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PDF LTC3730 Data sheet ( Hoja de datos )
| Número de pieza | LTC3730 | |
| Descripción | Synchronous Buck Controller | |
| Fabricantes | Linear | |
| Logotipo |  |
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LTC3730
3-Phase, 5-Bit Intel
Mobile VID, 600kHz,
Synchronous Buck Controller
FEATURES
■ 3-Phase Current Mode Controller with Onboard
MOSFET Drivers
■ ±5% Output Current Match Optimizes Thermal
Performance and Size of Inductors and MOSFETs
■ Operational Amplifier Accomodates Mode Switching
■ ±1% VREF Accuracy Over Temperature
■ Reduced Input and Output Capacitance
■ Reduced Power Supply Induced Noise
■ VOUT Programmable from 0.6V to 1.75V (IMVP III)
■ ±10% Power Good Output Indicator
■ 250kHz to 600kHz Per Phase, PLL, Fixed Frequency
■ PWM, Stage SheddingTM or Burst Mode® Operation
■ OPTI-LOOP® Compensation Minimizes COUT
■ Adjustable Soft-Start Current Ramping
■ 4V, VIN, Undervoltage RUN/SS Reset/Reattempt Circuit
■ Short-Circuit Shutdown Timer with Defeat Option
■ Overvoltage Soft Latch
■ Small 36-Lead Narrow (0.209”) SSOP Package
U
APPLICATIO S
■ Tablet Computers
■ High Performance Notebook Computers
■ High Output Current DC/DC Power Supplies
DESCRIPTIO
The LTC®3730 is a PolyPhase® synchronous step-down
switching regulator controller that drives all N-channel
external power MOSFET stages in a phase-lockable fixed
frequency architecture. The 3-phase controller drives its
output stages with 120° phase separation at frequencies of
up to 600kHz per phase to minimize the RMS losses in both
the input and output filter capacitors. The 3-phase tech-
nique effectively triples the fundamental frequency, im-
proving transient response while operating each controller
at an optimal frequency for efficiency and ease of thermal
design. Light load efficiency is optimized by using a choice
of output Stage Shedding or Burst Mode technology.
An internal operational amplifier provides mode selectable
output voltage programming in conjunction with the inter-
nal VID voltage control DAC.
Soft-start and a defeatable, timed short-circuit shutdown
protect the MOSFETs and the load. Current foldback
provides protection for the external MOSFETs under
short-circuit or overload conditions.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode,
OPTI-LOOP and PolyPhase are registered trademarks of Linear Technology Corporation.
Stage Shedding is a trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners. Protected by U.S. Patents including 5481178,
5929620, 6177787, 6144194, 6100678, 5408150, 6580258, 6462525, 6304066, 5705919.
TYPICAL APPLICATIO
VCC
4.5V TO 7V
10µF
0.1µF
SW3 SW2 SW1
POWER GOOD INDICATOR
OPTIONAL SYNC IN
5 VID BITS
680pF
5k
0.1µF
100pF
VCC TG1
LTC3730 SW1
BOOST1
BOOST2
BG1
BOOST3
SENSE1+
SENSE1–
PGOOD
PLLIN
PLLFLTR
VID0-VID4
ITH
RUN/SS
SGND
EAIN
AMPOUT
IN–
IN+
TG2
SW2
BG2
PGND
SENSE2+
SENSE2–
TG3
SW3
BG3
SENSE3+
SENSE3–
1µH 0.003Ω
VIN
+ 5V TO 28V
22µF
35V
VIN
1µH
0.003Ω
VOUT
1.2V
50A
VIN
1µH
0.003Ω
+ COUT
470µF
x4
2.5V 3730 F01
Figure 1. High Current Triple Phase Step-Down Converter
3730fa
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs IOUT (Figure 14)
100
90 VFCB = OPEN
80 VFCB = 5V
70 VFCB = 0V
60
50
40
30
20
10
0
0.1
VIN = 8V
VOUT = 1.5V
1 10
LOAD CURRENT (A)
100
3730 G01
Reference Voltage vs
Temperature
610
Efficiency vs VIN (Figure 14)
100
VOUT = 1.5V
95
IOUT = 15A
f = 250kHz
90
85
IOUT = 45A
80
75
70
65
60
55
50
0
5 10 15 20 25
VIN (V)
3730 G02
Error Amplifier gm vs
Temperature
6.0
LTC3730
Efficiency vs Frequency (Figure 14)
100
95
VIN = 5V
ILOAD = 20A
VOUT = 1.5V
90
VIN = 12V
85
VIN = 8V
VIN = 20V
80
75
200
300 400 500
FREQUENCY (kHz)
600
3730 G03
Maximum ISENSE Threshold vs
Temperature
85
