FEATURES
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LT3430/LT3430-1
High Voltage, 3A,
200kHz/100kHz Step-Down
Switching Regulators
DESCRIPTION
The LT
®
3430/LT3430-1 are monolithic buck switching
regulators that accept input voltages up to 60V. A high ef-
ficiency 3A, 0.1Ω switch is included on the die along with
all the necessary oscillator, control and logic circuitry. A
current mode architecture provides fast transient response
and excellent loop stability.
Special design techniques and a new high voltage process
achieve high efficiency over a wide input range. Efficiency
is maintained over a wide output current range by using
the output to bias the circuitry and by utilizing a supply
boost capacitor to saturate the power switch. Patented
circuitry* maintains peak switch current over the full duty
cycle range. A shutdown pin reduces supply current to
30µA and a SYNC pin can be externally synchronized with
a logic level input from 228kHz to 700kHz for the LT3430
or from 125kHz to 250kHz for the LT3430-1.
The LT3430/LT3430-1 are available in a thermally enhanced
16-pin TSSOP package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
*US Patent # 6498466
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Wide Input Range: 5.5V to 60V
3A Peak Switch Current over All Duty Cycles
Constant Switching Frequency:
200kHz (LT3430)
100kHz (LT3430-1)
0.1Ω Switch Resistance
Current Mode
Effective Supply Current: 2.5mA
Shutdown Current: 30µA
1.2V Feedback Reference Voltage
Easily Synchronizable
Cycle-by-Cycle Current Limiting
Small, 16-Pin Thermally Enhanced TSSOP Package
APPLICATIONS
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Industrial and Automotive Power Supplies
Portable Computers
Battery Chargers
Distributed Power Systems
TYPICAL APPLICATION
5V, 2A Buck Converter
MMSD914TI
Efficiency vs Load Current
100
V
OUT
= 5V
V
IN
= 12V
V
IN
4.7µF
100V
OFF ON
LT3430**
SHDN
SYNC
GND
SW
30BQ060
EFFICIENCY (%)
V
IN
5.5V*
TO 60V
BOOST
0.68µF
22µH
V
OUT
5V
2A
90
80
V
IN
= 42V
+
15.4k
FB
V
C
4.99k
BIAS
100µF 10V
SOLID
TANTALUM
70
60
LT3430-1 L = 68µH
LT3430 L =27µH
50
220pF
0
0.5
1.5
2.0
1.0
LOAD CURRENT (A)
2.5
3430 TA02
3.3k
0.022µF
3430 TA01
*FOR INPUT VOLTAGES BELOW 7.5V, SOME RESTRICTIONS MAY APPLY
** SEE LT3430-1 CIRCUIT IN APPLICATIONS INFORMATION SECTION
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LT3430/LT3430-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
GND
SW
V
IN
V
IN
SW
BOOST
NC
GND
1
2
3
4
5
6
7
8
17
16 GND
15 SHDN
14 SYNC
13 NC
12 FB
11 V
C
10 BIAS
9
GND
Input Voltage (V
IN
) .................................................. 60V
BOOST Pin Above SW (Note 11) .............................. 35V
BOOST Pin Voltage ................................................. 68V
SYNC Voltage ............................................................. 7V
⎯
S
⎯
H
⎯
D
⎯
N Voltage ............................................................ 6V
BIAS Pin Voltage ..................................................... 30V
FB Pin Voltage/Current .................................. 3.5V/2mA
Operating Junction Temperature Range
LT3430EFE (Notes 8, 10) .................. –40°C to 125°C
LT3430IFE (Notes 8, 10) .................. –40°C to 125°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec) ................ 300°C
FE PACKAGE
16-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 45°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LT3430EFE
LT3430IFE
LT3430EFE-1
LT3430IFE-1
FE PART MARKING
3430EFE
3430IFE
3430EFE-1
3430IFE-1
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Reference Voltage (V
REF
)
FB Input Bias Current
Error Amp Voltage Gain
Error Amp g
m
V
C
to Switch g
m
EA Source Current
EA Sink Current
V
C
Switching Threshold
V
C
High Clamp
Switch Current Limit
FB = 1V
(Note 2)
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 15V, V
C
= 1.5V,
⎯
S
⎯
H
⎯
D
⎯
N = 1V, BOOST = Open Circuit,
SW = Open Circuit, unless otherwise noted.
