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PDF LTC1709-9 Data sheet ( Hoja de datos )
| Número de pieza | LTC1709-9 | |
| Descripción | 2-Phase/ 5-Bit VID/ Current Mode/ High Efficiency/ Synchronous Step-Down Switching Regulators | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC1709-9 (archivo pdf) en la parte inferior de esta página. Total 28 Páginas | ||
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Final Electrical Specifications
LTC1709-8/LTC1709-9
2-Phase, 5-Bit VID,
Current Mode, High Efficiency,
Synchronous Step-Down Switching Regulators
FEATURES
DESCRIPTIO
May 2000
s Single Controller Operates Two Output Stages:
Antiphase Reducing Required Input Capacitance
and Power Supply Induced Noise
s Two 5-Bit Desktop VID Codes:
LTC1709-8 For VRM8.4 (VOUT from 1.3V to 3.5V)
LTC1709-9 For VRM9.0 (VOUT from 1.1V to 1.85V)
s Current Mode Control Ensures Best Current Sharing
s True Remote Sensing Differential Amplifier
s Power Good Output Indicator
s OPTI-LOOPTM Compensation Minimizes COUT
s Programmable Fixed Frequency: 150kHz to 300kHz
s ±1% Output Voltage Accuracy
s Wide VIN Range: 4V to 36V Operation
s Adjustable Soft-Start Current Ramping
s Internal Current Foldback and Short-Circuit Shutdown
s Overvoltage Soft Latch Eliminates Nuisance Trips
s Low Shutdown Current: 20µA
s Available in 36-Lead SSOP Package
U
APPLICATIO S
s Workstations
s Internet Servers
s Large Memory Arrays
s DC Power Distribution Systems
The LTC®1709-8/LTC1709-9 are 2-phase, VID program-
mable, synchronous step-down switching regulator con-
trollers that drive two all N-channel external power MOSFET
stages in a fixed frequency architecture. The 2-phase
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 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 for high current applications.
The RUN/SS pin provides 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 for a
wide range of output capacitors and ESR values. The
LTC1709-8/LTC1709-9 implement two different VID
tables compliant with VRM8.4 and VRM9.0 respectively.
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
0.1µF
VIN TG1
S
220pF
3.3k
RUN/SS
BOOST1
SW1
LTC1709-8
ITH BG1
0.47µF
S
SGND
PGND
PGOOD
5 VID BITS VID0–VID4
SENSE1+
SENSE1–
TG2
EAIN
ATTENOUT
BOOST2
SW2
0.47µF
ATTENIN
BG2
VDIFFOUT
VOS–
VOS+
INTVCC
SENSE2+
SENSE2–
10µF
+ 10µF
35V
×4
1µH
0.002Ω
0.002Ω
1µH
Figure 1. High Current Dual Phase Step-Down Converter
VIN
5V TO 28V
VOUT
1.3V TO 3.5V
40A
+ COUT
1000µF
4V
×2
17097 F01
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1
1 page  
LTC1709-8/LTC1709-9
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Input Voltage
and Mode (Figure 12)
1000
ON
800
600
400
200
SHUTDOWN
0
0 5 10 15 20 25 30 35
INPUT VOLTAGE (V)
170989 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)
170989 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)
170989 G10
EXTVCC Voltage Drop
250
200
150
100
50
0
0 10 20 30 40 50
CURRENT (mA)
170989 G05
Maximum Current Sense Threshold
vs Duty Factor
75
50
25
0
0 20 40 60 80 100
DUTY FACTOR (%)
170989 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
170989 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
170989 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 (%)
170989 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
VITH (V)
2 2.5
170989 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
allows selection of internal, precision feedback resistors
for high common mode rejection differencing applica-
tions, 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,
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 capaci-
tive loads with an output RMS current typically up to
35mA. The amplifier is not capable of sinking current and
therefore must be resistively loaded to do so.
Power Good (PGOOD)
The PGOOD pin is connected to the drain of an internal
MOSFET. The MOSFET turns on when the output voltage
is not within ±7.5% of its nominal output level as deter-
mined by the feedback divider. When the output is within
LTC1709-8/LTC1709-9
±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 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 LTC1709 application circuit is shown in Fig-
ure␣ 1 on the first page. External component selection
begins with the selection of the inductor(s) based on
ripple current requirements and continues with the
RSENSE1, 2 resistor selection using the calculated peak
inductor current and/or maximum current limit. Next, the
power MOSFETs and D1 and D2 are selected. The oper-
ating 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 inherent
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 peak output
current. The LTC1709 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.
PolyPhase is a trademark of Linear Technology Corporation.
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC1709-9.PDF ] | |
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