LTC3250 [Linear]
High Efficiency, Low Noise, Inductorless Step-Down DC/DC Converter; 高效率，低噪音，无电感器降压型DC / DC转换器
| 型号： | LTC3250 |
| 厂家： | 
Linear |
| 描述： | High Efficiency, Low Noise, Inductorless Step-Down DC/DC Converter |
| 文件： | 总12页 (文件大小：322K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3250-1.5/LTC3250-1.2
High Efficiency, Low Noise,
Inductorless Step-Down
DC/DC Converter
U
FEATURES
DESCRIPTIO
The LTC®3250-1.5/LTC3250-1.2 are charge pump step-
down DC/DC converters that produce a 1.5V or 1.2V
regulated output from a 2.7V to 5.5V input. The parts use
switched capacitor fractional conversion to achieve typi-
cal efficiency two times higher than that of a linear regu-
lator. No inductors are required.
■
2.7V to 5.5V Input Voltage Range
■
No Inductors
■
Li-Ion (3.6V) to 1.5V with 81% Efficiency
■
Low Noise Constant Frequency Operation
■
Output Voltages: 1.5V ±4%, 1.2V ±4%
■
Output Current: 250mA
■
Shutdown Disconnects Load from VIN
A unique constant frequency architecture provides a low
noise regulated output as well as lower input noise
than conventional charge pump regulators.* High
frequency operation (fOSC = 1.5MHz) simplifies filtering
to further reduce conducted noise. The part also uses
BurstMode® operationtoimproveefficiencyatlightloads.
■
Low Operating Current: IQ = 35µA
■
Low Shutdown Current: ISD < 1µA
■
Oscillator Frequency = 1.5MHz
■
Soft-Start Limits Inrush Current at Turn-On
■
Short-Circuit and Overtemperature Protected
■
Low Profile (1mm) SOT-23 Package
Low operating current (35µA with no load, <1µA in
shutdown) and low external parts count (three small
ceramic capacitors) make the LTC3250-1.5/LTC3250-1.2
ideallysuitedforspaceconstrainedbatterypoweredappli-
cations. The parts are short-circuit and overtemperature
protected, and are available in a low profile (1mm) 6-pin
ThinSOTTM package.
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APPLICATIO S
■
Handheld Computers
■
Cellular Phones
Digital Cameras
■
■
Handheld Medical Instruments
Low Power DSP Supplies
, LTC and LT are registered trademarks of Linear Technology Corporation
Burst Mode is a registered trademark of Linear Technology Corporation
ThinSOT is a trademark of Linear Technology Corporation.
*U.S. Patent #6, 411, 531
■
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TYPICAL APPLICATIO
Efficiency vs Input Voltage
(IOUT = 100mA)
100
Li-Ion to 1.5V Output with Shutdown
90
1µF
80
LTC3250-1.5
70
60
50
–
+
V
C
C
IN
V
= 1.5V ± 4%
OUT
3.2V TO 4.2V
V
V
IN
OUT
100mA
40
Li-Ion
1µF
LDO
LTC3250-1.5
SHDN
4.7µF
30
20
10
0
OFF
GND
ON
3250 TA1a
3.0
3.5
4.0
4.5
(V)
5.0
5.5
V
IN
3250 TA01b
3250fa
1
LTC3250-1.5/LTC3250-1.2
W W U W
ABSOLUTE AXI U RATI GS
(Note 1)
U
W
