MAX3228EBV-T Maxim Integrated, MAX3228EBV-T Datasheet - Page 8

• Manufacturer Part Number: MAX3228EBV-T
• Description: RS-232 Interface IC 2.5-5.5V Transceiver
• Manufacturer: Maxim Integrated
• Series: MAX3228, MAX3229r

Specifications of MAX3228EBV-T

• Data Rate: 250 Kbps
• Operating Supply Voltage: 2.5 V to 5.5 V
• Supply Current: 10 uA
• Operating Temperature Range: - 40 C to + 85 C
• Mounting Style: SMD/SMT
• Package / Case: UCSP-20 6 x 5
• Number Of Drivers: 2
• Number Of Receivers: 2

+2.5V to +5.5V RS-232 Transceivers
in UCSP
Figure 3. AutoShutdown Trip Levels
8
Figure 4. AutoShutdown with Initial Turn-On to Wake Up a System
RECEIVER
VOLTAGE
OUTPUT
INVALID
_______________________________________________________________________________________
a)
b)
INPUT
MANAGEMENT
(V)
(V)
POWER-
+2.7V
+0.3V
V
V
-0.3V
-2.7V
UNIT
CC
V+
CC
V-
0
0
0
AUTOSHUTDOWN, TRANSMITTERS DISABLED,
TRANSMITTERS ENABLED, INVALID HIGH
TRANSMITTERS ENABLED, INVALID HIGH
1µA SUPPLY CURRENT, INVALID LOW
MASTER SHDN LINE
t
INVL
INDETERMINATE
INDETERMINATE
FORCEOFF
MAX3228
MAX3229
0.1µF
FORCEON
1MΩ
t
INVH
INVALID
REGION
t
WU
The MAX3228/MAX3229 achieve a 1µA supply current
with Maxim’s AutoShutdown feature, which operates
when FORCEON is low and FORCEOFF is high. When
these devices sense no valid signal levels on all receiv-
er inputs for 30µs, the on-board charge pump and dri-
vers are shut off, reducing V
This occurs if the RS-232 cable is disconnected or the
connected peripheral transmitters are turned off. The
device turns on again when a valid level is applied to
any RS-232 receiver input. As a result, the system
saves power without changes to the existing BIOS or
operating system.
Table 3 and Figure 2c summarize the MAX3228/
MAX3229 operating modes. FORCEON and FORCEOFF
override AutoShutdown. When neither control is assert-
ed, the IC selects between these states automatically,
based on receiver input levels. Figures 2a, 2b, and 3a
depict valid and invalid RS-232 receiver levels. Figures
3a and 3b show the input levels and timing diagram for
AutoShutdown operation.
A system with AutoShutdown may need time to wake
up. Figure 4 shows a circuit that forces the transmitters
on for 100ms, allowing enough time for the other sys-
tem to realize that the MAX3228/MAX3229 are active. If
the other system transmits valid RS-232 signals within
that time, the RS-232 ports on both systems remain
enabled.
When shut down, the devices’ charge pumps are off,
V+ is pulled to V
transmitter outputs are high-impedance. The time
required to exit shutdown is typically 100µs (Figure 3b).
In case FORCEON and FORCEOFF are inaccessible,
these pins have 60Ω (typ) pullup resistors connected to
V
are not connected, the MAX3228 and MAX3229 will
always be active. Pulling these pins to ground will draw
current from the V
lated from the voltage supplied at V
(typ) pullup resistor.
Unlike other RS-232 interface devices, where the
receiver outputs swing between 0 and V
Table 2. Power-On Default States
L
FORCEOFF
PIN NAME
FORCEON
(Table 2). Therefore, if FORCEON and FORCEOFF
POWER-ON DEFAULT
CC
L
supply. This current can be calcu-
, V- is pulled to ground, and the
FORCEON and FORCEOFF
High
High
V
CC
L
Logic Supply Input
supply current to 1µA.
AutoShutdown
Internal pullup
Internal pullup
L
MECHANISM
and the 60kΩ
CC
, the