MAX3380ECUP+T ,+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic PinsELECTRICAL CHARACTERISTICS(V = +2.35V to +5.5V, V = +1.65V to +5.5V. When V < +4.5V, C1 = C2 = C3 = ..
MAX3381ECUP+ ,+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic Pinsapplications where noise and EMI are issues. TheC1+MAX3380E/MAX3381E have a unique V pin thatL C1V+ ..
MAX3381ECUP+ ,+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic PinsFeaturesThe MAX3380E/MAX3381E are +2.35V to +5.5V-pow-♦ ±15kV ESD Protection on All CMOS and RS-232 ..
MAX3381EEUP ,+2.35V to +5.5V, 1レA, 2Tx/2Rx RS-232 Transceivers with 【15kV ESD-Protected I/O and Logic PinsApplicationsTTL/CMOSRS-232Cell Phone Data Lump CablesINPUTS OUTPUTST2IN T2OUTPDA Data Lump CablesVL ..
MAX3381EEUP ,+2.35V to +5.5V, 1レA, 2Tx/2Rx RS-232 Transceivers with 【15kV ESD-Protected I/O and Logic PinsFeaturesThe MAX3380E/MAX3381E are +2.35V to +5.5V-pow- ±15kV ESD Protection on All CMOS and RS-232 ..
MAX3381EEUP+ ,+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic PinsApplicationsTTL/CMOSRS-232Cell Phone Data Lump CablesINPUTS OUTPUTST2IN T2OUTPDA Data Lump CablesVL ..
MAX704SESA+T ,3.0V/3.3V Microprocessor Supervisory CircuitsElectrical Characteristics(V = 3.17V to 5.5V for the MAX690T/MAX704T/MAX80_T, V = 3.02V to 5.5V for ..
MAX704SESA-T ,3.0V/3.3V Microprocessor Supervisory CircuitsApplications● Battery-Powered Computers and Controllers● Embedded Controllers● Intelligent Instrume ..
MAX704TCSA ,3.0V or 3.3V microprocessor supervisory circuit. Reset threshold 3.075V. Active-low reset. Manual reset input. Backup-battery switch. Power-fail threshold accuracy +-4%. Power-fail comparator. Reset window +-75mVGeneral Description ________
MAX704TCSA+ ,3.0V/3.3V Microprocessor Supervisory CircuitsFeaturesThese microprocessor (µP) supervisory circuits reduce the ● RESET and RESET Outputscomplexi ..
MAX704TCSA+T ,3.0V/3.3V Microprocessor Supervisory CircuitsFeaturesThese microprocessor (µP) supervisory circuits reduce the ● RESET and RESET Outputscomplexi ..
MAX704TESA ,3.0V or 3.3V microprocessor supervisory circuit. Reset threshold 3.075V. Active-low reset. Manual reset input. Backup-battery switch. Power-fail threshold accuracy +-4%. Power-fail comparator. Reset window +-75mVGeneral Description ________
MAX3380ECUP+-MAX3380ECUP+T-MAX3381ECUP+-MAX3381EEUP+
+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic Pins
General DescriptionThe MAX3380E/MAX3381E are +2.35V to +5.5V-pow-
ered EIA/TIA-232 and V.28/V.24 communication inter-
faces with low power requirements, high data-rate
capabilities, and enhanced electrostatic discharge
(ESD) protection on both the TTL and RS-232 sides.
The MAX3380E/MAX3381E have two receivers and two
transmitters. All RS-232 inputs, outputs, and logic input
pins are protected to ±15kV using IEC 1000-4-2 Air-
Gap Discharge method and the Human Body Model,
and ±8kV using IEC 1000-4-2 Contact Discharge
method.
The proprietary low-dropout transmitter output stage
enables true RS-232 performance from a +3.1V to
+5.5V supply with a dual charge pump. The parts
reduce the transmitter output levels to RS-232-compati-
ble levels with no increase in supply current for sup-
plies less than +3.1V and greater than +2.35V. The
+2.35V to +5.5V operating range is fully compatible
with lithium-ion (Li+) batteries. The charge pump
requires only four small 0.1µF capacitors for operation.