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PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
VIN to GND...................................................–0.3V to 6V
SHDN to GND ............................... –0.3V to (VIN + 0.3V)
IOUT (Note 2)....................................................... 350mA
Operating Ambient Temperature Range (Note 3)
........................................................... – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
LTC3250ES6-1.5
LTC3250ES6-1.2
+
V
1
6 C
5 V
4 C
IN
GND 2
OUT
–
SHDN 3
S6 PACKAGE
6-LEAD PLASTIC SOT-23
S6 PART MARKING
LTZE
LTAGJ
TJMAX = 150°C, θJA = 230°C/W,
θJC = 102°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, CFLY = 1µF, CIN = 1µF, COUT = 4.7µF unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
3.1
TYP
MAX
5.5
UNITS
V
V
LTC3250-1.5 Operating Voltage Range
LTC3250-1.2 Operating Voltage Range
LTC3250-1.5 Output Voltage Range
●
●
V
V
IN
2.7
5.5
I
I
I
≤ 50mA 3.1V ≤ V ≤ 5.5V
≤ 100mA 3.2V ≤ V ≤ 5.5V
≤ 250mA 3.5V ≤ V ≤ 5V
●
●
1.44
1.44
1.44
1.5
1.5
1.5
1.56
1.56
1.56
V
V
V
OUT
OUT
OUT
OUT
IN
IN
IN
LTC3250-1.2 Output Voltage Range
I
I
≤ 150mA 2.7V < V < 5.5V
●
1.15
1.15
1.2
1.2
1.25
1.25
V
V
OUT
OUT
IN
≤ 250mA 2.9V ≤ V ≤ 5V
IN
I
Operating Current
I
= 0mA
●
●
35
0.01
12
60
1
µA
µA
IN
OUT
Shutdown Current
SHDN = 0V
V
V
Burst Mode Operation Output Ripple
Continuous Mode Output Ripple
Switching Frequency
mV
mV
RB
RC
P-P
4
P-P
f
●
●
●
●
●
1.2
1.2
1.5
0.8
0.8
1.8
MHz
V
OSC
V
V
SHDN Input Hi Voltage
SHDN Input Low Voltage
SHDN Input Current
IH
IL
0.4
1
V
I
I
t
SHDN = V
–1
–1
µA
IH
IN
SHDN Input Current
SHDN = 0V
= 6Ω
1
µA
IL
Turn On Time
R
0.8
0.15
0.12
0.2
ms
ON
LOAD
LTC3250-1.5 Load Regulation
LTC3250-1.2 Load Regulation
Line Regulation
0 ≤ I
0 ≤ I
≤ 250mA
mV/mA
mV/mA
%/V
Ω
OUT
OUT
≤ 250mA
I
I
= 250mA
OUT
OUT
R
Open-Loop Output Impedance
= 250mA (Note 4)
1.0
OL
Note 1: Absolute Maximum Ratings are those values beyond which the life
Note 4: Output not in regulation; R = (V /2 - V )/I
.
OL
IN
OUT OUT
of a device may be impaired.
Note 2: Based on long term current density limitations.
Note 3: The LTC3250-1.5E/LTC3250-1.2E are guaranteed to meet
specified performance from 0°C to 70°C. Specifications over the –40°C
and 85°C operating temperature range are assured by design
characterization and correlation with statistical process controls.
Note 5: This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
3250fa
2
LTC3250-1.5/LTC3250-1.2
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency vs
Supply Voltage
VSHDN Threshold Voltage vs
Supply Voltage
No Load Supply Current vs
Supply Voltage
1200
1100
1000
900
50
45
40
35
30
25
20
1.8
1.7
1.6
1.5
1.4
1.3
1.2
3.1V < V < 5.5V (LTC3250-1.5)
IN
