LT3431
High Voltage, 3A,
500kHz Step-Down
Switching Regulator
FEATURES
s
s
s
s
s
s
DESCRIPTIO
s
s
s
s
s
Wide Input Range: 5.5V to 60V
3A Peak Switch Current
Small Thermally Enhanced 16-Pin TSSOP Package
Constant 500kHz Switching Frequency
Saturating Switch Design: 0.1Ω
Peak Switch Current Maintained Over
Full Duty Cycle Range
Effective Supply Current: 2.5mA
Shutdown Current: 30µA
1.2V Feedback Reference Voltage
Easily Synchronizable
Cycle-by-Cycle Current Limiting
The LT
®
3431 is a 500kHz monolithic buck switching regu-
lator that accepts input voltages up to 60V. A high efficiency
3A, 0.1Ω switch is included on the die along with all the nec-
essary oscillator, control and logic circuitry. A current mode
architecture provides fast transient response and good 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 the de-
vice can be externally synchronized from 580kHz to 700kHz
with logic level inputs.
The LT3431 is available in a thermally enhanced 16-pin
TSSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
s
s
s
s
Industrial and Automotive Power Supplies
Portable Computers
Battery Chargers
Distributed Power Systems
TYPICAL APPLICATIO
5V, 2A Buck Converter
6
V
IN
12V
(TRANSIENTS
TO 60V)
BOOST
3, 4
2.2µF
†
100V
CERAMIC
15
14
V
IN
LT3431
SHDN
SYNC
GND
1, 8, 9, 16
1.5k
15nF
BIAS
FB
V
C
11
220pF
10
12
SW
2, 5
30BQ060
0.22µF
MMSD914TI
10µH**
V
OUT
5V
2A
47µF
CERAMIC
15.4k
4.99k
EFFICIENCY (%)
** INCREASE INDUCTOR VALUE FOR LOAD CURRENTS ABOVE 2A
(SEE APPLICATIONS INFORMATION—MAXIMUM OUTPUT LOAD CURRENT)
†
UNITED CHEMI-CON THCS50EZA225ZT
3431 TA01
U
Efficiency vs Load Current
100
V
IN
= 12V
L = 15µH
90
V
OUT
= 5V
V
OUT
= 3.3V
80
70
60
50
0
0.5
1.5
2.0
1.0
LOAD CURRENT (A)
2.5
3431 TA02
U
U
sn3431 3431fs
1
LT3431
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
GND
SW
V
IN
V
IN
SW
BOOST
NC
GND
1
2
3
4
5
6
7
8
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 ............................................ 35V
BOOST Pin Voltage ................................................. 68V
SYNC Voltage ........................................................... 7V
SHDN Voltage ........................................................... 6V
BIAS Pin Voltage .................................................... 30V
FB Pin Voltage/Current .................................. 3.5V/2mA
Operating Junction Temperature Range
LT3431EFE (Notes 8, 10) ................. – 40°C to 125°C
LT3431IFE (Notes 8, 10) ................. – 40°C to 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LT3431EFE
LT3431IFE
FE PART MARKING
3431EFE
3431IFE
FE PACKAGE
16-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 45°C/ W,
θ
JC
(PAD) = 10°C/W
EXPOSED PAD MUST BE SOLDERED
TO GROUND PLANE
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
J
= 25°C.
V
IN
= 15V, V
C
= 1.5V, SHDN = 1V, BOOST open circuit, SW open circuit, unless otherwise noted.
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
Switch On Resistance
Maximum Switch Duty Cycle
Switch Frequency
f
SW
Line Regulation
f
SW
Shifting Threshold
FB = 1V or V
SENSE
= 4.1V
FB = 1.4V or V
SENSE
= 5.7V
Duty Cycle = 0
SHDN = 1V
V
C
Open, BOOST = V
IN
+ 5V, FB = 1V or V
SENSE
= 4.1V
(Note 9)
I
SW
= 2.5A, BOOST = V
IN
+ 5V (Note 7)
q
q
q
CONDITIONS
5.5V
≤
V
IN
≤
60V
V
OL
+ 0.2
≤
V
C
≤
V
OH
– 0.2
(Note 2)
dl (V
C
) =
±10µA
q
q
q
MIN
1.204
1.195
200
1650
1000
125
100
TYP
1.219
–0.2
475
2200
3.4
275
275
0.8
2.1
MAX
1.234
1.243
–1.5
3300
4200
450
500
UNITS
V
V
µA
V/V
µMho
µMho
A/V
µA
µA
V
V
–40°C
≤
Tj
≤
25°C
Tj = 125°C
3.0
2.5
5
4
0.1
6.5
5.5
0.14
0.18
FB = 1V or V
SENSE
= 4.1V
q
88
80
460
430
92
500
500
0.05
0.8
540
570
0.15
V
C
Set to Give DC = 50%
q
5.5V
≤
V
IN
≤
60V
Df = 10kHz
q
sn3431 3431fs
2
U
A
A
Ω
Ω
%
%
kHz
kHz
%/V
V
W
U
U
W W
W
LT3431
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
J
= 25°C.
V
IN
= 15V, V
C
= 1.5V, SHDN = 1V, BOOST open circuit, SW open circuit, unless otherwise noted.
PARAMETER
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 Thresholds
Minimum SYNC Amplitude
SYNC Frequency Range
SYNC Input Resistance
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
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
= 1.5mA, I
BIAS
= 3.1mA, I
TOTAL
= 2.5mA.
