TC1017 datasheet(10/28 Pages) MICROCHIP

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TC1017

DS20001813G-page 10

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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 VOUT

(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 noninverting

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-

channel is off, the power dissipation internal to the

device is almost zero. The device cools until the junction

temperature 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

temperature of the device is 125°C. Steady-state

operation at or near the 160°C overtemperature point

can lead to permanent 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 0.05 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

input

capacitance

can

compensate for this.

FIGURE 4-1:

TC1017 Block Diagram (5-Pin SC-70 Pinout).

FIGURE 4-2:

Typical Application Circuit (5-Pin SC-70 Pinout).

OUT

REF

SHDN

R1 R2

SHDN

GND

Current Limit

Over

Error

Feedback Resistors

Control

Temp.

Body

Diode

Amp

OUT

SHDN

GND

SOURCE

1 µF Ceramic

OUT

1 µF Ceramic

TC1017

Load

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