2.7V < V < 5.5V (LTC3250-1.2)
IN
3.1V < V < 5.5V (LTC3250-1.5)
IN
2.7V < V < 5.5V (LTC3250-1.2)
IN
3.1V < V < 5.5V (LTC3250-1.5)
IN
2.7V < V < 5.5V (LTC3250-1.2)
IN
T
T
= 85°C
= 25°C
A
A
T
= –40°C
A
T
= 85°C
A
T
= 25°C
800
A
T
= –40°C
T
= –40°C
A
A
700
T
= 25°C
T
= 85°C
A
A
600
500
400
2.7
3.2
3.7
4.2
(V)
4.7
5.2
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
(V)
2.7
3.2
3.7
4.2
(V)
4.7
5.2
V
V
V
IN
IN
IN
3250 G03
3250 G01
3250 G02
(LTC3250-1.5)
Output Voltage vs Load Current
Efficiency vs Output Current
Output Voltage vs Supply Voltage
1.60
1.58
1.56
1.54
1.52
1.50
1.48
1.46
1.44
1.42
1.40
100
90
80
70
60
50
40
30
20
10
0
1.60
1.58
1.56
1.54
1.52
1.50
1.48
1.46
1.44
1.42
1.40
T
= 25°C
T
= 25°C
V
A
= 3.6V
A
A
IN
V
= 3.3V
IN
T
= 25°C
V
= 3.6V
IN
V
= 4V
IN
I
= 0mA
OUT
V
= 5V
I
= 100mA
IN
OUT
I
= 250mA
OUT
0.1
1
10
(mA)
100
1000
0
50
150
(mA)
200
250
300
3.0
3.5
4.0
V
4.5
(V)
5.0
5.5
100
I
I
OUT
OUT
IN
3250 G05
3250 G04
3250 G06
(LTC3250-1.2)
Output Voltage vs Load Current
Efficiency vs Output Current
Output Voltage vs Supply Voltage
1.30
1.28
1.26
1.24
1.22
1.20
1.18
1.16
1.14
1.12
1.10
100
90
80
70
60
50
40
30
20
10
0
1.30
1.28
1.26
1.24
1.22
1.20
1.18
1.16
1.14
1.12
1.10
T
= 25°C
T
= 25°C
V
T
= 3.6V
A
A
IN
A
V
= 2.7V
= 25°C
IN
V
= 3V
IN
I
= 0mA
OUT
V
= 3.5V
IN
I
= 100mA
OUT
V
= 4.5V
IN
I
= 250mA
OUT
0.1
1
10
(mA)
100
1000
2.7
3.2
3.7
4.2
(V)
4.7
5.2
0
50
150
(mA)
200
250
300
100
I
I
OUT
V
OUT
IN
3250 G13
3250 G14
3250 G12
3250fa
3
LTC3250-1.5/LTC3250-1.2
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Output Voltage Soft-Start and
Shutdown (LTC3250-1.5)
Output Current Transient
Response (LTC3250-1.5)
HI
250mA
15mA
I
SHDN
OUT
LOW
V
OUT
20mV/DIV
AC
V
OUT
500mV/DIV
3250 G07
3250 G08
R
IN
= 6Ω
V
= 3.6V
L
IN
V
= 3.6V
Input Voltage Ripple vs Input
Capacitor (LTC3250-1.5)
Line Transient Response
(LTC3250-1.5)
4.5V
V
IN
V
IN
3.5V
50mV/DIV
AC
C = 1µF
I
V
V
OUT
C = 10µF
IN
I
20mV/DIV
AC
50mV/DIV
AC
3250 G10
3250 G09
I
= 250mA
SOURCE
I
= 200mA
OUT
OUT
R
= 0.2Ω
Output Voltage Ripple
(LTC3250-1.5)
V
OUT
20mV/DIV
AC
3250 G11
C
= 4.7µF 1X5R16.3V
OUT
OUT
IN
I
= 250mA
V
= 3.6V
3250fa
4
LTC3250-1.5/LTC3250-1.2
U
U
U
PI FU CTIO S
C– (Pin 4): Flying Capacitor Negative Terminal
VIN (Pin 1): Input Supply Voltage. Bypass VIN with a ≥1µF
low ESR ceramic capacitor.
V
OUT (Pin 5): Regulated Output Voltage. VOUT is discon-
GND (Pin 2): Ground. Connect to a ground plane for best
performance.
nected from VIN during shutdown. Bypass VOUT with a
≥4.7µF low ESR ceramic capacitor (2.5µF min, ESR
<100mΩ).
SHDN (Pin 3): Active Low Shutdown Input. A low voltage
on SHDN disables the LTC3250-1.5/LTC3250-1.2. SHDN
must not be allowed to float.
C+ (Pin 6): Flying Capacitor Positive Terminal.
