΩ
350
LOAD FROM VOUT2
300
65
250
60
200
55
150
100
50
45
40
0.1
3498 TA01
400
VIN = 3.6V
VOUT2 = 16V
POWER LOSS (mW)
15μH
0.47μF
EFFICIENCY (%)
VIN = 3V TO 5V
POWER LOSS
FROM VOUT2
1
10
LOAD CURRENT (mA)
50
0
100
3498 TA01b
3498fa
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LT3498
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Notes 1, 2)
Input Voltage (VIN) ....................................................12V
CTRL1 and CTRL2 Voltage ........................................12V
FB2 Voltage ..............................................................2.5V
VOUT2 Voltage ...........................................................32V
SW1 and SW2 Voltage ..............................................32V
CAP1 and CAP2 Voltage ............................................32V
LED1 Voltage ............................................................32V
Operating Junction Temperature Range ...–40°C to 85°C
Maximum Junction Temperature........................... 125°C
Storage Temperature Range...................–65°C to 150°C
TOP VIEW
LED1 1
12 CAP1
CTRL1 2
11 SW1
GND1 3
GND2 4
13
10 VIN
9 SW2
CTRL2 5
8 CAP2
FB2 6
7 VOUT2
DDB PACKAGE
12-LEAD (3mm × 2mm) PLASTIC DFN
TJMAX = 125°C, θJA = 160°C/W
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3498EDDB#PBF
LT3498EDDB#TRPBF
LCQF
12-Lead (3mm × 2mm) Plastic DFN
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VIN = 3V, VCTRL1 = VCTRL2 = 3V.
PARAMETER
CONDITIONS
MIN
TYP
MAX
2.5
Minimum Operating Voltage
UNITS
V
12
Maximum Operating Voltage
V
Supply Current (LED Off, OLED Off)
VIN = 3V, VCTRL1 = 0V, VCTRL2 = 0V
8
10
μA
Supply Current (LED On, OLED Off)
VIN = 3V, VCTRL1 = 3V, VCTRL2 = 0V, VCAP1 = 24V, VLED1
= 23V
1.6
2
mA
Supply Current (LED Off, OLED On)
VIN = 3V, VCTRL1 = 0V, VCTRL2 = 3V, VFB2 = 3V
230
280
μA
Supply Current (LED On, OLED On)
VIN = 3V, VCTRL1 = 3V, VCTRL2 = 3V, VCAP1 = 24V, VLED1
= 23V
1.65
2.05
mA
●
1.5
V
VCTRL1 or VCTRL2 to Turn On IC
●
125
mV
VCTRL1 and VCTRL2 to Shut Down IC
●
VCTRL1 for Full LED Current
VCTRL2 for Full OLED Brightness
75
CTRL1, CTRL2 Pin Bias Current
100
mV
nA
LED Driver
LED Current Sense Voltage (VCAP – VLED)
VCAP1 = 24V, ISW = 200mA
CAP1, LED1 Pin Bias Current
VCAP1 = 16V, VLED1 = 16V
●
190
200
210
mV
20
30
μA
3498fa
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LT3498
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VIN = 3V, VCTRL1 = VCTRL2 = 3V.
PARAMETER
CONDITIONS
MIN
TYP
VCAP1, VLED1 Common Mode Minimum Voltage
Switching Frequency
UNITS
2.5
V
2.8
MHz
●
1.8
88
90
%
●
300
425
mA
mV
Maximum Duty Cycle
Switch Current Limit
MAX
2.3
Switch VCESAT
ISW = 200mA
250
Switch Leakage Current
VSW1 = 16V, Switch OFF
0.1
5
μA
27
28
V
6
μA
CAP1 Pin Overvoltage Protection
26
Schottky Forward Voltage
ISCHOTTKY1 = 100mA
Schottky Reverse Leakage
VREVERSE1 = 20V, VCTRL1 = 0V
0.8
V
OLED Driver
Feedback Voltage
(Note 3)
Feedback Resistor
Minimum Switch Off Time
After Start-Up
Minimum Switch Off Time
During Start-Up (Note 4)
Maximum Switch Off Time
VFB2 = 1.5V
Switch Current Limit
Switch VCESAT
ISW2 = 200mA
●
1.18
1.215
1.25
V
●
177
182
186
kΩ
●
150
ns
1
μs
15
20
30
μs
180
300
400
mA
260
Switch Leakage Current
VSW2 = 16V, Switch OFF
0.1
Schottky Forward Voltage
ISCHOTTKY2 = 100mA
800
Schottky Reverse Leakage
VREVERSE2 = 20V
PMOS Disconnect VCAP2 – VOUT2
IOUT2 = 10mA, VCAP2 = 5V
CTRL2 to FB2 Offset
VCTRL2 = 0.5V
Maximum Shunt Current
VFB2 = 1.3V
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: The LT3498 is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C junction
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
mV
5
2
250
8
220
μA
mV
μA
mV
15
mV
μA
Note 3: Internal reference voltage is determined by finding VFB2 voltage
level which causes quiescent current to increase 20μA above “Not
Switching” level.
Note 4: If CTRL2 is overriding the internal reference, start-up mode
occurs when VFB2 is less then half the voltage on CTRL2. If CTRL2 is not
overriding the internal reference, start-up mode occurs when VFB2 is less
then half the voltage of the internal reference.
