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PDF LTC1705 Data sheet ( Hoja de datos )
| Número de pieza | LTC1705 | |
| Descripción | Dual 550kHz Synchronous Switching Regulator Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC1705
FEATURES
Dual 550kHz Synchronous
Switching Regulator Controller with
5-Bit VID and 150mA LDO
DESCRIPTIO
s Three Regulated Outputs: Core, I/O and CLK in One
Package
s Integrated Intel Mobile 5-Bit VID DAC
s No External Current Sense Resistors
s All N-Channel External MOSFET Architecture
s 550kHz Switching Frequency Minimizes External
Component Size and Cost
s Integrated 150mA LDO Linear Regulator
s Excellent DC Accuracy: 1.25% for Core, 2% for I/O
and CLK Supplies
s PGOOD Flag Monitors All Three Outputs
s High Efficiency Over Wide Load Current Range
s Low Shutdown Current: < 100µA
s Switchers Run Out-of-Phase to Minimize CIN
s Small 28-Pin Narrow SSOP Package
U
APPLICATIO S
s Complete Power Supply Controller for Intel
Mobile Pentium® Processors
s Intel Mobile Pentium Core, I/O, Clock Supplies
s Multiple Logic Supply Generator
The LTC®1705 is a complete power supply controller for
Intel Mobile Pentium processors. It includes two switch-
ing regulator controllers, each designed to drive a pair of
N-channel MOSFETs in a voltage mode feedback, syn-
chronous buck configuration, to provide the core and I/O
supplies. The core controller includes a 5-bit DAC that
conforms to the Intel Mobile VID specification. The IC also
includes a low dropout linear regulator (LDO) that delivers
up to 150mA of output current to provide the CLK supply.
The LTC1705 uses a constant-frequency 550kHz PWM
architecture, minimizing external component size and
cost, as well as optimizing load transient performance. It
provides better than 1.25% DC accuracy at its core output,
and 2% at I/0 and CLK outputs. The high performance
feedback loops allow the circuit to keep total output
regulation within ±5% under all transient conditions. An
open-drain PGOOD flag indicates that all three outputs are
within ±10% of their regulated values. A shutdown circuit
disables all three outputs if the RUN/SS pin is pulled to
ground. In this mode, the LTC1705 supply current drops
to below 100µA.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
TYPICAL APPLICATIO
Intel Mobile Pentium VRM Supply
VIN
5V
CIN
330µF
+
1µF
10V
DCPC
MBR
×3 0520LT1
QTCA QTCB
5
LC
0.68µH
CCPC
1µF
3
6
VOUTC
0.9V TO 2V
15A
1µF +
COUTC
180µF
4V
×6
QBCB
QBCA
4
RIMAXC, 27k 8
13
11
R31 C11
C31 1.8k 1800pF
1800pF
SHUTDOWN
CIN: KEMET T510X337K010AS
COUTC: PANASONIC EEFUE0G181R
COUTIO: AVX TPS0107M010R0065
LC: SUMIDA CEP125-4712-T007
LIO: SUMIDA CDRH6D28-3R0
QTCA, QTCB, QBCA, QBCB: FAIRCHILD FDS6670A
QTIO, QBIO: 1/2 FAIRCHILD NDS8926
R21, 11k
10k
C21
330pF
CSS
0.1µF
10
9
7
12
14–18
5-BIT VID
RPGOOD
5k
2 22
PVCC
TGC
BOOSTC
PGOOD
SWC
BGC
IMAXC
SENSEC
FBC
LTC1705
COMPC
RUN/SS
PGND
GND
VID4:0
10Ω 10µF
19
DCPIO
MBR
0520LT1
VCC 26
TGIO
27
BOOSTIO
25
SWIO
CCPIO
1µF
BGIO
IMAXIO
COMPIO
FBIO
28
1 RIMAXI0, 16k
21 R22, 11k
C22
20 100pF
QTIO
LIO
3µH
QBIO
COUTIO
100µF
+
10V
×2
C12
2200pF
RB2
10k
1%
VINCLK
VOUTCLK
24
+
23
CVINCLK
10µF
10V
+CVOUTCLK
10µF
10V
VINCLK
3.3V
VOUTCLK
2.5V
150mA
1µF
1µF
R12
8.87k
1%
VOUTIO
1.5V
3A
1705 TA01
1
1 page  
LTC1705
TYPICAL PERFOR A CE CHARACTERISTICS
I/O Supply Efficiency
100
VIN = 5V, VOUT = 1.5V, TA = 25°C,
CORE DISABLED, QTIO = QBIO = NDS8926
90
80
70
VOUTC 0A To 10A Load Step
0A TO 10A
LOAD
5A/DIV
VOUT = 1.6V
AC 50mV/
DIV
60
5ms/DIV
1705 G08
Current Limit Threshold vs
Temperature
24
VIN = 5V, VOUT = 1.6V, ∆VOUT = –1%,
22 RIMAXC = 24.9k, QTC = QBC = 2× FDS6670A
20
18
16
14
12
50
0 0.5 1 1.5
ILOAD (A)
VOUTC vs Load Current
2.0
2 2.5
1705 G07
1.5
1.0
0.5
0
0
TA = 25°C, VIN = 5V,
VOUT = 1.6V,
QBC = 2× FDS6670A,
RIMAXC = 24.9k,
CRUNSS = 0.01µF
4 8 12
LOAD CURRENT (A)
16
20
1705 G10
VOUTCLK vs Temperature
2.55
2.54 VINCLK = 3.3V
2.53
2.52
2.51
2.50
2.49
2.48
2.47
2.46
2.45
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1705 G11
10
–50 –25
0 25 50 75 100 125
TEMPERATURE (°C)
VOUTCLK Line Regulation
1705 G09
2.5
2.0 TA = 25°C
0.10
0.08
1.5 0.06
1.0 0.04
0.5 0.02
00
–0.5 –0.02
–1.0 –0.04
–1.5 –0.06
–2.0 –0.08
–2.5 –0.10
3 3.5 4 4.5 5 5.5 6
VINCLK (V)
1705 G12
VOUTCLK Load Regulation
0.5
TA = 25°C
0
0.02
0
–0.5 –0.02
–1.0 –0.04
–1.5 –0.06
–2.0 –0.08
–2.5
–150 –125 –100 –75 –50
IOUTCLK (mA)
–0.10
–25 0
1705 G13
VOUTCLK Dropout Voltage vs
Temperature
500
450 IOUTCLK = –150mA
400
VOUTCLK Short-Circuit Current vs
Temperature
–150
VINCLK = 3.3V
–190
350 –230
300
250 –270
200
–310
150
100
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1705 G14
–350
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1705 G15
5
5 Page 
LTC1705