605 5.5 80
VO = 1.75V
600 5.0 75
VO = 0.6V
595 4.5 70
590
–50 –30 –10 10 30 50 70
TEMPERATURE (°C)
90 110
3730 G04
Oscillator Frequency vs
Temperature
700
600 VPLLFLTR = 2.4V
500
VPLLFLTR = 5V
400
VPLLFLTR = 1.2V
300
200 VPLLFLTR = 0V
100
0
–45 –30 –15 0 15 30 45 60
TEMPERATURE (°C)
75 90
3730 G07
4.0
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
3730 G05
Oscillator Frequency vs VPLLFLTR
700
600
500
400
300
200
0
0.5 1 1.5 2
PLLFLTR PIN VOLTAGE (V)
2.5
3730 G08
65
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
3730 G06
Undervoltage Reset Voltage vs
Temperature
5
4
3
2
1
0
–45 –30 –15 0 15 30 45 60
TEMPERATURE (°C)
75 90
3730 G09
3730fa
5
5 Page 
U
OPERATIO (Refer to Functional Diagram)
aligns the turn on of the top MOSFET to the rising edge of
the synchronizing signal. When no frequency information
is supplied to the PLLIN pin, PLLFLTR goes low, forcing
the oscillator to minimum frequency. A DC source can be
applied to the PLLFLTR pin to externally set the desired
operating frequency. A discharge current of approxi-
mately 20µA will be present at the pin with no PLLIN
signal.
Input capacitance ESR requirements and efficiency losses
are reduced substantially in a multiphase architecture
because the peak current drawn from the input capacitor
is effectively divided by the number of phases used and
power loss is proportional to the RMS current squared. A
3-stage, single output voltage implementation can reduce
input path power loss by 90%.
Operational Amplifier
This amplifier can be used to satisfy output voltage re-
quirements that change according to the mode of circuit or
CPU operation. The output voltage can be dropped several
hundred millivolts when using an externally switched
resistive divider based upon the activity level or speed
requirement by changing the output voltage feedback
factor. The amplifier can swing to within 1.2V of the
positive power supply at low output current (≤1mA). The
amplifier has an output slew rate of 5V/µs and is capable
of driving capacitive loads at an output sourcing RMS
current of up to 10mA.
Power Good
The PGOOD pin is connected to the drain of an internal
N-channel MOSFET. The MOSFET is turned on once an
internal delay has elapsed and the output voltage has been
away from its nominal value by greater than 10%. If the
output returns to normal prior to the delay timeout, the
timer is reset. There is no delay time for the rising of the
PGOOD output once the output voltage is within the ±10%
“window.”
LTC3730
Short-Circuit Detection
The RUN/SS capacitor is used initially to turn on and 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 over-
ridden by providing >5µA at a compliance of 3.8V to the
RUN/SS pin. This additional current shortens the soft-
start period but 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. Foldback
current limit can be overridden by clamping the EAIN pin
such that the voltage is held above the (70%)(0.6V) or
0.42V level even when the actual output voltage is low.
Input Undervoltage Reset
The RUN/SS capacitor will be reset if the input voltage
(VCC) is allowed to fall below approximately 3.8V. The
capacitor on the pin will be discharged until the short-
circuit arming latch is disarmed. The RUN/SS capacitor
will attempt to cycle through a normal soft-start ramp up
after the VCC supply rises above 3.8V. This circuit prevents
power supply latchoff in the event of input power switch-
ing break-before-make situations. The PGOOD pin is held
low during start-up until the RUN/SS capacitor rises above
the short-circuit latchoff arming threshold of approxi-
mately 3.8V.
3730fa
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3730.PDF ] | |
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