LT3462/LT3462A
3462af
1
APPLICATIO S
U
DESCRIPTIO
U
FEATURES
TYPICAL APPLICATIO
U
■
Integrated Schottky Rectifier
■
Fixed Frequency 1.2MHz/2.7MHz Operation
■
Very Low Noise: 1mV
P-P
Output Ripple
■
Low V
CESAT
Switch: 270mV at 250mA
■
–5V at 100mA from 5V Input
■
–12V at 30mA from 3.3V Input
■
Low Input Bias Current GND Based FB Input
■
Low Impedance (40Ω) 1.265V Reference Output
■
High Output Voltage: Up to –38V
■
Wide Input Range: 2.5V to 16V
■
Uses Tiny Surface Mount Components
■
Low Shutdown Current: <10µA
■
Low Profile (1mm) SOT-23 (ThinSOT
TM
) Package
■
CCD Bias
■
LCD Bias
■
GaAs FET Bias
■
General Purpose Negative Voltage Supply
Inverting 1.2MHz/2.7MHz
DC/DC Converters with
Integrated Schottky in ThinSOT
The LT
®
3462/LT3462A are general purpose fixed fre-
quency current mode inverting DC/DC converters. Both
devices feature an integrated Schottky and a low V
CESAT
switch allowing a small converter footprint and lower parts
cost. The LT3462 switches at 1.2MHz while the LT3462A
switches at 2.7MHz. These high speeds enable the use of
tiny, low cost and low height capacitors and inductors.
The LT3462/LT3462A operate in a dual inductor inverting
topology that filters both the input and output currents.
Very low output voltage ripple approaching 1mV
P-P
can be
achieved when ceramic capacitors are used. Fixed fre-
quency switching ensures a clean output free from low
frequency noise typically present with charge pump solu-
tions. The 40V switch allows a V
IN
to V
OUT
differential of
up to 38V for dual inductor topologies.
Both devices provide a low impedance 1.265V reference
output to supply the feedback resistor network. A ground
referenced, high impedance FB input allows high feedback
resistor values without compromising output accuracy.
The LT3462/LT3462A are available in a 6-lead SOT-23
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
5V to –5V, 100mA Inverting DC/DC Converter Efficiency
ThinSOT is a trademark of Linear Technology Corporation
LOAD CURRENT (mA)
0
EFFICIENCY (%)
75
70
65
60
55
3462 TA01b
20 40 8060 100
V
IN
= 3.3V
V
IN
= 5V
T
A
= 25°C
V
IN
5V
22µH22µH
267k
68.1k 10µF
22pF
1µF
1µF
V
OUT
–5V
100mA
V
IN
SW FB
SDREF
GND
LT3462A
3462 TA01
D
LT3462/LT3462A
3462af
2
Input Voltage (V
IN
) .................................................. 16V
SW Voltage .............................................................. 40V
D Voltage ............................................................... –40V
SDREF, FB Voltage ................................................. 2.5V
Operating Ambient
Temperature Range (Note 3) ...............–40°C to 85°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10sec)................... 300°C
ABSOLUTE AXI U RATI GS
W
WW
U
PACKAGE/ORDER I FOR ATIO
UUW
(Note 1)
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VIN = 3V, unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Operating Voltage 2.5 V
Maximum Operating Voltage 16 V
SDREF Voltage 10µA > I
SDREF
≥ –80µA●1.245 1.265 1.285 V
FB Pin Bias Current (Note 2) 15 50 nA
SDREF Minus FB Voltage 10µA > I
SDREF
≥ –80µA●1.235 1.263 1.285 V
Error Amp Offset Voltage –12 12 mV
SDREF Reference Source Current SDREF >1.2V ●120 180 µA
Supply Current FB = –0.05V, Not Switching 2.9 3.6 mA
SDREF = 0V, FB = Open, V
IN
= 5V 6.5 10 µA
SDREF Line Regulation 0.007 %/V
Switching Frequency (LT3462) ●0.8 1.2 1.6 MHz
Switching Frequency (LT3462A) ●2.0 2.7 3.5 MHz
Maximum Duty Cycle (LT3462) ●90 %
Maximum Duty Cycle (LT3462A) ●77 %
Switch Current Limit 300 420 mA
Switch V
CESAT
I
SW
= 250mA 270 350 mV
Switch Leakage Current V
SW
= 5V 0.01 1 µA
Rectifier Leakage Current V
D
= –40V 0.03 4 µA
Rectifier Forward Drop I
SCHOTTKY
= 250mA 800 1100 mV
SDREF Voltage Low ●0.20 V
SDREF Off-State Pull-Up Current 123 µA
SDREF Turn-Off Current –300 –200 µA
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ORDER PART
NUMBER
S6 PART MARKING
LTBBV
LTBGB
LT3462ES6
LT3462AES6
T
JMAX
= 125°C
θ
JA
= 150°C ON BOARD OVER
GROUND PLANE
θ
JC
= 120°C/W
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: Current flows out of the pin.
