SC8863(2000) 查看數據表（PDF） - Semtech Corporation
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SC8863 Datasheet PDF : 9 Pages
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150mA ULTRA LOW DROPOUT,
LOW NOISE REGULATOR
SC8863
March 1, 2000
TYPICAL CHARACTERISTICS (Cont.)
Sense/Select Threshold
vs. Junction Temperature
80
VIN = 3.6V
70
60
50
40
30
20
-50
-25
0
25
50
75
100
125
TJ (°C)
APPLICATIONS INFORMATION
Theory Of Operation
The SC8863 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. Fixed out-
put voltage options require the use of only two external
capacitors for operation.
Each voltage option has both fixed and adjustable out-
put voltage modes. Grounding the SET pin (pulling it
below the Sense/Select threshold of 55mV) will con-
nect the internal resistor divider to the error amplifier
resulting with the internally preset output voltage. If
SET is pulled above this threshold, then the Sense/
Select switch will connect the SET pin to the error am-
plifier. The output will be regulated such that the volt-
age at SET will equal VSET, the SET reference voltage
(typically 1.250V).
An active high enable pin (EN) is provided to allow the
customer to shut down the part and enter an extremely
low power Off-state. A logic Low signal will reduce the
supply current to 0.1nA.
Component Selection - General
Output capacitor - Semtech recommends a minimum
capacitance of 1µF at the output with an equivalent se-
ries resistance (ESR) of <1Ω over temperature. Ce-
ramic capacitors are ideal for this application. Increas-
Output Spectral Noise Density
vs. Frequency
10
SC8863-2.8
VIN = 3.6V
IOUT = 50mA
TJ = 25°C
1
COUT = 1µF
0.1
0.01
0.1
COUT = 100µF
1
10
100
f (kHz)
ing 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 tran-
sients is reduced, improving load transient response.
Component Selection - Externally Set Output
Please refer to Figure 1 below. The output voltage can
be externally adjusted anywhere within the range from
1.25V to (VIN(MIN) - VD(MAX)). The output voltage will be
in accordance with the following equation:
VO = 1.250 • 1 + R1
R2
1% tolerance resistors are recommended. The values
of R1 and R2 should be selected such that the current
flow through them is ≥ 10µA (thus R2 ≤ 120kΩ).
At high input voltages and/or high output currents, sta-
C1
1uF Ceramic
U1
3 VIN
SC8863
VO 4
1 EN GND SET 5
2
R1
R2
10k
C2
2.2uF Ceramic
Figure 1: Externally set output
© 2000 SEMTECH CORP.
7
652 MITCHELL ROAD NEWBURY PARK CA 91320
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