APPLICATIO S I FOR ATIO
The LTC1705 includes two, step-down (buck), voltage
mode feedback switching regulator controllers and a low
dropout linear regulator. The three outputs are designed to
power the core, I/O and CLK supplies of an Intel Mobile
Pentium system. Each switching regulator controller em-
ploys a synchronous switching architecture with two
external N-channel MOSFETs per channel. The chip oper-
ates from a low voltage input supply (6V maximum) and
provides high power, high efficiency, precisely regulated
output voltages. Several features make the LTC1705 par-
ticularly suited for microprocessor supply regulation.
Output regulation at the core supply is extremely tight,
with initial accuracy and DC line and load regulation better
than 1.25%. Total regulation including transient response
is inside of 3.5% with a properly designed circuit. The
550kHz switching frequency and the high speed internal
feedback amplifiers allow the use of physically small, low
value external components without compromising perfor-
mance. An onboard 5-bit DAC sets the core output voltage,
consistent with the Intel Mobile VID specification (Table␣ 1).
The 800mV internal reference allows regulated output
voltages as low as 800mV without external level shifting
amplifiers. The linear regulator controls an internal P-
channel MOSFET that can provide more than 150mA of
current at an output voltage of 2.5V. A power good
(PGOOD) flag goes high when all the three outputs are in
regulation.
2-Step Conversion
“2-step” architectures use a primary regulator to convert
the input power source (batteries or AC line voltage) to an
intermediate supply voltage, often 5V. This intermediate
voltage is then converted to the low voltage, high current
supplies required by the system using a secondary regula-
tor, such as the LTC1705. 2-step conversion eliminates the
need for a single converter to convert a high input voltage
to a very low output voltage, often an awkward design
challenge. It also fits naturally into systems that continue to
use the 5V supply to power portions of their circuitry or have
excess 5V capacity available as newer circuit designs shift
the current load to lower voltage supplies.
Each regulator in a typical 2-step system maintains a
relatively low step-down ratio (5:1 or less), running at high
efficiency while maintaining reasonable duty cycle. In
contrast, a regulator converting in a single step from a high
input voltage to a 1.xV output must operate at a very
narrow duty cycle, mandating trade-offs in external com-
ponent values while compromising efficiency and tran-
sient response. The efficiency loss can exceed that of a
2-step solution. Further complicating the calculation is the
fact that many systems draw a significant fraction of their
total power off the intermediate 5V supply, bypassing the
low voltage supply. 2-step solutions using the LTC1705
usually match or exceed the total system efficiency of
single-step solutions and provide the additional benefits
of improved transient response, reduced PCB area and
simplified power trace routing.
2-step regulation can also buy advantages in thermal
management. Power dissipation in the LTC1705 portion
of a 2-step circuit is lower than it would be in a typical
1-step converter, even in cases where the 1-step converter
has higher total efficiency than the 2-step system. In a
typical microprocessor core supply regulator, for ex-
ample, the regulator is usually located directly next to the
CPU. In a 1-step design, all of the power dissipated by the
core regulator is located next to the already hot CPU,
aggravating thermal management. In a 2-step LTC1705
design, a significant percentage of the power lost in the
core regulation system happens in the 5V supply, which is
usually located away from the CPU. The power lost to heat
in the LTC1705 section of the system is relatively low,
minimizing the added heat near the CPU.
Fast Transient Response
The LTC1705 core and I/O supplies use fast 20MHz GBW
op amps as error amplifiers. This allows the compensation
network to be designed with several poles and zeros in a
more flexible configuration than with typical gm feedback
amplifiers. The high bandwidth of the amplifier, coupled
with the high 550kHz switching frequency and the low
values of the external inductor and output capacitor, allow
very high loop cross-over frequencies. Additionally, a
typical LTC1705 circuit uses an inductor value on the
order of 1µH, allowing very fast di/dt slew rates. The result
is superior transient response compared with conven-
tional solutions.
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC1705.PDF ] | |
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