W
BLOCK DIAGRA
LTC3250-1.5/
LTC3250-1.2
THERMAL
SHUTDOWN
(>160°C)
SWITCH
CONTROL
AND
1.5MHz
3
1
SHDN
OSCILLATOR
SOFT-START
CHARGE
PUMP
V
IN
+
6
5
C
V
OUT
–
4
C
–
+
BURST
DETECT
CIRCUIT
V
REF
2
3250 BD
GND
3250fa
5
LTC3250-1.5/LTC3250-1.2
U
OPERATIO
(Refer to Simplified Block Diagram)
The LTC3250-1.5/LTC3250-1.2 use a switched capacitor temperatureexceedsapproximately160°C.Itwillreenable
charge pump to step down VIN to a regulated 1.5V ±4% or the charge pump once the junction temperature drops
1.2V ±4% (respectively) output voltage. Regulation is backtoapproximately150°C.TheLTC3250-1.5/LTC3250-
achievedbysensingtheoutputvoltagethroughaninternal 1.2willcycleinandoutofthermalshutdownwithoutlatch-
resistor divider and modulating the charge pump output up or damage until the short-circuit on VOUT is removed.
currentbasedontheerrorsignal.A2-phasenonoverlapping Long term overstress (IOUT > 350mA, and/or TJ > 140°C)
clock activates the charge pump switches. On the first shouldbeavoidedasitcandegradetheperformanceofthe
phase of the clock current is transferred from VIN, through part.
the flying capacitor, to VOUT. Not only is current being
Soft-Start
delivered to VOUT on the first phase, but the flying capaci-
tor is also being charged up. On the second phase of the
clock the flying capacitor is connected from VOUT to
ground, deliveringthechargestoredduringthefirstphase
of the clock to VOUT. Using this method of switching, only
half of the output current is delivered from VIN, thus
achieving twice the efficiency over a conventional LDO.
The sequence of charging and dis-charging the flying
capacitor continues at a free running frequency of 1.5MHz
(typ). This constant frequency architecture provides a low
noise regulated output as well as lower input noise than
conventional switch-capacitor charge pump regulators.
The part also has a low current Burst Mode operation to
improve efficiency even at light loads.
To prevent excessive current flow at VIN during start-up,
the LTC3250-1.5/LTC3250-1.2 have a built-in soft-start
circuitry. Soft-start is achieved by increasing the amount
of current available to the output charge storage capacitor
linearly overa periodofapproximately 500µs. Soft-start is
enabled whenever the device is brought out of shutdown,
and is disabled shortly after regulation is achieved.
Low Current “Burst Mode” Operation
To improve efficiency at low output currents, Burst Mode
operation was included in the design of the LTC3250-1.5/
LTC3250-1.2. An output current sense is used to detect
when the required output current drops below an inter-
nallysetthreshold(30mAtyp.). Whenthisoccurs, thepart
shuts down the internal oscillator and goes into a low
current operating state. The LTC3250-1.5/LTC3250-1.2
will remain in the low current operating state until the
output has dropped enough to require another burst of
current. Unlike traditional charge pumps whose burst
current is dependant on many factors (i.e. supply voltage,
switchresistance, capacitorselection, etc.), theLTC3250-
1.5/LTC3250-1.2’sburstcurrentissetbytheburstthresh-
oldandhysteresis.ThismeansthattheVOUT ripplevoltage
in Burst Mode will be fixed and is typically 12mV for a
4.7µF output capacitor.
In shutdown mode all circuitry is turned off and the
LTC3250-1.5/LTC3250-1.2drawonlyleakagecurrentfrom
the VIN supply. Furthermore, VOUT is disconnected from
VIN. The SHDN pin is a CMOS input with a threshold
voltageofapproximately0.8V.TheLTC3250-1.5/LTC3250-
1.2 are in shutdown when a logic low is applied to the
SHDN pin. Since the SHDN pin is a high impedance CMOS
input it should never be allowed to float. To ensure that its
state is defined it must always be driven with a valid logic
level.
Short-Circuit/Thermal Protection
The LTC3250-1.5/LTC3250-1.2 have built-in short-circuit
current limiting as well as overtemperature protection.
