LTC3246
1
3246fa
For more information www.linear.com/LTC3246
TYPICAL APPLICATION
FEATURES DESCRIPTION
Wide VIN Range
Buck-Boost Charge Pump
with Watchdog Timer
The LT C
®
3246 is a switched capacitor buck-boost DC/DC
converter with integrated watchdog timer. The device
produces a regulated output (3.3V, 5V or adjustable) from
a 2.7V to 38V input. Switched capacitor fractional conver-
sion is used to maintain regulation over a wide range of
input voltage. Internal circuitry automatically selects the
conversion ratio to optimize efficiency as input voltage and
load conditions vary. No inductors are required.
The LTC3246’s reset time and watchdog timeout may
be set without external components, or adjusted using
external capacitors. A windowed watchdog function is
used for high reliability applications. The reset input can
be used for additional supply monitoring or be configured
as a pushbutton reset.
Low operating current (20µA without load, 1.5µA in shut-
down) and low external parts count make the LTC3246
ideally suited for low power, space constrained automo-
tive/industrial applications. The device is short-circuit and
overtemperature protected and is available in a thermally
enhanced 16-lead MSOP package.
Regulated 5V Output with Pushbutton Reset Output Voltage vs Input Voltage
n 2.7V – 38V Operating Range (42V Abs Max)
n IQ = 20µA Operating, 1.5µA in Shutdown
n Multimode Buck-Boost Charge Pump (2:1, 1:1, 1:2)
with Automatic Mode Switching
n 12V to 5V Efficiency = 81%
n IOUT Up to 500mA
n VOUT: Fixed 3.3V, 5V or Adjustable (2.5V to 5V)
n Ultralow EMI Emissions
n Engineered for Diagnostic Coverage in ISO 26262
Systems
n Overtemperature, Overvoltage and Short-Circuit
Protection
n Operating Junction Temperature: 150°C Max
n POR/Watchdog Controller w/External Timing Control
n Thermally Enhanced 16-Lead MSOP Package
APPLICATIONS
n Automotive ECU/CAN Transceiver Supplies
n Industrial/Telecom Housekeeping Supplies
n Low Power 12V to 5V Conversion All registered trademarks and trademarks are the property of their respective owners.
LTC3246
3246 TA01a
VIN
SEL2
SEL1
BIAS
RT
WT
C+C–
GND
VOUT
OUTS/ADJ
RST
WDI
RSTI
1µF 10µF
10µF
500k 500k
µC
RESET
2.2µF
VIN = 2.7V TO 38V
VOUT = 5V
IOUT UP TO 500mA
0
2
4
6
8
10
12
14
16
4.80
4.85
4.90
4.95
5.00
5.05
5.10
5.15
5.20
3246 TA01b
VOUT (V)
VIN (V)
IOUT = 50mA
IOUT = 500mA
LTC3246
2
3246fa
For more information www.linear.com/LTC3246
PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
VIN, SEL1, SEL2, WDI ................................. –0.3V to 42V
VOUT, OUTS/ADJ, RSTI, WT, RT, BIAS, RST . –0.3V to 6V
IRST ........................................................................10mA
VOUT Short Circuit Duration ............................. Indefinite
Lead Temperature (Soldering, 10 sec) ...................300°C
Operating Junction Temperature Range (Notes 3, 4)
(E-Grade/I-Grade) .................................. –40 to 125°C
(H-Grade) ...............................................–40 to 150°C
(MP-Grade) ............................................–55 to 150°C
Storage Temperature Range ......................–65 to 150°C
(Notes 1, 2)
1
2
3
4
5
6
7
8
WT
RT
RSTI
BIAS
SEL2
VIN
SEL1
BIAS
16
15
14
13
12
11
10
9
OUTS/ADJ
GND
RST
C–
VOUT
C+
WDI
VIN
TOP VIEW
MSE PACKAGE
16-LEAD PLASTIC MSOP
17
TJMAX = 150°C, JA = 40°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Operating Input Voltage Range (Note 5) l2.7 38 V
VUVLO VIN Undervoltage Lockout Threshold l2.35 2.7 V
IVIN VIN Quiescent Current
Shutdown
CP Enabled, Output in Regulation
SEL1 = SEL2 = 0V
SEL1 = VIN and/or SEL2 = VIN, RSTI = 5V
1.5
20
3
30
µA
µA
VHIGH SEL1, SEL2 Input Voltage l1.1 1.6 V
VLOW SEL1, SEL2 Input Voltage l0.4 0.8 V
ILOW SEL1, SEL2 Input Current VPIN = 0V l–1 0 1 µA
IHIGH SEL1, SEL2 Input Current VPIN = 38V l0.5 1 2 µA
Charge Pump Operation
VOUTS_5 VOUTS/ADJ Regulation Voltage
SEL1 = 0V, SEL2 = VIN
2.7V < VIN < 38V (Notes 5, 6) l4.8 5.2
V
VOUTS_3 VOUTS/ADJ Regulation Voltage
SEL1 = VIN, SEL2 = VIN
2.7V < VIN < 38V (Notes 5, 6) l3.17 3.43
V
VADJ VOUTS/ADJ Regulation Voltage
SEL1 = VIN, SEL2 = 0V
2.7V < VIN < 38V (Notes 5, 6) l1.08 1.11 1.14
V
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, CF LY = 2.2µF, COUT = 10µF, unless otherwise noted.
