LT1963AES8#TR Linear Technology, LT1963AES8#TR Datasheet - Page 15

• Manufacturer Part Number: LT1963AES8#TR
• Description: IC LDO REG LOW NOISE 1.5A 8-SOIC
• Manufacturer: Linear Technology

Specifications of LT1963AES8#TR

• Regulator Topology: Positive Adjustable
• Voltage - Output: 1.21 ~ 20 V
• Voltage - Input: 2.1 ~ 20 V
• Voltage - Dropout (typical): 0.34V @ 1.5A
• Number Of Regulators: 1
• Current - Output: 1.5A
• Current - Limit (min): 1.6A
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LT1963AES8TR

APPLICATIONS INFORMATION
Table 1. Capacitor Minimum ESR
Figures 3 through 8 show the effect of ESR on the transient
response of the regulator. These scope photos show the
transient response for the LT1963A at three different output
voltages with various capacitors and various values of ESR.
The output load conditions are the same for all traces. In
all cases there is a DC load of 500mA. The load steps up
to 1A at the first transition and steps back to 500mA at
the second transition.
At the worst case point of 1.2V
(Figure 3), a minimum amount of ESR is required. While
20mΩ is enough to eliminate most of the ringing, a value
closer to 50mΩ provides a more optimum response. At
2.5V output with 10µF C
at the transitions with 0Ω ESR but still settles to within
10mV in 20µs after the 0.5A load step. Once again a small
value of ESR will provide a more optimum response.
At 5V
damped with 0Ω ESR.
With a C
(Figure 6), the output rings although the amplitude is
only 20mV
20mΩ of ESR to provide good damping at 1.2V output.
Performance at 2.5V and 5V output with 100µF C
similar characteristics to the 10µF case (see Figures 7-8).
At 2.5V
At 5V
Capacitor types with inherently higher ESR can be combined
with 0mΩ ESR ceramic capacitors to achieve both good
high frequency bypassing and fast settling time. Figure
9 illustrates the improvement in transient response that
can be seen when a parallel combination of ceramic and
V
1.2V
1.5V
1.8V
2.5V
3.3V
≥5V
OUT
OUT
OUT
OUT
OUT
the response is well damped with 0Ω ESR.
with 10µF C
5mΩ to 20mΩ can improve transient response.
p-p
of 100µF at 0Ω ESR and an output of 1.2V
. With C
20mΩ
20mΩ
15mΩ
10µF
5mΩ
0mΩ
0mΩ
OUT
OUT
OUT
15mΩ
15mΩ
10mΩ
(Figure 5) the response is well
22µF
of 100µF it takes only 5mΩ to
5mΩ
0mΩ
0mΩ
(Figure 4) the output rings
OUT
10mΩ
10mΩ
10mΩ
47µF
5mΩ
0mΩ
0mΩ
with 10µF C
OUT
100µF
5mΩ
5mΩ
5mΩ
5mΩ
5mΩ
0mΩ
shows
OUT
POSCAP capacitors are used. The output voltage is at the
worst case value of 1.2V. Trace A, is with a 10µF ceramic
output capacitor and shows significant ringing with a peak
amplitude of 25mV. For Trace B, a 22µF/45mΩ POSCAP
is added in parallel with the 10µF ceramic. The output is
well damped and settles to within 10mV in less than 20µs.
For Trace C, a 100µF/35mΩ POSCAP is connected in
parallel with the 10µF ceramic capacitor. In this case the
peak output deviation is less than 20mV and the output
settles in about 10µs. For improved transient response
the value of the bulk capacitor (tantalum or aluminum
electrolytic) should be greater than twice the value of the
ceramic capacitor.
Tantalum and Polytantalum Capacitors
There is a variety of tantalum capacitor types available,
with a wide range of ESR specifications. Older types have
ESR specifications in the hundreds of mΩ to several Ohms.
Some newer types of polytantalum with multi-electrodes
have maximum ESR specifications as low as 5mΩ. In gen-
eral the lower the ESR specification, the larger the size and
the higher the price. Polytantalum capacitors have better
surge capability than older types and generally lower ESR.
Some types such as the Sanyo TPE and TPB series have
ESR specifications in the 20mΩ to 50mΩ range, which
provide near optimum transient response.
Aluminum Electrolytic Capacitors
Aluminum electrolytic capacitors can also be used with the
LT1963A. These capacitors can also be used in conjunction
with ceramic capacitors. These tend to be the cheapest
and lowest performance type of capacitors. Care must be
used in selecting these capacitors as some types can have
ESR which can easily exceed the 3Ω maximum value.
Ceramic Capacitors
Extra consideration must be given to the use of ceramic
capacitors. Ceramic capacitors are manufactured with a
variety of dielectrics, each with different behavior over
temperature and applied voltage. The most common
dielectrics used are Z5U, Y5V, X5R and X7R. The Z5U and
LT1963A Series
15
1963afe