The MAX3380E/MAX3381E transceivers use Maxim’s
revolutionary AutoShutdown Plus™ feature to auto-
matically enter a 1µA shutdown mode. These
devices shut down the on-board power supply and
drivers when they do not sense a valid signal transi-
tion for 30 seconds on either the receiver or trans-
mitter inputs.
The MAX3380E is capable of transmitting data at
rates of 460kbps while maintaining RS-232 output
levels, and the MAX3381E operates at data rates up
to 250kbps. The MAX3381E offers a slower slew rate
for applications where noise and EMI are issues. The
MAX3380E/MAX3381E have a unique VLpin that
allows interoperation in mixed-logic voltage systems
down to +1.65V. Both input and output logic levels
are referenced to the VLpin. The MAX3380E/MAX3381E
are available in a space-saving TSSOP package.
ApplicationsCell Phone Data Lump Cables
PDA Data Lump Cables
GPS Receivers
Digital Cameras
Features±15kV ESD Protection on All CMOS and RS-232
Inputs and Outputs (Except INVALID)
±15kV Human Body Model
±15kV IEC 1000-4-2 Air-Gap Discharge
±8kV IEC 1000-4-2 Contact DischargeOperates Over Entire Li+ Battery RangeLow Logic Threshold Down to +1.65V for
Compatibility with Cell Phone Logic Supply Voltages1µA Low-Power AutoShutdown Plus ModeCompatible with Next-Generation GSM Data Rates20-Pin TSSOP Package
MAX3380E/MAX3381E
+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins19-2128; Rev 0; 8/01
Ordering Information
PARTTEMP. RANGEPIN-PACKAGE
MAX3380ECUP0°C to +70°C20 TSSOP
MAX3380EEUP-40°C to +85°C20 TSSOP
MAX3381ECUP0°C to +70°C20 TSSOP
MAX3381EEUP-40°C to +85°C20 TSSOP
Pin Configuration appears at end of data sheet.MAX3380E/
MAX3381E
R2OUT
R1OUT
R2IN
GND
RS-232
OUTPUTS
TTL/CMOS
INPUTST2IN
T1IN
C2-
C2+
C1-
C1+
R1IN
T2OUT
T1OUT
VCCVL
C1
0.1μF
C2
0.1μF
0.1μF
+3.3V
RS-232
INPUTS
TTL/CMOS
OUTPUTS
5kΩ
5kΩ
0.1μF
0.1μF
FORCEON
FORCEOFF
Typical Operating CircuitAutoShutdown Plus is a trademark of Maxim Integrated Products
MAX3380E/MAX3381E
+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC= +2.35V to +5.5V, VL= +1.65V to +5.5V. When VCC< +4.5V, C1 = C2 = C3 = C4 = 0.1µF; when VCC≥+4.5V, C1 = 0.047µF,
C2 = C3 = C4 = 0.33µF; TA= TMINto TMAX, unless otherwise noted. Typical values are at VCC= VL= +3.3V, TA= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Note 1:V+ and V- can have maximum magnitudes of +7V, but their absolute difference cannot exceed +13V.
