LT3434
High Voltage 3A, 200kHz
Step-Down Switching Regulator
with 100µA Quiescent Current
FEATURES
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DESCRIPTIO
Wide Input Range: 3.3V to 60V
3A Peak Switch Current
Burst Mode
®
Operation: 100µA Quiescent Current**
Low Shutdown Current: I
Q
< 1µA
Power Good Flag with Programmable Threshold
Load Dump Protection to 60V
200kHz Switching Frequency
Saturating Switch Design: 0.1Ω
Peak Switch Current Maintained Over
Full Duty Cycle Range*
1.25V Feedback Reference Voltage
Easily Synchronizable
Soft-Start Capability
Small 16-Pin Thermally Enhanced TSSOP Package
The LT
®
3434 is a 200kHz monolithic buck switching
regulator that accepts input voltages up to 60V. A high
efficiency 3A, 0.1Ω switch is included on the die along with
all the necessary oscillator, control and logic circuitry.
Current mode topology is used for fast transient response
and good loop stability.
Innovative design techniques integrated in a new high
voltage process achieve high efficiency over a wide input
range. Efficiency is maintained over a wide output current
range by employing Burst Mode operation at low currents,
utilizing the output to bias the internal circuitry, and by
using a supply boost capacitor to fully saturate the power
switch. Patented circuitry maintains peak switch current
over the full duty cycle range.* Shutdown reduces input
supply current to less than 1µA. External synchronization
can be implemented by driving the SYNC pin with logic-level
inputs. A single capacitor from the C
SS
pin to the output
provides a controlled output voltage ramp (soft-start). The
device also has a power good flag with a programmable
threshold and time-out, and thermal shutdown protection.
The LT3434 is available in a 16-pin TSSOP package with
exposed pad leadframe for low thermal resistance.
APPLICATIO S
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High Voltage Power Conversion
14V and 42V Automotive Systems
Industrial Power Systems
Distributed Power Systems
Battery-Powered Systems
, LTC and LT are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Burst Mode is a registered
trademark of Linear Technology Corporation. *Protected by U.S. Patents including
6498466. **See Burst Mode Operation section for conditions.
TYPICAL APPLICATIO
14V to 3.3V Step-Down Converter with
100µA No Load Quiescent Current
4.7µF
100V
CER
0.68µF 33µH
SW
0.1µF
C
SS
V
BIAS
FB
1µF
C
T
SYNC
GND
PGFB
PG
100k
1%
27pF
165k
1%
100µF
6.3V
TANT
30MQ100
4148
SUPPLY CURRENT (µA)
Supply Current vs
Input Voltage
150
V
OUT
= 3.3V
100
V
IN
V
IN
SHDN
BOOST
LT3434
V
OUT
3.3V
2A
125
75
EFFICIENCY (%)
100
75
50
25
0
V
C
4700pF
10k
470pF
3434 TA01
0
10
30
40
20
INPUT VOLTAGE (V)
50
60
3434 TA02a
U
Efficiency and Power Loss
vs Load Current
V
IN
= 12V
L = 33µH
C
OUT
= 100µF
EFFICIENCY
V
OUT
= 3.3V
50
TYPICAL POWER
LOSS
25
0.01
0.1
10
V
OUT
= 5V
1
U
U
POWER LOSS (W)
0
0.0001
0.001
0.1
0.01
LOAD CURRENT (A)
1
0.001
10
3434 TA02b
3434f
1
LT3434
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
NC
SW
V
IN
V
IN
SW
BOOST
TCAP
GND
1
2
3
4
5
6
7
8
17
16 PGOOD
15 SHDN
14 SYNC
13 PGFB
12 FB
11 V
C
10 BIAS
9
C
SS
V
IN
, SHDN, BIAS ..................................................... 60V
BOOST Pin Above SW ............................................ 35V
BOOST Pin Voltage ................................................. 68V
SYNC, C
SS
, PGFB, FB ................................................ 6V
Operating JunctionTemperature Range
LT3434EFE (Note 2) ........................ – 40°C to 125°C
LT3434IFE (Note 2) ......................... – 40°C to 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LT3434EFE
LT3434IFE
FE PACKAGE
16-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 45°C/W,
θ
JC(PAD)
= 10°C/W
EXPOSED PAD IS GND (PIN 17)
MUST BE SOLDERED TO GND (PIN 8)
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, SHDN = 12V, BIAS = 5V, FB/PGFB = 1.25V,
C
SS
/SYNC = 0V unless otherwise noted.