CONDITIONS
V
OL
+ 0.2 ≤ V
C
≤ V
OH
– 0.2
5.5V ≤ V
IN
≤ 60V
●
●
MIN
1.204
1.195
200
●
TYP
1.219
–0.2
400
2200
3.4
MAX
1.234
1.243
–1.5
3300
4200
450
500
UNITS
V
µA
V/V
µMho
µMho
A/V
µA
µA
V
V
dl (V
C
) = ±10µA
1650
1000
125
100
●
●
225
225
0.9
2.1
FB = 1.4V
Duty Cycle = 0
⎯
S
⎯
H
⎯
D
⎯
N = 1V
V
C
Open, Boost = V
IN
+ 5V, FB = 1V
–40°C ≤ T
J
≤ 25°C
T
J
= 125°C (Note 9)
I
SW
= 2.5A, Boost = V
IN
+ 5V (Note 7)
FB = 1V
3
2.5
5
4
0.1
6.5
5.5
0.14
0.18
A
A
Ω
Ω
%
%
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Switch On Resistance
Maximum Switch Duty Cycle (LT3430)
●
93
90
96
2
LT3430/LT3430-1
ELECTRICAL CHARACTERISTICS
PARAMETER
Maximum Switch Duty Cycle (LT3430-1)
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 15V, V
C
= 1.5V,
⎯
S
⎯
H
⎯
D
⎯
N = 1V, BOOST = Open Circuit,
SW = Open Circuit, unless otherwise noted.
CONDITIONS
MIN
96
94
184
172
88
85
TYP
98
200
200
100
100
0.05
0.8
●
●
●
●
MAX
UNITS
%
%
Switch Frequency (LT3430)
Switch Frequency (LT3430-1)
V
C
Set to Give DC = 50%
●
●
216
228
115
120
0.15
5.5
3
50
120
2.2
4.2
100
200
2.53
0.58
0.60
700
250
kHz
kHz
kHz
kHz
%/V
V
V
V
mA
mA
mA
mA
µA
µA
V
V
V
V
kHz
kHz
kΩ
f
SW
Line Regulation
f
SW
Shifting Threshold
Minimum Input Voltage
Minimum Boost Voltage
Boost Current (Note 5)
Input Supply Current (I
VIN
)
Bias Supply Current (I
BIAS
)
Shutdown Supply Current
Lockout Threshold
Shutdown Threshold
Minimum SYNC Amplitude
SYNC Frequency Range (LT3430)
SYNC Frequency Range (LT3430-1)
SYNC Input Resistance
5.5V ≤ V
IN
≤ 60V
Df = 10kHz
(Note 3)
(Note 4) I
SW
≤ 2.5A
Boost = V
IN
+ 5V, I
SW
= 0.75A
Boost = V
IN
+ 5V, I
SW
= 2.5A
(Note 6) V
BIAS
= 5V
(Note 6) V
BIAS
= 5V
⎯
S
⎯
H
⎯
D
⎯
N = 0V, V
IN
≤ 60V, SW = 0V, V
C
Open
V
C
Open
V
C
Open, Shutting Down
V
C
Open, Starting Up
●
4.6
1.8
25
75
1.5
3.1
30
●
●
●
●
2.3
0.15
0.25
228
125
2.42
0.37
0.42
1.5
20
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:
Gain is measured with a V
C
swing equal to 200mV above the low
clamp level to 200mV below the upper clamp level.
Note 3:
Minimum input voltage is not measured directly, but is guaranteed
by other tests. It is defined as the voltage where internal bias lines are still
regulated so that the reference voltage and oscillator remain constant.
Actual minimum input voltage to maintain a regulated output will depend
upon output voltage and load current. See Applications Information.
Note 4:
This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the internal power switch.
Note 5:
Boost current is the current flowing into the BOOST pin with the
pin held 5V above input voltage. It flows only during switch on time.
Note 6:
Input supply current is the quiescent current drawn by the input
pin when the BIAS pin is held at 5V with switching disabled. Bias supply
current is the current drawn by the BIAS pin when the BIAS pin is held
at 5V. Total input referred supply current is calculated by summing input
supply current (I
VIN
) with a fraction of bias supply current (I
BIAS
):
I
TOTAL
= I
VIN
+ (I
BIAS
)(V
OUT
/V
IN
)
With V
IN
= 15V, V
OUT
= 5V, I
VIN
= 1.4mA, I
BIAS
= 2.9mA, I
TOTAL
= 2.4mA.
Note 7:
Switch on resistance is calculated by dividing V
IN
to SW voltage
by the forced current (3A). See Typical Performance Characteristics for the
graph of switch voltage at other currents.
Note 8:
The LT3430EFE/LT3430EFE-1 are 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 LT3430IFE/LT3430IFE-1 are guaranteed over the full –40°C to 125°C
operating junction temperature range.
Note 9:
See Peak Switch Current Limit vs Junction Temperature graph in
the Typical Performance Characteristics section.
Note 10:
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.
Note 11:
The maximum operational Boost-SW voltage is limited by
thermal and load current constraints. See ‘Boost Pin’ and ‘Thermal
Calculations’ in the Applications Information section.
