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TC1173

300mA CMOS LDO with Shutdown ERROR Output and Bypass

TelCom Semiconductor Inc => Microchip 

300mA CMOS LDO With Shutdown,

ERROR Output, And Bypass

DETAILED DESCRIPTION

The TC1173 is a fixed output, low drop-out regulator.

Unlike bipolar regulators, the TC1173 supply current does not

increase with load current. In addition, VOUT remains stable and

within regulation at very low load currents (an important consid-

eration in RTC and CMOS RAM battery back-up applications).

TC1173 pin functions are detailed below:

PIN DESCRIPTIONS

Pin

No. Symbol Description

1

VOUT Regulated voltage output

2

GND Ground terminal

3

NC

No connect

4

Bypass Reference bypass input. Connecting a 470pF

to this input further reduces output noise.

5

ERROR Out-of-Regulation Flag (Open Drain Out-

put). This output goes low when VOUT is out-

of-tolerance by approximately -5%.

6

SHDN Shutdown control input. The regulator is fully

enabled when a logic high is applied to this

input. The regulator enters shutdown when a

logic low is applied to this input. During

shutdown, output voltage falls to zero and

supply current is reduced to 0.05µA (typical).

7

NC

No connect

8

VIN

Unregulated supply input

TC1173

SHDN may be controlled by a CMOS logic gate, or I/O port

of a microcontroller. If the SHDN input is not required, it

should be connected directly to the input supply. While in

shutdown, supply current decreases to 0.05µA (typical),

VOUT falls to zero and ERROR is disabled.

ERROR Output

ERROR is driven low whenever VOUT falls out of regu-

lation by more than – 5% (typical). This condition may be

caused by low input voltage, output current limiting, or

thermal limiting.

The ERROR threshold is 5% below rated VOUT regard-

less of the programmed output voltage value (e.g., ERROR

= VOL at 4.75V (typ) for a 5.0V regulator and 2.85V (typ) for

a 3.0V regulator). ERROR output operation is shown in

Figure 2. Note that ERROR is active when VOUT is at or

below VTH, and inactive when VOUT is above VTH + VH.

As shown in Figure 1, ERROR can be used as a battery

low flag, or as a processor RESET signal (with the addition

of timing capacitor C2). R1 x C3 should be chosen to

maintain ERROR below VIH of the processor RESET input

for at least 200msec to allow time for the system to stabilize.

Pull-up resistor R1 can be tied to VOUT, VIN or any other

voltage less than (VIN + 0.3V.)

VOUT

VTH

Hysteresis (VH)

Figure 1 shows a typical application circuit. The regula-

tor is enabled any time the shutdown input (SHDN) is above

VIH, and shutdown (disabled) when SHDN is at or below VIL.

ERROR

VIH

VOL

VOUT

TC1173-2 2/2/00

1

VOUT

C1

1µF

2

GND

8

VIN

7

NC

TC1173

3

6

NC

SHDN

VIN

R3

1M

4 Bypass

5

ERROR

ERROR

CBYPASS

470pF

(Optional)

Shutdown Control

(from Power Control Logic)

Figure 1: Typical Application Circuit

Figure 2: ERROR Output Operation

Output Capacitor

A 1µF (min) capacitor from VOUT to ground is recom-

mended. The output capacitor should have an effective

series resistance of 5Ω or less. A 1µF capacitor should be

connected from VIN 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 electro-

lytic 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.

3

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