MAX212EAG 데이터 시트보기 (PDF) - Maxim Integrated
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MAX212EAG Datasheet PDF : 8 Pages
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+3V-Powered, Low-Power,
True RS-232 Transceiver
–S—D
and
EN
determine
the
Operating
operation of the
Modes
MAX212
as follows:
–S—D EN
RECEIVER DRIVER
DC-DC
SUPPLY
OUTPUTS OUTPUTS CONVERTER CURRENT
LL
LH
High-Z
Enabled
High-Z
High-Z
Off
Minimum
Off
Minimum
HL
High-Z
Enabled
On
H H Enabled Enabled
On
Normal
Normal
Shutdown
Va +hiagnhd-imV-paerdeadnicseabslteadteawndhethneS–—tDrainsstmakitetenrstoarleogpicut lionwto.
Receiver operation is not affected, but power consump-
tion is dramatically reduced while in shutdown mode.
Supply current is minimized when the receiver inputs are
static in any of three states: floating (ground), less than
GND, or greater than VCC. This will be true for all static
RS-232 conditions. The presence of AC signals on receiv-
er inputs will increase VCC current in shutdown.
From a low-power system perspective, powering-up with
non-critical or unused sections of circuitry shut down or
deselected is generally recommended. Activating these
sections only when required saves power and reduces
power-up current surges. Powering-up the MAX212 in
Ss–—hDu,
tdown
low until
mode
VCC >
(holding
2.7V), helps
the shutdown
to achieve this.
pin,
Driving the MAX212 from 5V Logic
The MAX212 can interface with 5V logic while it operates
S–f—roDmanad3Vthseup+p5lVy,
This protects the
however a 200kΩ series resistor between
logic signal
MAX212 by
ipsrerevqenutiirnegdS–—(DseferoFmigsuinrekin2g).
current while V+ is powering up. Also, the UART must not
be permitted to send
transmitter input pins
uanltoilgS–—iDc
high to the
is high (not
MAX212’s EN
shut down).
or
+3.3V
V+ LN
LP V-
DC-DC CONVERTER
+5V
LOGIC
SIGNALS
200k SD
T_IN
R_OUT
MAX212
TX
X3
RX
X5
EN
GND
T_OUT
R_IN
Figure 2. Connecting to +5V Logic
Mouse Driveability
The MAX212 has been specifically designed to power
serial mice while operating from low-voltage power
supplies. It has been tested with samples of ten major
mouse models from six manufacturers, including the
leading three, Logitech (5 models), Mouse Systems,
and Microsoft. The MAX212 successfully drove all seri-
al mice and met their respective current and voltage
requirements (Figure 1).
Figure 3 shows the transmitter output voltages under
increasing load current. The MAX212’s switching regu-
lator ensures the transmitters will supply at least ±5V
during worst-case load conditions.
EIA/TIA-232E and 562 Standards
Most of the power drawn by RS-232 circuits is con-
sumed because the EIA/TIA-232E standard demands
that at least ±5V be delivered by the transmitters to
impedances that can be as low as 3kΩ. For applica-
____________________________+3V Powered RS-232 Transceivers from Maxim
PART
MAX212
MAX560
MAX561
MAX562
POWER-SUPPLY
VOLTAGE
(V)
3.0 to 3.6
3.0 to 3.6
3.0 to 3.6
2.7 to 5.25
No. OF
TRANSMITTERS/
RECEIVERS
3/5
4/5
4/5
3/5
No. OF
RECEIVERS
ACTIVE IN
SHUTDOWN
5
2
0
5
DATA RATE
(kbps)
FEATURES
250
True RS-232 from +3V
120
2 receivers active in shutdown
120
Pin compatible with MAX241
250
Wide supply range
6 _______________________________________________________________________________________
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