Note 3: The LT3462E 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.
6 VIN
5 D
4 SDREF
SW 1
TOP VIEW
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
GND 2
FB 3
LT3462/LT3462A
3462af
3
TEMPERATURE (°C)
SDREF MINUS FB (V)
1.29
1.28
1.27
1.26
1.25
1.24
1.23
3462 G03
DUTY CYCLE (%)
10
CURRENT LIMIT (mA)
9080604020
3462 G02
30 50 70
480
360
240
120
0
3462 G05 3462 G06
TEMPERATURE (°C)
–40
FREQUENCY (MHz)
1.6
1.5
1.4
1.3
1.2
1.1
1.0 20 60
3462 G01
–20 0 40 80 100
TEMPERATURE (°C)
FREQUENCY (MHz)
3462 G04
3.2
3.0
2.8
2.6
2.4
2.2
2.0
T
A
= 25°C
SUPPLY VOLTAGE (V)
0
QUIESCENT CURRENT (µA)
16
4812
10
8
6
4
2
0
T
A
= 25°C
FB = N/C
TEMPERATURE (°C)
FB BIAS CURRENT (nA)
80 10040 60200–40 –20
0
–5
–10
–15
–20
–25
–30
–35
–40
–45
–50
–40 20 60
–20 0 40 80 100
–40 20 60
–20 0 40 80 100
T
A
= 25°C
LT3462
LT3462A
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Oscillator Frequency (LT3462) Current Limit SDREF Minus FB Pin Voltage
Oscillator Frequency (LT3462A) FB Bias Current Quiescent Current in
Shutdown Mode
UU
U
PI FU CTIO S
SW (Pin 1): Switch Pin. Connect to external inductor L1
and positive terminal of transfer cap.
GND (Pin 2): Ground. Tie directly to local ground plane.
FB (Pin 3): Feedback Pin. Connect resistive divider tap
here. Set R1 according to R1 = R2 • (V
OUT
/1.265V). In
shutdown, a proprietary shutdown bias current cancella-
tion circuit allows the internal 3µA source to pull up the
SDREF pin, even with residual negative voltage on V
OUT
.
SDREF (Pin 4): Dual Function Shutdown and 1.265V
Reference Output Pin. Pull to GND with external N-FET to
turn regulator off. Turn-off pull-down and a 2µA internal
source will pull SDREF up to turn-on the regulator. At turn-
on, a 180µA internal source pulls the pin to the regulation
voltage. The SDREF pin can supply up to 80µA at 1.265V
to bias the feedback resistor divider. An optional soft-start
circuit capacitor connects from this pin to –V
OUT
.
D (Pin 5): Anode Terminal of Integrated Schottky Diode.
Connect to negative terminal of transfer cap and external
inductor L2.
V
IN
(Pin 6): Input Supply Pin. Must be locally bypassed.
