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參數(shù)資料
| 型號： | MAX3228-MAX3229 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | +2.5V to +5.5V RS-232 Transceivers in UCSP |
| 中文描述： | 2.5V至5.5V的RS - 232收發(fā)器的UCSP封裝 |
| 文件頁數(shù)： | 7/14頁 |
| 文件大小： | 238K |
| 代理商： | MAX3228-MAX3229 |
M
+2.5V to +5.5V RS-232 Transceivers
in UCSP
_______________________________________________________________________________________
7
For example, a three-cell NiMh battery system starts at
V
CC
= +3.6V, and the charge pump will generate an
output voltage of ±5.5V. As the battery discharges, the
MAX3228/MAX3229 maintain the outputs in regulation
until the battery voltage drops below +3.1V. Then the
output regulation points change to ±4.0V
When V
CC
is rising, the charge pump will generate an
output voltage of ±4.0V, while V
CC
is between +2.5V
and +3.5V. When V
CC
rises above the switchover volt-
age of +3.5V, the charge pump switches modes to
generate an output of ±5.5V.
Table 1 shows different supply schemes and their
operating voltage ranges.
RS-232 Transmitters
The transmitters are inverting level translators that con-
vert CMOS-logic levels to RS-232 levels. The
MAX3228/MAX3229 will automatically reduce the RS-
232 compliant levels (±5.5V) to RS-232 compatible lev-
els (±4.0V) when V
CC
falls below approximately +3.1V.
The reduced levels also reduce supply current require-
ments, extending battery life. Built-in hysteresis of
approximately 400mV for V
CC
ensures that the RS-232
output levels do not change if V
CC
is noisy or has a
sudden current draw causing the supply voltage to
drop slightly. The outputs will return to RS-232 compli-
ant levels (±5.5V) when V
CC
rises above approximately
+3.5V.
The MAX3228/MAX3229 transmitters guarantee a
250kbps data rate with worst-case loads of 3k
in par-
allel with 1000pF.
When
FORCEOFF
is driven to ground, the transmitters
and receivers are disabled and the outputs become
high impedance. When the AutoShutdown circuitry
senses that all receiver and transmitter inputs are inac-
tive for more than 30μs, the transmitters are disabled
and the outputs go to a high-impedance state. When
the power is off, the MAX3228/MAX3229 permit the
transmitter outputs to be driven up to ±12V.
The transmitter inputs do not have pullup resistors.
Connect unused inputs to GND or V
L
.
RS-232 Receivers
The MAX3228/MAX3229 receivers convert RS-232 sig-
nals to logic output levels. All receivers have inverting
three-state outputs and can be active or inactive. In
shutdown (
FORCEOFF
= low) or in AutoShutdown, the
MAX3228/MAX3229 receivers are in a high-impedance
state (Table 3).
The MAX3228/MAX3229 feature an
INVALID
output that
is enabled low when no valid RS-232 signal levels have
been detected on any receiver inputs.
INVALID
is func-
tional in any mode (Figures 2 and 3).
Figure 2c. MAX322_ AutoShutdown Logic
FORCEOFF
POWER DOWN
INVALID
FORCEON
INVALID IS AN INTERNALLY GENERATED SIGNAL
THAT IS USED BY THE AUTOSHUTDOWN LOGIC
AND APPEARS AS AN OUTPUT OF THE DEVICE.
POWER DOWN IS ONLY AN INTERNAL SIGNAL.
IT CONTROLS THE OPERATIONAL STATUS OF
THE TRANSMITTERS AND THE POWER SUPPLIES.
V
L
V
L
V
CC
Figure 2a. MAX322_ Entering 1μA Supply Mode via
AutoShutdown
+0.3V
-0.3V
INVALID
TO MAX322 _
POWER SUPPLY
AND TRANSMITTERS
R_IN
*TRANSMITTERS ARE DISABLED, REDUCING SUPPLY CURRENT TO 1
μ
A IF
ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR
AT LEAST
30
μ
s.
30
μ
s
COUNTER
R
Figure 2b. MAX322_ with Transmitters Enabled Using
AutoShutdown
+2.7V
-2.7V
INVALID
TO MAX322 _
POWER SUPPLY
R_IN
*TRANSMITTERS ARE ENABLED IF:
ANY RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V.
ANY RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR
LESS THAN
30
μ
s.
30
μ
s
COUNTER
R
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