sc1457isk-1.5tr Semtech Corporation, sc1457isk-1.5tr Datasheet - Page 5

• Manufacturer Part Number: sc1457isk-1.5tr
• Description: Sc1457 150 Ma Ultra-low Dropout Regulator With Undervoltage Flag
• Manufacturer: Semtech Corporation

Theory Of Operation
The SC1457 is intended for applications where very low
dropout voltage, low supply current and output voltage
monitoring are critical. It provides a very simple, low cost
solution that uses very little pcb real estate. Only two
external capacitors and one resistor are required for
operation.
The SC1457 contains a bandgap reference trimmed for
optimal temperature coefficient which is fed into the
inverting input of an error amplifier. The output voltage
of the regulator is divided down internally using a
resistor divider and compared to the bandgap voltage.
The error amplifier drives the gate of a low R
P-channel MOSFET pass device.
An active high enable pin (EN) allows the regulator to be
shut down. Pulling this pin low causes the device to
enter a very low power shutdown mode, where it will draw
typically 0.1µA from the input supply.
An open drain flag pin (FLG) is provided to signal
whenever the output voltage is 6% (typically) below
nominal. A tap is taken from the internal resistor divider
and compared to the bandgap voltage to determine if
the output voltage is above or below this level. The flag
pin pulls low whenever the output is out of specification.
An external pullup resistor is required for a high signal
when the flag pin is not pulling low. Since this circuitry is
powered from the input supply, the FLG pin will pull low
for output voltages all the way down to zero, unlike
external devices powered from the LDO output.
POWER MANAGEMENT
Marking Information
Applications Information
2004 Semtech Corp.
x = package (5 for SOT-23-5, T for TSOT-23-5)
(examples: 5731 for 3.1V option in SOT-23-5,
T728 for 2.8V option in TSOT-23-5)
XX = voltage option
x7XX
7 = SC1457
Top Mark
DS(ON)
5
The regulator has its own current limit circuitry to
ensure that the output current will not damage the
device during output short, overload or start-up. The
current limit is guaranteed to be greater than 400mA to
allow fast charging of the output capacitor and high
initial currents for DSP initialization.
The SC1457 includes thermal shutdown circuitry to turn
off the device if T
device remaining off until T
Reverse battery protection circuitry ensures that the
device cannot be damaged if the input supply is
accidentally reversed, limiting the reverse current to less
than 1.5mA.
Component Selection - General
Output capacitor - Semtech recommends a minimum
capacitance of 1µF at the output with an equivalent
series resistance (ESR) of < 1
the SC1457 has been designed to be used with ceramic
capacitors, it does not have to be used with ceramic
capacitors, allowing the designer a choice. Increasing the
bulk capacitance will further reduce output noise and
improve the overall transient response.
Input capacitor - Semtech recommends the use of a
1µF ceramic capacitor at the input. This allows for the
device being some distance from any bulk capacitance
on the rail. Additionally, input droop due to load transients
is reduced, improving overall load transient response.
Flag pullup resistor - Semtech recommends a maximum
value of 100k
high even under worst-case flag pin leakage conditions
of 1µA when off.
(example: 0008 for week 8 of 2000)
for this resistor to ensure that this pin is
yyww = Date code
J
exceeds 150°C (typical), with the
Bottom Mark
yyww
J
drops by 20°C (typical).
over temperature. While
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SC1457