LT3462/LT3462A
3462af
4
OPERATIO
U
BLOCK DIAGRA
W
Figure 1. Block Diagram
–
+
–
+
–
+
–
+
1
3
2
∑
VOUT VOUT
D
R1 (EXTERNAL)
R2 (EXTERNAL)
FB
RAMP
GENERATOR
SHUTDOWN
BIAS CURRENT
CANCELLATION
1.2MHz*
OSCILLATOR
RSQ
A1
E AMP A2
COMP
DRIVER
RC
CC
SW
Q1
0.1Ω
GND
61.265V
REFERENCE
VIN
FB
4
SDREF
SDREF
SDREF
3462 F02
5
*LT3462A IS 2.7MHz
CS1 (EXTERNAL)
CS2 (EXTERNAL)
Q2
OFF → 3µA
ON → 180µA
ISRC
SHUTDOWN
CS1, CS2 OPTIONAL SOFT-START COMPONENTS
DO
LG
The LT3462 uses a constant frequency, current mode
control scheme to provide excellent line and load regula-
tion. Operation can be best understood by referring to the
Block Diagram in Figure 1. At the start of each oscillator
cycle, the SR latch is set, turning on the power switch Q1.
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. When this
voltage exceeds the voltage at the output of the EAMP, the
SR latch is reset, turning off the power switch. The level
at the output of the EAMP is simply an amplified version
of the difference between the feedback voltage and GND.
In this manner, the error amplifier sets the correct peak
current level to keep the output in regulation. If the error
amplifier’s output increases, more current is taken from
the output; if it decreases, less current is taken. One
function not shown in Figure 1 is the current limit. The
switch current is constantly monitored and not allowed to
exceed the nominal value of 400mA. If the switch current
reaches 400mA, the SR latch is reset regardless of the
output state of the PWM comparator. This current limit cell
protects the power switch as well as various external
components connected to the LT3462.
SDREF is a dual function input pin. When driven low it
shuts the part down, reducing quiescent supply current to
less than 10µA. When not driven low, the SDREF pin has an
internal pull-up current that turns the regulator on. Once
the part is enabled, the SDREF pin sources up to
180µA nominally at a fixed voltage of 1.265V through
external resistor R2 to FB. If there is no fault condition
present, FB will regulate to 0V, and V
OUT
will regulate to
1.265V • (–R1/R2). An optional soft-start circuit uses the
fixed SDREF pull-up current and a capacitor from SDREF
to V
OUT
to set the dV/dt on V
OUT
. In shutdown, an FB bias
current cancellation circuit supplies up to 150µA biasing
current to external resistor R1 while V
OUT
is lower than FB.
This function eliminates R2 loading of SDREF during
shutdown. As a result, supply current in shutdown may
exceed 10µA by the amount of current flowing in R1.
LT3462/LT3462A
3462af
5
R2
R1
GND
C3
L1
L2
C1
V
OUT
V
IN
+
C4
C2
3462 F03
1
2
34
5
6
Inrush Current
The LT3462 has a built-in Schottky diode. When supply
voltage is applied to the V
IN
pin, the voltage difference
between V
IN
and V
D
generates inrush current flowing from
input through the inductor and the Schottky diode to
charge the flying capacitor to V
IN
. The maximum
nonrepetitive surge current the Schottky diode in the
LT3462 can sustain is 1.5A. The selection of inductor and
capacitor value should ensure the peak of the inrush
current to be below 1.5A. The peak inrush current can be
calculated as follows:
IVO
L
C
L
C
PIN
=
–.
–
exp –
–
6
121
π
where L is the inductance between supply and SW, and C
is the capacitance between SW and D.
Table 3 gives inrush peak currents for some component
selections.
Table 3. Inrush Peak Current
V
IN
(V) L (µH) C (µF) I
P
(A)
5 22 1 0.70
5 33 1 0.60
12 47 1 1.40
Inductor Selection
Each of the two inductors used with LT3462 should have
a saturation current rating (where inductance is approxi-
mately 70% of zero current inductance ) of approximately
0.25A or greater. If the device is used in the charge pump
mode, where there is only one inductor, then its rating
should be 0.35A or greater. DCR of the inductors should
be less than 1Ω. For LT3462, a value of 22µH is suitable
if using a coupled inductor such as Sumida CLS62-220. If
using two separate inductors, increasing the value to
47µH will result in the same ripple current. For LT3462A,
a value of 10µH for the coupled inductor and 22µH for two
inductors will be acceptable for most applications.
