SC194AMLTRT Semtech, SC194AMLTRT Datasheet - Page 8

• 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

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
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 SC194A 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.
© 2006 Semtech Corp.
POWER MANAGEMENT
Applications Information (Cont.)
OUT
.
0.7%
1.5%
V
-2%
0 A
OUT
BURST
PSAVE Mode at Light Load
Inductor Current
OFF
Power Save Operation
OUT
OUT
, with the exit threshold at -2% below
OUT
OUT
is driven from a lower level to an
OUT
falls from the upper to lower levels
, and the upper comparator level
. For the SC194A to exit PSAVE
Higher Load
Applied
Time
PWM Mode at Medium/
High Load
V
OUT
to
8
100% Duty Cycle Operation
The 100% duty cycle mode may be selected by connecting
the MODE pin high. This will allow the SC194A to maintain
output regulation under 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
the PMOS is switched on continuously, the output voltage
tracks the input voltage minus the voltage drop across
the PMOS power device and inductor according to the
following relationship:
where,
The 100% duty cycle can only operate for a programmed
output voltage of 1.8V.
With an output voltage of 1.8V, 100% duty cycle mode will
only be required to maintain regulation if V
minimum value shown in the graph below.
Minimum V
2.95
2.85
2.75
2.9
2.8
2.7
3
0.05
V
V
I
R
R
OUT
OUT
IN
DSP
IND
IN
0.1
= Output voltage
= Input voltage
= Output current
= PMOS switch ON resistance
= Series resistance of the inductor
for Fixed Frequency Operation Vs. R
V
V
OUT
OUT
=
=
V
V
Inductor DC R esistance
N I
N I
0.15
−
−
I
I
OUT
OUT
×
×
R (
R (
0.2
DSP
DSP
(
Ω
)
+
+
R
R
IND
IND
PRELIMINARY
)
)
V
0.25
OUT
I
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OUT
IN
= 1.8V
=1A
SC194A
falls below a
0.3
IND