LT6654 datasheet(10/22 Pages) LINEAR

10 / 22 page

LT6657

6657fb

For more information www.linear.com/LT6657

Turn-On and Line Transient Response

The turn-on time is slew-limited and determined by the

short-circuit current, the output capacitor, and the output

voltage value as determined by the equation:

tON = VOUT •

COUT

ISC

For example, the LT6657-2.5V, with a 1µF output capaci-

tor and a typical current limit of 15mA the turn-on time

would be:

tON = 2.5V •

1µF

15mA

= 167µs

The resulting turn-on time is shown in Figure 1.

50µs/DIV

VIN

1V/DIV

GND

VOUT

1V/DIV

GND

6657 F01

COUT = 1µF

Figure 1. 2.5V Turn-On Characteristics

Line transient response with a 1µF output capacitor and

no output current is shown in Figure 2. The peak voltage

output response is less than 1mV.

50µs/DIV

VIN

0.2V/DIV

3V/DC

VOUT

2mV/DIV

2.5V/DC

6657 F02

COUT = 1µF, IOUT = 0mA

Figure 2. Line Transient Response with VIN = 0.4VP-P

Increasing the output load speeds up the response

(Figure 3).

50µs/DIV

VIN

0.2V/DIV

3V/DC

VOUT

2mV/DIV

2.5V/DC

6657 F03

COUT = 1µF, IOUT = 1mA SOURCING

Figure 3. Line Transient Response with VIN = 0.4VP-P

A larger output capacitor lowers the amplitude response

with a longer time response trade-off (Figure 4).

VIN

0.5V/DIV

3V/DC

VOUT

2mV/DIV

2.5V/DC

6657 F04

COUT = 10µF, IOUT = 0mA

50µs/DIV

Figure 4. Line Transient Response with VIN = 1VP-P

Load Transient Response

ThetestcircuitofFigure5isusedtomeasureloadtransient

response with various currents.

CIN

0.1µF

VIN = 3V

COUT

1µF

VOUT

VGEN

6657 F05

LT6657

OUT

GND

SHDN

Figure 5. Transient Load Test Circuit

applicaTions inForMaTion

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