LT1684 查看數據表（PDF） - Linear Technology

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LT1684

Micropower Ring Tone Generator

Linear Technology 

LT1684

PI FU CTIO S

BGOUT (Pin 13): Normalized PWM Buffered Output. PWM

differential input is amplitude normalized to ±1.25V (refer-

enced to the OUT pin). This signal is used to drive the

active filter/amplifier. Filter resistor values must be chosen

to limit the maximum current load on this pin to less than

2mA. The output is current limit protected to a typical value

of ±4.5mA.

IN A (Pin 14): PWM Positive Input. Input is isolated from

digital source by ~100pF series capacitor. A 10k resistor

should be connected to the IN A pin in series with the

isolation capacitor for transient protection. The PWM

receiver implements a diode forward drop of input hyster-

esis (relative to IN B). This hysteresis and internal signal

limiting assure common mode glitch rejection with isola-

tion capacitor mismatches up to 2:1. For maximum perfor-

mance, however, effort should be made to match the two

PWM input isolation capacitors. Pin IN A is differentially

clamped to pin IN B through back-to back isolation-base

diodes. This results in a high impedance differential input

±100mV beyond the input thresholds. 5k internal input

resistors yield a 10k (nominal) differential overdrive im-

pedance.

W

FUNCTIONAL BLOCK DIAGRA

+

PWM

INPUT

–

100pF

10k

100pF

10k

IN A 5k

IN B 5k

BGOUT

1.25V

–1.25V

FILTER

ELEMENTS

–

AMPIN 5k +

100pF

COMP1

COMP2

20pF

15k

CURRENT

LIMIT

RING

OUTPUT

(RING RETURN)

LT1684 Block Diagram

6

V+

GATE+

14V

ATREF

LIM+

OUT

14V

GATE–

LIM–

V–

V+

V–

1684 BD

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