3570 [Linear]
1.5A Buck Converter, 1.5A Boost Converter and LDO Controller; 1.5A降压转换器， 1.5A升压型转换器和LDO控制器
| 型号： | 3570 |
| 厂家： | 
Linear |
| 描述： | 1.5A Buck Converter, 1.5A Boost Converter and LDO Controller |
| 文件： | 总20页 (文件大小：283K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3570
1.5A Buck Converter,
1.5A Boost Converter and
LDO Controller
FEATURES
DESCRIPTION
n
2.5V to 36V Input Voltage Range
The LT®3570 is a buck and boost converter with internal
power switches and LDO controller. Each converter is
designed with a 1.5A current limit and an input range
from 2.5V to 36V, making the LT3570 ideal for a wide
variety of applications. Switching frequencies up to 2MHz
are programmed with an external timing resistor and the
oscillator can be synchronized to an external clock up to
2.75MHz.
n
Programmable Switching Frequency
from 500kHz to 2MHz
n
Synchronizable Up to 2.75MHz
n
V
: 0.8V
OUT(MIN)
n
n
n
n
Independent Soft-Start for Each Converter
Separate V Supplies for Each Converter
IN
Duty Cycle Range: 0% to 90% at 1MHz
Available in 24-Lead (4mm × 4mm) QFN and
20-Lead TSSOP Packages
The LT3570 features a programmable soft-start function
that limits the feedback voltage during start-up helping
prevent overshoot and limiting inrush current. The LDO
controller is capable of delivering up to 10mA of base
current to an external NPN transistor.
APPLICATIONS
n
Cable and Satellite Set-Top Boxes
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
n
Automotive Systems
n
Telecom Systems
n
“Dying Gasp” Systems
n
TFT LCD Displays
TYPICAL APPLICATION
V
IN
5V
10μF
V
V
V
BIAS
IN1 IN2 IN3
D3
Efficiency
SHDN1
SHDN2
SHDN3
SHDN1
SHDN2
SHDN3
BOOST
100
100nF
V
3.3V
1A
OUT2
SW2
3.3μH
95
D2
32.4k
6.8μH
D1
V
OUT1
12V
275mA
90
85
SW1
FB2
SS2
22μF
143k
V
C2
LT3570
f
= 1.2MHz
= 5V
10μF
SW
IN
10.2k
FB1
SS1
22k
1nF
10nF
V
V
V
V
80
75
70
= 12V
10.0k
OUT1
OUT2
OUT3
OUT1
OUT3
V
C1
= 3.3V
= 2.5V
22k
1nF
I
I
= 275mA
= 100mA
NPN_DRV
Q1
V
OUT3
2.5V
0
0.2
0.4
I
OUT2
0.6
(A)
0.8
1.0
10nF
100mA
22.1k
3570 TA01b
FB3
2.2μF
R
T
SYNC
15.8k
GND
10.2k
3570 TA01a
3570fa
1
LT3570
(Note 1)
ABSOLUTE MAXIMUM RATINGS
V , V Voltage..........................................................3V
V
, V , V , V
Voltage ..................................40V
C1 C2
IN1 IN2 IN3 BIAS
Maximum Junction Temperature........................... 125°C
BOOST Voltage .........................................................60V
BOOST Pin Above SW2.............................................25V
NPN_DRV Voltage.......................................................8V
SW1 Voltage .............................................................40V
SHDN1, SHDN2, SHDN3 Voltage ..............................40V
Operating Temperature Range (Note 2).. –40°C to 125°C
Storage Temperature Range
TSSOP ............................................... –65°C to 150°C
QFN.................................................... –65°C to 125°C
Lead Temperature (Soldering, 10 sec)
SYNC, R Voltage........................................................3V
T
TSSOP Only...................................................... 300°C
SS1, SS2 Voltage........................................................3V
FB1, FB2, FB3 Voltage...............................................10V
PIN CONFIGURATION
TOP VIEW
TOP VIEW
FB1
SHDN1
SHDN2
SHDN3
SYNC
1
2
3
4
5
6
7
8
9
20
19
18
17
16
15
14
13
12
11
V
C1
SS1
24 23 22 21 20 19
V
IN1
V
V
1
2
3
4
5
6
18
17
16
15
V
C2
IN2
IN2
GND
SW1
SW2
SS2
SW2
SW1
GND
GND
GND
21
25
R
T
R
T
SS2
V
IN2
14 SYNC
V
C2
BOOST
13 SHDN3
FB2
V
IN3
7
8
9 10 11 12
FB3 10
NPN_DRV
FE PACKAGE
20-LEAD PLASTIC TSSOP
UF PACKAGE
24-LEAD (4mm s 4mm) PLASTIC QFN
T
= 125°C, θ = 38°C/W
JA
EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
JMAX
T
JMAX
= 125°C, θ = 37°C/W
JA
EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT3570EUF#PBF
LT3570IUF#PBF
LT3570EFE#PBF
LT3570IFE#PBF
TAPE AND REEL
PART MARKING*
3570
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3570EUF#TRPBF
LT3570IUF#TRPBF
LT3570EFE#TRPBF
LT3570IFE#TRPBF
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
24-Lead (4mm × 4mm) Plastic QFN
24-Lead (4mm × 4mm) Plastic QFN
20-Lead Plastic TSSOP
3570
LT3570FE
LT3570FE
20-Lead Plastic TSSOP
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/
3570fa
2
LT3570
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN1,2,3 = 12V, VSHDN1,2,3 = 12V unless otherwise noted.
