2010 Microchip Technology Inc. DS21665D-page 7
TC2117
4.0 DETAILED DESCRIPTION
The TC2117 is a precision, positive output LDO. Unlike
bipolar regulators, the TC2117 supply current does not
increase proportionally with load current. In addition,
V
OUT
remains stable and within regulation over the
entire 0 mA to 800 mA operating load range.
FIGURE 4-1: Typical Application Circuit.
4.1 Output Capacitor
A 1 µF (min) capacitor from V
OUT
to ground is required.
The output capacitor should have an effective series
resistance of 0.2 to 10. A 1 µF capacitor should be
connected from V
IN
to GND if there is more than 10
inches of wire between the regulator and the AC filter
capacitor, or if a battery is used as the power source.
Aluminum electrolytic or tantalum capacitor types can
be used. (Since many aluminum electrolytic capacitors
freeze at approximately -30°C, solid tantalums are
recommended for applications operating below -25°C.)
When operating from sources other than batteries,
supply noise rejection and transient response can be
improved by increasing the value of the input and
output capacitors and employing passive filtering
techniques.
4.2 Thermal Considerations
4.2.1 THERMAL SHUTDOWN
Integrated thermal protection circuitry shuts the
regulator off when die temperature exceeds 160°C.
The regulator remains off until the die temperature
drops to approximately 150°C.
4.2.2 POWER DISSIPATION
The amount of power the regulator dissipates is
primarily a function of input and output voltage, and
output current. The following equation is used to
calculate the worst-case actual power dissipation:
EQUATION 4-1:
The maximum allowable power dissipation
(Equation 4-2) is a function of the maximum ambient
temperature (T
AMAX
), the maximum allowable die
temperature (+125°C) and the thermal resistance from
junction-to-air (
JA
).
EQUATION 4-2:
Table 4-2 shows various values of
JA
for the TC2117
mounted on a 1/16 inch, 2-layer PCB with 1 oz. copper
foil.
TABLE 4-2: THERMAL RESISTANCE
GUIDELINES FOR TC2117 IN
3-PIN SOT-223 PACKAGE
C
1
1µF
Battery
TC2117
V
IN
V
OUT
C
2
1µF
GND
V
OUT
Copper
Area
(Topside)*
Copper
Area
(Backside)
Board Area
Thermal
Resistance
2500 sq mm 2500 sq mm 2500 sq mm 45°C/W
1000 sq mm 2500 sq mm 2500 sq mm 45°C/W
225 sq mm 2500 sq mm 2500 sq mm 53°C/W
100 sq mm 2500 sq mm 2500 sq mm 59°C/W
1000 sq mm 1000 sq mm 1000 sq mm 52°C/W
1000 sq mm 0 sq mm 1000 sq mm 55°C/W
* Tab of device attached to topside copper.
Where:
V
INMAX
V
OUTMIN
I
LOADMAX
P
D
= Worst-case actual power dissipation
= Minimum regulator output voltage
= Maximum output (load) current
= Maximum voltage on V
IN
P
D
V
INMAX
V
OUTMIN
–I
LOADMAX
=
P
DMAX
= (T
JMAX
– T
AMAX
)
JA
Where all terms are previously defined.