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LT3498
TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Current
(VCTRL1 = VCTRL2 = 0V)
LED Switch Saturation
Voltage (VCESAT1)
15
T = –50°C
9
T = 25°C
T = 125°C
6
3
0
4
2
6
VIN (V)
10
8
400
450
T = –50°C
400
350
T = 25°C
300
T = 125°C
250
200
150
100
50
0
12
0
50
120
80
0
1500
202
202
198
194
50
25
0
75
TEMPERATURE (°C)
100
T = 25°C
125
125
3498 G07
T = –50°C
0
5
15
10
CAP1 VOLTAGE (V)
20
25
3498 G06
Input Current in Output
Open Circuit
6
5
INPUT CURRENT (mA)
CURRENT LIMIT (mA)
OUTPUT CLAMP VOLTAGE (V)
100
T = 125°C
194
186
–25
28
T = –50°C
T = 25°C
27
T = 150°C
26
T = 150°C
4
T = 25°C
3
T = –50°C
2
1
25
50
25
0
75
TEMPERATURE (°C)
1000
190
29
500
–25
200
400
800
600
SCHOTTKY FORWARD DROP (mV)
198
Open Circuit Output
Clamp Voltage
350
0
3498 G05
LED Current Limit
vs Temperature
400
T = –50°C
50
206
3498 G04
300
–50
100
206
186
–50
2000
450
T = 25°C
150
Sense Voltage (VCAP1 – VLED1)
vs VCAP1
190
40
1000
VCTRL1 (mV)
200
3498 G03
SENSE VOLTAGE (mV)
SENSE VOLTAGE (mV)
SENSE VOLTAGE (mV)
160
500
250
Sense Voltage (VCAP1 – VLED1)
vs Temperature
T = 25°C
T = –50°C
T = 125°C
0
T = 125°C
300
3498 G02
Sense Voltage (VCAP1 – VLED1)
vs VCTRL1
200
350
0
100 150 200 250 300 350 400
SWITCH CURRENT (mA)
3498 G01
240
SCHOTTKY FORWARD CURRENT (mA)
SWITCH SATURATION VOLTAGE (mV)
SHUTDOWN CURRENT (μA)
LED Schottky Forward
Voltage Drop
500
12
0
TA = 25°C, unless otherwise specified.
0
0
2
4
6
VIN (V)
8
10
12
2
4
6
8
10
12
VIN (V)
3498 G08
3498 G09
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LT3498
TYPICAL PERFORMANCE CHARACTERISTICS
LED Switching Frequency
vs Temperature
OLED Switch Saturation
Voltage (VCESAT2)
OLED Schottky Forward
Voltage Drop
300
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
–50 –25
75
50
25
TEMPERATURE (°C)
0
100
250
T = –50°C
T = 25°C
200
150
100
50
0
125
400
T = 125°C
SCHOTTKY FORWARD CURRENT (mA)
SWITCH SATURATION VOLTAGE (mV)
2.6
LED SWITCHING FREQUENCY (MHz)
TA = 25°C, unless otherwise specified.
0
50
250
100
150
200
SWITCH CURRENT (mA)
VOUT2 vs VCTRL2
(VOUT2 = 16V)
250
200
100
T = –50°C
50
0
300
8
6
4
400
800 1000
600
SCHOTTKY FORWARD DROP (mV)
1200
VOUT2 Load Regulation
1.5
VOUT2 VOLTAGE CHANGE (%)
OUTPUT VOLTAGE CHANGE (%)
10
200
2.0
16
12
0
3498 G12
6
14
T = 25°C
150
VOUT2 vs Temperature
(VOUT2 = 16V)
18
VOUT2 VOLTAGE (V)
T = 125°C
300
3498 G11
3498 G10
3
0
–3
1.0
0.5
0
–0.5
–1.0
–1.5
2
–6
–50
0
0
2000
500
1500
1000
CTRL2 VOLTAGE (mV)
–2.0
–25
50
25
0
75
TEMPERATURE (°C)
3498 G13
125
40
30
20
10
1000
800
600
400
200
100
125
3498 G16
50
550
500
450
400
350
300
250
0
75
50
25
TEMPERATURE (°C)
0
20
40
30
LOAD CURRENT (mA)
600
PEAK INDUCTOR CURRENT (mA)
SWITCHING FREQUENCY (kHz)
70
50
10
Peak Inductor Current
1200
60
0
3498 G15
OLED Switching Frequency
vs Load Current
80
0
–50 –25
100
3498 G14
OLED Minimum
Switching Frequency
SWITCHING FREQUENCY (kHz)
350
0.1
1
10
LOAD CURRENT (mA)
100
3498 G17
200
–50 –25
75
50
25
TEMPERATURE (°C)
0
100
125
3498 G18
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LT3498
TYPICAL PERFORMANCE CHARACTERISTICS
LED Switching Waveforms
OLED Switching Waveforms
with No Load
LED Transient Response
VSW
10V/DIV
VCAP1
50mV/DIV
IL
100mA/
DIV
500ns/DIV
VIN = 3.6V
FRONT PAGE APPLICATION
TA = 25°C, unless otherwise specified.
VCAP1
5V/DIV
VOUT2
10mV/DIV
AC COUPLED
VCTRL1
5V/DIV
SW2 VOLTAGE
10V/DIV
IL
200mA/
DIV
INDUCTOR
CURRENT
50mA/DIV
3498 G19
1ms/DIV
VIN = 3.6V
FRONT PAGE APPLICATION
3498 G20
VIN = 3.6V
VOUT2 = 16V
OLED Switching Waveforms
with 35mA Load
OLED Switching Waveforms
with 4mA Load
VOUT2
10mV/DIV
AC
COUPLED
SW2
VOLTAGE
10V/DIV
VIN = 3.6V
VOUT2 = 16V
2μs/DIV
VOUT2
10mV/DIV
AC COUPLED
CAP2
VOLTAGE
5V/DIV
SW2
VOLTAGE
10V/DIV
VOUT2
VOLTAGE
5V/DIV
3498 G22
VIN = 3.6V
VOUT2 = 16V
500ns/DIV
3498 G21
OLED Switching Waveforms
During Start-Up
INDUCTOR
CURRENT
200mA/DIV
INDUCTOR
CURRENT
200mA/DIV
5μs/DIV
3498 G23
INDUCTOR
CURRENT
100mA/DIV
VIN = 3.6V
VOUT2 = 16V
500μs/DIV
3498 G24
PIN FUNCTIONS
LED1 (Pin 1): Connection Point Between the Anode of the
Highest LED and the Sense Resistor. The LED current can
be programmed by:
200mV
ILED1 =
RSENSE1
CTRL1 (Pin 2): Dimming and Shutdown Pin. Connect this
pin below 75mV to disable the white LED driver. As the
pin voltage is ramped from 0V to 1.5V, the LED current
ramps from 0 to (ILED1 = 200mV / RSENSE1).
GND1, 2 (Pins 3, 4): Ground. Tie directly to local ground
plane. GND1 and GND2 are connected internally.
CTRL2 (Pin 5): Dimming and Shutdown Pin. Connect
it below 75mV to disable the low noise boost converter.