PARAMETER
CONDITIONS
(Note 3)
MIN
TYP
2.1
2.1
0
MAX
2.5
UNITS
l
l
Minimum Operating Voltage (V
Minimum Operating Voltage (V
Shutdown Current (Note 4)
)
)
V
V
IN1
(Note 3)
2.5
IN2
V
= 0V
1.5
μA
SHDN1,2,3
V
IN1
V
IN2
V
IN3
Quiescent Current
Quiescent Current
Quiescent Current
V
V
= 12V, V
= 0V, V = 0.4V (Not Switching)
3.2
65
4.5
mA
μA
SHDN1
SHDN1
SHDN2,3
C1
= 0V, V
= 12V
150
SHDN2,3
V
V
= 0V, V
= 12V, V
= 12V, V = 0.4V (Not Switching)
3.5
3.5
4.5
4.5
mA
mA
SHDN1,3
SHDN1,3
SHDN2
SHDN2
C2
= 0V
V
V
= 0V, V
= 12V, V
= 12V
= 0V
700
0
950
1.5
μA
μA
SHDN1,2
SHDN1,2
SHDN3
SHDN3
Bias Quiescent Current
V
= 2.5V
2.3
3.1
1.4
1.4
mA
V
BIAS
VIN2
V
V
V
Pin Threshold
Pin UVLO
I
> 100μA
0.3
1.1
SHDN1,2,3
SHDN1,2,3
l
1.25
V
Pin Current
V
V
= 12V, V
= 0V
= 0V (Note 5)
30
0.1
50
1.5
μA
μA
SHDNX
SHDNX
SHDN1,2,3
SHDNY,Z
Switching Frequency
Maximum Duty Cycle
R = 44.2k
T
450
500
2100
550
2300
kHz
kHz
T
R = 7.87k
1900
R = 44.2k
95
80
%
%
T
R = 7.87k
T
Synchronous Frequency Threshold
Synchronous Frequency Ratio, f /f
0.3
1.5
V
R = 44.2k
T
1.3
1.3
SYN OSC
T
R = 7.87k
Synchronous Frequency Minimum On/Off
Time
50
ns
l
FB1,2,3 Pin Voltage
772
788
0.01
30
804
mV
%/V
nA
FB1,2,3 Pin Voltage Line Regulation
FB1,2 Pin Bias Current
V
= 2.5V to 40V, V
= 1V
VIN1,2,3
C1,2
V
V
V
V
V
= 800mV, V
= 1V (Note 6)
200
200
FB1,2
C1,2
FB3 Pin Bias Current
= 800mV (Note 6)
30
nA
FB3
SS1,2 Pin Source Current
= 500mV
= 600mV
= 1V
4.5
12
μA
SS1,2
FB1,2
FB1,2
V
V
Pin Source Current
Pin Sink Current
μA
C1,2
C1,2
12
μA
SW1
Error Amplifier 1 Transconductance
Error Amplifier 1 Voltage Gain
190
100
750
5.9
μMho
V/V
mV
A/V
A
V
C1
V
C1
Pin Switching Threshold
to SW1 Current Gain
SW1 Current Limit
SW1 V
(Note 7)
= 1A (Note 7)
1.5
2.4
3.1
5
I
240
0.2
mV
μA
CESAT
SW1
SW1 Leakage Current
SW1 = 40V, V
= 0V
SHDN1
3570fa
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LT3570
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN1,2,3 = 12V, VSHDN1,2,3 = 12V unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
SW2
Error Amplifier 2 Transconductance
Error Amplifier 2 Voltage Gain
195
100
700
5.4
μMho
V/V
mV
A/V
A
V
C2
V
C2
Pin Switching Threshold
to SW2 Current Gain
SW2 Current Limit
SW2 V
(Note 7)
1.5
10
2.4
3.1
5
I
= 1A (Note 7)
SW2
240
0.2
mV
μA
CESAT
SW2 Leakage Current
BOOST Pin Current
SW2 = 0V, V = 40V, V
= 0V
IN2
SHDN2
I
I
= 0.5A
= 1.5A
15
30
mA
mA
SW2
SW2
LDO
LDO Maximum Output Current
V
FB3
= 600mV
20
mA
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 LT3570E is guaranteed to meet performance specifications
from 0°C to 125°C 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
LT3570I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 4: Shutdown current is for each individual input current.
Note 5: Current flows into the pin.
Note 6: Current flows out of the pin.
Note 7: Switch current limit and switch V
guaranteed by design
CESAT
and/or correlation to static test.
Note 8: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed the maximum operating junction temperature
range when overtemperature protection is active. Continuous operation
above the specified maximum operating junction temperature may impair
device reliability.
Note 3: V supplies power for the part. V supplies power only to the
IN2
IN1
boost converter. V supplies power only to the LDO Controller.
IN3
TYPICAL PERFORMANCE CHARACTERISTICS
Feedback Voltage vs Temperature
Frequency vs Temperature
Soft-Start Current vs Temperature
5.0
4.8
4.6
4.4
4.2
4.0
3.8
3.6
2500
0.800
0.795
0.790
0.785
0.780
0.775
0.770
R
= 7.87k
T
2000
1500
R
T
= 20k
1000
500
0
R
T
= 44.2k
75 100
TEMPERATURE (°C)
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3570 G03
–50 –25
0
25 50
125 150
50
TEMPERATURE (°C)
–50 –25
0
25
75 100 125 150
3570 G01
3570 G02
3570fa
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LT3570
TYPICAL PERFORMANCE CHARACTERISTICS
VIN1 Quiescent Current
vs Temperature
VIN2 Quiescent Current
vs Temperature
VIN3 Quiescent Current
vs Temperature
3.5
3.0
900
800
700
600
500
400
300
200
100
0
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
2.5
2.0
1.5
1.0
0.5
0
–25
0
150
–50
25 50 75 100 125
TEMPERATURE (°C)
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3570 G06
50 75
TEMPERATURE (°C)
–50 –25
0
25
100 125 150
3570 G04
3570 G05
Bias Pin Current vs Temperature
SHDN Pin UVLO vs Temperature
SHDN Pin Current vs Voltage
50
40
30
20
10
0
3.0
2.5
2.0
1.5
1.0
0.5
0
1.50
1.25
1.00
0.75
0.50
0.25
0
75 100
75 100
20
VOLTAGE (V)
–50 –25
0
25 50
125 150
–50 –25
0
25 50
125 150
0
5
10 15
25 30 35 40
TEMPERATURE (°C)
TEMPERATURE (°C)
3570 G07
3570 G08
3570 G09
SW1 Saturation Voltage
vs SW1 Current
SW1 Current Limit vs Duty Cycle
3.0
2.5
350
300
250
2.0
1.5
200
150
100
50
1.0
0.5
0
T
T
T
= 125°C
= 25°C
= –40°C
T
T
T
= 125°C
= 25°C
J
J
J
J
J
J
= –40°C
0
0
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
0
0.3
0.5 0.6 0.7 0.8 0.9 1.0
0.1 0.2
0.4
CURRENT (A)
3570 G10
3570 G11
3570fa
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LT3570
TYPICAL PERFORMANCE CHARACTERISTICS
SW2 Saturation Voltage
vs SW2 Current
SW2 Current Limit vs Duty Cycle
3.0
2.5
350
300
250
2.0
1.5
200
150
100
50
1.0
0.5
0
T
T
T
= 125°C
= 25°C
T
T
T
= 125°C
= 25°C
= –40°C
J
J
J
J
J
J
= –40°C
0
0
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
0
0.3
0.5 0.6 0.7 0.8 0.9 1.0
0.1 0.2
0.4
CURRENT (A)
3570 G12
3570 G13
BOOST Pin Current
vs Switch Current
NPN_DRV Output Current vs VIN3
30
25
18
16
14
12
10
8
T
= 25°C
J
T
= 25°C
J
T
= 125°C
J
20
15
T
= –40°C
T
= –40°C
J
J
T
= 125°C
J
10
5
6
4
2
0
0
0
0.2
0.4
0.6
0.8
1.0
1
5
20 25
10 15
VOLTAGE (V)
30 35 40
CURRENT (A)
3570 G14
3570 G15
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LT3570
PIN FUNCTIONS (QFN/TSSOP)
V
IN2
(Pins1,2/Pin14):InputVoltagefortheBuckRegulator.