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3246EMSE#PBF LTC3246EMSE#TRPBF 3246 16-Lead Plastic MSOP –40°C to 125°C
LTC3246IMSE#PBF LTC3246IMSE#TRPBF 3246 16-Lead Plastic MSOP –40°C to 125°C
LTC3246HMSE#PBF LTC3246HMSE#TRPBF 3246 16-Lead Plastic MSOP –40°C to 150°C
LTC3246MPMSE#PBF LTC3246MPMSE#TRPBF 3246 16-Lead Plastic MSOP –55°C to 150°C
Consult ADI Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult ADI Marketing for information on nonstandard 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/
http://www.linear.com/product/LTC3246#orderinfo
LTC3246
3
3246fa
For more information www.linear.com/LTC3246
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
IADJ VOUTS/ADJ Input Current
SEL1 = SEL2 = VIN
l–50 0 +50 nA
IOUT_SCKT IVOUT Short Circuit Foldback Current VOUT = 0V 250 mA
ROUT Charge Pump Output Impedance 2:1 Step-Down Mode
1:1 Step-Down Mode, VIN = 5.5V
1:2 Step-Up Mode, VIN = 3V, VOUT ≥ 3.3V (Note 6)
l
1
1.2
4
8
Ω
Ω
Ω
VOUT_OV_RST VOUT Overvoltage Reset % of Final Regulation Voltage at Which
VOUT Rising Makes RST Go Low
VOUT Falling Makes RST Go Hi-Z
l
l
106
109
108.5
111.5
%
%
VOUT_UV_RST VOUT Undervoltage Reset % of Final Regulation Voltage at Which
VOUT Rising Makes RST Go Hi-Z
VOUT Falling Makes RST Go Low
l
l
93
97.5
95
99
%
%
VOUT_PD VOUT Pull-Down in Shut Down SEL1 = SEL2 = 0V 100 kΩ
VOUT_RIPPLE VOUT Ripple Voltage COUT = 10µF
COUT = 22µF
50
25
mV
mV
Reset Timer Control Pin (RT)
IRT(UP) RT Pull-Up Current VRT = 0.3V l–2 –3.1 –4.2 µA
IRT(DOWN) RT Pull-Down Current VRT = 1.3V l2 3.1 4.2 µA
IRT(INT) Internal RT Detect Current VRT = VBIAS l0.4 1 µA
VRT(INT) RT Internal Timer Threshold VRT Rising l2.0 2.4 2.65 V
Reset Timer Input (RSTI)
VRSTI_H RSTI Input High Voltage l1.22 1.27 V
VRSTI_L RSTI Input Low Voltage l1.04 1.2 V
IRSTI_H RSTI Input High Current RSTI = 5V l–1 0 1 µA
IRSTI_L RSTI Input Low Current RSTI = 0V l–1 0 1 µA
Reset Timing
tRST(INT) Internal Reset Timeout Period VRT = VBIAS 150 200 270 ms
tRST(EXT) Adjustable Reset Timeout Period CRT = 2.2nF l14 21 28 ms
tRSTIL RSTI Low to RST Asserted l5 20 40 µs
Reset Output (RST)
VOL(RST)Output Voltage Low RST IRST = 2mA l0.1 0.4 V
IOH(RST)RST Output Voltage High Leakage VRST = 5V l–1 0 1 µA
Watchdog Timing
tWDU(INT) Internal Watchdog Upper Boundary VWT = VBIAS l1.2 1.6 2.2 s
tWDL(INT) Internal Watchdog Lower Boundary VWT = VBIAS l37.5 50 68 ms
tWDR(EXT) External Watchdog Timeout Period CWT = 2.2nF l100 160 220 ms
tWDU(EXT) External Watchdog Upper Boundary ltWDR(EXT) • (128/129) ms
tWDL(EXT) External Watchdog Lower Boundary ltWDR(EXT) • (5/129) ms
Watchdog Timer Input (WDI)
VIH WDI Input High Voltage l1.1 1.6 V
VOL WDI Input Low Voltage l0.4 0.8 V
IIH WDI Input High Current VWDI = 38V l–1 0 1 µA
IIL WDI Input Low Current VWDI = 0V l–1 0 1 µA
tPW(WDI) Input Pulsewidth l400 ns
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, CFLY = 2.2µF, COUT = 10µF, unless otherwise noted.
LTC3246
4
3246fa
For more information www.linear.com/LTC3246
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: All voltages are referenced to GND unless otherwise specified.
Note 3: The LTC3246E is guaranteed to meet performance specifications
from 0°C to 85°C operating junction temperature. Specifications over
the –40°C to 125°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The LTC3246I is guaranteed over the –40°C to 125°C operating junction
temperature range. The LTC3246H is guaranteed over the –40°C to 150°C
operating junction temperature range. The LTC3246MP is guaranteed and
tested over the –55°C to 150°C operating junction temperature range.
High junction temperatures degrade operating lifetimes; operating lifetime
is derated for junction temperatures greater than 125°C. Note that the
maximum ambient temperature consistent with these specifications is
determined by specific operating conditions in conjunction with board
layout, the rated package thermal resistance and other environmental
factors.
TYPICAL PERFORMANCE CHARACTERISTICS
Input Shutdown Current
vs Input Voltage
Input Operating Current
vs Input Voltage
Input Operating Current
vs Input Voltage
The junction temperature (TJ, in °C) is calculated from the ambient
temperature (TA, in °C) and power dissipation (PD, in watts) according to
the formula:
TJ = TA + (PD • JA), where JA (in °C/W) is the package thermal
impedance.
Note 4: This IC has overtemperature protection that is intended to protect
the device during momentary overload conditions. Junction temperatures
will exceed 150°C when overtemperature protection is active. Continuous
operation above the specified maximum operating junction temperature
may impair device reliability.
Note 5: The maximum operating junction temperature of 150°C must
be followed. Certain combinations of input voltage, output current and
ambient temperature will cause the junction temperature to exceed 150°C
and must be avoided. See Thermal Management section for information on
calculating maximum operating conditions.
Note 6: The LTC3246 will attempt to regulate the output voltage under
all load conditions, but like any regulator, the output will drop out if
inadequate supply voltage exists for the load. See VOUT Regulation section
for calculating available load current at low input operating voltages. Also
see “Boost Output Impedance at Dropout vs Temperature” for typical
impedance values at output voltages less than 3.3V.
TA = 25°C, unless otherwise noted.
0
4
8
12
16
20
24
28
32
36
40
0
1
2
3
4
5
6
7
8
9
10
3246 G01
TA = 125°C
TA = 25°C
VIN (V)
I
IN
(µA)
0
5
10
15
20
25
30
35
40
10
1000
3246 G02
NO LOAD
125°C
25°C
–55°C
VIN (V)
I
IN
(µA)
4
6
8
10
12
14
16
0
10
20
30
40
50
60
3246 G03
NO LOAD
TA = 125°C
TA = 25°C
TA = –55°C
VIN (V)
I
IN
(µA)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Watchdog Timer Control Pin (WT)
IWT(UP) WT Pull-Up Current VWT = 0.3V l–2 –3.1 –4.2 µA
IWT(DOWN) WT Pull-Down Current VWT = 1.3V l2 3.1 4.2 µA
IWT(INT) Internal WT Detect Current VWT = VBIAS l0.4 1 µA
VWT(INT) WT Internal Timer Threshold VWT Rising l2 2.2 2.65 V
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, CFLY = 2.2µF, COUT = 10µF, unless otherwise noted.
