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PDF LTC3613 Data sheet ( Hoja de datos )
| Número de pieza | LTC3613 | |
| Descripción | 15A Monolithic Step Down Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3613
FEATURES
24V, 15A Monolithic
Step Down Regulator with
Differential Output Sensing
DESCRIPTION
n Wide VIN Range: 4.5V to 24V;
VOUT Range: 0.6V to 5.5V at up to 15A
n 0.67% Output Voltage Accuracy
n Controlled On-Time Valley Current Mode Architecture,
Excellent Current Sharing Capability
n Frequency Programmable from 200kHz to 1MHz
and Synchronizable to External Clock
n RSENSE or Inductor DCR Current Sensing With
Accurate Current Limit
n Fast Transient Response
n Differential Output Voltage Sensing Allowing 500mV
Common Mode Remote Ground
n tON(MIN) = 65ns; tOFF(MIN) = 105ns
n Overvoltage Protection and Current Limit Foldback
n Power Good Output Voltage Monitor
n Voltage Tracking Start-Up
n External VCC Input for Bypassing Internal LDO
n Micropower Shutdown: IQ = 15μA
n 7mm × 9mm 56-pin QFN Package
APPLICATIONS
n Distributed Power System
n Point-of-Load Converters
n Servers
The LTC®3613 is a monolithic synchronous step-down
switching regulator capable of regulating outputs from 0.6V
to 5.5V with up to 15A output current. The controlled on-time
constantfrequencyvalleycurrentmodearchitectureallowsfor
both fast transient response and constant frequency switch-
ing in steady-state operation, independent of VIN, VOUT and
load. This also provides excellent current sharing capability.
Differential output voltage sensing along with a precision
internal reference combine to offer ±0.67% output regula-
tion, even if the output ground reference deviates from
local ground by 500mV. The switching frequency can be
programmed from 200kHz to 1MHz with an external resis-
tor. The switching frequency is also phase synchronizable
to an external clock in applications where switching noise/
EMI reduction is crucial.
Very low tON and tOFF times allow for near 0% and near 100%
duty cycles, respectively. Voltage tracking soft start-up is
provided for tracking and sequencing applications. Safety fea-
tures include output overvoltage protection, programmable
current limit with foldback, and power good monitoring.
L, LT, LTC, LTM, OPTI-LOOP, Linear Technology and the Linear logo are registered trademarks
and Hot Swap and No RSENSE is a trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents including
5481178, 5487554, 6580258, 6304066, 6476589, 6774611.
TYPICAL APPLICATION
High Efficiency High Power Step-Down Converter
INTVCC
PVIN
SVIN
100k
0.1μF
47pF
LTC3613
PGOOD
VOUT
RUN
VRNG
SENSE–
SENSE+
MODE/PLLIN
EXTVCC
SW
TRACK/SS BOOST
270pF
21k
115k
ITH
RT
SGND
INTVCC
PGND
VOSNS+
VOSNS–
3613 TA01
VIN
+ 4.5V TO 24V
0.1μF
82μF
10Ω
1000pF 10Ω
0.47μH
0.1μF
1.5mΩ
15k
4.7μF
10k
+
VOUT
1.5V
15A
330μF
×2
Efficiency and Power Loss
vs Load Current
100
90 PULSE-SKIPPING MODE
80
70
3.5
3.0
2.5
60
FORCED
2.0
50 CONTINUOUS
40 MODE 1.5
30
20
10
0
0.01
1.0
VIN = 12V
VOUT = 1.5V
0.1 1 10
LOAD CURRENT (A)
0.5
0
3613 TA01a
3613f
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LTC3613
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise noted
Transient Response:
Forced Continuous Mode
Load Step:
Forced Continuous Mode
Load Release:
Forced Continuous Mode
VOUT
100mV/DIV
IL
10A/DIV
ILOAD
10A/DIV
40μs/DIV
LOAD TRANSIENT = 0A TO 15A
VIN = 12V, VOUT = 1.5V
FIGURE 10 CIRCUIT
VOUT
100mV/DIV
IL
10A/DIV
3613 G01
ILOAD
10A/DIV
10μs/DIV
LOAD STEP = 0A TO 15A
VIN = 12V, VOUT = 1.5V
FIGURE 10 CIRCUIT
VOUT
100mV/DIV
IL
10A/DIV
ILOAD
10A/DIV
3613 G02
10μs/DIV
LOAD RELEASE = 15A TO 0A
VIN = 12V, VOUT = 1.5V
FIGURE 10 CIRCUIT
3613 G03
Transient Response:
Pulse-Skipping Mode
Load Step: Pulse-Skipping Mode
Load Release:
Pulse-Skipping Mode
VOUT
100mV/DIV
IL
10A/DIV
ILOAD
10A/DIV
VOUT
100mV/DIV
IL
10A/DIV
ILOAD
10A/DIV
40μs/DIV
LOAD TRANSIENT = 500mA TO 15A
VIN = 12V, VOUT = 1.5V
FIGURE 10 CIRCUIT
3613 G04
10μs/DIV
LOAD STEP = 500mA TO 15A
VIN = 12V, VOUT = 1.5V
FIGURE 10 CIRCUIT
VOUT
100mV/DIV
IL
10A/DIV
ILOAD
10A/DIV
3613 G05
10μs/DIV
LOAD RELEASE = 15A TO 500mA
VIN = 12V, VOUT = 1.5V
FIGURE 10 CIRCUIT
3613 G06
Normal Soft Start-Up