SHDN3 (Pin13/Pin 4): Shutdown Pin. Tie to 1.5V or more
This pin also supplies the current to the internal circuitry
of the LT3570. This pin must be locally bypassed with a
capacitor.
to enable the NPN LDO. Ground to shut down the part.
SYNC (Pin 14/Pin 5): Synchronization Pin. The SYNC pin
is used to synchronize the internal oscillator to an exter-
nal signal. The synchronizing range is equal to the initial
SW2 (Pin 3/Pin15): Switch Node. This pin connects to
the emitter of an internal NPN power switch. Connect a
diode, inductor and boost capacitor to this pin to form
the buck regulator
operating frequency set by the R pin up to 1.3 times the
T
initial operating frequency.
R (Pin 15/Pin 6): Frequency Set Pin. Place a resistor to
T
SW1 (Pin 4/Pin16): Switch Node. This pin connects to the
collectorofaninternalNPNpowerswitch.Connectadiode
and inductor to this pin to form the boost regulator
GND to set the internal frequency. The range of oscillation
is 500kHz to 2MHz.
SS2 (Pin 17/Pin 7): Soft-Start Pin. Place a soft-start
capacitor here. Upon start-up, a current charges the
capacitor to 2V. This pin ramps the reference voltage of
the buck switcher.
GND(Pins5,6,16,25/Pins17,21):Ground.TheExposed
Pad of the package provides both electrical contact to
ground and good thermal contact to the printed circuit
board. The Exposed Pad must be soldered to the circuit
board for proper operation.
V (Pin18/Pin8):ControlVoltageandCompensationPin
C2
for the Internal Error Amplifier. Connect a series RC from
this pin to ground to compensate the switching regulator
loop for the buck regulator.
V
(Pin 7/Pin18): Input Voltage for the Boost Regulator.
IN1
This pin supplies current to drive the boost NPN transistor
of the LT3570. This pin must be locally bypassed with a
capacitor.
FB2 (Pin 19/Pin 9): Feedback Pin. The LT3570 regulates
this pin to 788mV. Connect the feedback resistors to
this pin to set the output voltage for the buck switching
regulator.
SS1 (Pin 8/Pin 19): Soft-Start Pin. Place a soft-start
capacitor here. Upon start-up, a current charges the
capacitor to 2V. This pin ramps the reference voltage of
the boost switcher.
FB3 (Pin 20/Pin 10): Feedback Pin. The LT3570 regulates
this pin to 788mV. Connect the feedback resistors to this
pin to set the output voltage for the LDO controller.
V (Pin9/Pin20):ControlVoltageandCompensationPin
C1
for the Internal Error Amplifier. Connect a series RC from
this pin to ground to compensate the switching regulator
loop for the boost regulator.
NPN_DRIVE (Pin 21/Pin 11): Base Drive for the External
NPN. This pin provides a bias current to drive the base of
the NPN. This base current is driven from the IN3 supply
voltage.
FB1 (Pin 10/Pin 1): Feedback Pin. The LT3570 regulates
this pin to 788mV. Connect the feedback resistors to
this pin to set the output voltage for the boost switching
regulator.
V
(Pin 22/Pin 12): Input Voltage for the NPN LDO. This
IN3
pin supplies current to drive the base of the NPN. This pin
must be locally bypassed with a capacitor.
SHDN1 (Pin 11/Pin 2): Shutdown Pin. Tie to 1.5V or
more to enable the boost switcher. Ground to shutdown
the part.
BIAS(Pin23):QFNPackageOnly.Thispinsuppliescurrent
to the internal circuitry of the LT3570 if greater than 2.5V.
This pin must be locally bypassed with a capacitor.
SHDN2 (Pin 12/Pin 3): Shutdown Pin. Tie to 1.5V or
more to enable the buck switcher. Ground to shutdown
the part.
BOOST (Pin 24/Pin 13): Bias for the Base Drive of the
NPN Switch for the Buck Regulator. This pin provides a
bias voltage higher than V . The voltage on this pin is
IN2
charged up through an external Schottky diode.
3570fa
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LT3570
BLOCK DIAGRAM
3570fa
8
LT3570
OPERATION
The LT3570 is a constant frequency, current mode, buck
converter and boost converter with an NPN LDO regula-
tor. Operation can be best understood by referring to the
Block Diagram.
V
pin controls the current through the inductor to the
C1
output.TheinternalerroramplifierA1regulatestheoutput
voltage by continually adjusting the V pin voltage. The
threshold for switching on the V pin is approximately
C1
C1
750mV and an active clamp of 1.15V limits the output
current. The soft-start capacitor C6A allows the part to
slowly start up by ramping the internal reference.
If all of the SHDN pins are held low, the LT3570 is shut
down and draws zero quiescent current. When any of the
pins exceed 1.4V the internal bias circuits turn on. Each
regulatorwillonlybeginregulatingwhenitscorresponding
SHDN pin is pulled high.
The driver for the buck regulator can operate from either
V
IN2
or from the BOOST pin. An external capacitor and
diode are used to generate a voltage at the BOOST pin that
is higher than the input supply. This allows the driver to
saturatetheinternalbipolarNPNpowerswitchforefficient
operation. The driver for the boost regulator is operated
Each switching regulator controls the output voltage in
a similar manner. The operation of the switchers can be
understood by looking at the boost regulator. A pulse
from the oscillator sets the RS flip-flop A4 and turns on
the internal NPN bipolar power switch Q1. Current in Q1
and the external inductor L1 begins to increase. When
this current exceeds a level determined by the voltage at
from V
.
