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PDF LTC1430CN8 Data sheet ( Hoja de datos )
| Número de pieza | LTC1430CN8 | |
| Descripción | High Power Step-Down Switching Regulator Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC1430
High Power Step-Down
Switching Regulator Controller
FEATURES
s High Power 5V to 3.xV Switching Controller:
Can Exceed 10A Output
s All N-Channel External MOSFETs
s Constant Frequency Operation—Small Inductor
s Excellent Output Regulation: ±1% Over Line, Load
and Temperature Variations
s High Efficiency: Over 95% Possible
s Fixed Frequency Operation
s No Low Value Sense Resistor Needed
s Outputs Can Drive External FETs with Up to
10,000pF Gate Capacitance
s Quiescent Current: 350µA Typ, 1µA in Shutdown
s Fast Transient Response
s Adjustable or Fixed 3.3V Output
s Available in 8- and 16-Lead PDIP and SO Packages
U
APPLICATIO S
s Power Supply for P6 and Pentium®
Microprocessors
s High Power 5V to 3.xV Regulators
s Local Regulation for Dual Voltage Logic Boards
s Low Voltage, High Current Battery Regulation
DESCRIPTIO
The LTC®1430 is a high power, high efficiency switching
regulator controller optimized for 5V to 3.xV applications.
It includes a precision internal reference and an internal
feedback system that can provide output regulation of ±1%
over temperature, load current and line voltage shifts. The
LTC1430 uses a synchronous switching architecture with
two N-channel output devices, eliminating the need for a
high power, high cost P-channel device. Additionally, it
senses output current across the drain-source resistance
of the upper N-channel FET, providing an adjustable
current limit without an external low value sense resistor.
The LTC1430 includes a fixed frequency PWM oscillator for
low output ripple under virtually all operating conditions.
The 200kHz free-running clock frequency can be externally
adjusted from 100kHz to above 500kHz. The LTC1430
features low 350µA quiescent current, allowing greater
than 90% efficiency operation in converter designs from
1A to greater than 50A output current. Shutdown mode
drops the LTC1430 supply current to 1µA.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
TYPICAL APPLICATIO
+
4.7µF
Typical 5V to 3.3V, 10A Application
VIN 5V
+
100Ω
1µF
1N4148
0.1µF
0.01µF
PVCC2 PVCC1
VCC G1
SS IMAX
LTC1430 IFB
16k
NC FREQSET G2
SHUTDOWN
SHDN PGND
C1
220pF
COMP
GND
RC
7.5k
CC
4700pF
SENSE+
FB
SENSE–
NC
0.1µF
0.1µF
1k
+ CIN
220µF
×4
M1A, M1B
2 IN PARALLEL
L1, 2.8µH
+ COUT
M2 330µF
×6
LTC1430 • TA01
CIN: AVX-TPSE227M010R0100
COUT: AVX-TPSE337M006R0100
L1: ETQP6F1R6SFA
M1A, M1B, M2: MOTOROLA MTD20N03HL
3.3V
10A
Efficiency
100
TA = 25°C
90
VIN = 5V
VOUT = 3.3V
80
70
60
50
40
0.1
1
LOAD CURRENT (A)
10
LTC1430 • TA02
1
1 page  
BLOCK DIAGRA
SHDN
DELAY
50µs
INTERNAL
SHUTDOWN
FREQSET
COMP
SS
IMAX
VCC
12µA
ILIM
–+
12µA
PWM
FB
+–
+
1.26V
MIN
40mV
MAX
+
40mV
LTC1430
PVCC1
G1
PVCC2
G2
PGND
IFB
20.1k
12.4k
FB
SENSE+
SENSE –
LTC1430 • BD
TEST CIRCUITS
+
4.7µF
PVCC = 5V
+
100Ω
1µF
1N4148
0.1µF
PVCC2 PVCC1
VCC G1
SS IMAX
0.01µF
LTC1430 IFB
NC FREQSET G2
SHUTDOWN
SHDN PGND
C1
220pF
COMP
GND
RC
7.5k
CC
4700pF
SENSE+
FB
SENSE–
NC
0.1µF
+ CIN
220µF
×4
M1A, M1B
2 IN PARALLEL
2.7µH/15A
M2
+ COUT
330µF
×6
M1A, M1B, M2: MOTOROLA MTD20N03HL
CIN: AVX-TPSE227M010R0100
COUT: AVX-TPSE337M006R0100
3.3V
Figure 1
FB MEASUREMENT
LTC1430
SENSE+
FB
SENSE–
VOUT
NC 1.61k
1k
NC
LTC1430 • F01
VSHDN VCC
PVCC
SHDN VCC PVCC2 PVCC1 IFB
NC IMAX
G1 NC
NC FREQSET LTC1430
NC COMP
NC SS
G2 NC
FB NC
GND PGND SENSE– SENSE+
Figure 2
LTC1430 • TC02
5V
VCC PVCC1 PVCC2
G1
LTC1430
G2
GND PGND
10µF
10,000pF
10,000pF
Figure 3
0.1µF
G1 RISE/FALL
