LT1307CS8 datasheet(11/20 Pages) LINER

11 / 20 page

LT1307/LT1307B

APPLICATIONS INFORMATION

51mA

1mA

5ms/DIV

1307 F11a

VOUT

200mV/DIV

AC COUPLED

Figure 11a. VC Pin Left Unconnected. Output Ripple

Voltage is 300mVP-P Under Load

51mA

1mA

5ms/DIV

1307 F11b

Figure 11b. Inclusion of a 100k/22nF Series RC on VC

Pin Results in Overdamped Stable Response

VOUT

200mV/DIV

AC COUPLED

51mA

1mA

1ms/DIV

1307 F11a

VOUT

200mV/DIV

AC COUPLED

Figure 11c. Reducing C to 2nF Speeds Up Response,

Although Still Overdamped

51mA

1mA

500

µs/DIV

1307 F11b

Figure 11d. A 100k/200pF Series RC Shows Some

Underdamping

VOUT

200mV/DIV

AC COUPLED

51mA

1mA

1ms/DIV

1307 F11b

Figure 11e. A 100k/680pF RC Provides Optimum

Settling Time with No Ringing

VOUT

200mV/DIV

AC COUPLED

pole, requiring added C at the VC pin network to prevent

loop oscillation.

Observant readers will notice R has been set to 100k for all

the photos in Figure 11. Usable R values can be found in

the 10k to 500k range, but after too many trips to the

resistor bins, 100k wins.

underdamping. Now settling time is about 300

µs.Increas-

ing C to 680pF results in the response shown in Figure 11e.

This response has minimum settling time with no over-

shoot or underdamping.

Converters using a 2-cell input need more capacitance at

the output. This added capacitance moves in the output

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