SC196ULTRT Semtech, SC196ULTRT Datasheet - Page 8

• Manufacturer Part Number: SC196ULTRT
• Description: IC SYNC BUCK CONV 1.5A 10-MLPD
• Manufacturer: Semtech
• Type: Step-Down (Buck)r

Specifications of SC196ULTRT

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 5.5 V
• Current - Output: 1.5A
• Frequency - Switching: 1MHz
• Voltage - Input: 2.5 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MLPD
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: SC196ULTR

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, which 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 SC196. In the
event of an over-voltage on the output, the PWM drive is
disabled, effectively tri-stating the LX output. The part will
not resume switching until the output voltage has fallen
2% below 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 through 1/8, 1/4, 1/2
and full internal oscillator frequency. The time at which
these steps are made is controlled by the output voltage
reaching predefi ned threshold levels. When 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 SC196
to automatically activate/deactivate operation at light
loads, maximizing effi ciency across the full load range.
The SC196 automatically detects the load current at which
it should enter PSAVE mode. The SC196 is optimized to
track maximum effi ciency with respect to V
In PSAVE mode, V
upper level by a switching burst. Once the upper level has
been reached, the switching is stopped and the quiescent
current is reduced. V
in this low current state as the load current discharges
© 2007 Semtech Corp.
POWER MANAGEMENT
Applications Information (Cont.)
OUT
OUT
is driven from a lower level to an
falls from the upper to lower levels
IN
.
8
the output capacitor. The burst-to-off period in PSAVE will
decrease as the load current reduces.
The PSAVE switching burst frequency is controlled so that
the inductor current ripple is similar to that in PWM mode.
The minimum switching frequency during this period is
limited to 650kHz.
The SC196 automatically detects when to exit PSAVE
mode by monitoring V
mode, the load must be increased, causing
decrease until the power save exit threshold is reached.
PSAVE levels are set high to minimize the undershoot
when exiting PSAVE. The lower PSAVE comparator level
is set +0.7% above V
at +1.5% above V
V
If PSAVE operation is required, then a 22μF output
capacitor must be used.
100% Duty Cycle Operation
The 100% duty cycle mode may be selected by connecting
the MODE pin high. This will allow the SC196 to maintain
output regulation under conditions of low input voltage/
high output voltage conditions.
In 100% duty cycle operation, as the input supply drops
toward the output voltage, the PMOS on-time increases
linearly above the maximum value in fi xed-frequency
operation until the PMOS is active continuously. Once
OUT
.
0.7%
1.5%
V
-2%
0 A
OUT
BURST
PSAVE Mode at Light Load
Inductor Current
Figure 1 — Power Save Operation
OFF
OUT
, with the exit threshold at -2% below
OUT
OUT
, and the upper comparator level
Higher Load
. For the SC196 to exit PSAVE
Applied
Time
PWM Mode at Medium/
PRELIMINARY
High Load
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SC196
V
OUT
to