During short-circuit conditions, the parts will automati-
cally limit the output current to approximately 500mA. At
higher temperatures, or if the input voltage is high enough
to cause excessive selfheating onchip, thermalshutdown
circuitrywillshutdownthechargepumponcethejunction
Power Efficiency
The power efficiency (η) of the LTC3250-1.5/LTC3250-
1.2 are approximately double that of a conventional linear
regulator. This occurs because the input current for a 2 to
1step-downchargepumpisapproximatelyhalftheoutput
3250fa
6
LTC3250-1.5/LTC3250-1.2
U
OPERATIO
(Refer to Simplified Block Diagram)
current. For an ideal 2 to 1 step-down charge pump the
power efficiency is given by:
0.15Ω for the LTC3250-1.5 and 0.12Ω for the
LTC3250-1.2.Fora250mAloadcurrentchangetheoutput
voltage will change by about 37mV for the LTC3250-1.5
andby30mVfortheLTC3250-1.2. IftheESRoftheoutput
capacitor is greater than the closed-loop-output imped-
ance the part will cease to roll-off in a simple one-pole
fashion and poor load transient response or instability
could result. Ceramic capacitors typically have excep-
tional ESR performance and combined with a tight board
layout should yield excellent stability and load transient
performance.
POUT
P
IN
VOUT •IOUT 2VOUT
η ≡
=
=
1
V
IN
V • IOUT
IN
2
The switching losses and quiescent current of the
LTC3250-1.5/LTC3250-1.2 are designed to minimize effi-
ciency loss over the entire output current range, causing
only a couple % error from the theoritical efficiency. For
example with VIN = 3.6V, IOUT = 100mA and VOUT regulat-
ing to 1.5V the measured efficiency is 80.6% which is in
close agreement with the theoretical 83.3% calculation.
Furtheroutputnoisereductioncanbeachievedbyfiltering
theLTC3250-1.5/LTC3250-1.2outputthroughaverysmall
series inductor as shown in Figure 1. A 10nH inductor will
VOUT Capacitor Selection
10nH
(TRACE INDUCTANCE)
V
V
The ESR and value of capacitors used with the LTC3250-
1.5/LTC3250-1.2determineseveralimportantparameters
such as regulator control loop stability, output ripple, and
charge pump strength.
OUT
OUT
LTC3250-1.5/
LTC3250-1.2
4.7µF
0.22µF
GND
3250 F01
The value of COUT directly controls the amount of output
ripple for a given load current. Increasing the size of COUT
will reduce the output ripple.
Figure 1. 10nH Inductor Used for
Additional Output Noise Reduction
reject the fast output transients, thereby presenting a
nearly constant output voltage. For economy the 10nH
inductorcanbefabricatedonthePCboardwithabout1cm
(0.4") of PC board trace.
To reduce output noise and ripple, it is suggested that a
low ESR (<0.1Ω) ceramic capacitor (4.7µF or greater) be
used for COUT. Tantalum and aluminum capacitors are not
recommended because of their high ESR.
Both ESR and value of the COUT can significantly affect the
stability of the LTC3250-1.5/LTC3250-1.2. As shown in
the block diagram, the LTC3250-1.5/LTC3250-1.2 use a
control loop to adjust the strength of the charge pump to
match the current required at the output. The error signal
of this loop is stored directly on the output charge storage
capacitor. Thus the charge storage capacitor also serves
to form the dominant pole for the control loop. To prevent
ringingorinstabilityitisimportantfortheoutputcapacitor
to maintain at least 2.5µF of capacitance over all condi-
tions (see “Ceramic Capacitor Selection Guidelines” sec-
tion).
VIN Capacitor Selection
The constant frequency architecture used by the
LTC3250-1.5/LTC3250-1.2 makes input noise filtering
much less demanding than conventional charge pump
regulators. On a cycle by cycle basis, the LTC3250-1.5/
LTC3250-1.2 input current will go from IOUT/2 to 0mA.
Lower ESR will reduce the voltage steps caused by chang-
ing input current, while the absolute capacitor value will
determine the level of ripple. For optimal input noise and
ripple reduction, it is recommended that a low ESR 1µF or
greater ceramic capacitor be used for CIN (see “Ceramic
Capacitor Selection Guidelines” section). Aluminum and
tantalum capacitors are not recommended because of
their high ESR.