LTC3246
5
3246fa
For more information www.linear.com/LTC3246
3.3V Fixed Output Voltage
vs Input Voltage
3.3V Fixed Output Voltage vs
Input Voltage
3.3V Efficiency and Power Loss
vs Input Voltage
5V Fixed Output Voltage
vs Input Voltage
5V Fixed Output Voltage vs
Input Voltage
5V Efficiency and Power Loss
vs Input Voltage
0
2
4
6
8
10
12
14
16
3.15
3.20
3.25
3.30
3.35
3.40
3.45
3246 G04
IOUT = 0mA
IOUT = 50mA
IOUT = 500mA
VIN (V)
V
OUT
(V)
0
4
8
12
16
20
24
28
32
36
40
3.15
3.20
3.25
3.30
3.35
3.40
3.45
3246 G05
IOUT = 0mA
IOUT = 50mA
IOUT = 500mA
VIN (V)
V
OUT
(V)
0
2
4
6
8
10
12
14
16
0
10
20
30
40
50
60
70
80
90
100
EFFICIENCY (%)
3246 G06
O
U
T
I
=
5
0
m
A
EFFICIENCY
LOSS
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
POWER LOSS (W)
VIN (V)
0
2
4
6
8
10
12
14
16
4.80
4.85
4.90
4.95
5.00
5.05
5.10
5.15
5.20
3246 G07
IOUT = 0mA
IOUT = 50mA
IOUT = 500mA
VIN (V)
V
OUT
(V)
0
4
8
12
16
20
24
28
32
36
40
4.80
4.85
4.90
4.95
5.00
5.05
5.10
5.15
5.20
3246 G08
IOUT = 0mA
IOUT = 50mA
IOUT = 500mA
VIN (V)
V
OUT
(V)
0
2
4
6
8
10
12
14
16
0
10
20
30
40
50
60
70
80
90
100
EFFICIENCY (%)
3246 G09
O
U
T
I
=
5
0
m
A
EFFICIENCY
LOSS
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
POWER LOSS (W)
VIN (V)
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
5V Efficiency and Power Loss
vs Input Voltage
3.3V Efficiency and Power Loss
vs Input Voltage
0
2
4
6
8
10
12
14
16
0
10
20
30
40
50
60
70
80
90
100
EFFICIENCY (%)
3246 G10
O
U
T
I
=
5
0
0
m
A
EFFICIENCY
LOSS
0
1
2
3
4
5
6
7
8
9
10
POWER LOSS (W)
VIN (V)
0
2
4
6
8
10
12
14
16
0
10
20
30
40
50
60
70
80
90
100
EFFICIENCY (%)
3246 G11
O
U
T
I
=
5
0
0
m
A
EFFICIENCY
LOSS
0
1
2
3
4
5
6
7
8
9
10
POWER LOSS (W)
VIN (V)
LTC3246
6
3246fa
For more information www.linear.com/LTC3246
TYPICAL PERFORMANCE CHARACTERISTICS
Boost Output Impedance at
Dropout vs Temperature
Reset Timeout Period
vs CRT Capacitance
Watchdog Timeout Period
vs CWT Capacitance
Internal Reset Timeout Period
vs Temperature
Internal Watchdog Timeout
Period vs Temperature
BIAS Output Voltage vs
Input Voltage
ADJ Regulation Voltage
vs Temperature
TA = 25°C, unless otherwise noted.
0.001
0.01
0.1
1
10
100
1000
1
10
100
1000
10000
100000
3246 G18
CWT (nF)
TIME (ms)
−40
−20
0
20
40
60
80
100
140
1.00
1.02
1.04
1.06
1.08
1.10
1.12
1.14
1.16
1.18
1.20
3246 G12
VADJ (V)
TEMPERATURE (°C)
−45
−30
0
15
30
45
60
75
90
TEMPERATURE (°C)
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
3246 G13
VOUT = 2.5V
VOUT = 3.0V
VOUT = 3.3V
VOUT = 5.0V
RO (Ω)
IOUT = 500mA
−60
−20
0
20
40
60
80
100
120
100
125
150
175
200
225
250
275
300
3246 G14
TEMPERATURE (°C)
TIME (ms)
−40
0
20
40
60
80
100
TEMPERATURE (°C)
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
3246 G15
TIME (s)
−60
−40
0
20
40
60
80
120
140
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
3.5
3246 G16
|IRT/WT| (µA)
TEMPERATURE (°C)
VIN = 12V
VIN = 2.7V
0.001
0.01
0.1
1
10
100
1000
0.1
1
10
1000
10000
3246 G17
CRT (nF)
TIME (ms)
0
5
10
15
20
25
30
35
40
3.0
3.5
4.0
4.5
5.0
5.5
6.0
3246 G19
O
U
T
V
S
D
O
U
T
V
E
N
VIN (V)
VBIAS (V)
RT/WT Timer Control Current
vs Temperature
LTC3246
7
3246fa
For more information www.linear.com/LTC3246
TA = 25°C, unless otherwise noted.
TYPICAL PERFORMANCE CHARACTERISTICS
Output Transient Response Output Voltage Ripple
5µs/DIV
3246 G20
I
N
V
=
1
4
V
O
U
T
V
=
5
V
O
U
T
C
=
1
0
µ
F
VOUT
50mV/DIV
440mA
IOUT
25mA
1µs/DIV
1:2 MODE
50mV/DIV
1:1 MODE
50mV/DIV
2:1 MODE
50mV/DIV
3246 G21
O
U
T
I
=
4
0
0
m
A
O
U
T
C
=
1
0
µ
F
Charge Pump Output Reset Timing
Watchdog Timing
TIMING DIAGRAMS
RSTI
RST
tRSTIL tRST
3246 TD01
WDI
RST
tWDR
tRST
3246 TD02
tRST
t < tWDL
tWDL < t < tWDU
LTC3246
8
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For more information www.linear.com/LTC3246
PIN FUNCTIONS
WT (Pin 1): Watchdog Timer Control Pin. Attach an ex-
ternal capacitor (CWT) to GND to set a watchdog upper
boundary timeout time (See “Watchdog Timeout Period
vs WT Capacitance” graph on page6). Tie WT to BIAS to
generate a timeout of about 1.6s. Tie WT and WDI to GND
to disable the watchdog timer.
RT (Pin 2): Reset Timeout Control Pin. Attach an external
capacitor (CRT) to GND to set a reset timeout time (See
“Reset Timeout Period vs RT Capacitance” graph on
page6). Tie RT to BIAS to generate a reset timeout of
about 200ms.
RSTI (Pin 3): Reset Logic Comparator Pin. The RSTI input
is compared to a reference threshold (1.2V typical). If RSTI
is below the reference voltage, the part will enter the reset
state and the RST pin will be low. Once RSTI exceeds the
reference voltage and VOUT in regulation, the reset timer
is started. RST pin will be low until the reset period times
out. RSTI is a high impedance pin and must be driven to
a valid level. Do not float.
