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PDF LTC1629-PG Data sheet ( Hoja de datos )
| Número de pieza | LTC1629-PG | |
| Descripción | PolyPhase/ High Efficiency/ Synchronous Step-Down Switching Regulators | |
| Fabricantes | Linear Technology | |
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LTC1629/LTC1629-PG
PolyPhase, High Efficiency,
Synchronous Step-Down Switching Regulators
FEATURES
s Dual Controller Operates from One to Twelve Phases
s Reduces Required Input Capacitance and Power
Supply Induced Noise
s Current Mode Control Ensures Current Sharing
s Phase-Lockable Fixed Frequency: 150kHz to 300kHz
s 1.8MHz Effective Switching Frequency
s True Remote Sensing Differential Amplifier
s OPTI-LOOPTM Compensation Reduces COUT
s ±1% Output Voltage Accuracy
s Power Good Output Voltage Monitor (LTC1629-PG)
s Wide VIN Range: 4V to 36V Operation
s Very Low Dropout Operation: 99% Duty Cycle
s Adjustable Soft-Start Current Ramping
s Internal Current Foldback Plus Shutdown Timer
s Overvoltage Soft-Latch Eliminates Nuisance Trips
s Micropower Shutdown
s Available in 28-Lead SSOP Package
U
APPLICATIO S
s Desktop Computers
s Internet Servers
s Large Memory Arrays
s DC Power Distribution Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP and PolyPhase are trademarks of Linear Technology Corporation.
DESCRIPTIO
The LTC®1629/LTC1629-PG are multiple phase, dual,
synchronous step-down current mode switching regula-
tor controllers that drive N-channel external power MOSFET
stages in a phase-lockable fixed frequency architecture.
The PolyPhaseTM controller drives its two output stages
out of phase at frequencies up to 300kHz to minimize the
RMS ripple currents in both input and output capacitors.
The output clock signal allows expansion for up to 12
evenly phased controllers for systems requiring 15A to
200A of output current. The multiple phase technique
effectively multiplies the fundamental frequency by the
number of channels used, improving transient response
while operating each channel at an optimum frequency for
efficiency. Thermal design is also simplified.
An internal differential amplifier provides true remote
sensing of the regulated supply’s positive and negative
output terminals as required for high current applications.
A RUN/SS pin provides both soft-start and optional timed,
short-circuit shutdown. Current foldback limits MOSFET
dissipation during short-circuit conditions when the
overcurrent latchoff is disabled. OPTI-LOOP compensa-
tion allows the transient response to be optimized over a
wide range of output capacitance and ESR values. The
LTC1629-PG includes a power good output pin that re-
places the AMPMD control pin of the LTC1629.
TYPICAL APPLICATIO
0.1µF
S
0.1µF
1000pF
3.3k
S
16k
S
16k
VIN LTC1629-PG TG1
BOOST1
RUN/SS
SW1
BG1
PGOOD
ITH
PGND
SENSE1+
SENSE1–
TG2
SGND
BOOST2
SW2
VDIFFOUT
EAIN
VOS–
VOS+
BG2
INTVCC
SENSE2+
SENSE2–
10Ω
S
0.47µF
S
S
S
0.47µF
S
S
10µF
10µF ×4
M1
35V
CERAMIC
0.003Ω
L1
M2 1µH
×2 D1
M3
0.003Ω
L2
M4 1µH
×2 D2
COUT: T510E108K004AS
D1, D2: UP5840
L1, L2: CEPH149-IROMC
M1, M3: IRF7811
M2, M4: IRF7809
Figure 1. High Current Dual Phase Step-Down Converter
VIN
5V TO 28V
VOUT
1.6V/40A
+ COUT
1000µF ×2
4V
1629 TA01
1
1 page  
LTC1629/LTC1629-PG
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Input Voltage
and Mode
1000
800
600
ON
400
200
SHUTDOWN
0
0 5 10 15 20 25 30 35
INPUT VOLTAGE (V)
1629 G04
Internal 5V LDO Line Reg
5.1
ILOAD = 1mA
5.0
4.9
4.8
4.7
4.6
4.5
4.4
0
5 10 15 20 25 30 35
INPUT VOLTAGE (V)
1629 G07
Maximum Current Sense Threshold
vs VRUN/SS (Soft-Start)
80
VSENSE(CM) = 1.6V
60
40
20
0
01 2 34 5 6
VRUN/SS (V)
1629 G10
EXTVCC Voltage Drop
250
200
LTC1629
150
LTC1629-PG
100
50
0
0 10 20 30 40 50
CURRENT (mA)
1629 G05
Maximum Current Sense Threshold
vs Duty Factor
75
50
25
0
0 20 40 60 80 100
DUTY FACTOR (%)
1629 G08
Maximum Current Sense Threshold
vs Sense Common Mode Voltage
80
76
72
68
64
60
0
1 2 34
COMMON MODE VOLTAGE (V)
5
1629 G11
INTVCC and EXTVCC Switch
Voltage vs Temperature
5.05
INTVCC VOLTAGE
5.00
4.95
4.90
4.85
4.80
EXTVCC SWITCHOVER THRESHOLD
4.75
4.70
– 50 – 25
0 25 50 75
TEMPERATURE (°C)
100 125
1629 G06
Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)
80
70
60
50
40
30
20
10
0
0 25 50 75 100
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
1629 G09
Current Sense Threshold
vs ITH Voltage
90
80
70
60
50
40
30
20
10
0
–10
–20
–30
0 0.5 1 1.5 2 2.5
VITH (V)
1629 G12
5
5 Page 
U
OPERATIO (Refer to Functional Diagram)
INTVCC/EXTVCC Power
Power for the top and bottom MOSFET drivers and most
of the IC circuitry is derived from INTVCC. When the
EXTVCC pin is left open, an internal 5V low dropout
regulator supplies INTVCC power. If the EXTVCC pin is
taken above 4.7V, the 5V regulator is turned off and an
internal switch is turned on connecting EXTVCC to INTVCC.