Likewise excessive ESR on the output capacitor will tend
todegradetheloopstabilityoftheLTC3250-1.5/LTC3250-
1.2. The closed-loop output resistance is designed to be
3250fa
7
LTC3250-1.5/LTC3250-1.2
U
OPERATIO
(Refer to Simplified Block Diagram)
Flying Capacitor Selection
Below is a list of ceramic capacitor manufacturers and
how to contact them:
Warning: A polarized capacitor such as tantalum or
aluminum should never be used for the flying capacitor
since its voltage can reverse upon start-up of the
LTC3250-1.5/LTC3250-1.2. Ceramic capacitors should
always be used for the flying capacitor.
AVX
1-(803)-448-1943
1-(864)-963-6300
1-(800)-831-9172
1-(800)-348-2496
1-(800)-487-9437
www.avxcorp.com
www.kemet.com
www.murata.com
www.t-yuden.com
www.vishay.com
Kemet
Murata
Taiyo Yuden
Vishay
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 0.4µF of
capacitance over operating temperature with a 2V bias
(see “Ceramic Capacitor Selection Guidelines” section). If
only 100mA or less of output current is required for the
application the flying capacitor minimum can be reduced
to 0.15µF.
Layout Considerations
Duetothehighswitchingfrequencyandtransientcurrents
producedbytheLTC3250-1.5/LTC3250-1.2carefulboard
layoutisnecessaryforoptimalperformance.Atrueground
plane and short connections to all capacitors will improve
performance and ensure proper regulation under all con-
ditions. Figure 2 shows the recommended layout configu-
ration.
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 X7R material will
retainmostofitscapacitancefrom–40°Cto85°Cwhereas
a Z5U or Y5V style capacitor will lose considerable capaci-
tanceoverthatrange(60%to80%losstyp.).Z5UandY5V
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 capaci-
tance for a given case size rather than discussing the
specified capacitance value. For example, over rated volt-
age and temperature conditions, a 4.7µF, 10V, Y5V
ceramic capacitor in a 0805 case may not provide any
more capacitance than a 1µF, 10V, X7R available in the
same 0805 case. In fact over bias and temperature range,
the 1µF, 10V, 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.
1µF
V
V
OUT
IN
1µF
4.7µF
GND
SHDN
3250 F02
LTC3250-1.5/LTC3250-1.2
VIA TO GROUND PLANE
Figure 2. Recommended Layout
The flying capacitor pins, C+ and C– will have very high
edge rate wave forms. The large dv/dt on these pins can
coupleenergycapacitivelytoadjacentprintedcircuitboard
runs. Magnetic fields can also be generated if the flying
capacitors are not close to the LTC3250-1.5/LTC3250-1.2
(i.e. the loop area is large). To decouple capacitive energy
transfer, a Faraday shield may be used. This is a grounded
PCtracebetweenthesensitivenodeandtheLTC3250-1.5/
LTC3250-1.2 pins. For a high quality AC ground it should
bereturnedtoasolidgroundplanethatextendsalltheway
to the LTC3250-1.5/LTC3250-1.2.
3250fa
8
LTC3250-1.5/LTC3250-1.2
U
OPERATIO
(Refer to Simplified Block Diagram)
Thermal Management
dissipation. The power dissipated in the LTC3250-1.5/
LTC3250-1.2 should always fall under the line shown (i.e.
within the safe region) for a given ambient temperature.
The power dissipated in the LTC3250-1.5/LTC3250-1.2 is
given by the expression:
For higher input voltages and maximum output current
there can be substantial power dissipation in the
LTC3250-1.5/LTC3250-1.2. If the junction temperature
increases above approximately 160°C the thermal shut-
down circuitry will automatically deactivate the output. To
reduce the maximum junction temperature, a good ther-
mal connection to the PC board is recommended. Con-
necting the GND pin (Pin 2) to a ground plane, and
maintaining a solid ground plane under the device can
reducethethermalresistanceofthepackageandPCboard
considerably.
