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PDF LT3434 Data sheet ( Hoja de datos )
| Número de pieza | LT3434 | |
| Descripción | High Voltage 3A & 200kHz Step-Down Switching Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT3434www.DataSheet4U.com
High Voltage 3A, 200kHz
Step-Down Switching Regulator
with 100µA Quiescent Current
FEATURES
■ Wide Input Range: 3.3V to 60V
■ 3A Peak Switch Current
■ Burst Mode® Operation: 100µA Quiescent Current**
■ Low Shutdown Current: IQ < 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
U
APPLICATIO S
■ 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.
DESCRIPTIO
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 CSS 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.
TYPICAL APPLICATIO
14V to 3.3V Step-Down Converter with
100µA No Load Quiescent Current
VIN
4700pF
10k
4.7µF
100V
CER
470pF
1µF
VIN BOOST
SHDN
SW
0.68µF 33µH 4148
LT3434 0.1µF
VC CSS
30MQ100
CT
SYNC
GND
VBIAS
FB
PGFB
PG
27pF
165k
1%
100k
1%
VOUT
3.3V
2A
100µF
6.3V
TANT
3434 TA01
Supply Current vs
Input Voltage
150
VOUT = 3.3V
125
100
75
50
25
0
0 10 20 30 40 50 60
INPUT VOLTAGE (V)
3434 TA02a
Efficiency and Power Loss
vs Load Current
100 VIN = 12V
L = 33µH
COUT = 100µF
75
EFFICIENCY
VOUT = 5V
10
1
VOUT = 3.3V
50
0.1
TYPICAL POWER
LOSS
25 0.01
0
0.0001 0.001 0.01
0.1
LOAD CURRENT (A)
0.001
1 10
3434 TA02b
3434f
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LT3434www.DataSheet4U.com
Switch Peak Current Limit
6.0
5.5
5.0
4.5
4.0
3.5
3.0
–50 –25
–0 25 50 75
TEMPERATURE (°C)
100 125
3434 G10
Switch On Voltage (VCESAT)
500
450
400
TJ = 125°C
350
300 TJ = 25°C
250
200
150 TJ = –40°C
100
50
0
0.5 1.0 1.5 2.0 2.5 3.0
LOAD CURRENT (A)
3434 G13
Burst Mode Threshold vs Input
Voltage
900
VOUT = 3.3V
800 L = 33µH
COUT = 100µF
700
600 BURST MODE EXIT
500 (INCREASING LOAD)
400
300
200 BURST MODE ENTER
(DECREASING LOAD)
100
0
5 10 15 20
INPUT VOLTAGE (V)
3434 G21
Soft-Start Threshold
vs FB Voltage
50
TJ = 25°C
45
40
35
SOFT-START
30 DEFEATED
25
20
15
10
5
0
0 0.2 0.4 0.6 0.8 1.0 1.2
FB VOLTAGE (V)
3434 G11
Supply Current vs Input Voltage
150
VOUT = 3.3V
125
100
75
50
25
0
0 10 20 30 40 50 60
INPUT VOLTAGE (V)
3434 G20
Minimum On Time for Continuous
Mode Operation
700
650
600
550
LOAD CURRENT = 0.5A
500
450
400
350 LOAD CURRENT = 1A
300
250 LOAD CURRENT = 2A
200
–50 –25
–0 25 50 75
TEMPERATURE (°C)
100 125
3434 G22
Oscillator Frequency
vs FB Voltage
250
TJ = 25°C
200
150
100
50
0
0 0.2 0.4 0.6 0.8 1.0 1.2
FB VOLTAGE (V)
3434 G12
Minimum Input Voltage
8.0
7.5
7.0
START-UP RUNNING
6.5
6.0 VOUT = 5V
5.5
5.0 START-UP
4.5 VOUT = 3.3V
4.0 RUNNING
3.5
3.0
0
0.5 1.0 1.5 2.0 2.5 3.0
LOAD CURRENT (A)
3434 G19
Boost Current vs Load Current
70
60
50
40
30
20
10
0
0 0.5 1.0 1.5 2.0 2.5 3.0
LOAD CURRENT (A)
3434 G23
3434f
5
5 Page 
LT3434www.DataSheet4U.com
APPLICATIO S I FOR ATIO
taken to ensure the ripple and surge ratings are not
exceeded. The AVX TPS and Kemet T495 series are surge
rated AVX recommends derating capacitor operating volt-
age by 2:1 for high surge applications.
