TC2117_06 Datasheet, PDF (7/18 Pages) Microchip Technology – 800 mA Fixed Low Dropout Positive Regulator

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
Battery
V_IN
V_OUT
C₁
1µF
TC2117
GND
C₂
1µF
V_OUT
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 0.2Ω to 10Ω. 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 regula-
tor off when die temperature exceeds 160°C. The
regulator remains off until the die temperature drops to
approximately 150°C.
TC2117
4.2.2 POWER DISSIPATION
The amount of power the regulator dissipates is prima-
rily a function of input and output voltage, and output
current. The following equation is used to calculate
worst case actual power dissipation:
EQUATION 4-1:
P_D = (V_INMAX – V_OUTMIN)I_LOADMAX
Where:
P_D = Worst-case actual power dissipation
V_INMAX = Maximum voltage on V_IN
V_OUTMIN = Minimum regulator output voltage
I_LOADMAX = Maximum output (load) current
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 (θ_JA).
EQUATION 4-2:
P_DMAX = (T_JMAX – T_AMAX)
θ_JA
Where all terms are previously defined.
Table 4-1 shows various values of θ_JA for the TC2117
mounted on a 1/16 inch, 2-layer PCB with 1 oz. copper
foil.
TABLE 4-1:
THERMAL RESISTANCE
GUIDELINES FOR TC2117 IN
3-PIN SOT-223 PACKAGE
Copper
Area
(Topside)*
Copper
Area
(Backside)
Board Area
2500 sq mm 2500 sq mm 2500 sq mm
1000 sq mm 2500 sq mm 2500 sq mm
225 sq mm 2500 sq mm 2500 sq mm
100 sq mm 2500 sq mm 2500 sq mm
1000 sq mm 1000 sq mm 1000 sq mm
1000 sq mm 0 sq mm 1000 sq mm
* Tab of device attached to topside copper.
Thermal
Resistance
45°C/W
45°C/W
53°C/W
59°C/W
52°C/W
55°C/W
© 2006 Microchip Technology Inc.
DS21665C-page 7