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SBVS001D − OCTOBER 1992 − REVISED JULY 2004
TYPICAL CHARACTERISTICS (continued)
At T = +25°C, all models, unless otherwise noted.
A
LOAD TRANSIENT RESPONSE
LINE TRANSIENT RESPONSE
= 1 F
60
40
20
0
C
µ
IN
0.1
0
COUT = 10 F Tantalum
µ
I
OUT = 0.1A
0.1
−
20
−
C
= 10 F
µ
IN
0.5
0
40
−
COUT = 10 F
Tantalum
µ
5.25
4.25
3.25
VIN = 4.25V
0.5
−
Preload = 0.1A
0
20
40
60
80
100
0
20 40 60 80 100 120 140 160 180 200
Time ( s)
Time ( s)
µ
µ
Figure 2 shows a hookup diagram for the adjustable
voltage model. Resistor values are shown for some
commonly-used output voltages. Values for other voltages
can be calculated from the equation shown in Figure 2. For
best load regulation, connect R1 close to the output pin and
R2 close to the ground side of the load as shown.
APPLICATIONS INFORMATION
Figure 1 shows the basic hookup diagram for fixed-voltage
models. All models require an output capacitor for proper
operation, and for improving high-frequency load
regulation; a 10µF tantalum capacitor is recommended.
Aluminum electrolytic types of 50µF or greater can also be
used. A high-quality capacitor should be used to assure
that the ESR (Effective Series Resistance) is less than
0.5Ω.
THERMAL CONSIDERATIONS
The REG1117 has current limit and thermal shutdown
circuits that protect it from overload. The thermal shutdown
activates at approximately TJ = 165°C. For continuous
operation, however, the junction temperature should not
be allowed to exceed 125°C. Any tendency to activate the
thermal shutdown in normal use is an indication of an
inadequate heat sink or excessive power dissipation. The
power dissipation is equal to:
VIN
VO
REG1117
µ
10 F
µ
+
+
10 F
Tantalum
Tantalum
PD = (VIN – VOUT) IOUT
The junction temperature can be calculated by:
TJ = TA + PD (qJA)
where TA is the ambient temperature, and qJA is the
junction-to-ambient thermal resistance.
Figure 1. Fixed-Voltage Model—Basic
Connections
VIN
VO
3
2
REG1117
(Adj)
VOUT
R1
R2
(
)
( )(2)
( )(2)
Ω
V
Ω
C
C1
µ
+
+
2µ
R1 + R2
R1
R1
R2
1.25
1.5
2.1
2.85
3
3.3
5
10
Open
750
158
169
137
115
113
113
Short
147
107
215
191
187
340
787
10 F
10 F
µ
VO
=
x (1.25V) + (50 A) (R2)
1
Load
(1)
C3
+
This term is negligible with
proper choice of values see
µ
10 F
−
table at right.
NOTES: (1) C3 optional. Improves high−frequency line rejection. (2) Resistors are standard 1% values.
Figure 2. Adjustable-Voltage Model—Basic Connections
8
BB [ BURR-BROWN CORPORATION ]