VCCto GND...........................................................-0.3V to +6.0Vto GND..............................................................-0.3V to +6.0V
V+ to GND.............................................................-0.3V to +7.0V
V- to GND..............................................................+0.3V to -7.0V
V+ + |V-| (Note 1).................................................................+13V
Input Voltages
T_IN, FORCEON, FORCEOFFto GND...............-0.3V to +6.0V
R_IN to GND.....................................................................±25V
Output Voltages
T_OUT to GND...............................................................±13.2V
R_OUT, INVALIDto GND...........................-0.3V to (VL+ 0.3V)
Short-Circuit Duration T_OUT to GND........................Continuous
Continuous Power Dissipation (TA= +70°C)
20-Pin TSSOP (derate 10.9mW/°C over +70°C).........879mW
Operating Temperature Ranges
MAX3380ECUP/MAX3381ECUP........................0°C to +70°C
MAX3380EEUP/MAX3381EEUP.....................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSReceivers idle, VT_IN = VCC or GND,
FORCEON = GND, FORCEOFF = VCC10Supply Current, AutoShutdown
PlusICC
FORCEOFF = GND110
Supply Current, Normal OperationICCFORCEON = FORCEOFF = VL, no load0.31mA
LOGIC INPUTS (T_IN, FORCEON, FORCEOFF)VCC = +5.5V, VL = +5.5V0.41.2Input Logic Threshold LowVILVCC = +2.5V, VL = +1.65V0.4V
VCC = +5.5V, VL = +5.5V VL ✕ 0.66Input Logic Threshold HighVIHVCC = +2.5V, VL = +1.65V VL ✕ 0.66V
Transmitter Input Hysteresis0.5V
Input Leakage Current±0.01±1µA
RECEIVER OUTPUTS (R_OUT) AND INVALIDOutput Voltage LowIOUT = 500µA0.5V
Output Voltage HighIOUT = -500µAVL - 0.4VL - 0.2V
RECEIVER INPUTS (R_IN)Input Voltage Range-25+25V
VL = +3.3V0.61.2Input Threshold LowTA = +25°CVL = +5.0V0.81.5V
VL = +3.3V1.52.4Input Threshold HighTA = +25°CVL = +5.0V1.82.4V
Input Hysteresis0.3V
Input ResistanceTA = +25°C357kΩ
MAX3380E/MAX3381E
+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
AutoShutdown Plus (FORCEON = GND, FORCEOFF = VL)Positive threshold2.7Receiver Input Threshold to
INVALID Output HighFigure 3Negative threshold-2.7V
Receiver Input Threshold to
INVALID Output LowFigure 3-0.30.3V
Receiver Positive or Negative
Threshold to INVALID HightINVLVCC = +5.0V, Figure 40.3µs
Receiver Positive or Negative
Threshold to INVALID LowtINVHVCC = +5.0V, Figure 430µs
Receiver or Transmitter Edge to
Transmitters EnabledtWUVCC = +5.0V, Figure 415µs
Receiver or Transmitter Edge to
Transmitters ShutdowntAU T OS H D N VCC = +5.0V, Figure 430s
TRANSMITTER OUTPUTSVCC Mode Switch Point
(VCC Falling)T_OUT = ±5.0V to ±3.7V2.953.13.25V
VCC Mode Switch Point
(VCC Rising)T_OUT = ±3.7V to ±5.5V3.33.53.7V
VCC Mode Switch Point
Hysteresis400mVC C = + 3.25V to + 5.5V ,C C fal l i ng ±5±5.4
Output Voltage Swing
All transmitter
outputs loaded
with 3kΩ to groundV C C = + 2.5V to + 2.95V ,C C fal l i ng ±3.7
Output ResistanceVCC = 0, transmitter output = ±2.0V30010MΩ
Output Short-Circuit Current±60mA
Output Leakage CurrentVOUT = ±12V, transmitters disabled±25µA
ESD PROTECTIONHuman Body Model±15
IEC 1000-4-2 Air-Gap Discharge Method±15R_IN, T_OUT, R_OUT, T_IN,
FORCEON, FORCEOFF
IEC 1000-4-2 Contact Discharge Method±8
ELECTRICAL CHARACTERISTICS (continued)(VCC= +2.35V to +5.5V, VL= +1.65V to +5.5V. When VCC< +4.5V, C1 = C2 = C3 = C4 = 0.1µF; when VCC≥+4.5V, C1 = 0.047µF,
C2 = C3 = C4 = 0.33µF; TA= TMINto TMAX, unless otherwise noted. Typical values are at VCC= VL= +3.3V, TA= +25°C.)