SYMBOL
V
SHDN
I
SHDN
I
VINS
PARAMETER
SHDN Threshold
SHDN Input Current
Minimum Input Voltage (Note 3)
Supply Shutdown Current
Supply Sleep Current (Note 4)
I
VIN
Supply Quiescent Current
Minimum BIAS Voltage (Note 5)
I
BIASS
I
BIAS
BIAS Sleep Current (Note 4)
BIAS Quiescent Current
Minimum Boost Voltage (Note 6)
Input Boost Current (Note 7)
V
REF
I
FB
Reference Voltage (V
REF
)
FB Input Bias Current
EA Voltage Gain (Note 8)
EA Voltage g
m
EA Source Current
EA Sink Current
V
C
to SW g
m
V
C
High Clamp
I
PK
SW Current Limit
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
SHDN = 12V
SHDN = 0V, BOOST = 0V, FB/PGFB = 0V
BIAS = 0V, FB = 1.35V
FB = 1.35V
BIAS = 0V, FB = 1.15V
BIAS = 5V, FB = 1.15V
●
●
●
●
●
●
MIN
1.15
TYP
1.3
5
2.4
0.1
170
45
3.2
2.6
2.7
110
700
1.8
65
MAX
1.45
20
3
2
250
75
6
5
3.1
180
900
85
1.275
200
900
55
40
2.4
6.5
UNITS
V
µA
V
µA
µA
µA
mA
mA
V
µA
µA
V
mA
V
nA
V/V
µMho
µA
µA
A/V
V
A
SYNC = 3.3V
I
SW
= 3A
I
SW
= 3A
3.3V < V
VIN
< 60V
●
1.225
1.25
75
900
dI(V
C
)=
±10µA
FB = 1.15V
FB = 1.35V
400
20
15
2.1
3
650
40
30
6
2.2
4.7
2
U
3434f
W
U
U
W W
W
LT3434
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, SHDN = 12V, BIAS = 5V, FB/PGFB = 1.25V,
C
SS
/SYNC = 0V unless otherwise noted.
SYMBOL
PARAMETER
Switch On Resistance (Note 9)
Switching Frequency
Maximum Duty Cycle
Minimum SYNC Amplitude
SYNC Frequency Range
SYNC Input Impedance
I
CSS
I
PGFB
V
PGFB
I
CT
V
CT
C
SS
Current Threshold (Note 10)
PGFB Input Current
PGFB Voltage Threshold (Note 11)
C
T
Source Current (Note 11)
C
T
Sink Current (Note 11)
C
T
Voltage Threshold (Note 11)
PG Leakage (Note 11)
PG Sink Current (Note 11)
PGFB = 1V, PG = 400mV
120
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
●
●
MIN
180
90
230
7
88
2
1
1.16
TYP
0.1
200
92
1.5
600
45
13
25
90
3.6
2
1.2
0.1
200
MAX
0.25
230
2.0
UNITS
Ω
kHz
%
V
kHz
kΩ
20
100
92
5.5
1.26
1
µA
nA
%
µA
mA
V
µA
µA
Note 1:
Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2:
The LT3434EFE 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
LT3434IFE is guaranteed and tested over the full –40°C to 125°C operating
junction temperature range.
Note 3:
Minimum input voltage is defined as the voltage where switching
starts. Actual minimum input voltage to maintain a regulated output will
depend upon output voltage and load current. See Applications Information.
Note 4:
Supply input current is the quiescent current drawn by the input
pin. Its typical value depends on the voltage on the BIAS pin and operating
state of the LT3434. With the BIAS pin at 0V, all of the quiescent current
required to operate the LT3434 will be provided by the V
IN
pin. With the
BIAS voltage above its minimum input voltage, a portion of the total
quiescent current will be supplied by the BIAS pin. Supply sleep current is
defined as the quiescent current during the “sleep” portion of Burst Mode
operation. See Applications Information for determining application supply
currents.
Note 5:
Minimum BIAS voltage is the voltage on the BIAS pin when I
BIAS
is
sourced into the pin.
Note 6:
This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the internal power switch.
Note 7:
Boost current is the current flowing into the BOOST pin with the pin
held 3.3V above input voltage. It flows only during switch on time.
Note 8:
Gain is measured with a V
C
swing from 1.15V to 750mV.
Note 9:
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 10:
The C
SS
threshold is defined as the value of current sourced into the
C
SS
pin which results in an increase in sink current from the V
C
pin. See the
Soft-Start section in Applications Information.
Note 11:
The PGFB threshold is defined as the percentage of V
REF
voltage
which causes the current source output of the C
T
pin to change from
sinking (below threshold) to sourcing current (above threshold). When
sourcing current, the voltage on the C
T
pin rises until it is clamped
internally. When the clamp is activated, the output of the PG pin will be set
to a high impedance state. When the C
T
clamp is inactive the PG pin will
be set active low with a current sink capability of 200µA.
