Figure 1 shows the basic hookup diagram for the REG1118.
An output capacitor is required for proper operation and to
improve high frequency load regulation. A high quality
capacitor should be used to assure that the ESR (effective
series resistance) is less than 0.5Ω. A capacitor of at least
1µF is recommended. Increasing COUT improves output
voltage deviation, see the typical curve “Load Transient
Response.” It is suggested that the input be decoupled with
10µF low ESR capacitor.
ambient temperature above that expected in normal opera-
tion until the device’s thermal shutdown is activated. If this
occurs at more than 40°C above the maximum expected
ambient temperature, then the TJ will be less than 125°C
during normal operation.
The REG1118 package is suitable for infrared reflow and
vapor-phase reflow soldering techniques. The high rate of
temperature change that occurs with wave soldering, or hand
soldering can damage the REG1118.
Total Area: 50 x 50mm
35 x 17 mm
FIGURE 1. Basic Connections.
The REG1118 has current limit and thermal shutdown
circuits that protect it from overload. The thermal shutdown
activates at approximately TJ = 150°C. For continuous op-
eration, 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:
PD = (VIN – VOUT) IOUT
The junction temperature can be calculated by:
TJ = TA + PD (θJA)
where TA is the ambient temperature, and
θJA is the junction-to-ambient thermal resistance
The REG1118 derives heat sinking from conduction through
its copper leads, especially the large mounting tab. These
must be soldered to a circuit board with a substantial amount
of copper remaining (see Figure 2). Circuit board traces
connecting to the tab and the leads should be made as large
as practical. Other nearby circuit traces, including those on
the back side of the circuit board, help conduct heat away
from the device, even though they are not electrically connected.
Make all nearby copper traces as wide as possible and leave
only narrow gaps between traces. In addition, multiple
contacts to internal power and ground planes increase heat
sinking with minimal increase in circuit board area.
Table I shows approximate values of θJA for various circuit
board and copper areas. Nearby heat dissipating compo-
nents, circuit board mounting conditions and ventilation can
dramatically affect the actual θJA.
A simple experiment will determine whether the maximum
recommended junction temperature is exceeded in an actual
circuit board and mounting configuration: Increase the
16 x 10 mm 16 x 10 mm
Without back-side copper: θJA ≈ 59°C/W
With solid back-side copper: θJA ≈ 49°C/W
FIGURE 2. Circuit Board Layout Example.
TOTAL PC BOARD
NOTE: (1) Tab is attached to the topside copper.
INSPEC Abstract Number: B91007604, C91012627
Kelly, E.G. “Thermal Characteristics of Surface 5WK9Ω
Packages.” The Proceedings of SMTCON. Surface Mount
Technology Conference and Exposition: Competitive Surface
Mount Technology, April 3-6, 1990, Atlantic City, NJ, USA.
Abstract Publisher: IC Manage, 1990, Chicago, IL, USA.