SC195ULTRT Semtech, SC195ULTRT Datasheet - Page 14

• Manufacturer Part Number: SC195ULTRT
• Description: IC BUCK ADJ .5A 8-MLPQ
• Manufacturer: Semtech
• Type: Step-Down (Buck)r

Specifications of SC195ULTRT

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 3.3 V
• Current - Output: 500mA
• Frequency - Switching: 3.5MHz
• Voltage - Input: 2.9 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-MLPQ
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: SC195ULTR

Applications Information (continued)
Protection Features
The SC195 provides the following protection features:
Soft-Start
The soft-start sequence is activated after a transition from
an all zeros CTL code to a non-zero CTL code enables the
device. At start-up, the PMOS current limit is stepped
through four levels: 25%, 40%, 60%, and 100%. Each step
is maintained for 60μs following an internal reference start
up of 20μs, resulting in a total nominal start-up period of
260μs. If V
steps, the device continues in PSAVE mode at the end of
soft-start; otherwise, it goes into PWM mode. Note the
V
PWM mode.
Over-Voltage Protection
Over-voltage protection ensures the output voltage does
not rise to a level that could damage its load. When V
exceeds the regulation voltage by 15%, the PWM drive is
Figure 2 — Transitions Between PWM and PSAVE Modes
V
OUT
Demand
•
•
•
•
•
OUT
V
(I
Load
OUT
ripple in PSAVE mode can be larger than the ripple in
OUT
+2.5%
V
Soft-Start Operation
Over-Voltage Protection
Current Limit
Thermal Shutdown
Under-Voltage Lockout
V
PWM Mode at
OUT
-2%
LX
Medium/High
)
OUT
Load
reaches 90% of the target within the first 2
BURST
OFF
PSAVE Mode at
Light Load
Time
PWM Mode at
Medium/High
Load
PSAVE
EXIT
OUT
disabled. Switching does not resume until V
below the regulation voltage by 2%.
Current Limit
The SC195 switching stage is protected by a current limit
function. If the output load exceeds the PMOS current
limit for 32 consecutive switching cycles, the device enters
fold-back current limit mode and the output current is
limited to approximately 150mA. Under these conditions,
the output voltage will be the product of I
resistance. The load must fall below I
exit fold-back current limit mode. This function makes the
device capable of sustaining an indefinite short circuit on
its output under fault conditions.
Thermal Shutdown
The SC195 has a thermal shutdown feature to protect the
device if the junction temperature exceeds 160°C. During
thermal shutdown, the PMOS and NMOS switches are
both disabled, tri-stating the LX output. When the junc-
tion temperature drops by the hysteresis value (20°C), the
device goes through the soft-start process and resumes
normal operation.
Under-Voltage Lockout
Under-Voltage Lockout (UVLO) activates when the supply
voltage drops below the UVLO threshold. This prevents
the device from entering an ambiguous state in which
regulation cannot be maintained. Hysteresis of approxi-
mately 200mV is included to prevent chattering near the
threshold.
Inductor Selection
The SC195 is designed to operate with a 1µH inductor
between the LX pin and the OUT pin. Other values may
lead to instability, malfunction, or out-of-specification
performance. The specified current levels for PSAVE entry,
PSAVE exit, and current limit are dependent on the induc-
tor value.
The SC195 converter has internal loop compensation. The
compensation is designed to work with a specific single-
FB-LIM
FB-LIM
for the device to
OUT
and the load
has fallen
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