As the pin voltage is ramped from 0V to 1.5V, the output
ramps up to the programmed output voltage.
FB2 (Pin 6): Feedback Pin. Reference voltage is 1.215V.
There is an internal 182kΩ resistor from FB2 to GND. To
achieve desired output voltage, choose RFB2 according to
the following formula:
V
RFB2 =182 • OUT2 1 k
1.215 3498fa
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LT3498
PIN FUNCTIONS
VOUT2 (Pin 7): Drain of Output Disconnect PMOS.
Place a bypass capacitor from this pin to GND. See the
Applications Information section.
SW1 (Pin 11): Switch Pin. Connect the inductor of the
white LED driver at this pin. Minimize metal trace area at
this pin to minimize EMI.
CAP2 (Pin 8): Output of the OLED Driver. This pin is
connected to the cathode of the internal Schottky diode.
Place a bypass capacitor from this pin to GND.
CAP1 (Pin 12): Output of the White LED Driver. This pin is
connected to the cathode of the internal Schottky. Connect
the output capacitor to this pin and the sense resistor from
this pin to the LED1 pin.
SW2 (Pin 9): Switch Pin. This is the collector of the internal NPN power switch. Minimize the metal trace area
connected to this pin to minimize EMI.
Exposed Pad (Pin 13): Ground. The Exposed Pad must
be soldered to the PCB.
VIN (Pin 10): Input Supply Pin. Must be locally bypassed.
BLOCK DIAGRAM
L1
15μF
L2
10μF
CIN
4.7μF
9
10
VIN
SW2
CAP2
8
START-UP
CONTROL
CAP1
12
–
R
A2
C2
0.47μF
11
SW1
COMPARATOR
Q1
Q
S
+
OVERVOLTAGE
PROTECTION
DRIVER
+
∑
RSENSE1
10Ω
R
A3
–
RAMP
GENERATOR
VOUT2
C1
1μF
7
DRIVER
C3
10μF
2.3MHz
OSCILLATOR
SWITCH
CONTROL
Q2
DISCONNECT
CONTROL
+
A1
RC
SHUNT
CONTROL
–
+
+
A4
LED1
–
1
CC
RFB2
2.21MΩ
A5
+
+
–
VREF
182kΩ
GND2
4
FB2
CTRL2
6
5
CTRL1 GND1
2
3
3498 BD
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LT3498
OPERATION— LED DRIVER
The LED portion of the LT3498 uses a constant-frequency,
current mode control scheme to provide excellent line
and load regulation. Operation can be best understood
by referring to the Block Diagram.
At power-up, the capacitor at the CAP1 pin is charged up
to VIN (input supply voltage) through the inductor and the
internal Schottky diode. If CTRL1 is pulled higher than
125mV, the bandgap reference, the start-up bias and the
oscillator are turned on. At the start of each oscillator cycle,
the power switch Q1 is turned on. A voltage proportional
to the switch current is added to a stabilizing ramp and the
resulting sum is fed into the positive terminal of the PWM
comparator, A2. When this voltage exceeds the level at the
negative input of A2, the PWM logic turns off the power
switch. The level at the negative input of A2 is set by the
error amplifier A1, and is simply an amplified version of
the difference between the VCAP1 and VLED1 voltage and
the bandgap reference. In this manner the error amplifier,
A1, sets the correct peak current level in inductor L1 to
keep the output in regulation. The CTRL1 pin is used to
adjust the LED current. The LED Driver is shutdown when
CTRL1 is pulled lower than 75mV.
Minimum Output Current
The LED Driver of the LT3498 can drive a 4-LED string at
2mA LED current, without pulse-skipping, using the same
external components shown in the application circuit on
the front page of this data sheet. As current is further
reduced, the device will begin skipping pulses. This will
result in some low frequency ripple, although the average
LED current remains regulated down to zero. The photo in
Figure 1 details circuit operation driving four white LEDs
at 2mA load. Peak inductor current is less than 60mA and
the regulator operates in discontinuous mode, meaning
the inductor current reaches zero during the discharge
phase. After the inductor current reaches zero, the SW1
pin exhibits ringing due to the LC tank circuit formed
by the inductor in combination with the switch and the
diode capacitance. This ringing is not harmful; far less
spectral energy is contained in the ringing than in the
switch transitions.
IL
50mA/DIV
VSW
10V/DIV
VIN = 4.2V
ILED = 2mA
4 LEDs
200ns/DIV
3498 F01
Figure 1. Switching Waveforms with
Four White LEDs at 2mA Load
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LT3498
OPERATION— OLED DRIVER
The low noise boost of the LT3498 uses a novel control
scheme to provide high efficiency over a wide range
of output current. In addition, this technique keeps the
switching frequency above the audio band over all load
conditions.
The operation of the part can be better understood by
referring to the Block Diagram. The part senses the
output voltage by monitoring the voltage on the FB2 pin.
The user sets the desired output voltage by choosing the
value of the external topside feedback resistor. The part
incorporates a precision 182kΩ bottom-side feedback
resistor. Assuming that output voltage adjustment is not
used (CTRL2 pin is tied to 1.5V, or greater), the internal
reference (VREF = 1.215V) sets the voltage to which FB2
will servo during regulation.
The Switch Control block senses the output of the amplifier and adjusts the switching frequency, as well as other
parameters to achieve regulation. During the start-up of
the circuit, special precautions are taken to ensure that
the inductor current remains under control.
Because the switching frequency is never allowed to fall
below approximately 50kHz, a minimum load must be
present to prevent the output voltage from drifting too
high. This minimum load is automatically generated within
the part via the Shunt Control block. The level of this current
is adaptable, removing itself when not needed to improve
efficiency at higher load levels.
The low-noise boost of the LT3498 also has an integrated
Schottky diode and PMOS output disconnect switch. The
PMOS switch is turned on when the part is enabled. When
the part is in shutdown, the PMOS switch turns off, allowing
the VOUT2 node to go to ground. This type of disconnect
function is often required in power supplies.
APPLICATIONS INFORMATION— LED DRIVER
Inductor Selection
80
A 15μH inductor is recommended for most applications
for the LED driver of the LT3498. Although small size and
high efficiency are major concerns, the inductor should
have low core losses at 2.3MHz and low DCR (copper
wire resistance). Some small inductors in this category
are listed in Table 1. The efficiency comparison of different
inductors is shown in Figure 2.
