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PDF LTC1430ACS Data sheet ( Hoja de datos )
| Número de pieza | LTC1430ACS | |
| Descripción | High Power Step-Down Switching Regulator Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC1430A
High Power Step-Down
Switching Regulator Controller
FEATURES
s High Power 5V to 1.xV-3.xV Switching Controller:
Can Exceed 10A Output
s Maximum Duty Cycle > 90% Permits 3.3V to 2.xV
Conversion Using a Low Power 5V Supply
s All N-Channel External MOSFETs
s Fixed Frequency Operation—Small L
s Excellent Output Regulation: ±1% Over Line, Load
and Temperature Variations
s High Efficiency: Over 95% Possible
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-Lead SO and 16-Lead GN
and SO Packages
APPLICATI S
s Power Supply for Pentium® II and AMD-K6®
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®1430A is a high power, high efficiency switching
regulator controller optimized for 5V to 1.xV-3.xV applica-
tions. It includes a precision internal reference and an
internal feedback system that can provide output regula-
tion of ±1% over temperature, load current and line voltage
shifts. The LTC1430A uses a synchronous switching archi-
tecture with two N-channel output devices, eliminating the
need for a high power, high cost P-channel device. Addi-
tionally, 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 LTC1430A includes a fixed frequency PWM oscillator
for low output ripple under virtually all operating condi-
tions. The 200kHz free-running clock frequency can be
externally adjusted from 100kHz to above 500kHz. The
LTC1430A’s maximum duty cycle is typically 93.5% com-
pared to 88% for the LTC1430. This permits 3.3V to 2.xV
conversion using a low power 5V supply. The LTC1430A
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 LTC1430A supply current to 1µA.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
AMD-K6 is a registered trademark of Advanced Micro Devices, Inc.
TYPICAL APPLICATI
+
4.7µF
Typical 5V to 3.3V, 10A Application
5V
+
100Ω
1µF
MBR0530T1
+ CIN
220µF
×4
0.1µF
0.01µF
PVCC2 PVCC1
VCC G1
SS IMAX
LTC1430A IFB
NC FREQSET G2
SHUTDOWN
SHDN PGND
16k 0.1µF
1k
Q1A, Q1B
2 IN PARALLEL
0.1µF 2.7µH/15A
Q2
+ COUT
330µF
×6
C1
220pF
COMP
GND
RC
7.5k
CC
4700pF
SENSE+
FB
SENSE–
NC
1430 TA01
Q1A, Q1B, Q2: MOTOROLA MTD20N03HL
CIN: AVX-TPSE227M010R0100
COUT: AVX-TPSE337M006R0100
3.3V
10A
Efficiency
100
TA = 25°C
90
PVCC = 5V
VOUT = 3.3V
80
70
60
50
40
0.1
1
LOAD CURRENT (A)
10
1430 TA02
1
1 page  
UU U
PI FU CTIO S (16-Lead Package/8-Lead Package)
LTC1430A
G1 (Pin 1/Pin 1): Driver Output 1. Connect this pin to the
gate of the upper N-channel MOSFET, Q1. This output will
swing from PVCC1 to PGND. It will always be low when G2
is high.
PVCC1 (Pin 2/Pin 2): Power VCC for Driver 1. This is the
power supply input for G1. G1 will swing from PGND to
PVCC1. PVCC1 must be connected to a potential of at least
PVCC + VGS(ON)(Q1). This potential can be generated using
an external supply or a simple charge pump connected to
the switching node between the upper MOSFET and the
lower MOSFET; see Applications Information for details.
PGND (Pin 3/Pin 3): Power Ground. Both drivers return to
this pin. It should be connected to a low impedance ground
in close proximity to the source of Q2. 8-lead parts have
PGND and GND tied together at Pin 3.
GND (Pin 4/Pin 3): Signal Ground. All low power internal
circuitry returns to this pin. To minimize regulation errors
due to ground currents, GND should be connected to
PGND right at the LTC1430A. 8-lead parts have PGND and
GND tied together internally at Pin 3.
SENSE –, FB, SENSE + (Pins 5, 6, 7/Pin 4): These three
pins connect to the internal resistor divider and to the
internal feedback node. To use the internal divider to set
the output voltage to 3.3V, connect SENSE + to the positive
terminal of the output capacitor and SENSE – to GND. FB
should be left floating in applications that use the internal
divider. To use an external resistor divider to set the output
voltage, float SENSE + and SENSE – and connect the exter-
nal resistor divider to FB.
SHDN (Pin 8/Pin 5): Shutdown. A TTL compatible low
level at SHDN for longer than 50µs puts the LTC1430A into
shutdown mode. In shutdown, G1 and G2 go low, all
internal circuits are disabled and the quiescent current
drops to 10µA max. A TTL compatible high level at SHDN
allows the part to operate normally.
SS (Pin 9/NA): Soft Start. The SS pin allows an external
capacitor to be connected to implement a soft start func-
tion. An external capacitor from SS to ground controls the
start-up time and also compensates the current limit loop,
allowing the LTC1430A to enter and exit current limit
cleanly. See Applications Information for more details.
COMP (Pin 10/Pin 6): External Compensation. The COMP
pin is connected directly to the output of the error amplifier
and the input of the PWM. An RC network is used at this
node to compensate the feedback loop to provide opti-
mum transient response. See Applications Information for
compensation details.
