REG1117
REG1117A
www.ti.com
SBVS001D − OCTOBER 1992 − REVISED JULY 2004
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, all models, unless otherwise noted.
LOAD TRANSIENT RESPONSE
60
Output Voltage
Deviations (V)
0.1
0
−0.1
C
IN
= 10
µ
F
C
OUT
= 10µF
Tantalum
V
IN
= 4.25V
Preload = 0.1A
0
20
40
60
80
100
Output Voltage
Deviation (mV)
40
20
0
−20
Load Current (A)
Input Voltage (V)
0.5
0
−
0.5
−40
5.25
4.25
3.25
0
20
40
60
80 100 120 140 160 180 200
Time (µs)
C
IN
= 1
µ
F
C
OUT
= 10µF Tantalum
I
OUT
= 0.1A
LINE TRANSIENT RESPONSE
Time (µs)
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.
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 R
1
close to the output pin and
R
2
close to the ground side of the load as shown.
THERMAL CONSIDERATIONS
The REG1117 has current limit and thermal shutdown
circuits that protect it from overload. The thermal shutdown
activates at approximately T
J
= 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:
V
IN
10
µ
F
Tantalum
+
REG1117
V
O
+ 10
µ
F
Tantalum
P
D
= (V
IN
– V
OUT
) I
OUT
The junction temperature can be calculated by:
T
J
= T
A
+ P
D
(q
JA
)
Figure 1. Fixed-Voltage Model—Basic
Connections
where T
A
is the ambient temperature, and
q
JA
is the
junction-to-ambient thermal resistance.
V
IN
C
1
+
10µF
3
REG1117
(Adj)
1
C
3(1)
+
10µF
2
V
O
+ C
2
10µF
Load
R
2
V
OUT
(V )
V
O
=
R
1
+ R
2
R
1
x (1.25V) + (50µA) (R
2
)
1.25
1.5
2.1
2.85
3
3.3
5
10
R
1
(
Ω
)
(2)
Open
750
158
169
137
115
113
113
R
2
(
Ω
)
(2)
Short
147
107
215
191
187
340
787
R
1
This term is negligible with
proper choice of values−see
table at right.
NOTES: (1) C
3
optional. Improves high−
frequency line rejection. (2) Resistors are standard 1% values.
Figure 2. Adjustable-Voltage Model—Basic Connections
8
BURR-BROWN [ BURR-BROWN CORPORATION ]