V
2
IN
PD =
– VOUT IOUT
This derating curve assumes a maximum thermal resis-
tance, θJA , of 175°C/W for the 6-pin ThinSOT-23. This
thermal resistances can be achieved from a printed circuit
board layout with a solid ground plane (2000mm2)on at
least one layer with a good thermal connection to the
ground pin of the LTC3250-1.5/LTC3250-1.2. Operation
outsideofthiscurvewillcausethejunctiontemperatureto
exceed 140°C which may trigger the thermal shutdown
circuitry and ultimately reduce the life of the device.
Derating Power at Higher Temperatures
To prevent an overtemperature condition in high power
applications Figure 3 should be used to determine the
maximumcombinationofambienttemperatureandpower
1.2
1.0
0.8
0.6
0.4
0.2
0
θ
T
= 175°C/W
JA
J
= 140°C
–50
0
25
50
75
100
–25
AMBIENT TEMPERATURE (°C)
3250 • F03
Figure 3. Maximum Power Dissipation vs Ambient Temperature
3250fa
9
LTC3250-1.5/LTC3250-1.2
U
TYPICAL APPLICATIO S
Efficiency vs Output Current
100
90
80
70
60
50
40
30
20
10
0
Fixed 3.3V Input to 1.5V Output with Shutdown
T
= 25°C
A
V
= 3.3V
IN
1µF
4
6
–
+
C
C
5
2
1
3
V
= 3.3V
V
V
= 1.5V ±4%
OUT
V
IN
OUT
IN
1µF
LTC3250-1.5
SHDN
4.7µF
OFF
GND
ON
3250 TA02a
0.1
1
10
(mA)
100
1000
I
OUT
3250 TA02b
Efficiency vs Output Current
Li-Ion or 3-Cell NiMH to 1.5V Output with Shutdown
100
90
80
70
60
50
40
30
20
10
0
T
= 25°C
A
1µF
V
= 3.6V
IN
4
6
V
= 4V
IN
–
+
C
C
5
2
1
3
V
= 1.5V ±4%
V
V
OUT
IN
OUT
V
= 5V
IN
1-CELL Li-Ion OR
3-CELL NiMH
1µF
LTC3250-1.5
SHDN
4.7µF
OFF
GND
ON
3250 TA03a
0.1
1
10
(mA)
100
1000
I
OUT
3250 TA03b
Efficiency vs Input Voltage
(IOUT = 100mA)
3-Cell NiMH to 1.2V Output with Shutdown
100
90
80
70
60
50
40
30
20
10
0
T
= 25°C
A
1µF
4
6
–
+
C
C
5
2
LTC3250
LDO
1
3
V
IN
= 2.7V TO 5V
3-CELL NiMH
V
= 1.2V ±4%
V
V
OUT
IN
LTC3250-1.2
SHDN
OUT
1µF
4.7µF
OFF
GND
ON
3250 TA05a
2.7
3.2
3.7
4.2
(V)
4.7
5.2
V
IN
3250 TA05b
3250fa
10
LTC3250-1.5/LTC3250-1.2
U
PACKAGE DESCRIPTIO
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
2.90 BSC
(NOTE 4)
0.62
MAX
0.95
REF
1.22 REF
1.4 MIN
1.50 – 1.75
2.80 BSC
3.85 MAX 2.62 REF
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45
6 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
0.20 BSC
DATUM ‘A’
0.01 – 0.10
1.00 MAX
0.30 – 0.50 REF
1.90 BSC
0.09 – 0.20
(NOTE 3)
S6 TSOT-23 0302
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
3250fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
11
LTC3250-1.5/LTC3250-1.2
U
TYPICAL APPLICATIO
Multiple High Efficiency Outputs from Single Li-Ion Battery
5
3
2
1
6
4
5V
100mA
V
V
IN
LTC3200-5
OUT
Li-Ion
1µF
1µF
+
SHDN
C
C
1µF
–
GND
7
2
8
1
5
6
3.3V
500mA
V
OUT
SW1
SW2
FB
IN
22µF
3
10µF
MODE
LTC3440
10µH
4
SHDN
340k
200k
60k
9
RT
10
GND