CONDITIONS
(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
SHDN = 0V, V
IN
≤
60V, SW = 0V, V
C
Open
q
q
q
q
q
MIN
TYP
4.6
1.8
25
75
1.5
3.1
30
MAX
5.5
3
50
120
2.2
4.2
100
200
2.53
0.58
0.6
2.2
700
UNITS
V
V
mA
mA
mA
mA
µA
µA
V
V
V
V
kHz
kΩ
V
C
Open,
V
C
Open, Shutting Down
V
C
Open, Starting Up
q
q
q
q
2.30
0.15
0.25
580
2.42
0.37
0.42
1.5
20
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 LT3431EFE 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
LT3431IFE is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 9:
See Typical Performance Graph of Peak Switch Current Limit vs
Junction Temperature.
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.
sn3431 3431fs
3
LT3431
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Peak Current Limit
6
T
j
= 25°C
1.234
1.229
SWITCH PEAK CURRENT (A)
VOLTAGE
1.219
CURRENT
1.214
0.5
1.209
1.0
CURRENT (µA)
TYPICAL
4
FEEDBACK VOLTAGE (V)
5
GUARANTEED MINIMUM
3
2
0
20
40
60
DUTY CYCLE (%)
80
100
3431 G01
Lockout and Shutdown
Thresholds
2.4
INPUT SUPPLY CURRENT (µA)
INPUT SUPPLY CURRENT (µA)
2.0
SHDN PIN VOLTAGE (V)
1.6
1.2
0.8
LOCKOUT
START-UP
0.4
SHUTDOWN
0
–50
–25
0
25
50
75
JUNCTION TEMPERATURE (°C)
3431 G04
Error Amplifier Transconductance
2500
2000
GAIN (µMho)
2500
GAIN
150
PHASE (DEG)
SWITICHING FREQUENCY (kHz)
OR FB CURRENT (µA)
TRANSCONDUCTANCE (µmho)
1500
1000
500
0
–50
–25
0
25
50
75
JUNCTION TEMPERATURE (°C)
3431 G07
4
U W
100
100
FB Pin Voltage and Current
2.0
SHDN Pin Bias Current
250
200
1.5
CURRENT REQUIRED TO FORCE SHUTDOWN
(FLOWS OUT OF PIN). AFTER SHUTDOWN,
CURRENT DROPS TO A FEW
µA
1.224
150
100
12
6
CURRENT (µA)
AT 2.38V STANDBY THRESHOLD
(CURRENT FLOWS OUT OF PIN)
1.204
50
100
25
75
–50 –25
0
JUNCTION TEMPERATURE (°C)
0
125
0
50
100
–50 –25
25
75
0
JUNCTION TEMPERATURE (°C)
125
3431 G02
3431 G03
Shutdown Supply Current
40
35
30
25
20
15
10
5
0
125
0
10
20
30
40
INPUT VOLTAGE (V)
50
60
3431 G05
Shutdown Supply Current
300
V
SHDN
= 0V
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
3431 G06
Error Amplifier Transconductance
3000
PHASE
200
625
Frequency Foldback
SWITCHING
FREQUENCY
500
2000
100
375
1500
V
FB
2 • 10
–3
(
)
R
OUT
200k
V
C
C
OUT
12pF
50
250
1000
ERROR AMPLIFIER EQUIVALENT CIRCUIT
0
125
FB PIN
CURRENT
R
LOAD
= 50Ω
125
500
100
1k
10k
100k
FREQUENCY (Hz)
1M
–50
10M
3431 G08
0
0
0.2
0.4
0.6
V
FB
(V)
0.8
1.0
1.2
3431
G09
sn3431 3431fs
LT3431
TYPICAL PERFOR A CE CHARACTERISTICS
Switching Frequency
575
550
INPUT VOLTAGE (V)
BOOST PIN CURRENT (mA)
FREQUENCY (kHz)
525
500
475
450
425
–50
–25
0
25
50
75
JUNCTION TEMPERATURE (°C)
3431
G10
V
C
Pin Shutdown Threshold
2.1
1.9
THRESHOLD VOLTAGE (V)
450
400
SWITCH VOLTAGE (mV)
T
J
= 125°C
SWITCH MINIMUM ON TIME (ns)
1.7
1.5
1.3
1.1
0.9
0.7
50
100
–50 –25
25
75
0
JUNCTION TEMPERATURE (°C)
SWITCH PEAK CURRENT LIMIT (A)
U W
100
3431 G13
Minimum Input Voltage
with 5V Output
7.5
90
80
7.0
70
60
50
40
30
20
10
0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
LOAD CURRENT (A)
3431 G11
BOOST Pin Current
6.5
MINIMUM INPUT
VOLTAGE TO START
6.0
5.5
MINIMUM INPUT
VOLTAGE TO RUN
125
5.0
0
1
2
SWITCH CURRENT (A)
3
3431 G12
Switch Voltage Drop
600
500
400
300
200
100
Switch Minimum ON Time
vs Temperature
350
300
250
200
150
100
50
T
J
= –40°C
T
J
= 25°C
125
0
0
1
2
SWITCH CURRENT (A)
3
3431 G14
0
50
100
25
75
–50 –25
0
JUNCTION TEMPERATURE (°C)
125
3431 G15
Switch Peak Current Limit
6.00
5.50
5.00
4.50
4.00
3.50
3.00
2.50
–50
–25
0
25
50
75
100
125
JUNCTION TEMPERATURE (°C)
3431
G16
sn3431 3431fs
5
京公网安备 11010802033920号
EEWORLD