BIAS (Pin 4, 8): Internal BIAS Voltage. The bias pin is for
internal operation only and should not be loaded or driven
externally. Bypass BIAS with a 10µF or greater ceramic
capacitor.
SEL2 (Pin 5): Logic Input Pin. See Table 1 for SEL1/SEL2
operating logic. SEL2 enables and disables the charge
pump along with the SEL1 pin. The SEL2 pin has a 1µA
(typical) pull down current to ground and can tolerate 38V
inputs allowing it to be pin-strapped to VIN.
VIN (Pin 6, 9): Power Input Pin. Input voltage for both charge
pump and IC control circuitry. The VIN pin operates from
2.7V to 38V. All VIN pins should be connected together at
pins and bypassed with a 1µF or greater ceramic capacitor.
SEL1 (Pin 7): Logic Input Pin. See Table 1 for SEL1/SEL2
operating logic. SEL1 enables and disables the charge
pump along with the SEL2 pin. The SEL1 pin has a 1µA
(typical) pull down current to ground and can tolerate 38V
inputs allowing it to be pin-strapped to VIN.
Table 1. VOUT Operating Modes
SEL2 SEL1 MODE
LOW LOW Shutdown
LOW HIGH Adjustable VOUT
HIGH LOW Fixed 5V
HIGH HIGH Fixed 3.3V
WDI (Pin 10): Watchdog Logic Input Pin. If the watchdog
timer is not disabled then WDI must be driven such that a
falling edge occurs within a time less than the watchdog
upper boundary time, or RST will be asserted low. The
WDI period must also be greater than the watchdog lower
boundary time, and only falling edges are considered. Tie
WT and WDI to GND to disable the watchdog timer. WDI
is a high impedance pin and must be driven to a valid
level. Do not float.
C+ (Pin 11): Connect to positive flying capacitor terminal
only. Do not load or drive externally.
VOUT (Pin 12): Charge Pump Output Voltage. The charge
pump output is enabled if either SEL1 or SEL2 are logic high.
C- (Pin 13): Connect to negative flying capacitor terminal
only. Do not load or drive externally.
RST (Pin 14): Reset Open Drain Logic Output. The RST pin
is low impedance during the reset period, and goes high
impedance during the watchdog period. RST is intended
to be pulled up to low voltage supply (such as VOUT) with
an external resistor.
GND (Pin 15, Exposed Pad): Ground. The exposed pack-
age pad is ground and must be soldered to the PC board
ground plane for proper functionality and for rated thermal
performance.
OUTS/ADJ (Pin 16): VOUT Sense/Adjust Input Pin. This pin
acts as VOUT sense (OUTS) for 5V or 3.3V fixed outputs
and adjust (ADJ) for adjustable output through external
feedback. The ADJ pin servos to 1.1V when the device is
enabled in adjustable mode. (OUTS/ADJ are selected by
SEL1 and SEL2 pins; See Table 1). Connect OUTS/ADJ to
VOUT or external divider as appropriate.
LTC3246
9
3246fa
For more information www.linear.com/LTC3246
SIMPLIFIED BLOCK DIAGRAM
10µF
1µF
10µF
2.2µF
1.2V
1.1V
MODE CLK
CHARGE PUMP
SEL1
UP TO 38V
VIN
2.7V TO 38V
SEL2
UP TO 38V
RSTI
0V TO 5V
WDI
UP TO 38V
VOUT
3.5V/5V/ADJ
500mA
3246 BD
ADJ
3.3V
5V
SD
MUX
VIN
VIN
BIAS
BIAS
VIN
VOUT
GND
VOUT
RST
SEL1
SEL2
RSTI
WDI
6
9
4
8
7
5
3
10
5V
LDO
OUT
OSC
EN
WATCHDOG
TIMER
PGOOD
+9%/–5%
RESET
TIMER
ILIM
MODE
COMP
–
+
–
+
OUTS/
ADJ
15
17
12
14
16
WT RT
1 2
C+C–
11 13
CWT CRT
2
LTC3246
10
3246fa
For more information www.linear.com/LTC3246
APPLICATIONS INFORMATION
General Operation
The LTC3246 uses switched capacitor based DC/DC
conversion to provide the efficiency advantages associ-
ated with inductor based circuits as well as the cost and
simplicity advantages of a linear regulator. The LTC3246
uses an internal switch network and fractional conversion
ratios to achieve high efficiency and regulation over widely
varying VIN and output load conditions.
Internal control circuitry selects the appropriate conversion
ratio based on VIN and load conditions. The device has
three possible conversion modes: 2:1 step-down mode, 1:1
step-down mode and 1:2 step-up mode. Only one external
flying capacitor is needed to operate in all three modes.
2:1 mode is chosen when VIN is greater than two times the
desired VOUT. 1:1 mode is chosen when VIN falls between
two times VOUT and VOUT. 1:2 mode is chosen when VIN
falls below the desired VOUT. The internal mode control
logic maintains output regulation over all load conditions.
Regulation is achieved by sensing the output voltage
and enabling charge transfer when the output falls below
regulation. When the charge pump is enabled, it controls
the current into the flying capacitor to limit the output
ripple beyond that of conventional switched capacitor
charge pumps. The part has two SEL pins that select the
output regulation (fixed 5V, fixed 3.3V or adjustable) as
well as shutdown.
The charge pump operates at a nominal frequency of about
450kHz, though actual output ripple frequency will vary
with output load, operating mode and output capacitance.
The LTC3246 is designed for applications requiring high
system reliability. The part includes output supply monitor-
ing and watchdog timing circuitry as well as overvoltage,
short-circuit and overtemperature protection.
VOUT Regulation and Mode Selection
Regulation is achieved by sensing the output voltage and
enabling charge transfer when the output falls below the
programmed regulation voltage. The amount of charge
transferred per cycle is controlled over the full input range
to minimize output ripple. The regulation voltage (fixed
5V, fixed 3.3V or adjustable) is selected through the SEL1
and SEL2 pins per Table 1 in the Pin Function section.
The optimal conversion ratio is chosen based on VIN, VOUT
and output conditions. Two internal comparators are used
to select the default conversion ratio. The conversion ratio
switch point is optimized to provide peak efficiency over all
supply and load conditions while maintaining regulation.
Each comparator also has built-in hysteresis to reduce the
tendency of oscillating between modes when a transition
point is reached.
