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TCL1117

TCL11 800mA LOW DROPOUT POSITIVE REGULATORS ADJUSTABLE AND FIXED 2.85V, 3.30V, 5.00V TCL11

TelCom Semiconductor, Inc 

800mA LOW DROPOUT POSITIVE REGULATORS

ADJUSTABLE AND FIXED 2.85V, 3.30V, 5.00V

PRELIMINARY INFORMATION

TCL1117

TCL1117-2.85

TCL1117-3.30

TCL1117-5.00

APPLICATIONS

Overload Protection

The TCL1117 is protected against current (short-circuit)

and thermal overload conditions. Thermal protection is

triggered by a chip temperature exceeding 165°C. Current

overload is triggered at approximately 950mA.

Stability and Load Regulation

The TCL1117 requires a capacitor from VOUT to GND to

provide compensation feedback to the internal gain stage.

This is to ensure stability at the output terminal. Typically, a

10µF tantalum or 50µF aluminum electrolytic is sufficient.

NOTE: It is important that the ESR for this capacitor does not

exceed 0.5Ω.

The output capacitor does not have a theoretical upper

limit and increasing its value will increase stability.

COUT = 100µF or more is typical for high current regulator

designs. NOTE: See Protection Diodes for limitations. An-

other benefit of larger output capacitance is improved tran-

sient load response (large di/dt in the load).

Protection Diodes

Typically no protection diodes are necessary for the

TCL1117. Unlike older regulators, the ADJ pin is protected

internally from excessive currents. The ADJ pin can be

driven with voltage transients as high as ±25V with respect

to the output without damage to the device.

Likewise, a diode between the input and output is not

typically required. If the input voltage collapses the internal

circuitry can absorb ~20A transient currents (<10µsec)

without damage. This reverse current is much larger than

most power supply designs can generate. However, if the

output capacitor is VERY large (>1000µF), instantaneous

currents can be high enough to damage the chip. In this

case, a high-current, fast-response diode is recommended.

(See Figure 1).

Output Voltage Adjust

Like most LDOs, the TCL1117 regulates the output by

comparing the output voltage, or a multiple thereof, to an

internally generated reference voltage. On the adjustable

version, the VREF is available externally as 1.25V (±1%)

between VOUT and ADJ (See Figure 2). The voltage divider

formed by R1 and R2 should be set to conduct 10mA

(minimum output load). The output voltage is given by the

following equation:

( ) VOUT = VREF 1+ R2 + IADJ R2

R1

On fixed voltage versions of the TCL1117, the voltage

divider is provided internally.

Load Regulation

The TCL1117 load regulation is limited by the resistance

of the wire connecting it to the load (Rp, Figure 3). For the

adjustable version, the best load regulation is accomplished

when the top of the resistor divider (R1) is connected directly

to the output pin of the TCL1117, NOT to the high side of the

load (Figure 3). When so connected, Rp is not multiplied by

the divider ratio. For the fixed output versions, the top of R1

is internally connected to the output and the ground pin can

be connected to the low side of the load as a negative side

sense if, so desired.

D1

1N4002

(OPTIONAL)

VIN

IN TCL1117 OUT

VOUT

VIN

IN TCL1117 OUT

VOUT

ADJ

+

R1

COUT

150µF

ADJ

IADJ

50µA

VREF

R1

+ CADJ

R2

10µF

R2

( ) VOUT = VREF

1+ R2

R1

+ IADJ R2

TCL1117-05 6/5/97

Figure 1.

Figure 2. Basic Adjustable Regulator

3

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