SC194BMLTRT Semtech, SC194BMLTRT Datasheet - Page 7

• Manufacturer Part Number: SC194BMLTRT
• Description: IC SYNC BUCK CONV 1A 10-MLP
• Manufacturer: Semtech
• Type: Step-Down (Buck)r

Specifications of SC194BMLTRT

• 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: SC194BMLTR

SC194B Detailed Description
The SC194B 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 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 is through the
PMOS current path, and it is amplifi ed 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 amplifi er. The period
is set by the onboard oscillator or by an external clock
attached to the SYNC/PWM pin.
The SC194B has an internal synchronous NMOS rectifi er
and does not require a Schottky diode on the LX pin.
Programmable Output Voltage
The SC194B 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.
Oscillator Synchronization Opotions
The SC194B is designed to operate in continuous
conduction, fi 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 SC194B provides the following protection features:
© 2006 Semtech Corp.
POWER MANAGEMENT
Applications Information
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Thermal shutdown
Current limit
7
Thermal Shutdown
The device has a thermal shutdown feature to protect the
SC194B 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 SC194B. 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 SC194B
to automatically activate/deactivate operation at light
loads maximizing effi ciency across the full load range. The
SC194B automatically detects the load current at which
it should enter PSAVE mode. The SC194B is optimized to
track maximum effi ciency with respect to V
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Over-voltage protection
Soft-start
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SC194B
IN
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