150mA Ultra Low Dropout
Regulator with Undervoltage Flag
POWER MANAGEMENT
Description
The SC1457 is a low dropout linear regulator that
operates from a +2.25V to +6.5V input range and
delivers up to 150mA. A PMOS pass transistor allows
the low 75µA supply current to remain independent of
load, making these devices ideal for battery operated
portable equipment such as cellular phones, cordless
phones and personal digital assistants.
The SC1457 has very low dropout voltage (typically 1.1mV
at light loads and 150mV at 150mA) with better than
1.5% initial output voltage accuracy. It has a logic
compatible enable control input and an internal output
undervoltage monitor.
Designed especially for hand held, battery powered
devices, the SC1457 can be switched by a CMOS or TTL
compatible logic signal. When disabled, power
consumption drops nearly to zero. Other features include
short circuit protection, thermal shutdown protection and
reverse battery protection.
The SC1457 is available in several fixed voltages in the
tiny 5 lead SOT-23 package and the ultra low profile 5
lead TSOT-23.
SC1457
Features
Guaranteed 150mA output current
Error flag indicates output undervoltage fault
2% output accuracy guaranteed over line, load and
temperature
Very small external components - designed to work
with ceramic capacitors
Low 110µV
RMS
output noise
Very low supply current
Thermal overload protection
Reverse battery protection
Low power shutdown
Full industrial temperature range
Very low profile packaging available (1mm max.
height)
Surface mount packaging (SOT-23-5 and
TSOT-23-5)
Applications
Battery Powered Systems
Cellular Telephones
Cordless Telephones
Personal Digital Assistants
Portable Instrumentation
Modems
PCMCIA cards
Typical Application Circuit
U1
VIN
C1
1uF
1
3
IN
EN
SC1457
OUT
GND
2
FLG
5
4
R1
100k
C2
1uF
UNDERVOLTAGE FLAG
VO
Revision: November 10, 2004
1
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SC1457
POWER MANAGEMENT
Absolute Maximum Ratings
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified
in the Electrical Characteristics section is not implied. Exposure to Absolute Maximum rated conditions for extended periods of time may affect device
reliability.
Parameter
Input Supply Voltage
I/O Pin Voltages
Thermal Resistance Junction to Ambient
Thermal Resistance Junction to Case
Operating Ambient Temperature Range
Operating Junction Temperature Range
Storage Temperature Range
Lead Temperature (Soldering) 10 seconds
ESD Rating (Human Body Model)
Symbol
V
IN
V
EN
, V
FLG
θ
J A
θ
J C
T
A
T
J
T
STG
T
LEAD
V
ESD
Maximum
-0.6 to +7
-0.6 to V
IN
256
81
-40 to +85
-40 to +125
-60 to +150
300
2
Units
V
V
°C/W
°C/W
°C
°C
°C
°C
kV
Electrical Characteristics
Unless specified: V
IN
= V
OUT
+ 1V, V
EN
= V
IN
, I
OUT
= 100µA, T
A
= 25°C. Values in
bold
apply over full operating ambient temperature range.
Parameter
IN
Supply Voltage Range
Supply Current
Symbol
Conditions
Min
Typ
Max
Units
V
IN
I
Q
I
OUT
= 0mA to150mA
2.25
75
6.50
130
160
V
µA
V
IN
= 6.5V, V
EN
= 0V
0.1
1.0
1.5
µA
OUT
Output Voltage
(1)
V
OUT
I
OUT
= 1mA
0mA
≤
I
OUT
≤
150mA, V
OUT
+1V
≤
V
IN
≤
5.5V
Line Regulation
(1)(2)
REG
(LINE)
(V
OUT(NOM)
+ 0.1V)
≤
V
IN
≤
5.5V, I
OUT
= 1mA
-1.5%
-2.0%
2.5
V
OUT
+1.5%
+2.0%
10
12
Load Regulation
(1)
REG
(LOAD)
I
OUT
= 0.1mA to 150mA
-3
-10
-20
mV
mV
V
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SC1457
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Unless specified: V
IN
= V
OUT
+ 1V, V
EN
= V
IN
, I
OUT
= 100µA, T
A
= 25°C. Values in
bold
apply over full operating ambient temperature range.