10001500500200025003000
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCEMAX3380E toc01
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE (V)
VOUT+
VOUT-
VCC = +4.2V10001500500200025003000
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCEMAX3380E toc02
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE (V)
VOUT+
VOUT-
VCC = +2.5V10005001500200025003000
MAX3380E
SLEW RATE vs. LOAD CAPACITANCEMAX3380E toc03
LOAD CAPACITANCE (pF)
SLEW RATE (V/
VCC = +4.2V
VCC = +2.5V
Typical Operating Characteristics(VCC= VL= +4.2V, C1 = 0.22µF, C2 = C3 = C4 = 1µF, C5 = 0.1µF parallel with 47µF, RL= 3kΩ, CL= 1000pF, data rate is 250kbps, = +25°C, unless otherwise noted.)
MAX3380E/MAX3381E
+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
TIMING CHARACTERISTICS(VCC= +2.35V to +5.5V, VL= +1.65V to +5.5V. When VCC< +4.5V, C1 = C2 = C3 = C4 = 0.1µF; when VCC≥+4.5V, C1 = 0.047µF,
C2 = C3 = C4 = 0.33µF; TA= TMINto TMAX, unless otherwise noted. Typical values are at VCC= VL= +3.3V, TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSMAX3381E250Maximum Data RateRL = 3kΩ, CL = 1000pF, one
transmitter switchingMAX3380E460kbps
tPLH0.15Receiver Propagation DelaytPHLReceiver input to receiver output, CL = 100pF0.15µs
Transmitter SkewtPHL- tPLH(Note 2)200ns
Receiver SkewtPHL- tPLH50ns
Transition Region Slew Rate
(MAX3380E)
VCC = +4.2V, -3.0V < T_OUT< +3.0V,
RL = 3kΩ, CL = 250pF to 1000pF, TA = +25°C20100V/µs
Transition Region Slew Rate
(MAX3381E)
VCC = +4.2V, -3.0V < T_OUT< +3.0V,
RL = 3kΩ, CL = 150pF to 1000pF, TA = +25°C630V/µs
Transition Region Slew Rate
(MAX3380E)
VCC = +2.35V, -3.0V < T_OUT< +3.0V,
RL = 3kΩ, CL = 250pF to 1000pF, TA = +25°C30V/µs
Transition Region Slew Rate
(MAX3381E)
VCC = +2.35V, -3.0V < T_OUT< +3.0V,
RL = 3kΩ, CL = 250pF to 1000pF, TA = +25°C10V/µs
Note 2:Transmitter skew is measured at the transmitter zero crosspoint.
MAX3380E/MAX3381E
+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins10005001500200025003000
MAX3381E
SLEW RATE vs. LOAD CAPACITANCEMAX3380E toc04
LOAD CAPACITANCE (pF)
SLEW RATE (V/VCC = +4.2V
VCC = +2.5V10005001500200025003000
SUPPLY CURRENT vs. LOAD CAPACITANCE
WHEN TRANSMITTING DATAMAX3381E toc05
LOAD CAPACITANCE (pF)
SUPPLY CURRENT (mA)
460kbps
250kbps
20kbps
1 TRANSMITTER SWITCHING
TRANSMITTER OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE (VCC FALLING)MAX3380E toc06
SUPPLY VOLTAGE (V)
TRANSMITTER OUTPUT VOLTAGE (V)
VOUT+
VOUT-
TRANSMITTER OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE (VCC RISING)MAX3380E toc07
SUPPLY VOLTAGE (V)
TRANSMITTER OUTPUT VOLTAGE (V)
VOUT+
VOUT-
SUPPLY CURRENT
vs. SUPPLY VOLTAGE (VCC FALLING)
MAX3380E toc08
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
1 TRANSMITTER SWITCHING
1μs/div
T_IN
5V/div
T_OUT
5V/div
MAX3380E toc09
MAX3380E
DATASTREAM VCC = +4.2V-5V
VCC = VL = +2.5V
1μs/div
T_IN
5V/div
T_OUT
5V/div
MAX3380E toc10
MAX3380E
DATASTREAM VCC = +2.5V-5V
Typical Operating Characteristics (continued)(VCC= VL= +4.2V, C1 = 0.22µF, C2 = C3 = C4 = 1µF, C5 = 0.1µF parallel with 47µF, RL= 3kΩ, CL= 1000pF, data rate is 250kbps, = +25°C, unless otherwise noted.)
