Texas Instruments ISO7220 Series, Руководство пользователя

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1.1 Overview
1.2 Functional Configuration of the Dual-Channel Digital Isolator
ISO7221x
1
2
3
4 5
6
7
8
GND2
Vcc2 Vcc1
GND1
OUTB
INA
OUTA
INB
IS
O
L
A
T
IO
N
ISO7220x
1
2
3
4 5
6
7
8
GND2
Vcc2 Vcc1
GND1
OUTB
INA
OUTA
INB
IS
O
L
A
T
IO
N
Introduction
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The ISO7220x and ISO721x dual digital isolators have a logic input and output buffer separated by a
silicon oxide (SiO
2
) insulation barrier. Used in conjunction with isolated power supplies, these devices
block high voltage, isolate grounds, and prevent noise currents on a data bus or other circuits from
entering the local ground and interfering with or damaging sensitive circuitry.
A binary input signal is conditioned, translated to a balanced signal, and then differentiated by the
capacitive isolation barrier. Across the isolation barrier, a differential comparator receives the logic
transition information, then sets or resets a flip-flop and the output circuit accordingly. A periodic update
pulse is sent across the barrier to ensure the proper dc level of the output. If this dc-refresh pulse is not
received for more than 4
µ
s, the input is assumed to be unpowered or not functional, and the failsafe
circuit drives the output to a logic-high state.
CAUTION
Note that although these devices provide galvanic isolation of up to 4000 V, this
EVM cannot be used for isolation voltage testing. It is designed for the
examination of device operating parameters only and will be damaged if high
voltage (> 5.5 V) is applied anywhere in the circuit.
The pin-outs of the dual-channel digital isolators are displayed in Figure 1 . The EVM comes with an
ISO7220M installed; however, the user may reconfigure the EVM for use with any of the footprints.
Figure 1. The ISO7220x and ISO7221x Pinouts
The ISO7220A, ISO7220B, ISO7220C, ISO7221A, ISO7221B and ISO7221C have TTL input thresholds
and an input noise filter that prevents transient pulses of up to 2 ns in duration from being passed to the
output of the device.
The ISO7220M and ISO7221M have a CMOS Vcc/2 input threshold, but do not have the noise filter and
the additional propagation delay.
Dual-Channel Digital Isolator EVM 2 SLLU098A – June 2007 – Revised July 2009
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