G2 RISE/FALL
LTC1430 • TC03
5
5 Page 
LTC1430
APPLICATIO S I FOR ATIO
Compensation and Transient Response
The LTC1430 voltage feedback loop is compensated at the
COMP pin; this is the output node of the internal gm error
amplifier. The loop can generally be compensated prop-
erly with an RC network from COMP to GND and an
additional small C from COMP to GND (Figure 8). Loop
stability is affected by inductor and output capacitor
values and by other factors. Optimum loop response can
be obtained by using a network analyzer to find the loop
poles and zeros; nearly as effective and a lot easier is to
empirically tweak the RC values until the transient recovery
looks right with an output load step. Table 1 shows
recommended compensation components for 5V to 3.3V
applications based on the inductor and output capacitor
values. The values were calculated using multiple paral-
leled 330µF AVX TPS series surface mount tantalum
capacitors as the output capacitor.
Table 1. Recommended Compensation Network for 5V to 3.3V
Application Using Multiple 330µF AVX Output Capacitors
L1 (µH)
1
COUT (µF)
990
RC (kΩ)
1.8
CC (µF)
0.022
C1 (pF)
820
1 1980 3.6 0.01 470
1
4950
9.1
0.0047
150
1
9900
18
0.0022
82
2.7 990 3.6
0.01 470
2.7
1980
7.5
0.0047
220
2.7
4950
18
0.0022
82
2.7 9900 39
0.001
39
5.6
990
9.1
0.0047
150
5.6
1980
18
0.0022
82
5.6 4950
47
820pF
33
5.6 9900
91
470pF
15
10
990
18
0.0022
82
10 1980 39
0.001
39
10
4950
91
470pF
15
10
9900 180
220pF
10
Output transient response is set by three major factors: the
time constant of the inductor and the output capacitor, the
more impact on overall transient recovery time than the
third; unless the loop compensation is way off, more
improvement can be had by optimizing the inductor and
the output capacitor than by fiddling with the loop com-
pensation components. In general, a smaller value induc-
tor will improve transient response at the expense of ripple
and inductor core saturation rating. Minimizing output
capacitor ESR will also help optimize output transient
response. See Input and Output Capacitors for more
information.
LTC1430
COMP
RC
CC C1
GND
SGND LTC1430 • F08
Figure 8. Compensation Pin Hook-Up
Soft-Start and Current Limit
The 16-lead versions of the LTC1430 include a soft-start
circuit at the SS pin; this circuit is used both for initial start-
up and during current limit operation. The soft-start and
current limit circuitry is disabled in 8-lead versions. SS
requires an external capacitor to GND with the value
determined by the required soft-start time. An internal
12µA current source is included to charge the external
capacitor. Soft-start functions by clamping the maximum
voltage that the COMP pin can swing to, thereby control-
ling the duty cycle (Figure 9). The LTC1430 will begin to
operate at low duty cycle as the SS pin rises to about 2V
below VCC. As SS continues to rise, the duty cycle will
increase until the error amplifier takes over and begins to
regulate the output. When SS reaches 1V below VCC the
LTC1430 will be in full operation. An internal switch shorts
the SS pin to GND during shutdown.
The LTC1430 detects the output current by watching the
voltage at IFB while M1 is ON. The ILIM amplifier compares
this voltage to the voltage at IMAX (Figure 10). In the ON
state, M1 has a known resistance; by calculating back-
wards, the voltage generated at IFB by the maximum
output current in M1 can be determined. As IFB falls below
IMAX, ILIM will begin to sink current from the soft-start pin,
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC1430CN8.PDF ] | |
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