TC1017R-3VLTTR Datasheet, PDF (10/22 Pages) Microchip Technology – 150 mA, Tiny CMOS LDO With Shutdown

TC1017
4.0 DETAILED DESCRIPTION
The TC1017 is a precision, fixed-output, linear voltage
regulator. The internal linear pass element is a
P-channel MOSFET. As with all P-channel CMOS
LDOs, there is a body drain diode with the cathode
connected to V_IN and the anode connected to V_OUT
(Figure 4-1).
As is shown in Figure 4-1, the output voltage of the
LDO is sensed and divided down internally to reduce
external component count. The internal error amplifier
has a fixed bandgap reference on the inverting input
and the sensed output voltage on the non-inverting
input. The error amplifier output will pull the gate
voltage down until the inputs of the error amplifier are
equal to regulate the output voltage.
Output overload protection is implemented by sensing
the current in the P-channel MOSFET. During a shorted
or faulted load condition in which the output voltage
falls to less than 0.5V, the output current is limited to a
typical value of 120 mA. The current-limit protection
helps prevent excessive current from damaging the
Printed Circuit Board (PCB).
An internal thermal sensing device is used to monitor
the junction temperature of the LDO. When the sensed
temperature is over the set threshold of 160°C (typical),
the P-channel MOSFET is turned off. When the P-chan-
nel is off, the power dissipation internal to the device is
almost zero. The device cools until the junction temper-
ature is approximately 150°C and the P-channel is
turned on. If the internal power dissipation is still high
enough for the junction to rise to 160°C, it will again shut
off and cool. The maximum operating junction tempera-
ture of the device is 125°C. Steady-state operation at or
near the 160°C overtemperature point can lead to per-
manent damage of the device.
The output voltage V_OUT remains stable over the entire
input operating voltage range (2.7V to 6.0V) and the
entire load range (0 mA to 150 mA). The output voltage
is sensed through an internal resistor divider and
compared with a precision internal voltage reference.
Several fixed-output voltages are available by
changing the value of the internal resistor divider.
Figure 4-2 shows a typical application circuit. The
regulator is enabled any time the shutdown input pin is
at or above V_IH. It is shut down (disabled) any time the
shutdown input pin is below V_IL. For applications where
the SHDN feature is not used, tie the SHDN pin directly
to the input supply voltage source. While in shutdown,
the supply current decreases to 0.006 µA (typical) and
the P-channel MOSFET is turned off.
As shown in Figure 4-2, batteries have internal source
impedance. An input capacitor is used to lower the
input impedance of the LDO. In some applications, high
input impedance can cause the LDO to become
unstable. Adding more input capacitance can
compensate for this.
FIGURE 4-1:
1 SHDN
2 NC
3 GND
Current Limit
V_IN
SHDN ^VREF
Control
+-EA
V_{IN 5}
Body
Diode
Over
Temp.
Error
Amp
R₁ R₂
Feedback Resistors
V_{OUT 4}
TC1017 Block Diagram (5-Pin SC-70 Pinout).
R_SOURCE
1 _{SHDN VIN} 5
TC1017
C_IN
2 _NC
3 _GND
V_OUT ⁴
C_OUT
1 µF Ceramic
Load
1 µF Ceramic
FIGURE 4-2:
Typical Application Circuit (5-Pin SC-70 Pinout).
DS21813D-page 10
© 2005 Microchip Technology Inc.