75
Table 1: Recommended Inductors
PART
LQH32CN150K53
LQH2MCN150K02
LQH32CN100K53
LQH2MCN100K02
SD3110-150
1001AS-150M
(TYPE D312C)
D03314-153ML
EFFICIENCY (%)
70
65
60
15uH Murata LQH32CN150K53
15uH Murata LQH2MCN150K02
15uH Cooper SD3110-150
15uH Toko D312C
15uH Coilcraft DO3314-153ML
55
50
45
L
(μH)
15
15
10
10
15
MAX
DCR
(Ω)
0.58
1.6
0.3
1.2
0.764
CURRENT
RATING
(mA)
300
200
450
225
380
15
0.80
360
15
0.86
680
0
5
10
LED CURRENT (mA)
VENDOR
Murata
www.murata.com
Cooper
www.cooperet.com
Toko
www.toko.com
Coilcraft
www.coilcraft.com
15
20
3498 F02
Figure 2. Efficiency Comparison of Different Inductors
Capacitor Selection
The small size of ceramic capacitors makes them ideal for
LT3498 LED driver applications. Use only X5R and X7R
types, because they retain their capacitance over wider
temperature ranges than other types, such as Y5V or
Z5U. A 4.7μF input capacitor and a 1μF output capacitor
are sufficient for most applications.
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LT3498
APPLICATIONS INFORMATION— LED DRIVER
Table 2: Recommended Ceramic Capacitor Manufacturers
Inrush Current
Taiyo Yuden
(800) 368-2496
www.t-yuden.com
AVX
(803) 448-9411
www.avxcorp.com
Murata
(714) 852-2001
www.murata.com
The LT3498 LED Driver has a built-in Schottky diode.
When supply voltage is applied to the VIN pin, an inrush
current flows through the inductor and Schottky diode
and charges up the CAP1 voltage. The Schottky diode
for the LED Driver of the LT3498 can sustain a maximum
current of 1A.
Overvoltage Protection
The LED driver of the LT3498 has an internal open-circuit
protection circuit. In the cases of output open circuit, when
the LEDs are disconnected from the circuit or the LEDs
fail open-circuit, VCAP1 is clamped at 27V (typ). The LED
driver will then switch at a very low frequency to minimize
input current. The VCAP1 and input current during output
open-circuit are shown in the Typical Performance Characteristics. Figure 3 shows the transient response when
the LEDs are disconnected.
=
r2
1
–
L • C 4 • L2
IPK =
VIN – 0.6
• exp – •
L•
2
where L is the inductance, r is the DCR of the inductor
and C is the output capacitance.
IL
200mA/DIV
VCAP1
10V/DIV
For low DCR inductors, which are usually the case for this
application, the peak inrush current can be simplified as
follows:
r
=
2 •L
LEDs DISCONNECTED
AT THIS POINT
500μs/DIV
VIN = 3.6V
FRONT PAGE APPLICATION CIRCUIT
3498 F03
Figure 3. Transient Response with
LEDs Disconnected From Output
Table 3 gives inrush peak currents for some component
selections.
Table 3: Inrush Peak Currents
VIN (V)
r (Ω)
L (μH)
COUT (μF)
IP (A)
4.2
0.58
15
1
0.828
4.2
1.6
15
1
0.682
4.2
0.8
15
1
0.794
4.2
0.739
15
1
0.803
3498fa
10
LT3498
APPLICATIONS INFORMATION— LED DRIVER
Programming LED Current
The LED current can be set by:
The feedback resistor (RSENSE1) and the sense voltage
(VCAP1 – VLED1) control the LED current. The CTRL1 pin
controls the sense reference voltage as shown in the
Typical Performance Characteristics. For CTRL1 higher
than 1.5V, the sense reference is 200mV, which results in
full LED current. To have accurate LED current, precision
resistors are preferred (1% is recommended). The formula
and table for RSENSE selection are shown below.
200mV
RSENSE1 =
ILED
Table 4: RSENSE1 Value Selection for 200mV Sense
ILED (mA)
RSENSE1 (Ω)
5
40
10
20
15
13.3
20
10
ILED ≈
200mV
, when VCTRL1 >1.5V
RSENSE1
ILED ≈
VCTRL1
, when VCTRL1 <1.25V
6.25 • RSENSE1
Feedback voltage variation versus control voltage is
given in the Typical Performance Characteristics.
Using a Filtered PWM Signal
A filtered PWM signal can be used to control the brightness of the LED string. The PWM signal is filtered (Figure 4)
by a RC network and fed to the CTRL1 pin.
The corner frequency of R1, C1 should be much lower
than the frequency of the PWM signal. R1 needs to be
much smaller than the internal impedance of the CTRL1
pin which is 10MΩ (typ).
Dimming Control
There are three different types of dimming control circuits.
The LED current can be set by modulating the CTRL1 pin
with a DC voltage, a filtered PWM signal or directly with
a PWM signal.
PWM
10kHz TYP
LT3498
R1
100kΩ
CTRL1
C1
0.1μF
3498 F04
Using a DC Voltage
For some applications, the preferred method of brightness
control is a variable DC voltage to adjust the LED current.
The CTRL1 pin voltage can be modulated to set the dimming of the LED string. As the voltage on the CTRL1 pin
increases from 0V to 1.5V, the LED current increases from
0 to ILED. As the CTRL1 pin voltage increases beyond 1.5V,
it has no effect on the LED current.
Figure 4. Dimming Control Using a Filtered PWM Signal
3498fa
11
LT3498
APPLICATIONS INFORMATION— LED DRIVER
Direct PWM Dimming
Changing the forward current flowing in the LEDs not only
changes the intensity of the LEDs, it also changes the color.
The chromaticity of the LEDs changes with the change in
forward current. Many applications cannot tolerate any
shift in the color of the LEDs. Controlling the intensity of
the LEDs with a direct PWM signal allows dimming of the
LEDs without changing the color. In addition, direct PWM
dimming offers a wider dimming range to the user.
Dimming the LEDs via a PWM signal essentially involves
turning the LEDs on and off at the PWM frequency. The
typical human eye has a limit of ~60 frames per second.
