sc1453itsk30trt Semtech Corporation, sc1453itsk30trt Datasheet - Page 7

• Manufacturer Part Number: sc1453itsk30trt
• Description: Sc1453 150 Ma Ultra-low Dropout Regulator With Low Noise Bypass
• Manufacturer: Semtech Corporation

Theory Of Operation
The SC1453 is intended for applications where very low
dropout voltage, low supply current and low output noise
are critical. It provides a very simple, low cost solution
that uses very little pcb real estate. Only three external
capacitors are required for operation (two if a low noise
output is not required).
The SC1453 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.
A bypass pin (BYP) is provided to decouple the bandgap
reference to reduce output noise and also to improve
power supply rejection. This pin can be left open if low
noise operation is not required.
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 SC1453 has a fast start-up circuit to speed up the
initial charging time of the bypass capacitor to enable
the output voltage to come up quicker (typically 1.3ms
with C
The SC1453 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.
POWER MANAGEMENT
Applications Information
2008 Semtech Corp.
BYP
= 10nF).
J
exceeds 150°C (typical), with the
J
drops by 20°C (typical).
DS(ON)
7
Component Selection - General
Output capacitor - Semtech recommends a minimum
capacitance of 1µF at the output with an equivalent
series resistance (ESR) of < 1
the SC1453 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.
Bypass capacitor - Semtech recommends the use of a
10nF ceramic capacitor to bypass the bandgap
reference. Increasing this capacitor to 100nF will
further improve power supply rejection and overall
output noise. C
is not required.
Thermal Considerations
The worst-case power dissipation for this part is given
by:
For all practical purposes, equation (1) can be reduced
to the following expression:
Looking at a typical application, 3.3V to 2.8V at 150mA:
V
V
I
T
P
P
OUT
A
IN(MAX)
OUT(MIN)
D
D
(
(
= 85°C
MAX
MAX
= 150mA
)
)
= 3.3 + 5% = 3.465V
= 2.8V - 2% = 2.744V
V
V
IN
IN
(
(
MAX
MAX
BYP
)
)
V
V
may be omitted if low noise operation
OUT
OUT
(
(
MIN
MIN
)
)
I
I
OUT
OUT
(
(
MAX
MAX
over temperature. While
)
)
V
IN
(
MAX
SC1453
www.semtech.com
)
I
Q
(
MAX
)
(1)
(2)