V
C
120k
300pF
1
8
2
3
6
7
5
4
1.8V
250mA
V
OUT
IN
LTC1911-1.8
10µF
10µF
+
SHDN
C1
C1
1µF
+
–
C2
1µF
–
C2
GND
1
3
5
6
1.5V
250mA
V
OUT
IN
+
SHDN
C
OFF
ON
4.7µF
LTC3250-1.5
1µF
1µF
2
4
–
GND
C
3250-1.5 TA04
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
V : 2.7V to 10V, V : 3V/5V,
LTC1514
50mA, 650kHz, Step Up/Down Charge Pump
with Low Battery Comparator
IN
OUT
Regulated Output, I : 60µA, I : 10µA, S8 Package
Q
SD
LTC1515
LT1776
50mA, 650kHz, Step Up/Down Charge Pump
with Power On Reset
V : 2.7V to 10V, V : 3.3V or 5V,
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Q
SD
500mA (I ), 200kHz, High Efficiency Step-Down
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: 1.24V,
OUT(MIN)
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IN
DC/DC Converter
I : 3.2mA, I : 30µA, N8,S8 Packages
Q SD
LTC1911-1.5/LTC1911-1.8 250mA,1.5MHz, High Efficiency Step-Down
Charge Pump
75% Efficiency, V : 2.7V to 5.5V, V : 1.5V/1.8V,
IN OUT
Regulated Output, I : 180µA, I : 10µA, MS8 Package
Q
SD
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500mA, Spread Spectrum, High Efficiency
Step-Down Charge Pump
Up to 90% Efficiency, V : 2.7V to 5.5V, V : 0.9V to 1.6V,
IN OUT
Regulated Output, I : 9µA, I : <1µA, MS Package
Q
SD
LTC3252
Dual 250mA (I ), Spread Spectrum, Inductorless (CS), Up to 90% Efficiency, V : 2.7V to 5.5V, V : 0.9V to 1.6V,
OUT IN OUT
Step-Down DC/DC Converter
I : 60µA, I : <1µA, DFN Package
Q SD
LTC3405/LTC3405A
LTC3406/LTC3406B
LTC3411
300mA (I ), 1.5MHz, Synchronous Step-Down
DC/DC Converter
95% Efficiency, V : 2.7V to 6V, V : 0.8V,
OUT(MIN)
I : 20µA, I : <1µA, ThinSOT Package
Q SD
OUT
IN
600mA (I ), 1.5MHz, Synchronous Step-Down
95% Efficiency, V : 2.5 to 5.5V, V
: 0.6V,
OUT(MIN)
OUT
IN
DC/DC Converter
I : 20µA, I : <1µA, ThinSOT Package
Q SD
1.25A (I ), 4MHz, Synchronous Step-Down
95% Efficiency, V : 2.5V to 5.5V, V
I : 60µA, I : <1µA, MS Package
Q SD
: 0.8V,
: 0.8V,
OUT
IN
OUT(MIN)
DC/DC Converter
LTC3412
2.5A (I ), 4MHz, Synchronous Step-Down
95% Efficiency, V : 2.5V to 5.5V, V
IN
OUT
OUT(MIN)
DC/DC Converter
I : 60µA, I : <1µA, TSSOP16E Package
Q SD
LTC3440
600mA (I ), 2MHz, Synchronous Buck-Boost
DC/DC Converter
95% Efficiency, V : 2.5V to 5.5V, V : 2.5V to 5.5V,
IN OUT
I : 25µA, I : <1µA, MS Package
Q SD
OUT
LTC3441
1.2A (I ), 1MHz, Synchronous Buck-Boost
DC/DC Converter
95% Efficiency, V : 2.4V to 5.5V, V : 2.4V to 5.25V,
IN OUT
I : 25µA, I : <1µA, DFN Package
Q SD
OUT
3250fa
LT/TP 1203 1K REV A • PRINTED IN USA
12 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
LINEAR TECHNOLOGY CORPORATION 2001
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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