Parameter
Out (Cont.)
Current Limit
Dropout Voltage
(1)(3)
Symbol
Conditions
Min
Typ
Max
Units
I
LIM
V
D
I
OUT
= 1mA
I
OUT
= 50mA
400
1
50
65
75
I
OUT
= 100mA
100
125
155
I
OUT
= 150mA
150
190
230
mA
mV
mV
mV
mV
Output Voltage Noise
e
n
10Hz to 100kHz, I
OUT
= 50mA, C
OUT
= 1µF
10Hz to 100kHz, I
OUT
= 50mA, C
OUT
= 100µF
135
110
60
µV
RMS
Power Supply Rejection Ratio
EN
Enable Input Threshold
PSRR
f = 120Hz
dB
V
IH
V
IL
2.25V
≤
V
IN
≤
6.5V
2.25V
≤
V
IN
≤
6.5V
0V
≤
V
EN
≤
V
IN
1.6
0.4
-0.5
0
+0.5
V
Enable Input Bias Current
(4)
FLG
Flag Threshold
I
EN
µA
V
TH(FLG)
Under voltage condition (below nominal)
-4
-4
-6
-8
-12
0.4
%
Output Logic Low Voltage
Flag Leakage Current
Over Temperature Protection
High Trip Level
Hysteresis
V
F LG
I
FLG
I
FLG
= 1mA, undervoltage condition
Flag OFF, V
FLG
= 0V to 6.5V
-1
0.1
V
µA
+1
T
HI
T
HYST
150
20
°C
°C
NOTES:
(1) Low duty cycle pulse testing with Kelvin connections required.
(2) V
IN(MIN)
= 2.25V.
(3) Defined as the input to output differential at which the output voltage drops 100mV below the value measured
at a differential of 1V. Not measurable on 1.5V and 1.8V parts due to minimum V
IN
constraints.
(4) Guaranteed by design.
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SC1457
POWER MANAGEMENT
Pin Configuration
Top View
Ordering Information
Part Number
SC1457ISK-X.XTR
(1)
SC1457ISKX.XTRT
(1)(4)
P ackag e
SOT-23-5
(2)
SC1457ITSK-XXTR
(1)
SC1457ITSKXXTRT
SC1457EVB
(3)
(1)(4)
TSOT-23-5
(2)
N/A
(SOT-23-5 & TSOT-23-5)
Block Diagram
Notes:
(1) Where X.X or XX denotes voltage options. Available
voltages are: 1.5V (1.5 or 15), 1.8V (1.8 or 18), 2.5V
(2.5 or 25), 2.7V (2.7 or 27), 2.8V (2.8 or 28), 2.9V (2.9
or 29), 3.0V (3.0 or 30), 3.1V (3.1 or 31), 3.2V (3.2 or
32) and 3.3V (3.3 or 33).
(2) Only available in tape and reel packaging. A reel
contains 3000 devices.
(3) Evaluation board for SC1457. Specify output voltage
option when ordering.
(4) Lead free product. This product is fully WEEE and
RoHS compliant.
Pin Descriptions
Pin
1
2
3
4
5
Pin Name
IN
GND
EN
F LG
OUT
Pin Function
Input pin
Ground pin. Can be used for heatsinking if needed.
Active high enable pin. Connect V
IN
if not being used.
Error Flag. Open drain output. Active low indicates an output undervoltage condition.
Regulator output sourcing up to 150mA.
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SC1457
POWER MANAGEMENT
Marking Information
Top Mark
Bottom Mark
x7XX
x = package (5 for SOT-23-5, T for TSOT-23-5)
7 = SC1457
XX = voltage option
(examples: 5731 for 3.1V option in SOT-23-5,
T728 for 2.8V option in TSOT-23-5)
yyww
yyww = Date code
(example: 0008 for week 8 of 2000)
Applications Information
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
DS(ON)
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.
2004 Semtech Corp.
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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
J
exceeds 150°C (typical), with the
device remaining off until T
J
drops by 20°C (typical).
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 < 1Ω over temperature. While
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 100kΩ for this resistor to ensure that this pin is
high even under worst-case flag pin leakage conditions
of 1µA when off.
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