LT1962EMS8-3#TR Linear Technology, LT1962EMS8-3#TR Datasheet - Page 12

• Manufacturer Part Number: LT1962EMS8-3#TR
• Description: IC LDO REG LOWNOISE 3V 8-MSOP
• Manufacturer: Linear Technology

Specifications of LT1962EMS8-3#TR

• Regulator Topology: Positive Fixed
• Voltage - Output: 3V
• Voltage - Input: Up to 20V
• Voltage - Dropout (typical): 0.27V @ 300mA
• Number Of Regulators: 1
• Current - Output: 300mA
• Current - Limit (min): 320mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LT1962EMS8-3TR

APPLICATIO S I FOR ATIO
LT1962 Series
plus the ADJ pin bias current. The ADJ pin bias current,
30nA at 25 C, flows through R2 into the ADJ pin. The
output voltage can be calculated using the formula in
Figure 2. The value of R1 should be no greater than 250k
to minimize errors in the output voltage caused by the ADJ
pin bias current. Note that in shutdown the output is turned
off and the divider current will be zero.
The adjustable device is tested and specified with the ADJ
pin tied to the OUT pin for an output voltage of 1.22V.
Specifications for output voltages greater than 1.22V will
be proportional to the ratio of the desired output voltage to
1.22V: V
output current change of 1mA to 300mA is – 2mV typical
at V
Bypass Capacitance and Low Noise Performance
The LT1962 regulators may be used with the addition of a
bypass capacitor from V
voltage noise. A good quality low leakage capacitor is
recommended. This capacitor will bypass the reference of
the regulator, providing a low frequency noise pole. The
noise pole provided by this bypass capacitor will lower the
output voltage noise to as low as 20 V
addition of a 0.01 F bypass capacitor. Using a bypass
capacitor has the added benefit of improving transient
response. With no bypass capacitor and a 10 F output
capacitor, a 10mA to 300mA load step will settle to within
1% of its final value in less than 100 s. With the addition
of a 0.01 F bypass capacitor, the output will settle to
within 1% for a 10mA to 300mA load step in less than
10 s, with total output voltage deviation of less than 2%
12
(12V/1.22V)(–2mV) = – 19.7mV
OUT
= 1.22V. At V
OUT
/1.22V. For example, load regulation for an
V
IN
Figure 2. Adjustable Operation
I
IN
V
V
OUTPUT RANGE = 1.22V TO 20V
ADJ
OUT
ADJ
U
LT1962
OUT
GND
30
1 22
1 22 1
.
.
OUT
nA
V
OUT
= 12V, load regulation is:
U
ADJ
V
AT 25 C
to the BYP pin to lower output
R
R
2
1
R2
R1
I
ADJ
W
+
R
2
1962 F02
V
RMS
OUT
U
with the
(see LT1962-5 Transient Response in the Typical Perfor-
mance Characteristics). However, regulator start-up time
is inversely proportional to the size of the bypass capaci-
tor, slowing to 15ms with a 0.01 F bypass capacitor and
10 F output capacitor.
Output Capacitance and Transient Response
The LT1962 regulators are designed to be stable with a
wide range of output capacitors. The ESR of the output
capacitor affects stability, most notably with small capaci-
tors. A minimum output capacitor of 3.3 F with an ESR of
3 or less is recommended to prevent oscillations. The
LT1962-X is a micropower device and output transient
response will be a function of output capacitance. Larger
values of output capacitance decrease the peak deviations
and provide improved transient response for larger load
current changes. Bypass capacitors, used to decouple
individual components powered by the LT1962, will in-
crease the effective output capacitor value. With larger
capacitors used to bypass the reference (for low noise
operation), larger values of output capacitance are needed.
For 100pF of bypass capacitance, 4.7 F of output capaci-
tor is recommended. With a 1000pF bypass capacitor or
larger, a 6.8 F output capacitor is recommended.
The shaded region of Figure 3 defines the range over which
the LT1962 regulators are stable. The minimum ESR
needed is defined by the amount of bypass capacitance
used, while the maximum ESR is 3 .
Extra consideration must be given to the use of ceramic
capacitors. Ceramic capacitors are manufactured with a
variety of dielectrics, each with different behavior across
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
1
C
BYP
= 0
C
BYP
OUTPUT CAPACITANCE ( F)
Figure 3. Stability
= 100pF
2
STABLE REGION
C
3
BYP
= 330pF
C
4
BYP
5 6 7 8 9
1000pF
1962 F03
10