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SC194A 데이터시트 PDF




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부품번호 SC194A 기능
기능 1A Synchronous Buck Converter
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SC194A 데이터시트, 핀배열, 회로
POWER MANAGEMENT
Description
The SC194A is a synchronous step-down converter with
integrated power devices. The SC194A is designed for
single-cell Li-Ion battery applications, but can also be used
in xed 3.3V or 5V applications. The switching frequency is
nominally set to 1MHz, allowing the use of small inductors
and capacitors. The 1.3A maximum current rating of the
internal MOSFET switches allows a DC output current of
1A.
The SC194A has a exible clocking methodology that
allows it to be synchronized to an external oscillator or
controlled by the internal oscillator. The device can
operate in either forced PWM mode or in PSAVE mode. If
PSAVE mode is enabled the part will automatically enter
PFM at light loads to maintain maximum efciency across
the full load range.
For noise sensitive applications, PSAVE mode can be
disabled by synchronizing to an external oscillator, or
pulling the SYNC/PWM pin high. Shutdown turns off all
the control circuitry to achieve a typical shutdown current
of 0.1μA.
SC194A
1A Synchronous Buck Converter
with Integrated Power Deviceswww.DataSheet4U.com
Features
‹ Up to 93% efciency
‹ Output current - 1A
‹ Input range - 2.7V to 5.5V
‹ Quiescent current - 17μA
‹ Four selectable output voltages
‹ Dynamic voltage positioning capability
‹ Fixed 1MHz frequency or 750kHz to 1.25MHz
synchronized operation
‹ PSAVE operation to maximize efciency at light loads
‹ Minimal external components
‹ Fast transient response
‹ 100% duty cycle in dropout
‹ Soft-start
‹ Over-temperature and short-circuit protection
‹ Space-saving lead-free package - MLP-10, 3 x 3mm
Applications
‹ Cell phones
‹ Wireless communication chipset power
‹ Personal media player
‹ Notebook and sub-notebook computers
‹ PDAs and mobile communicators
‹ WLAN peripherals
Typical Application Circuit
VIN
2.7V to 5.5V
CIN
10μF
SC194A
VIN LX
EN
SYNC/PWM
VOUT
VID0
VID1
PGND
MODE
GND
L1
4.7μH
COUT
VOUT
1.8V
1A
10μF
July 05, 2006
1 www.semtech.com




SC194A pdf, 반도체, 판매, 대치품
POWER MANAGEMENT
Pin Conguration
VIN
MODE
SYNC/
PWM
EN
VOUT
1
2
3
4
5
TOP VIEW
T
10 LX
9 PGND
8 GND
7 VID1
6 VID0
MLP10: 3X3 10 LEAD
Marking Information
SC194A
Ordering Information
www.DPatRaSEheLeItM4U.IcNomARY
DEVICE
PACKAGE
SC194AMLTRT(1)(2)
MLP 3x3-10
OrderSinC1g9I4nAfEoVrBmation
Evaluation Board
Notes:
1) Lead-free packaging only. This product is fully WEEE and RoHS compliant.
2) Available in tape and reel only. A reel contains 3000 devices.
Programmable Output Voltage
VID1
0
0
1
1
VID0
0
1
0
1
SC194A VOUT
1.0V
1.2V
1.5V
1.8V
© 2006 Semtech Corp.
4
www.semtech.com

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SC194A 전자부품, 판매, 대치품
SC194A
POWER MANAGEMENT
Applications Information
SC194A Detailed Description
The SC194A is a synchronous step-down Pulse Width
Modulated (PWM), DC-DC converter utilizing a 1MHz
xed-frequency current mode architecture. The device
is designed to operate in a xed-frequency PWM mode
across the full load range and can enter Power Save Mode
(PSAVE) utilizing Pulse Frequency Modulation (PFM) at
light loads to maximize efciency.
Operation
During normal operation the PMOS MOSFET is activated
on each rising edge of the internal oscillator. Current
feedback for the switching regulator uses the PMOS
current path, and it is amplied and summed with the
internal slope compensation network. The voltage
feedback loop uses an internal feedback divider. The on-
time is determined by comparing the summed current
feedback and the output of the error amplier. The period
is set by the onboard oscillator or by an external clock
attached to the SYNC/PWM pin.
www.DPatRaSEheLeItM4U.IcNomARY
• Over-voltage protection
• Soft-start
Thermal Shutdown
The device has a thermal shutdown feature to protect the
SC194A if the junction temperature exceeds 145°C. In
thermal shutdown the on-chip power devices are disabled,
tri-stating the LX output. Switching will resume when the
temperature drops by 10°C. During this time if the output
voltage decreases by more than 60% of its programmed
value, a soft-start will be invoked.
Current Limit
The PMOS and NMOS power devices of the buck switcher
stage are protected by current limit functions. In the
case of a short to ground on the output, the part enters
frequency foldback mode, that causes the switching
frequency to divide by a factor determined by the output
voltage. This prevents the inductor current from "stair-
casing".
The SC194A has an internal synchronous NMOS rectier
and does not require a Schottky diode on the LX pin.
Programmable Output Voltage
The SC194A has four pre-determined output voltage
values which can be individually selected by the correct
programmingoftheVID0andVID1pins(see Programmable
Output Voltage table on Page 4). This eliminates the need
for external programming resistors saving PCB area and
inventory. The VID pins can be statically tied to GND or
VIN for xed output congurations or they may be driven
by a microprocessor enabling the possibility of dynamic
voltage adjustment for host equipment "sleep" states.
Continuous Conduction & Oscillator Synchronization
The SC194A is designed to operate in continuous
conduction, xed-frequency mode. When the SYNC/
PWM pin is tied high the part runs in PWM mode using
the internal oscillator. The part can be synchronized to
an external clock by driving a clock signal into the SYNC/
PWM pin. The part synchronizes to the rising edge of the
clock.
Protection Features
The SC194A provides the following protection features:
• Thermal shutdown
• Current limit
Over-Voltage Protection
Over-voltage protection is provided on the SC194A. In the
event of an over-voltage on the output in switcher mode,
the PWM drive is disabled, tri-stating the LX output. The
part will not resume switching until the output voltage has
fallen below 2% of the regulation voltage.
Soft-Start
The soft-start mode is enabled after every shutdown cycle
to limit in-rush current. In conjunction with the frequency
foldback, this controls the maximum current during start-
up. The PMOS current limit is stepped up through seven
soft-start levels to the full value by a timer driven from
the internal oscillator. During soft-start, the switching
frequency is stepped by 1/8, 1/4, and 1/2 of the internal
oscillator frequency up to the full value, under control of
three output voltage thresholds. As soon as the output
voltage is within 2% of the regulation voltage, soft-start
mode is disabled.
Power Save Mode Operation
The PSAVE mode may be selected by tying the SYNC/PWM
pin to GND. Selecting PSAVE mode will enable the SC194A
to automatically activate/deactivate operation at light
loads maximizing efciency across the full load range. The
SC194A automatically detects the load current at which it
should enter PSAVE mode. The SC194A is optimized to
track maximum efciency with respect to VIN.
© 2006 Semtech Corp.
7
www.semtech.com

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