MAX3380E/MAX3381E
+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
Detailed DescriptionThe MAX3380E/MAX3381E are RS-232 transceivers that
maximize battery life by reducing current consumption
at low battery levels. When the supply voltage is above
+3.7V, the RS-232 outputs are at ±5.5V, which is com-
pliant with the RS-232 standard. As the supply voltage
drops below the +3.1V set point, the RS-232 outputs
change to ±3.7V, which is compatible with the RS-232
standard. The outputs will remain at the compatible lev-
els until the supply voltage rises above +3.5V, where
they return to compliant levels. 400mV of hysteresis pro-
tects against power-supply bounce that may cause
numerous mode changes.
Most devices that use charge pumps to double and
invert voltages consume higher current when the supply
voltage is less than half of the required output voltage.
This is due to the fact that the charge pump is constant-
ly operating because the output voltage is below the
regulation voltage. This requires more supply current
because the output will never reach the regulation volt-
age and switch off. The MAX3380E/MAX3381E reduce
the output voltage requirement allowing the charge
pump to operate with supply voltages down to +2.35V.
Dual-Mode Regulated Charge-Pump
Voltage ConverterThe MAX3380E/MAX3381Es’ internal power supply is a
dual-mode regulated charge pump. The output regula-
tion point depends on VCCand the direction in which
VCCmoves through the switchover region of +2.95V <
VCC< +3.7V.
For supply voltages above +3.7V, the charge pump will
generate +5.5V at V+ and -5.5V at V-. The charge
pumps operate in a discontinuous mode. If the output
voltages are less than ±5.5V, the charge pumps are
enabled; if the output voltages exceed ±5.5V, the
charge pumps are disabled.
For supply voltages below +2.95V, the charge pump
will generate +4.0V at V+ and -4.0V at V-. The charge
pumps operate in a discontinuous mode.
Each charge pump requires a flying capacitor (C1, C2)
and a reservoir capacitor (C3, C4) to generate the V+
and V- supplies (see Typical Operating Circuit).
Pin Description
PINNAMEFUNCTIONESD
PROTECTEDC1+Positive Terminal of Voltage-Doubler Charge-Pump Capacitor—V++5.5V/+4.0V Generated by the Charge Pump—C1-Negative Terminal of Voltage-Doubler Charge-Pump Capacitor—C2+Positive Terminal of Inverting Charge-Pump Capacitor—C2-Negative Terminal of Inverting Charge-Pump Capacitor—V--5.5V/-4.0V Generated by the Charge Pump—INVALIDINVALID is asserted if any inputs of the receivers are in an invalid state;
-0.3V < VR_IN < +0.3V—
8, 9T_INTTL/CMOS Transmitter Inputs Referenced to VL (T1IN, T2IN)✔
10, 11R_OUTTTL/CMOS Receiver Outputs Referenced to VL (R2OUT, R1OUT)✔FORCEONForce-On Input. Drive high to override automatic circuitry keeping transmitters on
(FORCEOFF must be high) (Table 1).✔VLLogic Level Supply. +1.65V to +5.5V, sets CMOS logic thresholds and CMOS
outputs.—
14, 15R_INRS-232 Receiver Inputs (R2IN, R1IN)✔
16, 17T_OUTRS-232 Transmitter Outputs (T2OUT, T1OUT)✔GNDGround—FORCEOFFForce-Off Input. Drive low to shut down transmitters and on-board power supply.
This overrides all automatic circuitry and FORCEON (Table 1).✔20VCC+2.35V to +5.5V Supply Voltage
MAX3380E/MAX3381E
+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
Voltage Generation in the
Switchover RegionThe MAX3380E/MAX3381E include a switchover circuit
between RS-232-compliant and RS-232-compatible
modes that has approximately 400mV of hysteresis
around the switchover point. The hysteresis is shown in
Figure 1. This large hysteresis helps to avoid mode
change under battery or power-supply bounce.