By increasing the PWM frequency to ~80Hz or higher,
the eye will interpret that the pulsed light source is continuously on. Additionally, by modulating the duty cycle
(amount of “on-time”), the intensity of the LEDs can be
controlled. The color of the LEDs remains unchanged in
this scheme since the LED current value is either zero or
a constant value.
signal should traverse between 0V to 5V, to ensure proper
turn-on and -off of the driver and the NMOS transistor Q1.
When the PWM signal goes high, the LEDs are connected
to ground and a current of ILED = 200mV / RSENSE1 flows
through the LEDs. When the PWM signal goes low, the
LEDs are disconnected and turn off. The MOSFET ensures
that the LEDs quickly turn off without discharging the
output capacitor which in turn allows the LEDs to turn on
faster. Figure 6 shows the PWM dimming waveforms for
the circuit in Figure 5.
ILED
20mA/DIV
IL
200mA/DIV
PWM
5V/DIV
2ms/DIV
VIN = 3V
4 LEDs
Figure 5 shows a Li-Ion powered driver for four white
LEDs. Direct PWM dimming method requires an external
NMOS tied between the cathode of the lowest LED in the
string and ground as shown in Figure 5. A simple logic
level Si2304 MOSFET can be used since its source is connected to ground. The PWM signal is applied to the CTRL1
pin of the LT3498 and the gate of the MOSFET. The PWM
3498 F06
Figure 6. Direct PWM Dimming Waveforms
80
VIN = 3.6V
4 LEDs
100Hz = PWM
75
RSENSE1
10Ω
CIN
1μH
L1
15μH
CAP1 SW1
VIN SW2 CAP2 VOUT2
LT3498
COUT1
1μF
LED1
CTRL1 GND1
GND2
EFFICIENCY (%)
VIN 3V TO 5V
70
65
60
55
CTRL2
FB2
Q1
Si2304BDS
50
0
5V
100k
PWM
FREQ
0V
2
4
6 8 10 12 14 16 18 20
LED CURRENT (mA)
3498 F07
3498 F05
Figure 7. PWM Dimming Efficiency
Figure 5. Li-Ion to Four White LEDs
with Direct PWM Dimming
3498fa
12
LT3498
APPLICATIONS INFORMATION— LED DRIVER
The time it takes for the LED current to reach its programmed value sets the achievable dimming range for a
given PWM frequency. For example, the settling time of
the LED current in Figure 6 is approximately 40μs for a
3V input voltage. The achievable dimming range for this
application and 100Hz PWM frequency can be determined
using the following method.
Example:
f = 100Hz, t SETTLE = 40μs
1
1
t PERIOD = =
= 0.01s
f 100
0.01s
t
Dim Range = PERIOD =
= 250 : 1
t SETTLE 40μs
Min Duty Cycle =
40μs
t SETTLE
• 100 =
• 100 = 0.4%
0.01s
t PERIOD
Duty Cycle Range = 100% → 0.4% at 100Hz
The dimming range can be further extended by changing
the amplitude of the PWM signal. The height of the PWM
signal sets the commanded sense voltage across the sense
resistor through the CTRL1 pin. In this manner both analog
dimming and direct PWM dimming extend the dimming
range for a given application. The color of the LEDs no
longer remains constant because the forward current of
the LED changes with the height of the CTRL1 signal. For
the four LED application described above, the LEDs can
be dimmed first, modulating the duty cycle of the PWM
signal. Once the minimum duty cycle is reached, the height
of the PWM signal can be decreased below 1.5V down to
125mV. The use of both techniques together allows the
average LED current for the four LED application to be
varied from 20mA down to less than 20μA. Figure 9 shows
the application for dimming using both analog dimming
and PWM dimming. A potentiometer must be added to
ensure that the gate of the NMOS receives a logic-level
signal, while the CTRL1 signal can be adjusted to lower
amplitudes.
VIN 3V TO 5V
The calculations show that for a 100Hz signal the dimming
range is 250:1. In addition, the minimum PWM duty cycle
of 0.4% ensures that the LED current has enough time to
settle to its final value. Figure 8 shows the dimming range
achievable for three different frequencies with a settling
time of 40μs.
RSENSE1
10Ω
CAP1 SW1
VIN SW2 CAP2 VOUT2
LT3498
COUT1
1μF
LED1
CTRL1 GND1
GND2
CTRL2
FB2
5V
10000
PWM
FREQ
PULSING MAY BE VISIBLE
1000
PWM DIMMING RANGE
CIN
1μH
L1
15μH
0V
3498 F09
Q1
Si2304BDS
100k
100
10
1
Figure 9. Li-Ion to Four White LEDs with
Both PWM Dimming and Analog Dimming
10
100
1000
PWM FREQUENCY (Hz)
10000
3498 F08
Figure 8. Dimming Ratio vs Freqeuncy
3498fa
13
LT3498
APPLICATIONS INFORMATION— OLED DRIVER
Inductor Selection
Capacitor Selection
Several recommended inductors that work well with the
OLED driver of the LT3498 are listed in Table 5, although
there are many other manufacturers and devices that can
be used. Consult each manufacturer for more detailed
information and for their entire selection of related parts.
Many different sizes and shapes are available. Use the
equations and recommendations in the next few sections
to find the correct inductance value for your design.
The small size and low ESR of ceramic capacitors makes
them suitable for most OLED Driver applications. X5R and
X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than
other types such as Y5V or Z5U. A 4.7μF input capacitor
and a 10μF output capacitor are sufficient for most applications for the OLED Driver. Always use a capacitor with
a sufficient voltage rating. Many capacitors rated at 10μF,
particularly 0805 or 0603 case sizes, have greatly reduced
capacitance when bias voltages are applied. Be sure to check
actual capacitance at the desired output voltage. Generally
a 1206 size capacitor will be adequate. A 0.47μF capacitor placed on the CAP node is recommended to filter the
inductor current while the larger 10μF placed on the VOUT
node will give excellent transient response and stability.
Table 6 shows a list of several capacitor manufacturers.
Consult the manufacturers for more detailed information
and for their entire selection of related parts.
