LT3060EDC 查看數據表（PDF） - Linear Technology

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LT3060EDC

45V VIN, Micropower, Low Noise, 100mA Low Dropout, Linear Regulator

Linear Technology 

LT3060 Series

Applications Information

Table 1 shows 1% resistor divider values for some com-

mon output voltages with a resistor divider current of

about 5µA.

Table 1. Output Voltage Resistor Divider Values

VOUT

R1

R2

(V)

(k Ω)

(k Ω)

1.2

118

118

1.5

121

182

1.8

124

249

2.5

115

365

3

124

499

3.3

124

562

5

115

845

Bypass Capacitance, Output Voltage Noise and

Transient Response

The LT3060 regulators provide low output voltage noise

over the 10Hz to 100kHz bandwidth while operating at

full load with the addition of a reference bypass capacitor

(CREF/BYP) from the REF/BYP pin to GND. A good quality,

low leakage capacitor is recommended. This capacitor

bypasses the internal reference of the regulator, provid-

ing a low frequency noise pole. With the use of 10nF for

CREF/BYP, the output voltage noise decreases to as low as

30µVRMS when the output voltage is set for 0.6V. For higher

output voltages (generated by using a feedback resistor

divider), the output voltage noise gains up accordingly

when using CREF/BYP by itself.

To lower the output voltage noise for higher output volt-

ages, include a feedforward capacitor (CFF) from VOUT

to the ADJ pin. A good quality, low leakage capacitor is

recommended. This capacitor bypasses the error amplifier

of the regulator, providing a low frequency noise pole. With

the use of 10nF for both CFF and CREF/BYP, output voltage

noise decreases to 30µVRMS when the output voltage is

set to 5V by a 5µA feedback resistor divider. If the current

in the feedback resistor divider is doubled, CFF must also

be doubled to achieve equivalent noise performance.

Higher values of output voltage noise are often measured

if care is not exercised with regard to circuit layout and

testing. Crosstalk from nearby traces induces unwanted

noise onto the LT3060’s output. Power supply ripple rejec-

tion must also be considered. The LT3060 regulators do

not have unlimited power supply rejection and will pass a

small portion of the input noise through to the output.

Using a feedforward capacitor (CFF) from VOUT to the ADJ

pin has the added benefit of improving transient response

for output voltages greater than 0.6V. With no feedforward

capacitor, the settling time will increase as the output

voltage is raised above 0.6V. Use the equation in Figure 2

to determine the minimum value of CFF to achieve a

transient response that is similar to 0.6V output voltage

performance regardless of the chosen output voltage

(see Figure 3 and Transient Response in the Typical Perf­

ormance Characteristics section).

IN

OUT

VIN

LT3060

R2

SHDN ADJ

GND REF/BYP R1

CREF/BYP

3060 F02

VOUT

CFF

COUT

( ) CFF

≥

4.7nF

5µA

•

IFB−DIVIDER

IFB−DIVIDER

=

VOUT

R1+ R2

0

100pF

1nF

10nF

LOAD CURRENT

100mA/DIV

VOUT = 5V

COUT = 10µF

IFB-DIVIDER = 5µA

100µs/DIV

3060 F03

Figure 2. Feedforward Capacitor for Fast Transient Response

Figure 3. Transient Response vs Feedforward Capacitor

3060fa

17

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