ASM206E/ASM207E/ASM208E/ASM2±±E/ASM2±3E
On the ADM2±3E, Receiver R4 and Receiver R5 remain
enabled in shutdown. Note that the transmitters are disabled
protection structure is shown in Figure 24 and Figure 25. Each
input and output contains two back-to-back high speed
but are not tristated in shutdown; it is not permitted to connect
multiple (RS-232) driver outputs together.
clamping diodes. During normal operation, with maximum
RS232 signal levels, the diodes have no effect because one or
the other is reverse biased, depending on the polarity of the
signal. If, however, the voltage exceeds about ±50 V, reverse
breakdown occurs, and the voltage is clamped at this level. The
diodes are large p-n junctions designed to handle the
The shutdown feature is very useful in battery-operated systems
since it reduces the power consumption to ± μW. During
shutdown, the charge pump is also disabled. The shutdown
control input is active high on the ADM2±±E, and it is active
low on the ADM2±3E. When exiting shutdown, the charge
pump is restarted, and it takes approximately ±00 μs for it to
reach its steady state operating condition.
instantaneous current surges that can exceed several amperes.
The transmitter outputs and receiver inputs have a similar
protection structure. The receiver inputs can also dissipate some
of the energy through the internal 5 kΩ resistor to GND as well
as through the protection diodes.
HIGH BAUD RATE
The ADM2xxE feature high slew rates, permitting data
transmission rates well in excess of the EIA-232-E
The protection structure achieves ESD protection up to
±±5 kV and EFT protection up to ±2 kV on all RS-232 I/O
lines. The methods used to test the protection scheme are
discussed in the ESD Testing (IEC ±00042) and EFT/Burst
Testing (IEC ±00044) sections.
specifications. RS-232 levels are maintained at data rates up to
230 kbps, even under worst-case loading conditions. This
allows for high speed data links between two terminals, making
it suitable for the new generation modem standards that require
data rates of 200 kbps. The slew rate is controlled internally to
less than 30 V/μs to minimize EMI interference.
R1
RECEIVER
RX
INPUT
3V
D1
EN INPUT
R
IN
D2
0V
tDR
VOH
Figure 24. Receiver Input Protection Scheme
VOH –0.1V
RECEIVER
OUTPUT
VOL +0.1V
T
OUT
TRANSMITTER
OUTPUT
RX
VOL
D1
D2
NOTES
1. EN IS THE COMPLEMENT OF EN FOR THE ADM213E.
Figure 22. Receiver Disable Timing
Figure 25. Transmitter Output Protection Scheme
3V
EN INPUT
ESD TESTING (IEC 1000-4-2)
0V
IEC ±000-4-2 (previously IEC 80±-2) specifies compliance
testing using two coupling methods, contact discharge and air-
gap discharge. Contact discharge calls for a direct connection to
the unit being tested. Air-gap discharge uses a higher test voltage
but does not make direct contact with the unit under test. With
air-gap discharge, the discharge gun is moved toward the unit
under test, developing an arc across the air gap. This method is
influenced by humidity, temperature, barometric pressure,
distance, and rate of closure of the discharge gun. The contact
discharge method, while less realistic, is more repeatable and is
gaining acceptance in preference to the air-gap method.
tER
+3.5V
RECEIVER
OUTPUT
+0.8V
NOTES
1. EN IS THE COMPLEMENT OF EN FOR THE ADM213E.
Figure 23. Receiver Enable Timing
ESD/EFT TRANSIENT PROTECTION SCHEME
The ADM2xxE use protective clamping structures on all inputs
and outputs that clamp the voltage to a safe level and dissipate
the energy present in ESD (electrostatic) and EFT (electrical
fast transient) discharges. A simplified schematic of the
Although very little energy is contained within an ESD pulse,
the extremely fast rise time, coupled with high voltages, can
cause failures in unprotected semiconductors. Catastrophic
Rev. E | Page ±± of 20
ROCHESTER [ Rochester Electronics ]