The LTC3246 will attempt to regulate its output over the
full operating range (2.7V to 38V), but like any regulator
the output will drop out of regulation if inadequate supply
voltage exists to the operating load. As the input voltage
drops, the LTC3246 will eventually end up in the 1:2 step
up mode. As the input voltage drops further, the output
will eventually drop out of regulation. At this point, the 1:2
step-up charge pump impedance can be calculated as:
ROUT =
2 • V
IN
– V
OUT
I
OUT
This equation can be rewritten to determine the output
current at which the output will drop out for a given input
voltage as:
IOUT =2 • VIN – VOUT
R
OUT
IOUT 500mA
For a typical 1:2 step-up charge pump impedance of 4Ω
with 5V output voltage and 3V input voltage, the output
current at dropout will be about:
IOUT =2 • 3 – 4.8
4
mA =300mA
Thus, typically the part should be able to output 300mA
without dropping out. To be conservative, the max 1:2
step-up charge pump impedance of 8Ω should be used
which gives a more conservative output current of 150mA.
Any supply impedance in series with the LTC3246 must
be doubled and added to the 1:2 step-up charge pump
impedance. It is also important to have the specified COUT
and CF LY capacitance to achieve the specified output imped-
ance. Observing dropout will allow the user to calculate
the output impedance for their specific application.
LTC3246
11
3246fa
For more information www.linear.com/LTC3246
Short-Circuit/Thermal Protection
The LTC3246 has built-in short-circuit current limiting
on both the VOUT and BIAS outputs to protect the part in
the event of a short. During short-circuit conditions, the
device will automatically limit the output current from
both outputs.
The LTC3246 has thermal protection that will shut
down the device if the junction temperature exceeds the
overtemperature threshold (typically 175°C). Thermal
shutdown is included to protect the IC in cases of exces-
sively high ambient temperatures, or in cases of excessive
power dissipation inside the IC. The charge transfer will
reactivate once the junction temperature drops back to
approximately 165°C.
When the thermal protection is active, the junction tempera-
ture is beyond the specified operating range. The thermal
and short-circuit protection are intended for momentary
overload conditions outside normal operation. Continu-
ous operation above the specified maximum operating
conditions may impair device reliability.
Programming the Output Voltage (OUTS/ADJ Pin)
The LTC3246 output voltage programming is very flexible
offering a fixed 3.3V output, fixed 5V output as well as
adjustable output that is programmed through an external
resistor divider. The desired output regulation method is
selected through the SEL pins.
For a fixed output simply short OUTS (OUTS/ADJ pin) to
VOUT as shown in Figure 1. Fixed 3.3V operation is enabled
by driving both SEL1 and SEL2 pins high, while fixed 5V
operating is selected by driving SEL2 high with SEL1 low.
Driving both SEL1 and SEL2 low shuts down the device
causing VOUT to be pulled low by an internal impedance
of about 80kΩ.
LTC3246
COUT
3246 F01
VOUT
FIXED 3.3V OR
FIXED 5.0V
VOUT
OUTS/ADJ
GND
Figure1. Fixed Output Operation
APPLICATIONS INFORMATION
Adjustable output programming is accomplished by con-
necting ADJ (OUTS/ADJ pin) to a resistor divider between
VOUT and GND as shown in Figure 2. Adjustable operation
is enabled by driving SEL1 high and SEL2 low. Driving both
SEL1 and SEL2 low shuts down the device, causing VOUT
to be pulled low by an internal impedance of about 80kΩ.
LTC3246
COUT
3246 F02
VOUT
1.1V 1RA
RB
RA
RB
VOUT
OUTS/ADJ
GND
Figure2. Adjustable Output Operation
Using adjustable operation, the output (VOUT) can be
programmed to regulate from 2.5V to 5V. The limited
programming range provides the required VOUT operating
voltage without overstressing the VOUT pin.
The desired adjustable output voltage is programmed by
solving the following equation for RA and RB:
R
A
R
B
=
V
OUT
1.11V – 1
Select a value for RB in the range of 1k to 1M and solve
for RA. Note that the resistor divider current adds to the
total no load operating current. Thus, a larger value for
RB will result in lower operating current.
2:1 Step-Down Charge Pump Operation
When the input supply is greater than about two times
the output voltage, the LTC3246 will operate in 2:1 step-
down mode. Charge transfer happens in two phases. On
the first phase, the flying capacitor (CF LY ) is connected
between VIN and VOUT. On this phase, CF LY is charged up
and current is delivered to VOUT. On the second phase,
the flying capacitor (CF LY ) is connected between VOUT and
GND. The charge stored on CF LY during the first phase is
transferred to VOUT on the second phase. When in 2:1
step-down mode, the input current will be approximately
LTC3246
12
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For more information www.linear.com/LTC3246
half of the total output current. The efficiency () and chip
power dissipation (PD) in 2:1 are approximately:
P
OUT
PIN
=
V
OUT
• I
OUT
VIN •1
2
IOUT
=
2V
OUT
VIN
PD=VIN
2– VOUT
IOUT
1:1 Step-Down Charge Pump Operation
When the input supply is less than about two times the
output voltage, but more than the programmed output
voltage, the LTC3246 will operate in 1:1 step-down mode.
This method of regulation is very similar to a linear regula-
tor. Charge is delivered directly from VIN to VOUT through
most of the oscillator period. The charge transfer is briefly
interrupted at the end of the period. When in 1:1 step-down
mode, the input current will be approximately equal to the
total output current. Thus, efficiency () and chip power
dissipation (PD) in 1:1 are approximately:
POUT
P
IN
=VOUT • IOUT
V
IN
• I
OUT
=VOUT
V
IN
PD=VIN – VOUT
IOUT
1:2 Step-Up Charge Pump Operation
When the input supply is less than the output voltage,
the LTC3246 will operate in 1:2 step-up mode. Charge
transfer happens in two phases. On the first phase, the
flying capacitor (CF LY ) is connected between VIN and GND.
On this phase, CF LY is charged up. On the second phase,
the flying capacitor (CF LY ) is connected between VIN and
VOUT and the charge stored on CF LY during the first phase
is transferred to VOUT. When in 1:2 step-up mode, the
input current will be approximately twice the total output
current. Thus, efficiency () and chip power dissipation
(PD) in 1:2 are approximately:
P
OUT
P
IN
=
V
OUT
• I
OUT
V
IN
• 2I
OUT
=
V
OUT
2V
IN
PD=2VIN – VOUT
IOUT
VOUT Ripple and Capacitor Selection
The type and value of capacitors used with the LTC3246
determine output ripple and charge pump strength. The
value of COUT directly controls the amount of output ripple
for a given load current. Output ripple decreases with
output capacitance until about 20µF, at which point output
peak to peak ripple remains more or less constant. See
Figure3 for graph of output ripple vs output capacitance.