Table 5: Recommended Inductors
L
(μH)
MAX
DCR
(Ω)
LQH32CN100K53
LQH2MCN100K02
LQH32CN150K53
LQH2MCN150K02
10
10
15
15
0.3
1.2
0.58
1.6
450
225
300
200
Murata
www.murata.com
SD3110-100
SD3110-150
10
15
0.505
0.764
470
380
Cooper
www.cooperet.com
PART
CURRENT
RATING
(mA)
VENDOR
Inductor Selection—Boost Regulator
The formula below calculates the appropriate inductor
value to be used for the low noise boost regulator of
the LT3498 (or at least provides a good starting point).
This value provides a good tradeoff in inductor size and
system performance. Pick a standard inductor close to
this value. A larger value can be used to slightly increase
the available output current, but limit it to around twice
the value calculated below, as too large of an inductance
will decrease the output voltage ripple without providing
much additional output current. A smaller value can be
used (especially for systems with output voltages greater
than 12V) to give a smaller physical size. Inductance can
be calculated as:
μH)
L = (VOUT2 − VIN(MIN) + 0.5V) • 0.66(μH)
where VOUT2 is the desired output voltage and VIN(MIN)
is the minimum input voltage. Generally, a 10μH or 15μH
inductor is a good choice.
Table 6. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER
PHONE
URL
Taiyo Yuden
408-573-4150
www.t-yuden.com
AVX
843-448-9411
www.avxcorp.com
Murata
814-237-1431
www.murata.com
Kemet
408-986-0424
www.kemet.com
Setting Output Voltage and the Auxiliary
Reference Input
The OLED driver of the LT3498 is equipped with both an
internal 1.215V reference and an auxiliary reference input.
This allows the user to select between using the built-in
reference, and supplying an external reference voltage.
The voltage at the CTRL2 pin can be adjusted while the
chip is operating to alter the output voltage of the LT3498
for purposes such as display dimming or contrast adjustment. To use the internal 1.215V reference, the CTRL2
pin must be held higher than 1.5V. When the CTRL2 pin
is held between 0V and 1.5V the OLED driver will regulate
the output such that the FB2 pin voltage is nearly equal to
the CTRL2 pin voltage. At CTRL2 voltages close to 1.215V,
3498fa
14
LT3498
APPLICATIONS INFORMATION— OLED DRIVER
a soft transition occurs between the CTRL2 pin and the
internal reference. Figure 10 shows this behavior.
1.500
FB2 VOLTAGE (V)
1.250
1.000
0.750
0.500
Choosing a Feedback Node
The single feedback resistor may be connected to the VOUT2
pin or to the CAP2 pin (see Figure 11). Regulating the
VOUT2 pin eliminates the output offset resulting from the
voltage drop across the output disconnect PMOS. Regulating the CAP2 pin does not compensate for the voltage
drop across the output disconnect, resulting in an output
voltage VOUT2 that is slightly lower than the voltage set by
the resistor divider. Under most conditions, it is advised
that the feedback resistor be tied to the VOUT2 pin.
0.250
Connecting the Load to the CAP2 Node
0
0
0.5
0.8
1.0
CTRL2 VOLTAGE (V)
0.3
1.3
1.5
3498 F10
Figure 10. CTRL2 to FB2 Transfer Curve
To set the maximum output voltage, select the values of
RFB2 according to the following equation:
V
RFB2 =182 • OUT2 – 1 , k
1.215 When CTRL2 is used to override the internal reference,
the output voltage can be lowered from the maximum
value down to nearly the input voltage level. If the voltage source driving the CTRL2 pin is located at a distance
to the LT3498, a small 0.1μF capacitor may be needed to
bypass the pin locally.
CAP1
SW1
VIN
SW2
CAP2
VOUT2
LT3498
LED1
CTRL1
GND1
GND2
C2
The efficiency of the converter can be improved by connecting the load to the CAP2 pin instead of the VOUT2 pin.
The power loss in the PMOS disconnect circuit is then
made negligible. By connecting the feedback resistor to
the VOUT2 pin, no quiescent current will be consumed
in the feedback resistor string during shutdown since
the PMOS transistor will be open (see Figure 12). The
disadvantage of this method is that the CAP2 node cannot go to ground during shutdown, but will be limited to
around a diode drop below VIN . Loads connected to the
part should only sink current. Never force external power
supplies onto the CAP2 or VOUT2 pins. The larger value
output capacitor should be placed on the node to which
the load is connected.
CAP1
SW1
SW2
CAP2
VOUT2
LT3498
RFB2
CTRL2
VIN
FB2
LED1
CTRL1
GND1
GND2
C3
ILOAD
RFB2
CTRL2
FB2
3498 F12
C2
Figure 12. Improved Efficiency
CAP1
SW1
VIN
SW2
CAP2
VOUT2
LT3498
LED1
CTRL1
GND1
GND2
C3
RFB2
CTRL2
FB2
3498 F11
Figure 11. Feedback Connection Using
the CAP2 Pin or the VOUT2 Pin
3498fa
15
LT3498
APPLICATIONS INFORMATION— OLED DRIVER
Maximum Output Load Current
Step 4: Calculate the nominal output current:
The maximum output current of a particular LT3498
circuit is a function of several circuit variables. The following method can be helpful in predicting the maximum
load current for a given circuit:
Step 1: Calculate the peak inductor current:
IPK = ILIMIT +
VIN • 400 • 10 –9
amps
L
where ILIMIT is 0.3A for the OLED driver. L is the inductance value in Henrys and VIN is the input voltage to the
boost circuit.
Step 2: Calculate the inductor ripple current:
IRIPPLE =
(VOUT2 + 1 – VIN) • 150 • 10
–9
L
amps
where VOUT2 is the desired output voltage.
If the inductor ripple current is less then the peak current,
then the circuit will only operate in discontinuous conduction mode. The inductor value should be increased so
that IRIPPLE < IPK. An application circuit can be designed
to operate only in discontinuous mode, but the output
current capability will be reduced.
Step 3: Calculate the average input current:
IIN( AVG) = IPK –
IRIPPLE
amps
2
IOUT(NOM) =
IIN( AVG) • VIN • 0.75
VOUT 2
amps
Step 5: Derate output current:
IOUT = IOUT(NOM) • 0.7 amps
For low output voltages the output current capability will
be increased. When using output disconnect (load current
taken from VOUT2), these higher currents will cause the
drop in the PMOS switch to be higher resulting in reduced
output current capability than those predicted by the
preceding equations.