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LT3430/LT3430-1
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Peak Current Limit
6
T
J
= 25°C
1.229
SWITCH PEAK CURRENT (A)
5
TYPICAL
4
FEEDBACK VOLTAGE (V)
1.5
VOLTAGE
1.219
CURRENT
1.214
0.5
1.209
2
1.204
50
100
–50 –25
25
75
0
JUNCTION TEMPERATURE (°C)
0
125
6
0
50
100
–50 –25
25
75
0
JUNCTION TEMPERATURE (°C)
1.0
CURRENT (µA)
1.224
150
100
12
CURRENT (µA)
200
1.234
FB Pin Voltage and Current
2.0
250
⎯
S
⎯
H
⎯
D
⎯
N Pin Bias Current
CURRENT REQUIRED TO FORCE SHUTDOWN
(FLOWS OUT OF PIN). AFTER SHUTDOWN,
CURRENT DROPS TO A FEW
µA
3
GUARANTEED MINIMUM
AT 2.38V STANDBY THRESHOLD
(CURRENT FLOWS OUT OF PIN)
0
20
40
60
DUTY CYCLE (%)
80
100
3430 G01
125
3430 G02
3430 G03
Lockout and Shutdown Threshold
2.4
INPUT SUPPLY CURRENT (µA)
2.0
SHDN PIN VOLTAGE (V)
1.6
1.2
0.8
START-UP
0.4
SHUTDOWN
0
–50
0
–25
0
25
50
75
100
125
LOCKOUT
40
Shutdown Supply Current
V
SHDN
= 0V
35 T
A
= 25°C
INPUT SUPPLY CURRENT (µA)
30
25
20
15
10
5
0
10
20
30
40
INPUT VOLTAGE (V)
50
60
3430 G05
Shutdown Supply Current
300
250
V
IN
= 60V
200
V
IN
= 15V
150
100
50
0
0
0.1
0.2
0.3
0.4
SHUTDOWN VOLTAGE (V)
0.5
3430 G06
T
A
= 25°C
JUNCTION TEMPERATURE (°C)
3430 G04
Error Amplifier Transconductance
2500
3000
Error Amplifier Transconductance
200
PHASE
600
SWITICHING FREQUENCY (kHz)
OR FB CURRENT (µA)
500
400
Frequency Foldback
T
A
= 25°C
TRANSCONDUCTANCE (µmho)
2000
GAIN (µMho)
2500
GAIN
150
PHASE (DEG)
1500
2000
100
V
C
FB PIN
CURRENT
300
200
100
0
3430
3430-1
SWITCHING
FREQUENCY
1000
1500
V
FB
2 • 10
–3
(
)
R
OUT
200k
C
OUT
12pF
50
500
1000
ERROR AMPLIFIER EQUIVALENT CIRCUIT
0
0
–50
–25
0
25
50
75
100
125
500
100
R
LOAD
= 50Ω
T
A
= 25°C
1k
10k
100k
FREQUENCY (Hz)
1M
–50
10M
3430 G08
0
0.5
V
FB
(V)
1.0
1.5
3430 G09
JUNCTION TEMPERATURE (°C)
3430 G07
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LT3430/LT3430-1
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency
230
220
INPUT VOLTAGE (V)
FREQUENCY (kHz)
210
200
190
180
170
–50
(LT3430)
7.5
Minimum Input Voltage with
5V Output
T
A
= 25°C
BOOST PIN CURRENT (mA)
90
80
7.0
70
60
50
40
30
20
10
0
BOOST Pin Current
T
A
= 25°C
6.5
MINIMUM INPUT
VOLTAGE TO START
6.0
5.5
MINIMUM INPUT
VOLTAGE TO RUN
–25
0
25
50
75
100
125
5.0
0
JUNCTION TEMPERATURE (°C)
3430 G10
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
LOAD CURRENT (A)
3430 G11
0
1
2
SWITCH CURRENT (A)
3
3430 G12
V
C
Pin Shutdown Threshold
2.1
1.9
THRESHOLD VOLTAGE (V)
1.7
1.5
1.3
1.1
0.9
0.7
50
100
–50 –25
25
75
0
JUNCTION TEMPERATURE (°C)
SWITCH VOLTAGE (mV)
450
400
350
300
250
200
150
100
50
125
0
Switch Voltage Drop
T
J
= 125°C
T
J
= 25°C
T
J
= –40°C
0
1
2
SWITCH CURRENT (A)
3
3430 G14
3430 G13
Switch Peak Current Limit
6.0
SWITCH PEAK CURRENT LIMIT (A)
SWITCH MINIMUM ON TIME (ns)
5.5
5.0
4.5
4.0
3.5
3.0
2.5
–50
600
500
400
300
200
100
Switch Minimum ON Time
vs Temperature
–25
0
25
50
75
100
125
JUNCTION TEMPERATURE (°C)
3430 G16
0
50
100
–50 –25
25
75
0
JUNCTION TEMPERATURE (°C)
125
3430 G15
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