SC198MLTRT Semtech, SC198MLTRT Datasheet - Page 8

• Manufacturer Part Number: SC198MLTRT
• Description: IC DUAL DC-DC BUCK CONV 20-MLPQ
• Manufacturer: Semtech
• Type: Step-Down (Buck)r

Specifications of SC198MLTRT

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: Programmable
• Current - Output: 600mA
• Frequency - Switching: 1MHz
• Voltage - Input: 2.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-MLPQ
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: SC198MLTR

In PSAVE mode, V
in switching. While the output voltage is between the
low and high voltage thresholds, switching is stopped to
reduce loss in the regulator due to switching. When the
voltage drops to the lower threshold, the switch bursts
at a fi xed on time until the upper threshold is met. At
this point the output voltage is allowed to ramp down to
the lower threshold again without switching to conserve
power. In the PSAVE mode, less switching is used. Less
switching results in less power loss which can be seen
in the difference of effi ciency between PWM mode and
PSAVE mode at light loads.
The PSAVE switching burst frequency is controlled such
that the inductor current ripple during the burst is similar
to that in PWM mode. The minimum switching frequency
during this period is limited to 650kHz.
The SC198 automatically detects when to exit PSAVE
mode.
PSAVE mode, and then detects when V
load increasing above the level that the peak current will
support.
For the SC198 to exit PSAVE mode, the load must be
increased, which causes V
exit threshold is reached. PSAVE levels are set high to
minimize the undershoot when the SC198 exits PSAVE.
POWER MANAGEMENT
Applications Information (Cont.)
© 2007 Semtech Corp.
Threshold Limit
Threshold Limit
PSAVE Exit
Threshold
Upper
Lower
V
0 A
OUT
The device sets a maximum peak current in
PSAVE Mode at Light Load
BURST
Inductor Current
OFF
OUT
PSAVE Operation
regulation is controlled by bursts
OUT
Higher Load
Applied
Time
to decrease until the PSAVE
NOT RECOMMENDED FOR NEW DESIGN
PWM Mode at Medium/
OUT
falls due to the
High Load
8
Protection Features
The SC198 provides the following protection features:
Thermal Shutdown
The device has a thermal shutdown feature to protect the
SC198 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 frequen-
cy foldback mode, that causes the switching frequency to
divide by a factor determined by the output voltage. This
prevents the inductor current from “staircasing”.
Over-Voltage Protection
Over-voltage protection is provided on the SC198.
Hysteresis is provided to prevent toggling in and out of
operation.
Soft-Start
The soft-start mode operates by limiting the current through
the inductor and controlling the switching frequency. The
current limit is increased over several milliseconds the in
discrete steps. This has the desired effect of limiting in-
rush current from the input supply. The soft-start mode is
cancelled once the output reaches regulation. Soft-start
is only re-enabled by power cycling, toggling enable, UVLO
event, or shutdown.
Thermal Shutdown
Current Limit
Over-Voltage Protection
Soft-Start
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SC198