LT1316CS8 datasheet(10/16 Pages) LINER

10 / 16 page

LT1316

APPLICATIONS INFORMATION

VOUT

100mV/DIV

AC COUPLED

100mA/DIV

100

µs/DIV

1316 F07

Figure 7. Switching Waveforms for the Circuit

Shown in Figure 7 Without C1. The Output Ripple

Voltage is Approximately 140mVP-P

µs/DIV

1316 F08

Figure 8. By Adding C1, Output Ripple Voltage

is Reduced to Less Than 80mVP-P

100mA/DIV

VOUT

100mV/DIV

AC COUPLED

µF ceramic capacitor acts to smooth voltage spikes at

switch turn-on and turn-off. If the power source is far away

from the IC, inductance in the power source leads results

in high impedance at high frequency. A local high capaci-

tance bypass is then required to restore low impedance at

the IC.

Low-Battery Detector

The LT1316 contains an independent low-battery detector

that remains active when the device is shut down. This

detector, actually a hysteretic comparator, has an open

collector output that can sink up to 500

µA. The compara-

tor also operates below the switcher’s undervoltage lock-

out threshold, operating until VIN reaches approximately

1.4V.

Layout/Input Bypassing

The LT1316’s high speed switching mandates careful

attention to PC board layout. Suggested component place-

ment is shown in Figure 9. The input supply must have low

impedance at AC and the input capacitor should be placed

as indicated in the figure. The value of this capacitor

depends on how close the input supply is to the IC. In

situations where the input supply is more than a few

inches away from the IC, a 47

µF to 100µF solid tantalum

bypass capacitor is required. If the input supply is close to

the IC, a 1

µF ceramic capacitor can be used instead. The

LT1316 switches current in pulses up to 0.5A, so a low

impedance supply must be available. If the power source

(for example, a 2 AA cell battery) is within 1 or 2 inches of

the IC, the battery itself provides bulk capacitance and the

1316 F09

LT1316

COUT

RSET

VIN

GND

VOUT

CIN

Figure 9. Suggested PC Layout

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