APPLICATIO S I FOR ATIO
WUUU
Figure 2. Suggested Layout
Capacitor Selection
Ceramic capacitors are recommended. An X7R or X5R
dielectric should be used to avoid capacitance decreasing
severely with applied voltage and at temperature limits.
The “flying” capacitor between the SW and D pins should
be a ceramic type of value 1µF or more. When used in the
dual inductor or coupled inductor topologies the flying
capacitor should have a voltage rating that is more than the
difference between the input and output voltages. For the
charge pump inverter topology, the voltage rating should
be more than the output voltage. The output capacitor
should be a ceramic type. Acceptable output capacitance
varies from 1µF for high V
OUT
(–36V), to 10µF for low V
OUT
(–5V). The input capacitor should be a 1µF ceramic type
and be placed as close as possible to the LT3462/LT3462A.
Layout Hints
The high speed operation of the LT3462 demands careful
attention to board layout. You will not get advertised
performance with careless layout. Figure 2 shows the
recommended component placement. A ceramic capaci-
tor of 1µF or more must be placed close to the IC for input
supply bypassing.
LT3462/LT3462A
3462af
6
TYPICAL APPLICATIO S
U
Li+ to –8V Supply
–12V Efficiency
LOAD CURRENT (mA)
0
EFFICIENCY (%)
80
75
70
65
60
55
50
3462 TA02b
1052015 25 3530
T
A
= 25°C
V
IN
= 3.3V
3.3V to –12V with Soft-Start Circuit
V
IN
3.3V
L1
47µHL2
47µH
R1
267k
R2
27.4k
C3
2.2µF
C
S1
100nF
22nF
C4
15pF
C1
4.7µF
C2
1µF
V
OUT
–12V
30mA
V
IN
SW FB
SDREF
GND
LT3462
C1: TAIYO YUDEN X5R JMK212BJ475MG
C2: TAIYO YUDEN X5R EMK212BJ105MG
C3: TAIYO YUDEN EMK316BJ225
L1, L2: MURATA LQH32CN470
3462 TA02a
OFF M1
D
V
IN
2.7V
TO 4.2V
L1A
22µHL1B
22µH
R1
267k
R2
42.2k C3
4.7µF
C4
15pF
C1
4.7µF
C2
1µF
V
OUT
–8V
V
IN
SW FB
SDREF
GND
LT3462
C1: TAIYO YUDEN X5R JMK212BJ475MG
C2: TAIYO YUDEN X5R EMK212BJ105MG
C3: TAIYO YUDEN LMK316BJ475
L1: SUMIDA CLS62-220 OR 2X MURATA LQH32CN330
3462 TA03a
D
LOAD CURRENT (mA)
0
EFFICIENCY (%)
3462 TA03b
20 3010 40 50
80
75
70
65
60
55
50
T
A
= 25°C
V
IN
= 3.3V
–8V Efficiency
2ms/DIV
I
IN
100mA/DIV
OFF
V
OUT
10V/DIV
3462 TA02c
VOUT Reaches –12V in 750µs; Input
Current Peaks at 300mA without CS1
VOUT Reaches –12V in 7.5ms; Input
Current Peaks at 125mA with CS1 = 100nF
2ms/DIV
I
IN
50mA/DIV
OFF
V
OUT
10V/DIV
3462 TA02d
LT3462/LT3462A
3462af
7
PACKAGE DESCRIPTIO
U
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
1.50 – 1.75
(NOTE 4)
2.80 BSC
0.30 – 0.45
6 PLCS (NOTE 3)
DATUM ‘A’
0.09 – 0.20
(NOTE 3)
S6 TSOT-23 0302
2.90 BSC
(NOTE 4)
0.95 BSC
1.90 BSC
0.80 – 0.90
1.00 MAX 0.01 – 0.10
0.20 BSC
0.30 – 0.50 REF
PIN ONE ID
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD
FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3.85 MAX
0.62
MAX 0.95
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
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-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
TYPICAL APPLICATIO S
U
V
IN
2.7V
TO 4.2V
L1A
10µHL1B
10µH
R1
267k
R2
42.2k C3
4.7µF
C4
22pF
C1
1µF
C2
1µF
V
OUT
–8V
35mA
V
IN
SW FB
SDREF
GND
LT3462A
C1: TAIYO YUDEN JMK107BJ105MA
C2: TAIYO YUDEN EMK212BJ105MA
C3: TAIYO YUDEN LMK316BJ475
L1: WURTH 50310057-100
3462 TA04a
D
..