This allows the INTVCC power to be derived from a high
efficiency external source such as the output of the regu-
lator itself or a secondary winding, as described in the
Applications Information section. An external Schottky
diode can be used to minimize the voltage drop from
EXTVCC to INTVCC in applications requiring greater than
the specified INTVCC current. Voltages up to 7V can be
applied to EXTVCC for additional gate drive capability.
Differential Amplifier
This amplifier provides true differential output voltage
sensing. Sensing both VOUT+ and VOUT– benefits regula-
tion in high current applications and/or applications hav-
ing electrical interconnection losses. The AMPMD pin
(available on the LTC1629 only) allows selection of inter-
nal precision feedback resistors for high common mode
rejection differencing applications, or direct access to the
actual amplifier inputs without these internal feedback
resistors for other applications. The AMPMD pin is
grounded to connect the internal precision resistors in a
unity-gain differencing application or tied to the INTVCC
pin to bypass the internal resistors and make the amplifier
inputs directly available. The amplifier is a unity-gain
stable, 2MHz gain-bandwidth, >120dB open-loop gain
design. The amplifier has an output slew rate of 5V/µs and
is capable of driving capacitive loads with an output RMS
current typically up to 25mA. The amplifier is not capable
LTC1629/LTC1629-PG
of sinking current and therefore must be resistively loaded
to do so. The differential amplifier is configured as a unity-
gain differencing amplifier in the LTC1629-PG.
Power Good (PGOOD) (LTC1629-PG Only)
The PGOOD pin is connected to the drain of an internal
MOSFET. The MOSFET turns on when the output is not
within ±7.5% of its nominal output level as determined by
the feedback divider. When the output is within ±7.5% of
its nominal value, the MOSFET is turned off within 10µs
and the PGOOD pin should be pulled up by an external
resistor to a source of up to 7V.
Short-Circuit Detection
The RUN/SS capacitor is used initially to limit the inrush
current from the input power source. Once the controllers
have been given time, as determined by the capacitor on
the RUN/SS pin, to charge up the output capacitors and
provide full load current, the RUN/SS capacitor is then
used as a short-circuit timeout circuit. If the output voltage
falls to less than 70% of its nominal output voltage the
RUN/SS capacitor begins discharging assuming that the
output is in a severe overcurrent and/or short-circuit
condition. If the condition lasts for a long enough period
as determined by the size of the RUN/SS capacitor, the
controller will be shut down until the RUN/SS pin voltage
is recycled. This built-in latchoff can be overidden by
providing a >5µA pull-up current at a compliance of 5V to
the RUN/SS pin. This current shortens the soft-start
period but also prevents net discharge of the RUN/SS
capacitor during a severe overcurrent and/or short-circuit
condition. Foldback current limiting is activated when the
output voltage falls below 70% of its nominal level whether
or not the short-circuit latchoff circuit is enabled.
APPLICATIO S I FOR ATIO
The basic LTC1629 application circuit is shown in Figure␣ 1
on the first page. External component selection is driven
by the load requirement, and begins with the selection of
RSENSE1, 2. Once RSENSE1, 2 are known, L1 and L2 can be
chosen. Next, the power MOSFETs and D1 and D2 are
selected. The operating frequency and the inductor are
chosen based mainly on the amount of ripple current.
Finally, CIN is selected for its ability to handle the input
ripple current (that PolyPhase operation minimizes) and
COUT is chosen with low enough ESR to meet the output
ripple voltage and load step specifications (also minimized
with PolyPhase). The circuit shown in Figure␣ 1 can be
configured for operation up to an input voltage of 28V
(limited by the external MOSFETs).
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC1629-PG.PDF ] | |
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