LT1302CS8 查看數據表（PDF） - Linear Technology

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LT1302CS8

Micropower High Output Current Step-Up Adjustable and Fixed 5V DC/DC Converters

Linear Technology 

LT1302/LT1302-5

APPLICATIONS INFORMATION

VOUT

100mV/DIV

AC COUPLED

510mA

ILOAD

10mA

2ms/DIV

1302 F07c

Figure 7c. 0.01µF from VC to Ground.

Underdamped Response Requires Series R

VOUT

100mV/DIV

AC COUPLED

510mA

ILOAD 10mA

2ms/DIV

1302 F07d

Figure 7d. 0.1µF with 10k Series RC.

Classic Overdamped Response

VOUT

100mV/DIV

AC COUPLED

510mA

ILOAD 10mA

2ms/DIV

1302 F07e

Figure 7e. 0.01µF, 10k Series RC Shows Good

Transient Response. Slight Underdamping

Still Noticeable

IT Pin

The IT pin is used to disable Burst Mode, forcing the

LT1302 to operate in current mode even at light load. To

disable Burst Mode, 3.3k resistor R1 is connected from IT

to gound. More conservative frequency compensation

must be used when in this mode. A 0.1µF capacitor and

4.7k resistor from VC to ground has been found to be

adequate. Low frequency Burst Mode ripple can be

reduced or eliminated using this technique in many appli-

cations.

To illustrate, the transient load response of Figure 8’s

circuit is pictured without and with R1. Figure 8a shows

output voltage and inductor current without the resistor.

Note the 6kHz burst rate when the converter is delivering

25mA. By adding the 3.3k resistor, the low frequency

bursting is eliminated, as shown in Figure 8b. This feature

is useful in systems that contain audio circuitry. At very

light or zero load, switching frequency drops and eventu-

VIN

2.5V

+

C1

330µF MBRS130LT3

10µH

+ 220µF

10V

+ 220µF

10V

0.1µF

VIN

SW

SENSE

LT1302-5

PGND

VC

GND

IT

R1

3.3k

4.7k

0.1µF

VOUT

5V

600mA

1302 F08

Figure 8. Addition of R1 Eliminates Low Frequency

Output Ripple in This 2.5V to 5V Boost Converter

VOUT

100mV/DIV

AC COUPLED

510mA

ILOAD

10mA

2ms/DIV

1302 F07f

Figure 7f. 0.01µF, 24k Series RC

Results in Optimum Response

10

VOUT

100mV/DIV

AC COUPLED

INDUCTOR

CURRENT

1A/DIV

ILOAD

525mA

25mA

1ms/DIV

1302 F08a

Figure 8a. IT Pin Floating. Note 6kHz Burst Rate at

ILOAD = 25mA. 0.1µF/4.7k Compensation Network

Causes 220mV Undershoot

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