MAX3160(2000) 데이터 시트보기 (PDF) - Maxim Integrated
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MAX3160 Datasheet PDF : 23 Pages
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+3.0V to+5.5V, 1µA, RS-232/RS-485/422
Multiprotocol Transceivers
are enabled; if the magnitude of both output voltages
exceeds 5.5V, the charge pumps are disabled. Each
charge pump requires a flying capacitor (C1, C2) and a
reservoir capacitor (C3, C4) to generate the V+ and V-
supplies (see Functional Diagrams).
RS-485/422 Transceivers
The MAX3160/MAX3161/MAX3162 RS-485/422 trans-
ceivers feature fail-safe circuitry that guarantees a
logic-high receiver output when the receiver inputs are
open or shorted, or when they are connected to a ter-
minated transmission line with all drivers disabled (see
Fail-Safe). The MAX3160/MAX3161/MAX3162 also fea-
ture pin-selectable reduced slew-rate drivers that mini-
mize EMI and reduce reflections caused by improperly
terminated cables, allowing error-free data transmission
up to 250kbps (see Reduced EMI and Reflections). The
transmitters may operate at speeds up to 10Mbps with
the slew-rate limiting disabled. Drivers are short-circuit
current limited and thermally limited to protect them
against excessive power dissipation. Half-duplex com-
munication is enabled by driving HDPLX high.
Fail-Safe
The MAX3160/MAX3161/MAX3162 guarantee a logic-
high RS-485 receiver output when the receiver inputs
are shorted or open, or when they are connected to a
terminated transmission line with all drivers disabled.
This is done by having the receiver threshold between
-50mV and -200mV. If the differential receiver input volt-
age (A-B) is greater than or equal to -50mV, RO is logic
high. If A-B is less than or equal to -200mV, RO is logic
low. In the case of a terminated bus with all transmitters
disabled, the receiver’s differential input voltage is
pulled to GND by the termination. This results in a logic
high with a 50mV minimum noise margin. Unlike other
fail-safe devices, the -50mV to -200mV threshold com-
plies with the ±200mV EIA/TIA-485 standard.
RS-232 Transceivers
The MAX3160/MAX3161/MAX3162 RS-232 transmitters
are inverting-level translators that convert CMOS-logic
levels to ±5.0V EIA/TIA-232-compliant levels. The trans-
mitters are guaranteed at a 250kbps data rate in slew-
rate limited mode (FAST = GND) with worst-case loads
of 3kΩ in parallel with 1000pF. Data rates up to
1Mbps can be achieved by asserting FAST.
When powered down or in shutdown, the MAX3160/
MAX3161/MAX3162 outputs are high impedance and
can be driven to ±12V. The transmitter inputs do not
have pullup resistors. Connect unused inputs to ground
or VCC.
The receivers convert RS-232 signals to CMOS-logic out-
put levels. All receivers have inverting outputs that
remain active in shutdown. The MAX3160/MAX3161/
MAX3162 permit their receiver inputs to be driven to
±25V. Floating receiver input signals are pulled to
ground through internal 5kΩ resistors, forcing the out-
puts to a logic high. The MAX3162 has transmitter and
receiver enable pins that allow its outputs to be three-
stated.
Applications Information
Capacitor Selection
The capacitor type used for C1–C4 is not critical for
proper operation; polarized or nonpolarized capacitors
can be used. Ceramic chip capacitors with an X7R
dielectric provide the best combination of performance,
cost, and size. The charge pump requires 0.1µF
capacitors for 3.3V operation. For other supply volt-
ages, see Table 13 for required capacitor values. Do
not use values smaller than those listed in Table 13.
Increasing the capacitor values reduces ripple on the
transmitter outputs and slightly reduces power con-
sumption. C2, C3, and C4 can be changed without
changing C1’s value. However, do not increase C1
without also increasing the values of C2, C3, C4,
and CBYPASS to maintain the proper ratios to the
other capacitors.
When using the minimum required capacitor values,
make sure the capacitance value does not degrade
excessively with temperature or voltage. This is typical
of Y5V and Z5U dielectric ceramic capacitors. If in
doubt, use capacitors with a larger nominal value. The
capacitor’s equivalent series resistance (ESR), which
usually rises at low temperatures, influences the
amount of ripple on V+ and V-.
Power-Supply Decoupling
In applications that are sensitive to power-supply noise,
decouple VCC to ground with a capacitor of the same
value as reservoir capacitors C2, C3, and C4. Connect
the bypass capacitor as close to the IC as possible.
RS-232 Transmitter Outputs
when Exiting Shutdown
Figure 10 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
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 V- exceeds
approximately -3V.
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