REG113
10 SBVS031D
www.ti.com
POWER DISSIPATION
The REG113 is available in two different package configura-
tions. The ability to remove heat from the die is different for each
package type and, therefore, presents different considerations
in the printed circuit board (PCB) layout. On the MSOP-8
package, leads 5 through 8 are fused to the lead frame and may
be used to improve the thermal performance of the package.
The PCB area around the device that is free of other compo-
nents moves the heat from the device to the ambient air.
Although it is difficult or impossible to quantify all of the
variables in a thermal design of this type, performance data for
several simplified configurations are shown in Figure 6. In all
cases the PCB copper area is bare copper, free of solder resist
mask, and not solder plated. All examples are for 1-ounce
copper and in the case of the MSOP-8, the copper area is
connected to fused leads 5 to 8. See Figure 7 for thermal
resistance for varying areas of copper. Using heavier copper
can increase the effectiveness in removing the heat from the
device. In those examples where there is copper on both sides
of the PCB, no connection has been provided between the two
sides. The addition of plated through holes will improve the heat
sink effectiveness.
For large step changes in load current, the REG113 requires
a larger voltage drop across it to avoid degraded transient
response. The boundary of this transient dropout region is
shown as the top line in Figure 5. Values of VIN to VOUT voltage
drop above this line insure normal transient response.
In the transient dropout region between DC and Transient,
transient response recovery time increases. The time required to
recover from a load transient is a function of both the magnitude
and rate of the step change in load current and the available
headroom V
IN
to V
OUT
voltage drop. Under worst-case condi-
tions (full-scale load change with (V
IN
– V
OUT
) voltage drop close
to DC dropout levels), the REG113 can take several hundred
microseconds to re-enter the specified window of regulation.
TRANSIENT RESPONSE
The REG113 response to transient line and load conditions
improves at lower output voltages. The addition of a capacitor
(nominal value 0.47µF) from the output pin to ground may
improve the transient response. In the adjustable version, the
addition of a capacitor, C
FB
(nominal value 10nF), from the
output to the adjust pin also improves the transient response.
THERMAL PROTECTION
Power dissipated within the REG113 can cause the junction
temperature to rise, however, the REG113 has thermal
shutdown circuitry that protects the regulator from damage.
The thermal protection circuitry disables the output when
the junction temperature reaches approximately 160°C,
allowing the device to cool. When the junction temperature
cools to approximately 140°C, the output circuitry is again
enabled. Depending on various conditions, the thermal
protection circuit can cycle on and off. This limits the
dissipation of the regulator, but can have an undesirable
effect on the load.
Any tendency to activate the thermal protection circuit indi-
cates excessive power dissipation or an inadequate heat sink.
For reliable operation, junction temperature should be limited
to 125°C, maximum. To estimate the margin of safety in a
complete design (including heat sink), increase the ambient
temperature until the thermal protection is triggered. Use
worst-case loads and signal conditions. For good reliability,
thermal protection should trigger more than 35°C above the
maximum expected ambient condition of th e application. This
produces a worst-case junction temperature of 125°C at the
highest expected ambient temperature and worst-case load.
The internal protection circuitry of the REG113 is designed to
protect against overload conditions and is not intended to
replace proper heat sinking. Continuously running the REG113
into thermal shutdown will degrade reliability.
3.0
2.5
2.0
1.5
1.0
0.5
0
Power Dissipation (W)
MAXIMUM POWER DISSIPATION vs TEMPERATURE
–50 –25 0 25 50 75 100 125
Ambient Temperature (°C)
Condition 1
Condition 2
Condition 3
CONDITION PACKAGE PCB AREA
θ
JA
1 MSOP-8 1 sq. in. Cu, 1 Side 71
2 MSOP-8 0.25 sq. in. Cu, 1 Side 90
3 SOT-23-8 None 200
FIGURE 6. Maximum Power Dissipation versus Ambient Tem-
perature for the Various Packages and PCB Heat
Sink Configurations.