MAX562
Complete 230kbps, 2.7V to 5.25V
Serial Interface for Notebook Computers
_______________________________________________________________________________________ 7
the MAX562 transmitter outputs when
SHDN
rises. Two
transmitter outputs are shown going to opposite EIA/TIA-
562 levels (one transmitter input is high, the other is low).
Each transmitter is loaded with 3kΩ in parallel with
2500pF. The transmitter outputs are well behaved, with
no ringing or undesirable transients as they come out of
shutdown.
Driving Multiple Receivers
Each transmitter is designed to drive a single receiver.
Transmitters can be paralleled to drive multiple
receivers.
EIA/TIA-562 Receivers
All 5 receivers are identical and accept EIA/TIA-562 or
EIA/TIA-232 signals. The CMOS receiver outputs swing
between V
CC
and GND. They are inverting, maintaining
compatibility with the driver outputs.
The guaranteed 0.8V and 2.4V receiver input thresh-
olds are significantly tighter than the ±3.0V thresholds
required by the EIA/TIA-562 specification. This allows
the receiver inputs to respond to TTL/CMOS logic lev-
els as well as EIA/TIA-562/232 levels. Also, the
MAX562's guaranteed 0.8V lower threshold ensures
that receivers shorted to ground will have a logic 1 out-
put. The 5kΩ input resistance to ground ensures that a
receiver with its input left open will also have a logic 1
output.
The receiver inputs have approximately 0.3V hysteresis
when
SHDN
is high. This provides clean output transi-
tions, even with slowly moving input signals with mod-
erate noise and ringing.
The receivers are active when EN is high. When EN is
low, the receiver outputs are high impedance. This
allows wire-OR connection of two EIA/TIA-562 ports (or
ports of different types) at the UART.
The receivers are always active,when EN is high, irre-
spective of
SHDN
's state. When
SHDN
is high, the
receivers have hysteresis and experience the shortest
propagation delays (typically 100ns falling, 250ns ris-
ing). When
SHDN
is low, the receivers have longer
propagation delays (typically 3µs falling, 2µs rising)
and have no hysteresis. The receiver outputs are not
valid for 50µs after
SHDN
goes low.
Shutdown and Enable Control
SHDN
and EN determine the operation of the MAX562
as shown in Table 1.
__________Applications Information
Capacitor Selection
The capacitor type is not critical for proper MAX562
operation. Any low cost ceramic capacitor (e.g., Z5U,
Y5V) is acceptable for operating at room temperature,
0
200 300100
SHDN
5
0
6
4
2
0
-2
-4
V
CC
= +2.2V V
CC
= +2.7V V
CC
= +5.0VV
CC
= +3.3V
TIME (µs)
VOLTS (V)
Figure 5. Time for Transmitters to Exit Shutdown
Table 1. MAX562 Control Pin Configurations
EN
CHARGE-PUMP
OPERATION
STATUS
TRANSMITTERS
T1-T3
RECEIVERS
R1-R5
SUPPLY
CURRENT
TYP (A)
0 0 Shutdown High-Z High-Z 1µ
0 1 Shutdown High-Z Active* 45µ
1 0 Normal Operation Active High-Z 24m
1 1 Normal Operation Active Active 24m
* Active, but with reduced performance (see
EIA/TIA-562 Receivers
section). This is “keep-awake” mode.
