MAX3227EEAE Datasheet, PDF (12/19 Pages) Maxim Integrated Products – 1muA Supply Current, 1Mbps, 3.0V to 5.5V, RS-232 Transceivers

MAX3224–MAX3227/MAX3244/MAX3245
1µA Supply Current, 1Mbps, 3.0V to 5.5V,
RS-232 Transceivers with AutoShutdown Plus
Software-Controlled Shutdown
If direct software control is desired, use INVALID to
indicate DTR or Ring Indicator signal. Tie FORCEOFF
and FORCEON together to bypass the AutoShutdown
Plus so the line acts like a SHDN input.
__________Applications Information
Capacitor Selection
The capacitor type used for C1–C4 is not critical for
proper operation; polarized or nonpolarized capacitors
can be used. The charge pump requires 0.1µF capaci-
tors for 3.3V operation. For other supply voltages, see
Table 3 for required capacitor values. Do not use val-
ues smaller than those listed in Table 3. Increasing the
capacitor values (e.g., by a factor of 2) reduces ripple
on the transmitter outputs and slightly reduces power
consumption. C2, C3, and C4 can be increased without
changing C1’s value. However, do not increase C1
without also increasing the values of C2, C3, C4,
and C_BYPASS, to maintain the proper ratios (C1 to
the other capacitors).
When using the minimum required capacitor values,
make sure the capacitor value does not degrade
excessively with temperature. If in doubt, use capaci-
tors with a larger nominal value. The capacitor’s equiva-
lent series resistance (ESR), which usually rises at low
temperatures, influences the amount of ripple on V+
and V-.
Power-Supply Decoupling
In most circumstances, a 0.1µF V_CC bypass capacitor
is adequate. In applications that are sensitive to power-
supply noise, use a capacitor of the same value as
charge-pump capacitor C1. Connect bypass capaci-
tors as close to the IC as possible.
Transmitter Outputs
when Exiting Shutdown
Figure 6 shows two transmitter outputs when exiting
shutdown mode. As they become active, the two trans-
mitter outputs are shown going to opposite RS-232 lev-
els (one transmitter input is high; the other is low). Each
Table 3. Required Minimum Capacitance
Values
V_CC
(V)
3.0 to 3.6
4.5 to 5.5
3.0 to 5.5
C1, C_BYPASS
(µF)
0.1
0.047
0.22
C2, C3, C4
(µF)
0.1
0.33
1
transmitter is loaded with 3kΩ in parallel with 1000pF.
The transmitter outputs display no ringing or undesir-
able transients as they come out of shutdown. Note that
the transmitters are enabled only when the magnitude
of V- exceeds approximately -3V.
5V/div
0
FORCEON =
FORCEOFF
T1OUT
2V/div
0
5V/div
0
V_CC = 3.3V
C1–C4 = 0.1μF
5μs/div
T2OUT
READY
Figure 6. Transmitter Outputs when Exiting Shutdown or
Powering Up
V_CC
C_BYPASS
C1+
V_CC
V+
C1
C3*
C1-
MAX3224
MAX3225
C2+
MAX3226
V-
C2
MAX3227
C4
C2-
MAX3244
MAX3245
T_ IN
T_ OUT
R_ OUT
R_ IN
FORCEON
5kΩ
V_CC
FORCEOFF
GND
*C3 CAN BE RETURNED TO V_CC OR GND.
Figure 7. Loopback Test Circuit
1000pF
12
Maxim Integrated