Soft Start-Up into
a Pre-Biased Output
Output Tracking
VIN
5V/DIV
TRACK/SS
500mV/DIV
VOUT
1V/DIV
VIN = 12V
4ms/DIV
VOUT = 1.5V
FIGURE 10 CIRCUIT
VIN
5V/DIV
TRACK/SS
500mV/DIV
VOUT
1V/DIV
VOUT PRE-BIASED TO 0.75V
3613 G07
VIN = 12V
2ms/DIV
VOUT = 1.5V
FIGURE 10 CIRCUIT
TRACK/SS
500mV/DIV
3613 G08
VOUT
1V/DIV
VIN = 12V
10ms/DIV
VOUT = 1.5V
FIGURE 10 CIRCUIT
3613 G09
3613f
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OPERATION (Refer to Functional Diagram)
LTC3613
Main Control Loop
The LTC3613 uses valley current mode control to regulate
the output voltage in a monolithic, all N-channel MOSFET
DC/DC step-down converter. Current control is achieved by
sensing the inductor current across SENSE+ and SENSE–,
either by using an explicit resistor connected in series with
the inductor or by implicitly sensing the inductor’s resis-
tive (DCR) voltage drop through an RC filter connected
across the inductor.
In normal steady-state operation, the top MOSFET is turned
on for a fixed time interval proportional to the delay in the
one-shot timer. The PLL system adjusts the delay in the
one-shot timer until the top MOSFET turn-on is synchro-
nized either to the internal oscillator or the external clock
input if provided. As the top MOSFET turns off, the bottom
MOSFET turns on with a small time delay (dead time) to
avoid shoot-through current. The next switching cycle is
initiated when the current comparator, ICMP, senses that
inductor current has reached the valley threshold point
and turns the bottom MOSFET off immediately and the
top MOSFET on. Again in order to avoid shoot-through
current there is a small dead time delay before the top
MOSFET turns on.
The voltage on the ITH pin sets the ICMP valley threshold
point. The error amplifier, EA, adjusts this ITH voltage
by comparing the differential feedback signal, VOSNS+ −
VOSNS–, to a 0.6V internal reference voltage. Consequently,
the LTC3613 regulates the output voltage by forcing the
differential feedback voltage to be equal to the 0.6V internal
reference. The difference amplifier, DA, converts the dif-
ferential feedback signal to a single-ended input for the
EA. If the load current increases, it causes a drop in the
differential feedback voltage relative to the reference. The
EA forces ITH voltage to rise until the average inductor
current again matches the load current.
Differential Output Sensing
The output voltage is resistively divided externally to create
a feedback voltage for the controller. The internal difference
amplifier, DA, senses this feedback voltage along with the
output’s remote ground reference to create a differential
feedback voltage. This scheme overcomes any ground
offsets between local ground and remote output ground,
resulting in a more accurate output voltage. The LTC3613
allows for remote output ground deviations as much as
±500mV with respect to local ground.
INTVCC/EXTVCC Power
Power for the top and bottom MOSFET drivers and most
otherinternalcircuitryisderivedfromtheINTVCC pin.Power
on the INTVCC pin is derived in two ways: if the EXTVCC
pin is below 4.6V, then an internal 5.3V low dropout linear
regulator, LDO, supplies INTVCC power from PVIN; if the
EXTVCC pin is tied to an external source larger than 4.6V,
then the LDO is shut down and an internal switch shorts
the EXTVCC pin to the INTVCC pin, thereby powering the
INTVCC pin with the external source and helping to increase
overall efficiency and decrease internal self heating through
power dissipated in the LDO. This external power source
could be the output of the step-down switching regulator
itself if the output is programmed to higher than 4.6V.
The top MOSFET driver is biased from the floating boot-
strap capacitor, CB, which normally recharges during
each off cycle through an external Schottky diode when
the top MOSFET turns off. If the VIN voltage is low and
INTVCC drops below 3.65V, undervoltage lockout circuitry
disables the external MOSFET driver and prevents the
power switches from turning on.
3613f
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| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3613.PDF ] | |
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