Inrush Current
When VIN is stepped from ground to the operating voltage
while the output capacitor is discharged, a higher level of
inrush current will flow through the inductor and integrated
Schottky diode into the output capacitor. Conditions that
increase inrush current include a larger more abrupt voltage
step at VIN, a larger output capacitor tied to the CAP2 pin,
and an inductor with a low saturation current. While the
internal diode is designed to handle such events, the inrush
current should not be allowed to exceed 1A. For circuits
that use output capacitor values within the recommended
range and have input voltages of less than 5V, inrush current remains low, posing no hazard to the device. In cases
where there are large steps at VIN (more than 5V) and/or
a large capacitor is used at the CAP2 pin, inrush current
should be measured to ensure safe operation.
3498fa
16
LT3498
APPLICATIONS INFORMATION— LED AND OLED DRIVER
Board Layout Considerations
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To prevent electromagnetic interference (EMI) problems,
proper layout of high frequency switching paths is essential.
Minimize the length and area of all traces connected to
the switching node pins (SW1 and SW2). Keep the sense
voltage pins (CAP1 and LED1) away from the switching
LED1
node. The FB2 connection for the feedback resistor RFB2
should be tied directly from the VOUT2 pin to the FB2
pin and be kept as short as possible, ensuring a clean,
noise-free connection. Place COUT1 and COUT2 next to the
CAP1 and CAP2 pins respectively. Always use a ground
plane ender the switching regulator to minimize interplane
coupling. Recommended component placement is shown
in Figure 13.
RSENSE1
CAP1
C1
SW1
1
12
2
11
3
10
4
9
5
8
6
7
CTRL1
GND
L1
GND
VIN
CIN
CTRL2
RFB2
VOUT2
L2
SW2
C3
VOUT2
FB2
C2
GND
CAP2
3498 F13
VIAS TO GROUND PLANE REQUIRED TO
IMPROVE THERMAL PERFORMANCE
VIAS TO VOUT2
Figure 13. Recommended Board Layout
3498fa
17
LT3498
TYPICAL APPLICATIONS
Li-Ion to Two White LEDs and OLED/LCD Bias
VIN = 3V TO 5V
CIN
4.7μF
L1
10μH
C1
1μF
CAP1 SW1
C2
0.47μF
L2
10μH
16V
24mA
SW2
VIN
CAP2 VOUT2
C3
10μF
LT3498
20mA
LED1
RSENSE1
10Ω
CTRL1
GND1
GND2
OFF ON
SHUTDOWN
AND
DIMMING
CONTROL
CTRL2
RFB2
2.21MΩ
FB2
OFF ON
SHUTDOWN
AND
CONTROL
3498 TA02
CIN, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING
C1: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN TMK316BJ106ML
L1, L2: MURATA LQH32CN100K53
LED Efficiency
VIN = 3.6V, 2 LEDs
75
70
EFFICIENCY (%)
65
60
55
50
45
40
0
5
10
15
20
LED CURRENT (mA)
3498 TA02b
3498fa
18
LT3498
TYPICAL APPLICATIONS
Li-Ion to Two White LEDs and OLED/LCD Bias
VIN = 3V TO 5V
CIN
4.7μF
L1
10μH
CAP1 SW1
C1
1μF
C2
0.47μF
L2
10μH
16V
24mA
SW2
VIN
CAP2 VOUT2
C3
10μF
LT3498
RSENSE1
10Ω
LED1
CTRL1
GND1
GND2
OFF ON
SHUTDOWN
AND
DIMMING
CONTROL
20mA
CTRL2
FB2
RFB2
2.21MΩ
OFF ON
SHUTDOWN
AND
CONTROL
3498 TA03
CIN, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING
C1: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN TMK316BJ106ML
L1, L2: MURATA LQH32CN100K53
LED Efficiency
VIN = 3.6V, 2 LEDs
80
75
EFFICIENCY (%)
70
65
60
55
50
45
40
0
5
10
15
20
LED CURRENT (mA)
3498 TA03b
3498fa
19
LT3498
TYPICAL APPLICATIONS
Li-Ion to Three White LEDs and OLED/LCD Bias
VIN = 3V TO 5V
L1
15μH
CAP1 SW1
C1
1μF
C2
0.47μF
CIN
4.7μF
L2
10μH
16V
24mA
SW2
VIN
CAP2 VOUT2
C3
10μF
LT3498
RSENSE1
10Ω
LED1
CTRL1
GND1
GND2
OFF ON
SHUTDOWN
AND
DIMMING
CONTROL
20mA
CTRL2
FB2
RFB2
2.21MΩ
OFF ON
SHUTDOWN
AND
CONTROL
3498 TA04
CIN, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING
C1: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN TMK316BJ106ML
L1: MURATA LQH32CN150K53
L2: MURATA LQH32CN100K53
LED Efficiency
VIN = 3.6V, 3 LEDs
80
75
EFFICIENCY (%)
70
65
60
55
50
45
0
5
10
15
20
LED CURRENT (mA)
3498 TA04b
3498fa
20
LT3498
TYPICAL APPLICATIONS
Li-Ion to Four White LEDs and OLED/LCD Bias
VIN = 3V TO 5V
CIN
4.7μF
L1
15μH
CAP1 SW1
C1
1μF
C2
0.47μF
L2
10μH
16V
24mA
SW2
VIN
CAP2 VOUT2
C3
10μF
LT3498
RSENSE1
10Ω
LED1
CTRL1
GND1
GND2
OFF ON
SHUTDOWN
AND
DIMMING
CONTROL
20mA
CTRL2
FB2
RFB2
2.21MΩ
OFF ON
SHUTDOWN
AND
CONTROL
3498 TA05
CIN, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING
C1: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN TMK316BJ106ML
L1: MURATA LQH32CN150K53
L2: MURATA LQH32CN100K53
LED Efficiency
VIN = 3.6V, 4 LEDs
80
EFFICIENCY (%)
75
70
65
60
55
50
0
5
10
15
20
LED CURRENT (mA)
3498 TA05b
