LCXW datasheet(8/16 Pages) LINER

Teilenummer	LCXW

Bauteilbeschribung	1.1A, Low Noise, Low Dropout Linear Regulator

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Hersteller	LINER [Linear Technology]

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LT1965

8

1965f

APPLICATIONS INFORMATION

The LT1965 is a 1.1A low dropout regulator with shut-

down. The device is capable of supplying 1.1A at a typical

dropout voltage of 290mV. The low operating quiescent

current (500μA) drops to less than 1μA in shutdown. In

addition to its low quiescent current, the LT1965 regulator

incorporates several protection features that make it ideal

for use in battery-powered systems. The device protects

itself against both reverse input and reverse output volt-

ages. In battery backup applications, if a backup battery

holds up the output when the input is pulled to ground,

the LT1965 performs like it has a diode in series with its

output, preventing reverse current ﬂow. Also, in dual sup-

ply applications where the regulator load is returned to a

negative supply, the output can be pulled below ground

by as much as 20V. The LT1965 still starts and operates

normally in this situation.

Adjustable Operation

The LT1965 has an output voltage range of 1.20V to 20V.

Figure 1 illustrates that the ratio of two external resistors

sets the output voltage. The device servos the output to

maintain the ADJ pin voltage at 1.20V referenced to ground.

R1’s current equals 1.20V/R1. R2’s current equals R1’s

current plus the ADJ pin bias current. The ADJ pin bias

current, 1.3μA at 25°C, ﬂows through R2 into the ADJ pin.

Use the formula in Figure 1 to calculate output voltage.

Linear Technology recommends that R1’s value be less

than 12.1k to minimize output voltage errors due to the

ADJ pin bias current. In shutdown, the output turns off

and the divider current is zero. For curves depicting ADJ

Pin Voltage vs Temperature and ADJ Pin Bias Current vs

Temperature, see the Typical Performance Characteristics

section.

The adjustable device is tested and speciﬁed with the ADJ

pin tied to the OUT pin for an output voltage of 1.20V.

Speciﬁcations for output voltages greater than 1.20V are

proportional to the ratio of the desired output voltage to

1.20V: VOUT/1.20V. For example, load regulation for an

output current change of 1mA to 1.1A is typically –4.25mV

at VOUT = 1.20V. At VOUT = 5V, load regulation is:

5

120

425

1771

V

mV

.

•– .

–

.

=

Output Capacitance

The LT1965’s design is stable with a wide range of out-

put capacitors. The ESR of the output capacitor affects

stability, most notably with small capacitors. A minimum

output capacitor of 10μF with an ESR of 3Ω or less is

recommended to prevent oscillations. The LT1965 is a

low quiescent current device and output load transient

response is a function of output capacitance. Larger values

of output capacitance decrease the peak deviations and

provide improved transient response for larger current

changes.

Ceramic capacitors require extra consideration. Manufac-

turers make ceramic capacitors with a variety of dielectrics,

each with different behavior across temperature and applied

voltage. The most common dielectrics used are speciﬁed

with EIA temperature characteristic codes of Z5U, Y5V,

X5R and X7R. The Z5U and Y5V dielectrics provide high

C-V products in a small package at low cost, but exhibit

strong voltage and temperature coefﬁcients as shown in

Figures 2 and 3. When used with a 5V regulator, a 16V

10μF Y5V capacitor can exhibit an effective value as low

as 1μF to 2μF for the DC bias applied and over the operat-

ing temperature range. The X5R and X7R dielectrics yield

much more stable characteristics and are more suitable

for use as the output capacitor. The X7R type works over

a wider temperature range and has better temperature

stability whereas X5R is less expensive and is available in

higher values. Care still must be exercised when using X5R

and X7R capacitors; the X5R and X7R codes only specify

operating temperature range and maximum capacitance

change over temperature. Capacitance change due to DC

bias with X5R and X7R capacitors is better than Y5V and

Z5U capacitors, but can still be signiﬁcant enough to drop

Figure 1. Adjustable Operation

IN

1965 F01

R2

OUT

VIN

VOUT

ADJ

GND

LT1965

R1

+

VV

R

IR

VV

I

OUT

ADJ

AD

=+

⎛

⎝⎜

⎞

⎠⎟

+

=

120

1

2

1

2

120

.•

.

JJ

µA AT

C

OUTPUT RANGE

V TO

V

=

13

25

120

195

.º

..

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