SC194AMLTRT Semtech, SC194AMLTRT Datasheet - Page 7

• Manufacturer Part Number: SC194AMLTRT
• Description: IC SYNC BUCK CONV 1A 10-MLP
• Manufacturer: Semtech
• Type: Step-Down (Buck)r

Specifications of SC194AMLTRT

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: Adjustable
• Current - Output: 1A
• Frequency - Switching: 1MHz
• Voltage - Input: 2.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MLP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: SC194AMLTR

SC194A Detailed Description
The SC194A is a synchronous step-down Pulse Width
Modulated (PWM), DC-DC converter utilizing a 1MHz
fi xed-frequency current mode architecture. The device
is designed to operate in a fi 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 effi ciency.
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 amplifi ed and summed with the
internal slope compensation network.
feedback loop uses an internal feedback divider. The on-
time is determined by comparing the summed current
feedback and the output of the error amplifi er. The period
is set by the onboard oscillator or by an external clock
attached to the SYNC/PWM pin.
The SC194A has an internal synchronous NMOS rectifi er
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
programming of the VID0 and VID1 pins (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 fi xed output confi gurations 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, fi xed-frequency mode.
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
© 2006 Semtech Corp.
POWER MANAGEMENT
Applications Information
When the SYNC/
The voltage
7
• 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".
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 effi ciency 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 effi ciency with respect to V
PRELIMINARY
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IN
SC194A
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