3498fa
21
LT3498
TYPICAL APPLICATIONS
Li-Ion to Six White LEDs and OLED/LCD Bias
VIN = 3V TO 5V
RSENSE1
10Ω
CIN
4.7μF
L1
15μH
CAP1 SW1
L2
10μH
C2
0.47μF
D1
CAP2 VOUT2
SW2
VIN
16V
24mA
C3
10μF
LT3498
C1
1μF
LED1
20mA
CTRL1
GND1
OFF ON
SHUTDOWN AND
DIMMING CONTROL
GND2
CTRL2
FB2
RFB2
2.21MΩ
OFF ON
SHUTDOWN AND
CONTROL
3498 TA06
CIN, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING
C1: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN TMK316BJ106ML
D1: CENTRAL SEMICONDUCTOR CMDSH-3
L1: MURATA LQH32CN150K53
L2: MURATA LQH32CN100K53
LED Efficiency,
VIN = 3.6V, 6 LEDs
OLED Efficiency and Power Loss
VIN = 3.6V, VOUT2 = 16V
80
EFFICIENCY (%)
70
65
60
55
50
0
5
10
15
20
LED CURRENT (mA)
400
75
350
70
300
65
250
60
200
55
150
50
100
45
50
40
0.1
1
10
POWER LOSS (mW)
EFFICIENCY (%)
75
80
0
100
LOAD CURRENT (mA)
3498 TA06b
LOAD FROM VOUT2
LOAD FROM CAP2
POWER LOSS FROM VOUT2
POWER LOSS FROM CAP2
3498 TA06c
3498fa
22
LT3498
PACKAGE DESCRIPTION
DDB Package
12-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1723 Rev Ø)
0.64 ±0.05
(2 SIDES)
0.70 ±0.05
2.55 ±0.05
1.15 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.45 BSC
2.39 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
3.00 ±0.10
(2 SIDES)
R = 0.05
TYP
R = 0.115
TYP
7
0.40 ± 0.10
12
2.00 ±0.10
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
0.75 ±0.05
0.64 ± 0.10
(2 SIDES)
6
0.23 ± 0.05
0 – 0.05
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
1
(DDB12) DFN 0106 REV Ø
0.45 BSC
2.39 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
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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.
23
LT3498
TYPICAL APPLICATION
Output Voltage Ripple
vs Load Current
VOUT2 PEAK-TO-PEAK RIPPLE (mV)
7
6
5
VOUT
RFB2 VALUE REQUIRED
(MΩ)
MAXIMUM OUTPUT
CURRENT AT 3V INPUT
(mA)
25
3.57
12.5
24
3.40
13.4
23
3.24
14.4
4
22
3.09
15.6
3
21
2.94
16.8
20
2.80
18.1
19
2.67
19.6
18
2.49
21.2
17
2.37
22.5
16
2.21
24.2
15
2.05
26
2
1
0
0.1
1
100
10
LOAD CURRENT (mA)
3498 TA06d
RELATED PARTS
PART
NUMBER
DESCRIPTION
COMMENTS
LT1932
Constant-Current, 1.2MHz, High Efficiency White LED
Boost Regulator
VIN : 1V to 10V; VOUT(MAX) = 34V; IQ = 1.2mA; ISD = <1μA; ThinSOTTM Package
LT1937
Constant-Current, 1.2MHz, High Efficiency White LED
Boost Regulator
VIN : 2.5V to 10V; VOUT(MAX) = 34V; IQ = 1.9μA; ISD = <1μA; ThinSOT and
SC70 Packages
LT3463/
LT3463A
Dual Output, Boost/Inverter, 250mA ISW, Constant OffTime, High Efficiency Step-Up DC/DC Converter with
Integrated Schottky Diodes
VIN : 2.3V to 15V; VOUT(MAX) = ±40V; IQ = 40μA; ISD = <1μA; 3mm × 3mm
DFN-10 Package
LT3465/
LT3465A
Constant-Current, 1.2/2.7MHz, High Efficiency White LED VIN : 2.3V to 16V; VOUT(MAX) = 40V; IQ = 40μA; ISD = <1μA; 3mm × 3mm
Boost Regulator with Integrated Schottky Diode
DFN-10 Package
LT3466/
LT3466-1
Dual Constant-Current, 2MHz, High Efficiency White LED
Boost Regulator with Integrated Schottky Diode
VIN : 2.3V to 16V; VOUT(MAX) = 40V; IQ = 65μA; ISD = <1μA; 3mm × 2mm
DFN-8 Package
LT3471
Dual Output, Boost/Inverter, 1.3A ISW, 1.2MHZ, High
Efficiency Boost-Inverting DC/DC Converter
VIN : 2.4V to 16V; VOUT(MAX) = ±40V; IQ = 2.5μA; ISD = <1μA; 3mm × 3mm
DFN-10 Package
LT3473/
LT3473A
40V, 1A , 1.2MHz Micropower Low Noise Boost Converter VIN : 2.2V to 16V; VOUT(MAX) = 36V; IQ = 150μA; ISD = <1μA; 3mm × 3mm
DFN-12 Package
with Output Disconnect
LT3491
Constant-Current, 2.3MHz, High Efficiency White LED
Boost Regulator with Integrated Schottky Diode
VIN : 2.5V to 12V; VOUT(MAX) = 27V; IQ = 12.6μA; ISD = <8μA; 2mm × 2mm
DFN-6 and SC70 Packages
LT3494/
LT3494A
40V, 180mA/350mA Micropower Low Noise Boost
Converter with Output Disconnect
VIN : 2.3V to 16V; VOUT(MAX) = 40V; IQ = 65μA; ISD = <1μA; 3mm × 2mm
DFN-8 Package
LT3497
Dual 2.3MHz, Full Function LED Driver with Integrated
Schottky Diode and 250:1 True Color PWMTM Dimming
VIN : 2.5V to 10V; VOUT(MAX) = 32V; IQ = 6mA; ISD = <12μA; 3mm × 2mm
DFN-10 Package
LT3591
Constant-Current, 1MHz, High Efficiency White LED
Boost Regulator with Integrated Schottky Diode and 80:1
True Color PWM Dimming
VIN : 2.5V to 12V; VOUT(MAX) = 40V; IQ = 4mA; ISD = <9μA; 3mm × 2mm
DFN-8 Package
ThinSot and True Color PWM are trademarks of Linear Technology Corporation
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24 Linear Technology Corporation
LT 0508 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2007