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PDF LTC1929-PG Data sheet ( Hoja de datos )
| Número de pieza | LTC1929-PG | |
| Descripción | Synchronous Step-Down Switching Regulators | |
| Fabricantes | Linear | |
| Logotipo |  |
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FEATURES
s 2-Phase Single Output Controller
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 True Remote Sensing Differential Amplifier
s OPTI-LOOPTM Compensation Improves Transient
Response
s ±1% Output Voltage Accuracy
s Power Good Output Voltage Monitor (LTC1929-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
s Short-Circuit Shutdown Timer with Defeat Option
s Overvoltage Soft-Latch Eliminates Nuisance Trips
s Available in 28-Lead SSOP Package
U
APPLICATIO S
s Desktop Computers
s Internet/Network Servers
s Large Memory Arrays
s DC Power Distribution Systems
LTC1929/LTC1929-PG
2-Phase, High Efficiency,
Synchronous Step-Down
Switching Regulators
DESCRIPTIO
The LTC®1929/LTC1929-PG are 2-phase, single output,
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 2-phase controllers drive their two output stages out
of phase at frequencies up to 300kHz to minimize the RMS
ripple currents in both input and output capacitors. The
2-phase technique effectively multiplies the fundamental
frequency by two, 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 by high current applications.
The RUN/SS pin provides soft-start and a defeatable,
timed, latched short-circuit shutdown to shut down both
channels. Internal foldback current limit provides protec-
tion for the external synchronous MOSFETs in the event of
an output fault. OPTI-LOOP compensation allows the
transient response to be optimized over a wide range of
output capacitance and ESR values.
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
0.1µF
0.1µF
VIN TG1
BOOST1
LTC1929 SW1
RUN/SS
BG1
1000pF
10k
100pF
ITH
PGND
SENSE1+
SENSE1–
TG2
SGND
BOOST2
16k
16k
VDIFFOUT
EAIN
VOS–
VOS+
SW2
BG2
INTVCC
SENSE2+
SENSE2–
10Ω
0.47µF
0.47µF
10µF
10µF
35V
CERAMIC
×4
L1
1µH
D1
0.002Ω
L2
D2 1µH
0.002Ω
COUT: T510E108K004AS L1, L2: CEPH149-1ROMC
Figure 1. High Current 2-Phase Step-Down Converter
VIN
5V TO 28V
VOUT
1.6V/40A
+ COUT
1000µF
4V
×2
1929 F01
1
1 page  
LTC1929/LTC1929-PG
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Input Voltage
and Mode
1000
800
VOUT = 5V
VEXTVCC = VOUT
600
ON
400
200
SHUTDOWN
0
0 5 10 15 20 25 30 35
INPUT VOLTAGE (V)
1929 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)
1929 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)
1929 G10
EXTVCC Voltage Drop
250
200
LTC1929
150
LTC1929-PG
100
50
0
0 10 20 30 40 50
CURRENT (mA)
1929 G05
Maximum Current Sense Threshold
vs Duty Factor
75
50
25
0
0 20 40 60 80 100
DUTY FACTOR (%)
1929 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
1929 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
1929 G06
Maximum Current Sense Threshold
vs Percent on Nominal Output
Voltage (Foldback)
80
70
60
50
40
30
20
10
0
0 25 50 75 100
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
1929 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)
1929 G12
5
5 Page 
U
OPERATIO (Refer to Functional Diagram)
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
(LTC1929 only) allows selection of internal, precision feed-
back resistors for high common mode rejection differencing
applications, or direct access to the actual amplifier inputs
without these internal feedback resistors for other applica-
tions. The AMPMD pin is grounded to connect the internal
precision resistors in a unity-gain differencing application
(default for the LTC1929-PG), 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 am-
plifier has an output slew rate of 5V/µs and is capable of
driving capacitive loads with an output RMS current typi-
cally up to 25mA. The amplifier is not capable of sinking
current and therefore must be resistively loaded to do so.
Power Good (PGOOD) Pin (LTC1929-PG Only)
The PGOOD pin is connected to an open drain of a
MOSFET. The MOSFET turns on and pulls the pin low when
the output is not within ±7.5% of its nominal output level
as determined by its resistive feedback divider. When the
LTC1929/LTC1929-PG
output meets the ±7.5% requirement, the MOSFET is
turned off within 10µs and the pin is allowed to be pulled
up by an external source.
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 current >5µA 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 condi-
tion. 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 LTC1929 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 PolyPhaseTM operation minimizes) and
COUT is chosen with low enough ESR to meet the output
ripple voltage and load step specifications (also minimized
with PolyPhase). Current mode architecture provides in-
herent current sharing between output stages. The circuit
shown in Figure␣ 1 can be configured for operation up to an
input voltage of 28V (limited by the external MOSFETs).
RSENSE Selection For Output Current
RSENSE1, 2 are chosen based on the required output
current. The LTC1929 current comparator has a maxi-
mum threshold of 75mV/RSENSE and an input common
mode range of SGND to 1.1( INTVCC). The current com-
parator threshold sets the peak inductor current, yielding
a maximum average output current IMAX equal to the peak
value less half the peak-to-peak ripple current, ∆IL.
Allowing a margin for variations in the LTC1929 and
external component values yields:
RSENSE = 2(50mV/IMAX)
PolyPhase is a trademark of Linear Technology Corporation.
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC1929-PG.PDF ] | |
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