IN1
The BIAS pin allows the internal circuitry to draw its
current from a lower voltage supply than the input. This
reduces power dissipation and increases efficiency. If the
voltage on the BIAS pin falls below 2.5V, then the LT3570
V , comparator A3 resets A4, turning off Q1. The current
C1
in L1 flows through the external Schottky diode D1 and
begins to decrease. The cycle begins again at the next
pulse from the oscillator. In this way, the voltage on the
quiescent current will flow from V
.
IN2
3570fa
9
LT3570
APPLICATIONS INFORMATION
FB Resistor Network
The optimum inductor for a given application may differ
from the one indicated by this simple design guide. A
larger value inductor provides a slightly higher maximum
load current and will reduce the output voltage ripple. If
your load is lower than the maximum load current, then
you can relax the value of the inductor and operate with
higher ripple current. This allows you to use a physically
smaller inductor or one with a lower DCR resulting in
higher efficiency. Be aware that if the inductance differs
fromthesimpleruleabove,thenthemaximumloadcurrent
will depend on input voltage. In addition, low inductance
mayresultindiscontinuousmodeoperation,whichfurther
reduces maximum load current. For details of maximum
output current and discontinuous mode operation, see
Linear Technology’s Application Note 44. Finally, for duty
The output voltage is programmed with a resistor divider
(refer to the Block Diagram) between the output and the
FB pin. Choose the resistors according to:
VOUT
788mV
⎛
⎞
⎠
R1=R2
–1
⎜
⎝
⎟
Buck Inductor Selection and Maximum Output Current
A good first choice for the inductor value is
VOUT2 + V
0.75• f
F
L =
for SW2
where V is the voltage drop of the catch diode (~0.4V)
F
and f is the switching frequency. With this inductance
value or greater, the maximum load current will be 1A,
independent of input voltage. The inductor’s RMS current
ratingmustbegreaterthanthemaximumloadcurrentand
its saturation current should be at least 30% higher. For
highest efficiency, the series resistance (DCR) should be
less than 0.1Ω. Table 1 lists several vendors and types
that are suitable.
cycles greater than 50% (V
/V > 0.5) a minimum
OUT2 IN2
inductance is required to avoid subharmonic oscillations,
see Application Note 19.
Thecurrentintheinductorisatrianglewavewithanaverage
value equal to the load current. The peak switch current
is equal to the output current plus half the peak-to-peak
inductor ripple current. The LT3570 limits its switch cur-
rent in order to protect itself and the system from overload
faults. Therefore, the maximum output current that the
LT3570 will deliver depends on the switch current limit,
the inductor value and the input and output voltages.
Table 1. Inductors
VALUE
(μH)
I
DCR
(Ω)
HEIGHT
(mm)
SAT
PART NUMBER
Sumida
(A)
When the switch is off, the potential across the inductor
is the output voltage plus the catch diode drop. This gives
the peak-to-peak ripple current in the inductor:
CDRH4D28-3R3
CDRH4D28-4R7
CDC5D23-2R2
CR43-3R3
3.3
4.7
2.2
3.3
10
1.57
1.32
2.50
1.44
1.3
0.049
0.072
0.03
3.0
3.0
2.5
3.5
3.0
0.086
0.048
1–DC2 VOUT2 + V
(
)
(
)
F
CDRH5D28-100
Coilcraft
ΔIL2 =
L • f
DO1608C-332
DO1608C-472
MOS6020-332
D03314-103
D03314-222
Toko
3.3
4.7
3.3
10
2.00
1.50
1.8
0.080
0.090
0.046
0.520
0.200
2.9
2.9
2.0
1.4
1.4
where DC2 is the duty cycle and is defined as:
VOUT2
DC2 =
0.8
V
IN2
2.2
1.6
The peak inductor and switch current is:
(D62F)847FY-2R4M
(D73LF)817FY-2R2M
Coiltronics
2.4
2.2
2.5
2.7
0.037
0.03
2.7
3.0
ΔIL2
2
ISWPK2 =ILPK2 =IOUT2
+
TP3-4R7
4.7
2.2
10
1.5
1.3
1.5
0.181
0.188
0.146
2.2
1.8
3.0
To maintain output regulation, this peak current must be
less than the LT3570’s switch current limit I . I is
TP1-2R2
LIM2 LIM2
TP4-100
at least 1.5A at low duty cycles and decreases linearly
3570fa
10
LT3570
APPLICATIONS INFORMATION
to 1.2A at DC2 = 0.8. The maximum output current is a
function of the chosen inductor value:
Powdered iron cores are forgiving because they saturate
softly, whereas ferrite cores saturate abruptly. Other
core materials fall somewhere in between. The following
formula assumes continuous mode operation but it errs
only slightly on the high side for discontinuous mode, so
it can be used for all conditions.
ΔIL2
2
IOUT2(MAX) =ILIM2
–
ΔIL2
2
=1.5• 1– 0.25•DC2 –
(
)
V
VOUT1 – V
IN1
IOUT1 • VOUT1
(
)
IN1
IPEAK1
=
+
V
2• f •L • VOUT1
Choosing an inductor value so that the ripple current is
smallwillallowamaximumoutputcurrentneartheswitch
current limit.
IN1
Make sure that I
LIM1
is less than the switch current I
.
LIM1
PEAK1
I
is at least 1.5A at low duty cycles and decreases
linearly to 1.2A at DC1 = 0.8. The maximum switch current
limit can be calculated by the following formula:
One approach to choosing the inductor is to start with the
simple rule given above, look at the available inductors
and choose one to meet cost or space goals. Then use
these equations to check that the LT3570 will be able to
deliver the required output current. Note again that these
equations assume that the inductor current is continu-
I
= 1.5 • (1 – 0.25 • DC1)
LIM1
where DC1 is the duty cycle and is defined as:
V
VOUT1
IN1
DC1=1–
ous. Discontinuous operation occurs when I
is less
OUT2
than ΔI /2.
L2
Rememberalsothatinductancecandropsignificantlywith
DC current and manufacturing tolerance. Consideration
should also be given to the DC resistance of the inductor
as this contributes directly to the efficiency losses in the
overall converter. Table 1 lists several inductor vendors
and types that are suitable.
Boost Inductor Selection
For most applications the inductor will fall in the range
of 2.2μH to 22μH. Lower values are chosen to reduce
physical size of the inductor. Higher values allow more
output current because they reduce peak current seen by
the power switch, which has a 1.5A current limit. Higher
values also reduce input ripple voltage and reduce core
loss. The following procedure is suggested as a way of
choosing a more optimum inductor.