FREQSET (Pin 11/NA): Frequency Set. This pin is used to
set the free running frequency of the internal oscillator.
With the pin floating, the oscillator runs at about 200kHz.
A resistor from FREQSET to ground will speed up the
oscillator; a resistor to VCC will slow it down. See Applica-
tions Information for resistor selection details.
IMAX (Pin 12/NA): Current Limit Set. IMAX sets the thresh-
old for the internal current limit comparator. If IFB drops
below IMAX with G1 on, the LTC1430A will go into current
limit. IMAX has a 12µA pull-down to GND. It can be adjusted
with an external resistor to PVCC or an external voltage
source.
IFB (Pin 13/NA): Current Limit Sense. Connect to the
switched node at the source of Q1 and the drain of Q2
through a 1k resistor. The 1k resistor is required to prevent
voltage transients from damaging IFB. This pin can be
taken up to 18V above GND without damage.
VCC (Pin 14/Pin 7): Power Supply. All low power internal
circuits draw their supply from this pin. Connect to a clean
power supply, separate from the main PVCC supply at the
drain of Q1. This pin requires a 4.7µF or greater bypass
capacitor. 8-lead parts have VCC and PVCC2 tied together
at Pin 7 and require at least a 10µF bypass to GND.
PVCC2 (Pin 15/Pin 7): Power VCC for Driver 2. This is the
power supply input for G2. G2 will swing from GND to
PVCC2. PVCC2 is usually connected to the main high power
supply. 8-lead parts have VCC and PVCC2 tied together at
Pin 7 and require at least a 10µF bypass to GND.
G2 (Pin 16/Pin 8): Driver Output 2. Connect this pin to the
gate of the lower N-channel MOSFET, Q2. This output will
swing from PVCC2 to PGND. It will always be low when G1
is high.
5
5 Page 
LTC1430A
APPLICATI S I FOR ATIO
are only 1.1W per device or less — large TO-220 packages
and heat sinks are not necessarily required in high effi-
ciency applications. Siliconix Si4410DY (in SO-8) and
Motorola MTD20N03HL (in DPAK) are two small, surface
mount devices with RON values of 0.03Ω or below with 5V
of gate drive; both work well in LTC1430A circuits with up
to 10A output current. A higher PMAX value will generally
decrease MOSFET cost and circuit efficiency and increase
MOSFET heat sink requirements.
Inductor
The inductor is often the largest component in an LTC1430A
design and should be chosen carefully. Inductor value and
type should be chosen based on output slew rate require-
ments and expected peak current. Inductor value is prima-
rily controlled by the required current slew rate. The
maximum rate of rise of the current in the inductor is set
by its value, the input-to-output voltage differential and the
maximum duty cycle of the LTC1430A. In a typical 5V to
3.3V application, the maximum rise time will be:
90% (VIN – VOUT) AMPS =
L SECOND
1.53A
µs
I
L
where L is the inductor value in µH. A 2µH inductor would
have a 0.76A/µs rise time in this application, resulting in a
6.5µs delay in responding to a 5A load current step. During
this 6.5µs, the difference between the inductor current and
the output current must be made up by the output capaci-
tor, causing a temporary droop at the output. To minimize
this effect, the inductor value should usually be in the 1µH
to 5µH range for most typical 5V to 2.xV-3.xV LTC1430A
circuits. Different combinations of input and output volt-
ages and expected loads may require different values.
Once the required value is known, the inductor core type
can be chosen based on peak current and efficiency
requirements. Peak current in the inductor will be equal to
the maximum output load current added to half the peak-
to- peak inductor ripple current. Ripple current is set by the
inductor value, the input and output voltage and the
operating frequency. If the efficiency is high and can be
approximately equal to 1, the ripple current is approxi-
mately equal to:
∆I
=
(VIN – VOUT)
(fOSC)(L)
DC
DC =
VOUT
VIN
fOSC = LTC1430A oscillator frequency
L = inductor value
Solving this equation with our typical 5V to 3.3V applica-
tion, we get:
(1.7)(0.66)
(200kHz)(2µH)
=
2.8AP–P
Peak inductor current at 10A load:
10A + 2.8A = 11.4A
2
The inductor core must be adequate to withstand this peak
current without saturating, and the copper resistance in
the winding should be kept as low as possible to minimize
resistive power loss. Note that the current may rise above
this maximum level in circuits under current limit or under
fault conditions in unlimited circuits; the inductor should
be sized to withstand this additional current.
Input and Output Capacitors
A typical LTC1430A design puts significant demands on
both the input and output capacitors. Under normal steady
load operation, a buck converter like the LTC1430A draws
square waves of current from the input supply at the
switching frequency, with the peak value equal to the
output current and the minimum value near zero. Most of
this current must come from the input bypass capacitor,
since few raw supplies can provide the current slew rate to
feed such a load directly. The resulting RMS current flow
in the input capacitor will heat it up, causing premature
capacitor failure in extreme cases. Maximum RMS current
occurs with 50% PWM duty cycle, giving an RMS current
value equal to IOUT/2. A low ESR input capacitor with an
adequate ripple current rating must be used to ensure
reliable operation. Note that capacitor manufacturers’
ripple current ratings are often based on only 2000 hours
(3 months) lifetime; further derating of the input capacitor
ripple current beyond the manufacturer’s specification is
recommended to extend the useful life of the circuit.
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC1430ACS.PDF ] | |
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