Figure3. Typical VOUT Ripple Voltage vs COUT Capacitance
0
5
10
15
20
25
30
35
40
0
25
50
75
100
125
150
175
200
3246 TA01b
BOOST, 500mA
BOOST, 50mA
BUCK, 500mA
BUCK, 50mA
LDO, 500mA
LDO, 50mA
COUT CAPACITANCE (µF)
VOUT RIPPLE (mVP-P)
To reduce output noise and ripple, it is suggested that a
low ESR (equivalent series resistance < 0.1Ω) ceramic
capacitor (10µF or greater) be used for COUT. For optimal
performance, it is best to increase COUT for low VOUT as
the ripple becomes a larger percentage of the regulation
voltage degrading performance. Tantalum and aluminum
capacitors can be used in parallel with a ceramic capacitor
to increase the total capacitance but are not recommended
to be used alone because of their high ESR.
VOUT Overvoltage Protection
An internal comparator monitors the voltage at VOUT and
will prevent charge transfer in the event that VOUT exceeds
the overvoltage threshold (5.9V typ.). Overvoltage protec-
tion is added as a safety feature to prevent damage to the
part in the event of a fault such as VOUTS/ADJ pin shorted
to ground or not connected to VOUT. Charge transfer will
start once the output falls to about 5.75V.
APPLICATIONS INFORMATION
LTC3246
13
3246fa
For more information www.linear.com/LTC3246
VIN Capacitor Selection
The finite charge transfer architecture used by the LTC3246
makes input noise filtering much less demanding than the
sharp current spikes of conventional regulated charge
pumps. Depending on the mode of operation, the input
current of the LTC3246 can step from about 1A to 0A on
a cycle-by-cycle basis. Low ESR will reduce the voltage
steps caused by changing input current, while the ab-
solute capacitor value will determine the level of ripple.
The total amount and type of capacitance necessary for
input bypassing is very dependent on the applied source
impedance as well as existing bypassing already on the
VIN node. For optimal input noise and ripple reduction, it
is recommended that a low ESR ceramic capacitor be used
for CIN bypassing. An electrolytic or tantalum capacitor
may be used in parallel with the ceramic capacitor on CIN
to increase the total capacitance, but, due to the higher
ESR, it is not recommended that an electrolytic or tan-
talum capacitor be used alone for input bypassing. The
LTC3246 will operate with capacitors less than 1µF, but,
depending on the source impedance, input noise can feed
through to the output causing degraded performance.
For best performance 1µF or greater total capacitance is
suggested for CIN.
Flying Capacitor Selection
Ceramic capacitors should always be used for the flying
capacitor. The flying capacitor controls the strength of
the charge pump. In order to achieve the rated output
current, it is necessary for the flying capacitor to have
at least 1µF of capacitance over operating temperature
with a bias voltage equal to the programmed VOUT (see
Ceramic Capacitor Selection Guidelines). If only 100mA
or less of output current is required for the application,
the flying capacitor minimum can be reduced to 0.2µF.
The voltage rating of the ceramic capacitor should be
VOUT+1V or greater.
Ceramic Capacitor Selection Guidelines
Capacitors of different materials lose their capacitance
with higher temperature and voltage at different rates.
For example, a ceramic capacitor made of X5R or X7R
material will retain most of its capacitance from –40°C
to 85°C, whereas a Z5U or Y5V style capacitor will lose
considerable capacitance over that range (60% to 80%
loss typical). Z5U and Y5V capacitors may also have a
very strong voltage coefficient, causing them to lose an
additional 60% or more of their capacitance when the rated
voltage is applied. Therefore, when comparing different
capacitors, it is often more appropriate to compare the
amount of achievable capacitance for a given case size
rather than discussing the specified capacitance value. For
example, over rated voltage and temperature conditions,
a 4.7µF, 10V, Y5V ceramic capacitor in an 0805 case may
not provide any more capacitance than a 1µF, 10V, X5R
or X7R available in the same 0805 case. In fact, over bias
and temperature range, the 1µF, 10V, X5R or X7R will
provide more capacitance than the 4.7µF, 10V, Y5V. The
capacitor manufacturer’s data sheet should be consulted
to determine what value of capacitor is needed to ensure
minimum capacitance values are met over operating
temperature and bias voltage. Below is a list of ceramic
capacitor manufacturers and how to contact them:
MANUFACTURER WEBSITE
AVX www.avxcorp.com
Kemet www.kemet.com
Murata www.murata
Taiyo Yuden www.t-yuden.com
TDK www.tdk.com
Wurth Elektronik www.we-online.com
BIAS Pin and Capacitor Selection
The BIAS pin of the LTC3246 is a 5V output that is generated
by an internal Low Drop-Out (LDO) regulator supplied by
VIN. The BIAS voltage is used as a supply for the internal
low voltage circuitry. A capacitor on the BIAS pin is neces-
sary to stabilize the LDO output and minimize ripple during
transient conditions. A low ESR ceramic capacitor with a
minimum capacitance of 2µF over temperature with 5V
bias should be used. Since the BIAS voltage comes from
an LDO, the BIAS voltage will drop with VIN as VIN goes
below 5V. This is normal and expected operation. The
BIAS pin voltage is for internal circuitry only and should
not be loaded externally.
APPLICATIONS INFORMATION
LTC3246
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For more information www.linear.com/LTC3246
APPLICATIONS INFORMATION
Reset Generation (RSTI input, RST output)
The LTC3246 pulls the RST open-drain output low when-
ever RSTI is below threshold (typically 1.2V) or VOUT is
greater than the overvoltage threshold or less than the
undervoltage threshold. RST remains asserted low for
a reset timeout period (tRST) once RSTI goes above the
threshold and VOUT is in regulation (within the overvoltage
and undervoltage thresholds). RST de-asserts by going
high impedance at the end of the reset timeout period.
The reset timeout can be configured to use an internal
timer without external components or an adjustable timer
programmed by connecting an external capacitor from
the RT pin to GND. Glitch filtering ensures reliable reset
operation without false triggering.
During initial power up, the RST output asserts low while
VIN is below the VIN undervoltage lockout threshold. The
state of VOUT and RSTI have no effect on RST while VIN
is below the undervoltage lockout threshold. The reset
timeout period cannot start until VIN exceeds the under-
voltage lockout threshold.