Buck Output Capacitor Selection
For 5V and 3.3V outputs, a 10μF, 6.3V ceramic capacitor
(X5R or X7R) at the output results in very low output volt-
agerippleandgoodtransientresponse.Forlowervoltages,
10μF is adequate for ripple requirements but increasing
Assume that the average inductor current for a boost
converter is equal to the load current times V
/V
OUT1 IN1
C
OUT
will improve transient performance. Other types and
and decide whether or not the inductor must withstand
continuous overload conditions. If average inductor cur-
rent at maximum load current is 0.5A, for instance, a 0.5A
inductor may not survive a continuous 1.5A overload
condition. Also be aware that boost converters are not
short-circuit protected, and that under short conditions,
inductor current is limited only by the available current
of the input supply
values will also work; the following discusses tradeoffs in
output ripple and transient performance.
Theoutputcapacitorfilterstheinductorcurrenttogenerate
an output with low voltage ripple. It also stores energy in
order to satisfy transient loads and stabilize the LT3570’s
control loop. Because the LT3570 operates at a high
frequency, minimal output capacitance is necessary. In
addition, the control loop operates well with or without
the presence of output capacitor series resistance (ESR).
Ceramic capacitors, which achieve very low output ripple
Calculate peak inductor current at full load current to en-
sure that the inductor will not saturate. Peak current can
be significantly higher than output current, especially with
smallerinductorsandlighterloads,sodon’tomitthisstep.
3570fa
11
LT3570
APPLICATIONS INFORMATION
and small circuit size, are therefore an option. You can
estimate output ripple with the following equations:
response for large changes in load current. Table 2 lists
several capacitor vendors.
ΔIL2
8 • f •COUT
Table 2. Low ESR Surface Mount Capacitors
VRIPPLE
=
for ceramic capacitors
VENDOR
Taiyo Yuden
AVX
TYPE
SERIES
Ceramic
X5R, X7R
and
Ceramic
Tantalum
X5R, X7R
TPS
V
=ΔI •ESRforelectrolyticcapacitors(tantalum
L2
and aluminum)
RIPPLE
Kemet
Tantalum
Ta Organic
Al Organic
T491, T494, T495
T520
A700
The RMS content of this ripple is very low so the RMS
current rating of the output capacitor is usually not of
concern. It can be estimated with the formula:
Sanyo
Ta or Al Organic
Al Organic
POSCAP
SP CAP
Panasonic
TDK
Ceramic
X5R, X7R
ΔIL2
12
IC(RMS)
=
Boost Output Capacitor Selection
Low ESR capacitors should be used at the output to
minimize the output ripple voltage. Multilayer ceramic
capacitors are the best choice, as they have a very low
ESR and are available in very small packages. Always use
a capacitor with a sufficient voltage rating. Boost regula-
tors have large RMS ripple current in the output capacitor,
which must be rated to handle the current. The formula
to calculate this is:
Another constraint on the output capacitor is that it must
havegreaterenergystoragethantheinductor;ifthestored
energyintheinductortransferstotheoutput, theresulting
voltage step should be small compared to the regulation
voltage. For a 5% overshoot, this requirement indicates:
2
⎛
⎞
ILIM2
COUT >10 •L •
⎜
⎟
V
⎝
⎠
OUT2
VOUT1 – V
DC1
1–DC1
IN1
The low ESR and small size of ceramic capacitors make
them the preferred type for LT3570 applications. Not all
ceramic capacitors are the same, however. Many of the
higher value capacitors use poor dielectrics with high
temperature and voltage coefficients. In particular, Y5V
and Z5U types lose a large fraction of their capacitance
withappliedvoltageandattemperatureextremes.Because
loop stability and transient response depend on the value
IRIPPLE(RMS) =IOUT
= IOUT1
V
IN1
and is largest when V is at its minimum value if V
IN1
OUT1
and I
are constant. With a 1.5A current limit, the
OUT1
maximum that the output current ripple can be is ~0.75A.
Table 2 lists several capacitor vendors.
Buck Input Capacitor Selection
of C , this loss may be unacceptable. Use X7R and X5R
OUT
types.
Bypass the input of the LT3570 circuit with a 10μF or
higher ceramic capacitor of X7R or X5R type. A lower
value or a less expensive Y5V type will work if there is
additional bypassing provided by bulk electrolytic capaci-
tors, or if the input source impedance is low. The following
paragraphs describe the input capacitor considerations
in more detail.
Electrolytic capacitors are also an option. The ESRs of
most aluminum electrolytic capacitors are too large to
deliver low output ripple. Tantalum, as well as newer,
lower ESR organic electrolytic capacitors intended for
power supply use are suitable. Chose a capacitor with a
low enough ESR for the required output ripple. Because
the volume of the capacitor determines its ESR, both the
size and the value will be larger than a ceramic capacitor
that would give similar ripple performance. One benefit
is that the larger capacitance may give better transient
Step-down regulators draw current from the input supply
in pulses with very fast rise and fall times. The input ca-
pacitor is required to reduce the resulting voltage ripple
at the LT3570 input and to force this switching current
3570fa
12
LT3570
APPLICATIONS INFORMATION
into a tight local loop, minimizing EMI. The input capaci-
tor must have low impedance at the switching frequency
to do this effectively and it must have an adequate ripple
current rating. The RMS input current is:
Boost Input Capacitor Selection
The capacitor of a boost converter is less critical due to
the fact that the input current waveform is triangular and
does not contain large squarewave currents as found in
the output capacitor. Capacitors in the range of 10μF to
100μF with an ESR of 0.3Ω or less work well up to the
full 1.5A switch current. Higher ESR capacitors may be
acceptable at low switch currents. Input capacitor ripple
current for boost converters is:
VOUT2
VIN2 – VOUT2
(
)
<
IOUT2
IIN2(RMS) =IOUT2
•
V
2
IN2
and is largest when V = 2 • V
(50% duty cycle).
IN2
OUT2
Consideringthatthemaximumloadcurrentis~1.5A,RMS
ripple current will always be less than 0.75A.
VOUT1 – V
f •L • VOUT1
IN1
IRIPPLE = 0.3• V •
IN1
The high frequency of the LT3570 reduces the energy
storage requirements of the input capacitor, so that the
capacitance required is often less than 10μF. The combi-
nation of small size and low impedance (low equivalent
series resistance or ESR) of ceramic capacitors makes
them the preferred choice. The low ESR results in very
low voltage ripple. Ceramic capacitors can handle larger
magnitudes of ripple current than other capacitor types
of the same value. Use X5R and X7R types.
