LT1764AEQ-3.3#PBF Linear Technology, LT1764AEQ-3.3#PBF Datasheet - Page 12

• Manufacturer Part Number: LT1764AEQ-3.3#PBF
• Description: IC LDO LOW NOISE 3A 3.3V DDPAK-5
• Manufacturer: Linear Technology

Specifications of LT1764AEQ-3.3#PBF

• Regulator Topology: Positive Fixed
• Voltage - Output: 3.3V
• Voltage - Input: Up to 20V
• Voltage - Dropout (typical): 0.34V @ 3A
• Number Of Regulators: 1
• Current - Output: 3A
• Current - Limit (min): 3.1A
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: TO-263-5, D²Pak (5 leads + Tab), TO-263BA
• Primary Input Voltage: 20V
• Output Voltage Fixed: 3.3V
• Dropout Voltage Vdo: 340mV
• No. Of Pins: 5
• Output Current: 3A
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 1 - Unlimited
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIO S I FOR ATIO
LT1764A Series
ing the capacitor value improves the stability and reduces
the ringing. Table 1 gives some recommended values of
ESR to minimize ringing caused by fast, hard current
transitions.
Table 1. Capacitor Minimum ESR
V
1.2V
1.5V
1.8V
2.5V
3.3V
≥ 5V
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 LT1764A at three different
output voltages with various capacitors and various val-
ues of ESR. The output load conditions are the same for all
traces. In all cases there is a DC load of 1A. The load steps
up to 2A at the first transition and steps back to 1A at the
second transition.
At the worst case point of 1.2V
(Figure 3), a minimum amount of ESR is required. While
5mΩ is enough to eliminate most of the ringing, a value
closer to 20mΩ 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 1A 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
10mV
of ESR to provide good damping at 1.2V output. Perfor-
mance at 2.5V and 5V output with 100µF C
ilar characteristics to the 10µF case (see Figures 7-8). At
2.5V
At 5V
12
OUT
OUT
OUT
OUT
p-p
OUT
. With C
5mΩ to 20mΩ can improve transient response.
the response is well damped with 0Ω ESR.
with 10µF C
10mΩ
10
7mΩ
5mΩ
0mΩ
0mΩ
0mΩ
of 100µF at 0Ω ESR and an output of 1.2V
µ
F
OUT
U
of 100µF it takes only 5mΩ to 20mΩ
OUT
22
5mΩ
5mΩ
5mΩ
0mΩ
0mΩ
0mΩ
OUT
U
(Figure 5) the response is well
µ
F
(Figure 4) the output rings
W
OUT
47
3mΩ
3mΩ
3mΩ
0mΩ
0mΩ
0mΩ
µ
with 10µF C
F
OUT
shows sim-
U
100
0mΩ
0mΩ
0mΩ
0mΩ
0mΩ
0mΩ
µ
F
OUT
Capacitor types with inherently higher ESR can be com-
bined 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 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 5µs.
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 5µs. For improved transient response the
value of the bulk capacitor (tantalum or aluminum electro-
lytic) 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 general 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
LT1764. 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.
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