V
IN
5V
L1
22µHL2
22µH
R1
267k
R2
68.1k
C3
10µF
C4
22pF
C1
1µF
C2
1µF
V
OUT
–5V
100mA
V
IN
SW FB
SDREF
GND
LT3462A
C1: TAIYO YUDEN JMK107BJ105MA
C2: TAIYO YUDEN EMK212BJ105MA
C3: MURATA GRM219R60J106KE19B
L1, L2: MURATA LQH32CN220
3462 TA05a
D
5V to –5V Supply (LT3462A)3.3V to –8V (LT3462A)
Switching Waveform
200ns/DIV
V
OUT
1mV/DIV
AC COUPLED
V
SW
10V/DIV
3462 TA05b
INDUCTOR
50mA/DIV
LT3462/LT3462A
3462af
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
LINEAR TECHNO LOGY CORPORATION 2004
LT/TP 0304 1K • PRINTED IN USA
RELATED PARTS
TYPICAL APPLICATIO S
U
12V to –36V DC/DC Converter
V
IN
12V
L1
47µH
R1
432k
R2
15k C3
1µF
50V
C4
5pF
C1
1µF
C2
0.47µF
V
OUT
–36V
36mA
V
IN
SW FB
SDREF
GND
LT3462
C1: TAIYO YUDEN X5R EMK212BJ105
C2: MURATA GRM42-6X7R474K50
C3: MURATA GRM42-6X7R474K50 ×2
D1: CENTRAL CMSH5-4-LTN
L1: MURATA LQH32CN470
3462 TA06a
D
D1
100nF
–36V Efficiency
LOAD CURRENT (mA)
0
EFFICIENCY (%)
40
3462 TA06b
20 3010
85
80
75
70
65
60
T
A
= 25°C
V
IN
= 12V
PART NUMBER DESCRIPTION COMMENTS
LT1617/LT1617-1 350mA/100mA (I
SW
) High Efficiency V
IN
: 1.2V to 15V, V
OUT(MAX)
= –34V, I
Q
= 20µA, I
SD
<1µA
Micropower Inverting DC/DC Converter ThinSOT Package
LT1931/LT1931A 1A (I
SW
), 1.2MHz/2.2MHz, High Efficiency V
IN
: 2.6V to 16V, V
OUT(MAX)
= –34V, I
Q
= 5.8mA, I
SD
<1µA
Micropower Inverting DC/DC Converter ThinSOT Package
LT1945 Dual Output, Boost/Inverter, 350mA (I
SW
), Constant V
IN
: 1.2V to 15V, V
OUT(MAX)
= ±34V, I
Q
= 40µA, I
SD
<1µA,
Off-Time, High Efficiency Step-Up DC/DC Converter MS10 Package
LT1946/LT1946A 1.5A (I
SW
), 1.2MHz/2.7MHz, High Efficiency V
IN
: 2.45V to 16V, V
OUT(MAX)
= 34V, I
Q
= 3.2mA, I
SD
<1µA
Step-Up DC/DC Converter MS8 Package
LT3463 Dual Output, Boost/Inverter, 250mA (I
SW
), Constant V
IN
: 2.3V to 15V, V
OUT(MAX)
= ±40V, I
Q
= 40µA, I
SD
<1µA
Off-Time, High Efficiency Step-Up DC/DC Converter DFN Package
with Integrated Schottky Diodes
LT3464 85mA (I
SW
), High Efficiency Step-Up DC/DC Converter V
IN
: 2.3V to 10V, V
OUT(MAX)
= 34V, I
Q
= 25µA, I
SD
<1µA
with Integrated Schottky and PNP Disconnect ThinSOT Package
