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PDF LT1959C Data sheet ( Hoja de datos )
| Número de pieza | LT1959C | |
| Descripción | 4.5A/ 500kHz Step-Down Switching Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT1959
4.5A, 500kHz Step-Down
Switching Regulator
FEATURES
s Operates with Input as Low as 4V
s Output Range Down to 1.21V
s Constant 500kHz Switching Frequency
s Uses All Surface Mount Components
s Inductor Size Reduced to 1.8µH
s Saturating Switch Design: 0.07Ω
s Shutdown Current: 20µA
s Easily Synchronizable
s Cycle-by-Cycle Current Limiting
s 4.5A Switch
s Current Mode Control
U
APPLICATIO S
s Portable Computers
s Battery-Powered Systems
s Battery Chargers
s Distributed Power
s 5V to 3.3V Conversion
s 5V to 2.5V Conversion
s 5V to 1.8V Conversion
DESCRIPTIO
The LT®1959 is a 500kHz monolithic buck mode switching
regulator functionally identical to the LT1506 but optimized
for lower output voltage applications. It will operate down
to 1.21V output compared to 2.42V for the LT1506. A 4.5A
switch is included on the die along with all the necessary
oscillator, control and logic circuitry. High switching fre-
quency allows a considerable reduction in the size of ex-
ternal components. The topology is current mode for fast
transient response and good loop stability.
A special high speed bipolar process and new design tech-
niques achieve high efficiency at high switching frequency.
Efficiency is maintained over a wide output current range
by keeping quiescent supply current to 4mA and by utiliz-
ing a supply boost capacitor to saturate the power switch.
The LT1959 fits into standard 7-pin DD and fused lead
SO-8 packages. Full cycle-by-cycle short-circuit protection
and thermal shutdown are provided. Standard surface
mount external parts are used, including the inductor and
capacitors. There is the optional function of shutdown or
synchronization. A shutdown signal reduces supply current
to 20µA. Synchronization allows an external logic level sig-
nal to increase the internal oscillator from 580kHz to 1MHz.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
INPUT
5V
10µF
C3
TO
+
50µF
CERAMIC
5V to 1.8V Down Converter
D2
1N914
OPEN
OR
HIGH
= ON
BOOST
VIN VSW
LT1959
SHDN
FB
GND VC
CC
1.5nF
C2
0.68µF
L1
5µH
R1
1.21k
OUTPUT
1.8V
4A
R2 +
D1 2.49k
MBRS330T3
C1
100µF, 10V
SOLID
TANTALUM
1959 TA01
Efficiency vs Load Current
90
VOUT = 3.3V
VIN = 5V
L = 10µH
85
80
75
70
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
LOAD CURRENT (A)
1959 TA02
1
1 page  
LT1959
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency Foldback
500
SWITCHING
FREQUENCY
400
300
200
100
0
0
FEEDBACK
PIN CURRENT
0.2 0.4 0.6 0.8 1.0 1.2
FEEDBACK PIN VOLTAGE (V)
1959 • G10
Switching Frequency
550
540
530
520
510
500
490
480
470
460
450
– 50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1959 G11
Maximum Load Current
at VOUT = 5V
4.4
L= 10µH
4.2
4.0 L= 5µH
3.8
3.6 L= 3µH
3.4
3.2
3.0 L= 1.8µH
2.8
2.6
5
7 9 11
INPUT VOLTAGE (V)
13 15
1959 G13
Maximum Load Current
at VOUT = 3.3V
4.4
L= 10µH
4.2
L= 5µH
4.0
3.8 L= 3µH
3.6
3.4
L= 1.8µH
3.2
3.0
4
6 8 10 12
INPUT VOLTAGE (V)
14
1959 G14
BOOST Pin Current
100
DUTY CYCLE = 100%
90
80
70
60
50
40
30
20
10
0
0 12 34 5
SWITCH CURRENT (A)
1959 G15
Current Limit Foldback
7 FOLDBACK
CHARACTERISTICS
6
POSSIBLE UNDESIRED
CURRENT
5
STABLE POINT FOR
CURRENT SOURCE
SOURCE
LOAD
LOAD*
4 RESISTOR
LOAD
3
2
MOS LOAD
1
0
0 20 40 60 80 100
OUTPUT VOLTAGE (%)
1959 G16
VC Pin Shutdown Threshold
1.4
SHUTDOWN
1.2
1.0
0.8
0.6
0.4
–50
–25 0 25 50 75 100
JUNCTION TEMPERATURE (°C)
125
1959 G17
Switch Voltage Drop
500
450
125°C
400
350
25°C
300
250
– 40°C
200
150
100
50
0
0 1 23 45
SWITCH CURRENT (A)
1959 G18
*See “More Than Just Voltage Feedback” in the Applications Information section.