3434f
3
LT3434
TYPICAL PERFOR A CE CHARACTERISTICS
FB Voltage
1.30
1.29
1.28
FREQUENCY (kHz)
1.27
VOLTAGE (V)
1.26
1.25
1.24
1.23
1.22
1.21
1.20
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
210
200
190
180
170
160
150
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
VOLTAGE (V)
SHDN Pin Current
5.5
5.0
4.5
4.0
CURRENT (µA)
T
J
= 25°C
CURRENT (µA)
3.5
3.0
2.5
2.0
1.5
1.0
0
0
10
30
40
20
SHDN VOLTAGE (V)
50
60
3434 G04
15
CURRENT (µA)
Bias Sleep Current
200
180
160
140
1.20
1.18
1.16
1.14
1.12
1.10
1.08
1.06
1.04
1.02
50
25
0
75
TEMPERATURE (°C)
100
125
CURRENT (µA)
120
100
80
60
40
20
0
–50 –25
CURRENT (µA)
VOLTAGE (V)
4
U W
3434 G01
3434 G07
Oscillator Frequency
250
240
230
220
1.30
1.25
1.20
0.15
1.10
1.05
1.40
1.35
SHDN Threshold
1.00
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
3434 G02
3434 G03
Shutdown Supply Current
25
200
180
20
V
IN
= 60V
160
140
120
100
80
60
5
V
IN
= 42V
0
–50 –25
V
IN
= 12V
100
125
40
20
Sleep Mode Supply Current
V
BIAS
= 0V
10
V
BIAS
= 5V
50
25
0
75
TEMPERATURE (°C)
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
3434 G05
3434 G06
PGFB Threshold
250
PG Sink Current
200
150
100
50
1.00
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
3434 G08
3434 G09
3434f
LT3434
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Peak Current Limit
6.0
5.5
5.0
4.5
4.0
3.5
3.0
–50 –25
50
45
PEAK SWITCH CURRENT (A)
40
CURRENT (µA)
SOFT-START
DEFEATED
FREQUENCY (kHz)
35
30
25
20
15
10
5
–0
25
50
75
TEMPERATURE (°C)
100
125
0
0
0.2
0.6
0.8
0.4
FB VOLTAGE (V)
1.0
1.2
3434 G11
Switch On Voltage (V
CESAT
)
500
450
400
350
VOLTAGE (mV)
SUPPLY CURRENT (µA)
T
J
= 125°C
T
J
= 25°C
100
75
50
25
0
INPUT VOLTAGE (V)
300
250
200
150
100
50
0
0.5
1.0
2.0
1.5
LOAD CURRENT (A)
T
J
= –40°C
Burst Mode Threshold vs Input
Voltage
900
800
700
LOAD CURRENT (mA)
ON TIME (ns)
600
500
400
300
200
100
0
5
15
10
INPUT VOLTAGE (V)
20
3434 G21
V
OUT
= 3.3V
L = 33µH
C
OUT
= 100µF
BOOST CURRENT (mA)
BURST MODE EXIT
(INCREASING LOAD)
BURST MODE ENTER
(DECREASING LOAD)
U W
3434 G10
Soft-Start Threshold
vs FB Voltage
T
J
= 25°C
250
Oscillator Frequency
vs FB Voltage
T
J
= 25°C
200
150
100
50
0
0
0.2
0.6
0.8
0.4
FB VOLTAGE (V)
1.0
1.2
3434 G12
Supply Current vs Input Voltage
150
125
V
OUT
= 3.3V
Minimum Input Voltage
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
V
OUT
= 3.3V
RUNNING
START-UP
V
OUT
= 5V
START-UP
RUNNING
2.5
3.0
3434 G13
0
10
30
40
20
INPUT VOLTAGE (V)
50
60
3434 G20
3.0
0
0.5
1.0
1.5
2.0
LOAD CURRENT (A)
2.5
3.0
3434 G19
Minimum On Time for Continuous
Mode Operation
700
650
600
550
500
450
400
350
300
250
LOAD CURRENT = 2A
75
–0
25
50
TEMPERATURE (°C)
100
125
LOAD CURRENT = 1A
LOAD CURRENT = 0.5A
Boost Current vs Load Current
70
60
50
40
30
20
10
0
0
0.5
1.0
1.5
2.0
LOAD CURRENT (A)
2.5
3.0
200
–50 –25
3434 G22
3434 G23
3434f
5
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