VOUT Undervoltage/Overvoltage Reset
A built-in VOUT supply monitor ensures the VOUT is in regu-
lation before RST is allowed to go high impedance. The
monitor detects both overvoltage and undervoltage faults.
If VOUT is greater than the overvoltage threshold or less
than the undervoltage threshold, the part registers a fault
and pulls RST low. The fault condition is removed when
VOUT is within the overvoltage and undervoltage thresholds.
Load transients within the operating range of the part will
not registering as a fault by design.
Selecting the Reset Timing Capacitor
The reset timeout period can be set to a fixed internal
timer or programmed with a capacitor in order to accom-
modate a variety of applications. Connecting a capacitor,
CRT, between the RT pin and GND sets the reset timeout
period, tRST.
Figure 4 shows the desired reset timeout period as a
function of the value of the timer capacitor. Leaving RT
open without external capacitor generates a reset timeout
of approximately 0.5ms. Shorting RT to BIAS generates a
reset timeout of approximately 0.2s.
0.001
0.01
0.1
1
10
100
1000
0.1
1
10
100
1000
10000
3246 F04
CRT (nF)
TIME (ms)
Figure4. Reset Timeout Period vs CRT Capacitance
RST Output Characteristics
RST is an open-drain pin and, thus, requires an external
pull-up resistor to a logic supply. RST may be pulled up to
any valid logic level (such as VOUT) providing the voltage
limits of the pin are observed (See Absolute Maximum
Ratings section).
Watchdog Timer (WDI input, RST output)
The LTC3246 includes a windowed watchdog function
that can continuously monitor the application’s logic or
microprocessor and issue automatic resets to aid recovery
from unintended lockups or crashes. With the RSTI input
held above threshold, the application must periodically
toggle the logic state of the watchdog input (WDI pin) in
order to clear the watchdog timer. Specifically, successive
falling edges on the WDI pin must be spaced by more than
the watchdog lower boundary but less than the watchdog
upper boundary. As long as this condition holds, RST
remains high impedance.
If a falling edge arrives before the watchdog lower bound-
ary, or if the watchdog timer reaches the upper bound-
ary without seeing a falling edge on WDI, the watchdog
timer immediately enters its reset state and asserts RST
LTC3246
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APPLICATIONS INFORMATION
low for the reset timeout period. Once the reset timeout
completes, RST is released to go high and the watchdog
timer starts again.
During power-up, the watchdog timer remains cleared while
RST is asserted low. As soon as the reset timer times out,
RST goes high and the watchdog timer is started.
Setting the Watchdog Timeout Period
The watchdog upper boundary (tWDU) and lower bound-
ary (tWDL) are not observable outside the part; only the
watchdog timeout period (tWDR) of the part is observable
via the RST pin. The watchdog upper boundary (tWDU)
occurs one watchdog clock cycle before the watchdog
timeout period (tWDR). The internal watchdog timeout
period consists of 8193 clock cycles, so the internal
watchdog upper boundary time is essentially the same
as the internal watchdog timeout period. Conversely, the
external watchdog timeout period consists of only 129
clock cycles, so the external watchdog upper boundary
should be more accurately calculated as:
tWDU(EXT) =tWDR(EXT) •
128
129
The external watchdog lower boundary (tWDL(EXT)) oc-
curs five clock cycles into the watchdog timeout period
(tWDR(EXT)). Thus the external watchdog lower boundary
can be calculated from the external watchdog timeout
period as:
tWDL EXT
=tWDR(EXT) •5
129
The internal watchdog lower boundary can be calcu-
lated from the internal watchdog timeout period by the
following:
tWDL(INT) =
t
WDR(INT)
32
The watchdog upper boundary is adjustable and can be
optimized for software execution. The watchdog upper
boundary is adjusted by connecting a capacitor, CWT,
between the WT and GND pins.
Figure 5 shows the approximate external watchdog
timeout period as a function of the watchdog capacitor.
Shorting WT to BIAS sets an upper and lower watchdog
timeout period of about 50ms and 1.6s respectively.
Figure5. External Watchdog Timeout Period vs CWT Capacitance
0.001
0.01
0.1
1
10
100
1000
1
10
100
1000
10000
100000
3246 F05
CWT (nF)
TIME (ms)
Layout Considerations
Due to the high switching frequency and transient cur-
rents produced by the LTC3246, careful board layout is
necessary for optimal performance. A true ground plane
and short connections to all capacitors will optimize
performance, reduce noise and ensure proper regulation
over all conditions.
When using the LTC3246 with an external resistor divider it
is important to minimize any stray capacitance to the ADJ
(OUTS/ADJ pin) node. Stray capacitance from ADJ to C+
or C– can degrade performance significantly and should
be minimized and/or shielded if necessary. Minimize stray
capacitance from WT and RT to C+ and C– when using
external timing capacitors to minimize timing variation.
Thermal Management/Thermal Shutdown
The on-chip power dissipation in the LTC3246 will cause the
junction to ambient temperature to rise at rate of typically
40°C/W in still air with a good thermal connection to the
PC board. Connecting the die pad (Pin 17) with multiple
vias to a large gro und plane under the device can reduce
the thermal resistance of the package and PC board con-
LTC3246
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For more information www.linear.com/LTC3246
APPLICATIONS INFORMATION
siderably. Poor board layout and failure to connect the die
pad (Pin 17) to a large ground plane can result in thermal
junction to ambient impedance well in excess of 40°C/W.
It is also possible to get thermal rates less than 40°C/W
with good airflow over the part and PC board.
Because of the wide input operating range, it is possible
to exceed the specified operating junction temperature
and even reach thermal shutdown (175°C typ). Figure6
and Figure7 show the available output current vs ambi-
ent temperature to ensure the 150°C operating junction
temperature is not exceeded.
The figures assume worst-case operating conditions and a
thermal impedance of 40°C/W. It is always safe to operate
under the line shown on the graph. Operation above the
line is conditional and is the responsibility of the user to
calculate worst-case operating conditions (temperature
and power) to make sure the part does not exceed the
150°C operating junction temperature for extended pe-
riods of time.
The 2:1 Step-Down Charge Pump Operation, 1:1 Step-
Down Charge Pump Operation, and 1:2 Step-Up Charge
Pump Operation sections provide equations for calculating
power dissipation (PD) in each mode.
For example, if it is determined that the maximum power
dissipation (PD) is 1.2W under normal operation, then the
junction to ambient temperature rise will be:
TJA = 1.2W • 40°C/W = 48°C
Thus, the ambient temperature under this condition can-
not exceed 102°C if the junction temperature is to remain
below 150°C, and, if the ambient temperature exceeds
about 127°C, the device will cycle in and out of the thermal
shutdown.