5
5 Page 
LT1959
APPLICATIONS INFORMATION
Table 2
VENDOR/
PART NO.
SERIES CORE
VALUE DC CORE RESIS- MATER- HEIGHT
(µH) (Amps) TYPE TANCE(Ω) IAL (mm)
Coiltronics
CTX2-1
2 4.1 Tor 0.011 KMµ 4.2
CTX5-4
5 4.4 Tor 0.019 KMµ 6.4
CTX8-4
8 3.5 Tor 0.020 KMµ 6.4
CTX2-1P
2 3.4 Tor 0.014 52 4.2
CTX2-3P
2 4.6 Tor 0.012 52 4.8
CTX5-4P
5 3.3 Tor 0.027 52 6.4
Sumida
CDRH125
10 4.0 SC 0.025
Fer
6
CDRH125
12 3.5 SC 0.027
Fer
6
CDRH125
15 3.3 SC 0.030
Fer
6
CDRH125
18 3.0 SC 0.034
Fer
6
Coilcraft
DT3316-222 2.2
5
SC 0.035
Fer
5.1
DT3316-332 3.3
5
SC 0.040
Fer
5.1
DT3316-472 4.7
3
SC 0.045
Fer
5.1
Pulse
PE-53650
4 4.8 Tor 0.017
52
9.1
PE-53651
5 5.4 Tor 0.018
52
9.1
PE-53652
9 5.5 Tor 0.022
52
10
PE-53653
16 5.1 Tor 0.032
52
10
Dale
IHSM-4825 2.7 5.1 Open 0.034 Fer 5.6
IHSM-4825 4.7 4.0 Open 0.047 Fer 5.6
IHSM-5832 10 4.3 Open 0.053 Fer 7.1
IHSM-5832 15 3.5 Open 0.078 Fer 7.1
IHSM-7832 22 3.8 Open 0.054 Fer 7.1
Tor = Toroid
SC = Semiclosed geometry
Fer = Ferrite core material
52 = Type 52 powdered iron core material
KMµ = Kool Mµ®
Output Capacitor
The output capacitor is normally chosen by its Effective
Series Resistance (ESR), because this is what determines
output ripple voltage. At 500kHz, any polarized capacitor
is essentially resistive. To get low ESR takes volume, so
physically smaller capacitors have high ESR. The ESR
Kool Mµ is a registered trademark of Magnetics, Inc.
range for typical LT1959 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 will be terrible. Table 3 shows some typical solid
tantalum surface mount capacitors.
Table 3. Surface Mount Solid Tantalum Capacitor ESR
and Ripple Current
E Case Size
ESR (Max., Ω) Ripple Current (A)
AVX TPS, Sprague 593D
0.1 to 0.3
0.7 to 1.1
AVX TAJ
0.7 to 0.9
0.4
D Case Size
AVX TPS, Sprague 593D
0.1 to 0.3
0.7 to 1.1
C Case Size
AVX TPS
0.2 (typ)
0.5 (typ)
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
Lf
VIN − VOUT
VIN
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT1959C.PDF ] | |
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