OUTPUT CAPACITOR
The output capacitor is normally chosen by its effective
series resistance (ESR) because this is what determines
output ripple voltage. To get low ESR takes volume, so
physically smaller capacitors have higher ESR. The ESR
range for typical LT3434 applications is 0.05Ω to 0.2Ω. A
typical output capacitor is an AVX type TPS, 100µF at 10V,
with a guaranteed ESR less than 0.1Ω. This is a “D” size
surface mount solid tantalum capacitor. TPS capacitors
are specially constructed and tested for low ESR, so they
give the lowest ESR for a given volume. The value in
microfarads is not particularly critical and values from
22µF to greater than 500µF work well, but you cannot
cheat Mother Nature on ESR. If you find a tiny 22µF solid
tantalum capacitor, it will have high ESR and output ripple
voltage could be unacceptable. Table 2 shows some
typical solid tantalum surface mount capacitors.
Table 2. Surface Mount Solid Tantalum Capacitor ESR
and Ripple Current
E CASE SIZE
ESR MAX (Ω)
RIPPLE CURRENT (A)
AVX TPS
0.1 to 0.3
0.7 to 1.1
D CASE SIZE
AVX TPS
0.1 to 0.3
0.7 to 1.1
C CASE SIZE
AVX TPS
0.2
0.5
Many engineers have heard that solid tantalum capacitors
are prone to failure if they undergo high surge currents.
This is historically true and type TPS capacitors are
specially tested for surge capability but surge ruggedness
is not a critical issue with the output capacitor. Solid
tantalum capacitors fail during very high turn-on surges
which do not occur at the output of regulators. High
discharge surges, such as when the regulator output is
dead shorted, do not harm the capacitors.
Unlike the input capacitor RMS, ripple current in the
output capacitor is normally low enough that ripple cur-
rent rating is not an issue. The current waveform is
triangular with a typical value of 200mARMS. The formula
to calculate this is:
Output capacitor ripple current (RMS)
IRIPPLE(RMS)
=
0.29(VOUT)(VIN – VOUT)
(L)(f)(VIN)
=
IP-P
12
CERAMIC CAPACITORS
Higher value, lower cost ceramic capacitors are now
becoming available. They are generally chosen for their
good high frequency operation, small size and very low
ESR (effective series resistance). Low ESR reduces output
ripple voltage but also removes a useful zero in the loop
frequency response, common to tantalum capacitors. To
compensate for this a resistor RC can be placed in series
with the VC compensation capacitor CC (Figure 10). Care
must be taken however since this resistor sets the high
frequency gain of the error amplifier including the gain at
the switching frequency. If the gain of the error amplifier
is high enough at the switching frequency output ripple
voltage (although smaller for a ceramic output capacitor)
may still affect the proper operation of the regulator. A
filter capacitor CF in parallel with the RC/CC network, along
with a small feedforward capacitor CFB, is suggested to
control possible ripple at the VC pin. The LT3434 can be
stabilized using a 100µF ceramic output capacitor and VC
component values of CC = 4700pF, RC = 10k, CF = 470pF
and CFB = 27pF.
OUTPUT RIPPLE VOLTAGE
Figure 3 shows a typical output ripple voltage waveform
for the LT3434. Ripple voltage is determined by the
impedance of the output capacitor and ripple current
through the inductor. Peak-to-peak ripple current through
the inductor into the output capacitor is:
IP-P
=
( )VOUT VIN – VOUT
(VIN)(L)(f)
3434f
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT3434.PDF ] | |
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