Under a decaying VCC, the charge pump will generate
an output voltage of ±5.5V with a VCCinput range
between +3.1V and +5.5V. When VCCdrops below the
switchover point of +3.1V, the charge pump switches
into RS-232-compatible mode generating ±4V.
When VCCis rising, the charge pump will generate an
output voltage of ±4.0V, while VCCis between +2.5V
and +3.5V. When VCCrises above the switchover volt-
age of +3.5V, the charge pump switches to RS-232-
compliant mode to generate an output voltage of ±5.5V.
RS-232 TransmittersThe transmitters are inverting level translators that con-
vert CMOS-logic levels to RS-232-compatible levels.
The MAX3380E/MAX3381E will automatically reduce
the RS-232-compliant levels from ±5.5V to ±3.7V when
VCCfalls below approximately +3.1V. The reduced lev-
els are RS-232-compatible and reduce supply current
requirements that help preserve the battery. Built-in
hysteresis of approximately 400mV for VCCensures
that the RS-232 output levels do not change if VCCis
noisy or has a sudden current draw causing the supply
voltage to drop slightly. The outputs will return to RS-
232-compliant levels (±5.5V) when VCCrises above
approximately +3.5V.
The MAX3380E/MAX3381E transmitters guarantee a data
rate of 460kbps/250kbps, respectively, with worst-case
loads of 3kΩin parallel with 1000pF. Transmitters can be
paralleled to drive multiple receivers.
When FORCEOFFis driven to ground, the transmitters
are disabled and the outputs go into high impedance;
receivers remain active. When the AutoShutdown Plus
circuitry senses that all receiver and transmitter inputs
are inactive for more than 30s, the transmitters are dis-
abled and the outputs go into a high-impedance state,
and the receivers remain active. When the power is off,
the MAX3380E/MAX3381E permit the outputs to be dri-
ven up to ±12V.
The transmitter inputs have a 400kΩactive positive
feedback resistor. They will retain a valid logic level if
the driving signal is removed or goes high impedance.
Connect unused transmitter inputs to VCCor ground.
RS-232 ReceiversThe receivers convert RS-232 signals to logic levels
referred to VL. Both receivers are active in shutdown
(Table 1).
AutoShutdown Plus ModeThe MAX3380E/MAX3381E achieve a1µA supplycurrent
with Maxim’s AutoShutdown Plus feature, which operates
when FORCEOFFis high and FORCEON is low. When
these devices do not sense a valid signal transition on
any receiver and transmitter input for 30s, the on-board
charge pumps are shut down, reducing supply current
to 1µA. This occurs if the RS-232 cable is disconnected
or if the connected peripheral transmitters are turned off,
and if the UART driving the transmitter inputs is inactive.
The system turns on again when a valid transition is
applied to any RS-232 receiver or transmitter input. As a
result, the system saves power without changes to the
existing BIOS or operating system.
Figures 2a and 2b show valid and invalid RS-232
receiver voltage levels. INVALIDindicates the receiver
input’s condition, and is independent of the FORCEON
and FORCEOFFstates. Figure 2 and Table 1 summa-
rize the MAX3380E/MAX3381E’s operating modes.
FORCEON and FORCEOFFoverride AutoShutdown
Plus circuitry. When neither control is asserted, the IC
selects between these states automatically based on
the last receiver or transmitter input edge received.
By connecting FORCEON to INVALID, the MAX3380E/
MAX3381Eis shut down when no valid receiver level and
no receiver or transmitter edge is detected for 30s, and
wakes up when a receiver or transmitter edge is detect-
ed (Figure 2c).
20ms/div
VCC
2V/div
2V/div
+4.5V
+2.5V
+5.8V
+4.4V
Figure 1. V+ Switchover for Changing Vcc