Buck Diode Selection
The catch diode (D2 from Figure 1) conducts current only
during switch off time. Average forward current in normal
operation can be calculated from:
V – VOUT1
IN1
ID(AVG) =IOUT1
•
V
IN1
An alternative to a high value ceramic capacitor is a lower
valuealongwithalargerelectrolyticcapacitor, forexample
a1μFceramiccapacitorinparallelwithalowESRtantalum
capacitor. For the electrolytic capacitor, a value larger than
10μF will be required to meet the ESR and ripple current
requirements. Because the input capacitor is likely to see
high surge currents when the input source is applied,
tantalum capacitors should be surge rated. The manu-
facturer may also recommend operation below the rated
voltage of the capacitor. Be sure to place the 1μF ceramic
The only reason to consider a diode with a larger current
rating than necessary for nominal operation is for the
worst-case condition of shorted output. The diode current
will then increase to the typical peak switch current.
Peakreversevoltageisequaltotheregulatorinputvoltage.
Use a diode with a reverse voltage rating greater than the
input voltage. Table 3 lists several Schottky diodes and
their manufacturers.
Table 3. Schottky Diodes
as close as possible to the V and GND pins on the IC
IN2
PART NUMBER
On Semiconductor
MBRM120E
MBRM140
V (V)
I
(A)
V AT 1A (mV)
R
AVE
F
for optimal noise immunity.
A final caution is in order regarding the use of ceramic
capacitors at the input. A ceramic input capacitor can
combine with stray inductance to form a resonant tank
circuit.Ifpowerisappliedquickly(forexamplebyplugging
the circuit into a live power source), this tank can ring,
doubling the input voltage and damaging the LT3570. The
solution is to either clamp the input voltage or dampen the
tank circuit by adding a lossy capacitor in parallel with the
ceramic capacitor. For details, see Application Note 88.
20
40
1
530
550
1
Diodes Inc.
B120
20
30
1
1
500
500
B130
International Rectifier
10BQ030
30
1
420
3570fa
13
LT3570
APPLICATIONS INFORMATION
Boost Diode Selection
D3
A Schottkydiodeisrecommendedforusewiththe LT3570
inverter/boost regulator. The Microsemi UPS120 is a very
good choice. Where the input to output voltage differen-
tial exceeds 20V, use the UPS140 (a 40V diode). These
diodes are rated to handle an average forward current of
1A. For applications where the average forward current
of the diode is less than 0.5A, use an ON Semiconductor
MBR0520L diode.
BOOST
LT3570
C3
D2
V
SW
IN
C2
GND
(2a)
D3
BOOST Pin Considerations
BOOST
LT3570
C5
D2
The capacitor and diode tied to the BOOST pin generate
a voltage that is higher than the input voltage. In most
cases, a 0.1μF capacitor and fast switching diode (such
as the CMDSH-3 or MMSD914LT1) will work well. Fig-
ure 2 shows three ways to arrange the boost circuit. The
BOOST pin must be more than 2.5V above the SW pin for
full efficiency. For outputs of 3.3V and higher, the standard
circuit (Figure 2a) is best. For outputs between 2.8V and
3.3V, use a small Schottky diode (such as the BAT-54).
For lower output voltages, the boost diode can be tied
to the input (Figure 2b). The circuit in Figure 2a is more
efficient because the BOOST pin current comes from a
lower voltage source. Finally, as shown in Figure 2c, the
anode of the boost diode can be tied to another source
that is at least 3V. For example, if you are generating 3.3V
and 1.8V and the 3.3V is on whenever the 1.8V is on, the
1.8V boost diode can be connected to the 3.3V output. In
any case, be sure that the maximum voltage at the BOOST
pin is less than 60V and the voltage difference between
the BOOST and SW2 pins is less than 25V.
V
SW
IN
C2
GND
(2b)
D3
V
EXT
BOOST
LT3570
C5
D2
V
IN
SW
C2
GND
3570 F02
(2c)
Figure 2. Boost Pin Configurations
once the circuit has started. Even without an output load
current,inmanycasesthedischargedoutputcapacitorwill
present a load to the switcher that will allow it to start.
The minimum operating voltage of an LT3570 application
is limited by the undervoltage lockout (2.5V) and by the
maximum duty cycle. The boost circuit also limits the
minimum input voltage for proper start-up. If the input
voltage ramps slowly, or the LT3570 turns on when the
output is already in regulation, the boost capacitor may
not be fully charged. Because the boost capacitor charges
with the energy stored in the inductor, the circuit will rely
on some minimum load current to get the boost circuit
running properly. This minimum load will depend on input
and output voltages, and on the arrangement of the boost
circuit. The minimum load current generally goes to zero
Switcher Frequency Compensation
The LT3570 uses current mode control to regulate the
output.Thissimplifiesloopcompensation.Inparticular,the
LT3570 does not depend on the ESR of the output capaci-
tor for stability so you are free to use ceramic capacitors
to achieve low output ripple and small circuit size.
To compensate the feedback loop of the LT3570, a series
resistor-capacitor network should be connected from
the V pin to GND. For most applications, a capacitor in
C
the range of 500pF to 4.7nF will suffice. A good starting
value for the compensation capacitor, C , is 1nF. The
C
3570fa
14
LT3570
APPLICATIONS INFORMATION
compensation resistor, R , is usually in the range of 5k to
Soft-Start
C
50k. A good technique to compensate a new application
TheSoft-starttimeisprogrammedwithanexternalcapaci-
tor to ground on SS. An internal current source charges it
with a nominal 4.5μA. The voltage on the soft-start pin is
used to control the feedback voltage. The soft-start time
is determined by the equation:
is to use a 50k potentiometer in place of R , and use a
C
1nFcapacitorforC .Byadjustingthepotentiometerwhile
C
observing the transient response, the optimum value for
R can be found. Figures 3a to 3c illustrate this process
C
for the circuit of Figure 1 with load current stepped from
t
= 0.2 • C
SS
100mAto500mAforthebuckconverter.Figure3ashows
SS
the transient response with R equal to 1.6k. The phase
C
where C is in nF and t is in ms. In the event of a
SS
SS
margin is poor as evidenced by the excessive ringing in
commanded shutdown, ULVO on the input or a thermal
shutdown, the capacitor is discharged automatically. The
soft-start will remain low and only charge back up after
the fault goes away and the voltage on SS is less than
approximately 100mV.
the output voltage and inductor current. In Figure 3b,
the value of R is increased to 5.75k, which results in a
C
moredampedresponse.Figure3cshowstheresultwhen
R is increased further to 25k. The transient response
C
is nicely damped and the compensation procedure is
complete. The same procedure is used to compensate
the boost converter.