Every application will have a slightly different thermal rise
than the specified 40°C/W, especially applications with
good airflow. Calculating the actual thermal rate for a
specific application circuit is too complex to be presented
here, but the thermal rate can be measured in application.
This is done by first taking the final application circuit and
enabling the LTC3246 under a known power dissipation
(PD) and raising the ambient temperature slowly until
the LTC3246 shuts down. Note this temperature as T1.
Now, remove the load from the part and raise the ambi-
ent temperature slowly until the LTC3246 shuts down
again. Note this temperature as T2. The thermal rate can
be calculated as:
JA = PD/(T2 – T1)
Another method for determining maximum safe operating
temperature in application is to configure the LTC3246 to
operate under the worst case operating power dissipa-
tion. Then slowly raise the ambient temperature until the
LTC3246 shuts down. At this point the LTC3246 junction
temperature will be about 175°C, so simply subtract
25°C from the shutdown temperature and this is the safe
operating temperature for the application.
Figure6.
AMBIENT TEMPERATURE (°C)
0
IOUT (A)
0.5
0.4
0.1
0.3
0.2
0.0 12575
3246 F06
1501005025
2.7V < VIN < 22V
θJA = 40°C/W
CONDITIONAL
OPERATION
SAFE OPERATION
5V Output Operation vs Ambient Temperature Figure7.
AMBIENT TEMPERATURE (°C)
0
IOUT (A)
0.5
0.4
0.1
0.3
0.2
0.0 12575
3246 F07
1501005025
2.7V < VIN < 15V
θJA = 40°C/W
CONDITIONAL
OPERATION
SAFE OPERATION
3.3V Output Operation vs Ambient Temperature
LTC3246
17
3246fa
For more information www.linear.com/LTC3246
TYPICAL APPLICATIONS
Regulated 2.5V Output with Externally Programmed Watchdog Timing
LTC3246
3246 TA02
VIN
SEL1
SEL2
BIAS
RSTI
C+C–
VOUT
RST
WDI
OUTS/ADJ
1µF 47µF
10µF
10nF 22nF
500k
1270k
1000k
µC
2.2µF
VIN = 2.7V TO 38V
VOUT = 2.5V
IOUT UP TO 500mA
GNDRT WT
LTC3246
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For more information www.linear.com/LTC3246
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/product/LTC3246#packaging for the most recent package drawings.
MSOP (MSE16) 0213 REV F
0.53 ±0.152
(.021 ±.006)
SEATING
PLANE
0.18
(.007)
1.10
(.043)
MAX
0.17 –0.27
(.007 – .011)
TYP
0.86
(.034)
REF
0.50
(.0197)
BSC
16
16151413121110
12345678
9
9
18
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL
NOT EXCEED 0.254mm (.010") PER SIDE.
0.254
(.010) 0° – 6° TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
5.10
(.201)
MIN
3.20 – 3.45
(.126 – .136)
0.889 ±0.127
(.035 ±.005)
RECOMMENDED SOLDER PAD LAYOUT
0.305 ±0.038
(.0120 ±.0015)
TYP
0.50
(.0197)
BSC
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845 ±0.102
(.112 ±.004)
2.845 ±0.102
(.112 ±.004)
4.039 ±0.102
(.159 ±.004)
(NOTE 3)
1.651 ±0.102
(.065 ±.004)
1.651 ±0.102
(.065 ±.004)
0.1016 ±0.0508
(.004 ±.002)
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
0.280 ±0.076
(.011 ±.003)
REF
4.90 ±0.152
(.193 ±.006)
DETAIL “B”
DETAIL “B”
CORNER TAIL IS PART OF
THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
NO MEASUREMENT PURPOSE
0.12 REF
0.35
REF
MSE Package
16-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1667 Rev F)
LTC3246
19
3246fa
For more information www.linear.com/LTC3246
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 12/17 Changed ROUT VIN condition
Changed VRSTI_L lower limit
Changed IOUT equation resultant to 300mA and text to 150mA
Changed circuit pin names
3
3
10
17
LTC3246
20
3246fa
For more information www.linear.com/LTC3246
ANALOG DEVICES, INC. 2016
LT 1217 REV A • PRINTED IN USA
www.linear.com/LTC3246
RELATED PARTS
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
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in (2mm × 2mm) DFN Package
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LTC3440 600mA (IOUT) 2MHz Synchronous
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Package
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Synchronous Buck-Boost DC/DC
Converter
95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V, IQ = 25µA, ISD ≤ 1µA, DFN Package
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Synchronous Buck-Boost DC/DC
Converter
96% Efficiency, VIN: 2.4V to 5.5V, VOUT(MIN) = 2.4V, IQ = 28µA, ISD < 1µA, DFN Package
LTC3240-3.3/
LTC3240-2.5
3.3V/2.5V Step-Up/Step-Down Charge
Pump DC/DC Converter
VIN: 1.8V to 5.5V, VOUT(MAX) = 3.3V/2.5V, IQ = 65µA, ISD < 1µA, 2mm × 2mm DFN Package
LTC3260 Low Noise Dual Supply Inverting
Charge Pump
VIN Range: 4.5V to 32V, IQ = 100µA, 100mA Charge Pump, 50mA Positive LDO, 50mA
Negative LDO
LTC3261 High Voltage Low IQ Inverting Charge
Pump
VIN Range: 4.5V to 32V, IQ = 60µA, 100mA Charge Pump
LTC3245 High Voltage, Low Noise 250mA
Buck-Boost Charge Pump
VIN Range: 2.7V to 38V, VOUT Range: 2.5V to 5V, IQ = 18µA, ISD = 4µA, 3mm × 4mm DFN and
12-Pin MSE Packages
LTC3255 Wide VIN Range Fault Protected 50mA
Step-Down Charge Pump
VIN Range: 4V to 48V, VOUT Range: 2.4V to 15V, IQ = 20µA, 10-Pin 3mm × 3mm DFN and
MSE Packages
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Step-Down Charge Pump with WDT
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LTC3246
3246 TA03
VIN
SEL2
SEL1
BIAS
RT
WT
WDI
C+C–
VOUT
OUTS/ADJ
RST
RSTI
1µF 22µF
10µF
500k
2.2µF
VIN = 2.7V TO 38V
VOUT = 3.3V
IOUT UP TO 500mA
GND
RST
Reduced Ripple 3.3V Output with Watchdog Timing Disabled