I
I
OUT
OUT
500mA/DIV
500mA/DIV
V
V
OUT
OUT
3570 F03b
3570 F03a
200μs/DIV
200μs/DIV
Figure 3a. Transient Response Shows Excessive Ringing
Figure 3b. Transient Response is Better
I
OUT
500mA/DIV
V
OUT
3570 F03c
200μs/DIV
Figure 3c. Transient Response Well Damped
3570fa
15
LT3570
APPLICATIONS INFORMATION
Oscillator
25
20
15
10
The free-running frequency is set through a resistor from
the R pin to ground. The oscillator frequency vs R can
T
T
be seen in Figure 4. The oscillator can be synchronized
with an external clock applied to the SYNC pin. When
synchronizing the oscillator, the free running frequency
must be set approximately 10% lower than the desired
synchronized frequency.
5
0
2250
2000
1750
1500
1250
1000
750
500
1000 1250 1500 1750 2000
FREQUENCY (kHz)
750
3570 F05
Figure 5. Minimum Duty Cycle vs Frequency
LDO Regulator
The LT3570 LDO regulator is capable of delivering up to
10mA of base drive for an external NPN transistor. For
stable operation the total output capacitance can be from
1μF up to 100μF. The regulator has its own independent
supply voltage which allows for the base of the NPN to be
driven from a higher voltage than its collector. This allows
for the NPN regulator to run more efficiently. The power
Dissipated in the external NPN is equal to:
500
250
25 30
10 15 20
RESISTANCE (kꢀ)
5
35 40 45
3570 F04
Figure 4. Frequency vs RT Resistance
Buck Regulator Minimum On-Time
P
= (V
– V
) • I
OUT3 LOAD
DISS
COL
As the input voltage is increased, the LT3570 is required
to turn on for shorter periods of time. Delays associated
with turning off the power switch determine the minimum
on-time that can be achieved and limit the minimum duty
cycle. Figure 5 shows the minimum duty cycle versus
frequency for the LT3570. When the required on-time has
decreased below the minimum on-time of the LT3570 the
inductor current will increase, exceeding the current limit.
Ifthecurrentthroughtheinductorexceedsthecurrentlimit
of the LT3570, the switch is prevented from turning on for
10μs allowing the inductor current to decrease. The 10μs
off-time limits the average current that can be delivered to
the load. To return to normal switching frequency either
the input voltage or load current must decrease.
where V
is the collector voltage of the NPN. The maxi-
COL
mum output voltage is limited to:
V
– 1.4V and V – 0.2V or 8V
IN3
COL
The short-circuit protection of the NPN regulator is set by
the max output current of the NPN_DRV pin multiplied by
the beta of the NPN.
Thermal Shutdown
An internal temperature monitor will turn off the internal
circuitry and prevent the switches from turning on when
the die temperature reaches approximately 160°C. When
the die temperature has dropped below this value the part
3570fa
16
LT3570
APPLICATIONS INFORMATION
will be enabled again going through a soft-start cycle.
Note:Overtemperatureprotectionisintendedtoprotectthe
deviceduringmomentaryoverloadconditions.Continuous
operationabovethespecifiedmaximumoperatingjunction
temperature may result in device degradation or failure.
to system ground at one location. Additionally, keep
the SW and BOOST nodes as small as possible. This is
implemented in the suggested layout of Figure 8 for the
QFN package which shows the topside metal from the
DC1106A demonstration board.
PCB Layout
Thermal Considerations
For proper operation and minimum EMI, care must be
taken during printed circuit board (PCB) layout. Figure 6
shows the high current paths in the step-down regulator
circuit.Notethatinthestep-downregulator,largeswitched
currents flow in the power switch, the catch diode and the
input capacitor.
To deliver the power that the LT3570 is capable of, it
is imperative that a good thermal path be provided to
dissipate the heat generated within the package. This can
be accomplished by taking advantage of the large ther-
mal pad on the underside of the IC. It is recommended
that multiple vias in the printed circuit board be used to
conduct heat away from the IC and into a copper plane
with as much area as possible.
Figure 7 shows the high current paths in the step-up
regulator. In the boost regulator, large switched currents
flow through the power switch, the switching diode, and
the output capacitor.
Related Linear Technology Publications
Application notes 19, 35, 44, 76 and 88 contain more
detailed descriptions and design information for buck
regulatorsandotherswitchingregulators.TheLT1375data
sheet has a more extensive discussion of output ripple,
loop compensation, and stability testing.
The loop formed by these large switched current com-
ponents should be as small as possible. Place these
components on the same side of the circuit board and
connectthemonthatlayer. Placealocal, unbrokenground
plane below these components and tie this ground plane
LT3570
L2
HIGH
FREQUENCY
CIRCULATING
PATH
C
IN
D1 C
OUT
LOAD
3570 F06
Figure 6. Buck High Speed Switching Path
D1
L2
LT3570
HIGH
FREQUENCY
SWITCHING
PATH
C
OUT
LOAD
C
IN
3750 F07
Figure 7. Boost High Speed Switching Path
Figure 8. Suggested Layout
3570fa
17
LT3570
TYPICAL APPLICATIONS
DSL Modem
V
IN
8V TO 28V
C9
10μF
V
V
V
BIAS
IN1 IN2 IN3
D3
SHDN1
SHDN2
SHDN3
SHDN1
SHDN2
SHDN3
BOOST
C8
100nF
V
OUT2
SW2
5V
L2
10μH
D2
R3
118k
L1
4.7μH
D1
V
OUT1
8V
SW1
FB2
SS2
C2
22μF
250mA
R1
V
C2
105k
C1
10μF
LT3570
C5
10nF
R8
25k
C7
1nF
R4
22.1k
FB1
SS1
R2
11.5k
V
C1
R7
25k
NPN_DRV
Q1
R5
C6
1nF
V
OUT3
3.3V
10nF
500mA
34.0k
C3
2.2μF
FB3
GND
R6
10.7k
R
T
SYNC
R9
20.0k
3570 TA02
“Dying Gasp” System
V
IN
12V
C9
10μF
C10
0.1μF
V
V
V
BIAS
IN1 IN2 IN3
D3
SHDN1
SHDN2
SHDN3
BOOST
C8
V
OUT2
100nF
3.3V
SW2
L2
22μH
200mA
D2
R3
205k
L1
D1 47μH
V
OUT1
SW1
FB1
FB2
SS2
34V
C2
22μF
R1
V
C2
442k
C1
10μF
LT3570
C5
10nF
R8
51k
C7
1nF
R4
64.9k
SS1
R2
10.5k
V
C1
R7
20k
NPN_DRV
Q1
R5
C6
1nF
V
OUT3
2.5V
C4
10nF
200mA
137k
C3
2.2μF
FB3
R6
64.9k
R
T
SYNC
GND
R9
44.2k
3570 TA03
3570fa
18
LT3570
PACKAGE DESCRIPTION
UF Package
24-Lead Plastic QFN (4mm × 4mm)
(Reference LTC DWG # 05-08-1697)
BOTTOM VIEW—EXPOSED PAD
R = 0.115
PIN 1 NOTCH
R = 0.20 TYP OR
0.35 × 45° CHAMFER
0.75 ± 0.05
4.00 ± 0.10
(4 SIDES)
TYP
23 24
0.70 ±0.05
PIN 1
TOP MARK
(NOTE 6)
0.40 ± 0.10
1
2
4.50 ± 0.05
3.10 ± 0.05
2.45 ± 0.05
(4 SIDES)
2.45 ± 0.10
(4-SIDES)
PACKAGE
OUTLINE
(UF24) QFN 0105
0.200 REF
0.25 ± 0.05
0.25 ±0.05
0.50 BSC
0.00 – 0.05
0.50 BSC
NOTE:
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGD-X)—TO BE APPROVED
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE, IF PRESENT
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
FE Package
20-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1663)
Exposed Pad Variation CB
6.40 – 6.60*
(.252 – .260)
3.86
(.152)
3.86
(.152)
20 1918 17 16 15 14 1312 11
6.60 0.10
2.74
(.108)
4.50 0.10
6.40
2.74
(.108)
SEE NOTE 4
(.252)
BSC
0.45 0.05
1.05 0.10
0.65 BSC
5
7
8
1
2
3
4
6
9 10
RECOMMENDED SOLDER PAD LAYOUT
1.20
(.047)
MAX
4.30 – 4.50*
(.169 – .177)
0.25
REF
0° – 8°
0.65
(.0256)
BSC
0.09 – 0.20
(.0035 – .0079)
0.50 – 0.75
(.020 – .030)
0.05 – 0.15
(.002 – .006)
FE20 (CB) TSSOP 0204
0.195 – 0.30
(.0077 – .0118)
TYP
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS 4. RECOMMENDED MINIMUM PCB METAL SIZE
FOR EXPOSED PAD ATTACHMENT
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
MILLIMETERS
(INCHES)
2. DIMENSIONS ARE IN
3. DRAWING NOT TO SCALE
3570fa
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
19
LT3570
TYPICAL APPLICATION
PDA Core
V
IN
4V TO 12V
C9
10μF
V
V
V
BIAS
IN1 IN2 IN3
D3
SHDN1
SHDN2
SHDN3
SHDN1
SHDN2
SHDN3
BOOST
C8
V
OUT2
100nF
3.3V
SW2
L2
8.2μH
500mA
D2
R3
34k
L1
D1 12μH
V
OUT1
15V
SW1
FB2
SS2
C2
22μF
200mA
R1
V
C2
191k
C1
10μF
LT3570
C5
10nF
R8
25k
R4
10.7k
FB1
SS1
R2
10.7k
C7
1nF
V
C1
R7
25k
NPN_DRV
Q1
R5
C6
1nF
V
OUT3
1.8V
C4
10nF
500mA
13.7k
C3
4.7μF
FB3
GND
R6
10.7k
R
SYNC
T
R9
20k
3570 TA04
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1767
1.5A, 1.25MHz Step-Down Switching Regulator
3V to 25V Input, V = 1.2V, Synchronizable up to 2MHz,
REF
MSOP Package
LT1930/LT1930A
LT1939
1A (I ), 1.2MHz/2.2MHz, High Efficiency Step-Up DC/DC
V : 2.6V to 16V, V
= 34V, I = 4.2mA/5.5mA,
SW
IN
OUT(MAX) Q
Converter
I
< 1μA, ThinSOTTM Package
SD
25V, 2.4MHz Step-Down DC/DC Converter and LDO Controller
V : 3V to 40V, V
= 0.8V, I = 2mA, I < 1μA,
IN
OUT(MIN) Q SD
3mm × 3mm DFN
LT1943
Quad Output, 2.6A Buck, 2.6A Boost, 0.3A Boost, 0.4A Inverter
1.2MHz TFT DC/DC Converter
V : 4.5V to 22V, V
= 40V, I = 10mA, I < 35μA,
OUT(MAX) Q SD
IN
TSSOP28E Package
LT1945
Dual Output Pos/Neg 350mA (I ), Constant Off-Time,
V : 1.2V to 15V, V
=
=
34V, I = 20μA, I < 1μA,
Q SD
SW
IN
OUT(MAX)
High Efficiency Step-Up DC/DC Converter
10-Pin MS Package
LT3463
Dual Output Pos/Neg 250mA (I ), Constant Off-Time, High
V : 2.4V to 15V, V
40V, I = 40μA, I < 1μA,
Q SD
SW
IN
OUT(MAX)
Efficiency Step-Up DC/DC Converter with Integrated Schottkys
3mm × 3mm DFN10 Package
1.1A, 1.3MHz Step Up DC/DC Converter with Integrated Soft-Start V : 2.4V to 16V, V = 40V, I < 1 μA, Low profile
IN OUT(MAX)
LT3467
SD
(1mm) SOT-23 Package
LT3500
40V, 2A, 2.4MHz Step-Down DC/DC Converter and LDO Controller V : 3V to 40V, V
= 0.8V, I = 2mA, I < 1μA,
Q SD
IN
OUT(MIN)
3mm × 3mm DFN
LT3507
36V, 2.5MHz Triple (2.4A, 1.5A, 1.5A) Step-Down DC/DC Converter V : 4V to 36V, V
= 0.8V, I = 7mA, I < 1μA,
Q SD
IN
OUT(MIN)
and LDO Controller
5mm × 7mm QFN38 Package
ThinSOT is a trademark of Linear Technology Corporation.
3570fa
LT 1108 REV A • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
20
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© LINEAR TECHNOLOGY CORPORATION 2008
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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