FN6041 Rev 2.00 Page 1 of 13
June 16, 2010
FN6041
Rev 2.00
June 16, 2010
ISL4270E
QFN Packaged, ±15kV ESD Protected, +3V to +5.5V, 300nA, 250kbps, RS-232
Transceivers with Enhanced Automatic Powerdown and a Separate Logic Supply
DATASHEET
The Intersil ISL4270E is a 3.0V to 5.5V powered RS-232
transceiver which meets ElA/TIA-232 and V.28/V.24
specifications, even at VCC = 3.0V. Additionally, it provides
15kV ESD protection (IEC61000-4-2 Air Gap and Human
Body Model) on transmitter outputs and receiver inputs
(RS-232 pins). Targeted applications are PDAs, Palmtops,
and notebook and laptop computers where the low
operational, and even lower standby power consumption is
critical. Efficient on-chip charge pumps, coupled with manual
and enhanced automatic powerdown functions, reduce the
standby supply current to a 300nA trickle. Tiny 5mmx5mm
Quad Flat No-Lead (QFN) packaging, and the use of small,
low value capacitors ensure board space savings as well.
Data rates greater than 250kbps are guaranteed at worst
case load conditions.
The ISL4270E features a VL pin that adjusts the logic pin
output levels and input thresholds to values compatible with
the VCC powering the external logic (e.g., a UART).
This device includes an enhanced automatic powerdown
function which powers down the on-chip power-supply and
driver circuits. This occurs when all receiver and transmitter
inputs detect no signal transitions for a period of 30 seconds.
It power back up, automatically, whenever it senses a
transition on any transmitter or receiver input.
Table 1 summarizes the features of the ISL4270E, while
Application Note AN9863 summarizes the features of each
device comprising the 3V RS-232 family.
Features
• Available in Near Chip Scale QFN (5mmx5mm) Package
•V
L Supply Pin for Compatibility with Mixed Voltage
Systems
• ESD Protection for RS-232 I/O Pins to 15kV (IEC61000)
• Manual and Enhanced Automatic Powerdown Features
• Meets EIA/TIA-232 and V.28/V.24 Specifications at 3V
• On-Chip Charge Pumps Require Only Four External
0.1F Capacitors
• Receivers Stay Active in Powerdown
• Very Low Supply Current . . . . . . . . . . . . . . . . . . . . 300A
• Guaranteed Minimum Data Rate . . . . . . . . . . . . . 250kbps
• Wide Power Supply Range . . . . . . . Single +3V to +5.5V
• Low Supply Current in Powerdown State. . . . . . . . 300nA
• Pb-Free (RoHS Compliant)
Applications
• Any System Requiring RS-232 Communication Ports
- Battery Powered, Hand-Held, and Portable Equipment
- Laptop Computers, Notebooks, Palmtops
- Digital Cameras
- PDA’s and PDA Cradles
- Cellular/Mobile Phones
Ordering Information
PART NUMBER
(Note)
PART
MARKING
TEMP.
RANGE
(°C) PACKAGE
PKG.
DWG. #
ISL4270EIRZ* ISL4270 EIRZ -40 to +85 32 Ld QFN
(Pb-free)
L32.5x5B
*Add “-T” suffix for tape and reel. Please refer to TB347 for details on
reel specifications.
NOTE: These Intersil Pb-free plastic packaged products employ
special Pb-free material sets, molding compounds/die attach
materials, and 100% matte tin plate plus anneal (e3 termination
finish, which is RoHS compliant and compatible with both SnPb and
Pb-free soldering operations). Intersil Pb-free products are MSL
classified at Pb-free peak reflow temperatures that meet or exceed
the Pb-free requirements of IPC/JEDEC J STD-020.
TABLE 1. SUMMARY OF FEATURES
PART NUMBER
NO. OF
Tx.
NO. OF
Rx.
DATA RATE
(kbps)
Rx. ENABLE
FUNCTION?
VL LOGIC
SUPPLY PIN?
MANUAL
POWER- DOWN?
ENHANCED AUTOMATIC
POWERDOWN FUNCTION?
ISL4270E 3 3 250 NO YES YES YES
ISL4270E
FN6041 Rev 2.00 Page 2 of 13
June 16, 2010
Pinout
ISL4270E (QFN)
TOP VIEW
NC
C2+
C2-
V-
T1IN
T2IN
INVALID
T1OUT
T2OUT
T3OUT
R1IN
R2IN
R3IN
NC
NC
T3IN
FORCEON
R3OUT
R2OUT
VL
R1OUT
C1-
V+
C1+
FORCEOFF
VCC
NC
GND
NC
7
11 12 13 14 15910
6
1
2
3
4
5
8
16
18
19
24
23
22
21
20
17
2728293031 252632
NC
NC
NC
PD
Pin Descriptions
PIN FUNCTION
VCC System power supply input (3.0V to 5.5V).
V+ Internally generated positive transmitter supply (+5.5V).
V- Internally generated negative transmitter supply (-5.5V).
GND Ground connection. This is also the potential of the thermal pad (PD).
C1+ External capacitor (voltage doubler) is connected to this lead.
C1- External capacitor (voltage doubler) is connected to this lead.
C2+ External capacitor (voltage inverter) is connected to this lead.
C2- External capacitor (voltage inverter) is connected to this lead.
TIN TTL/CMOS compatible transmitter Inputs. The switching point is a function of the VL voltage.
TOUT 15kV ESD Protected, RS-232 level (nominally 5.5V) transmitter outputs.
RIN 15kV ESD Protected, RS-232 compatible receiver inputs.
ROUT TTL/CMOS level receiver outputs. Swings between GND and VL.
VLLogic-Level Supply. All TTL/CMOS inputs and outputs are powered by this supply.
INVALID Active low output that indicates if no valid RS-232 levels are present on any receiver input. Swings between GND and VL.
FORCEOFF Active low to shut down transmitters and on-chip power supply. This overrides any automatic circuitry and FORCEON (see Table 2).
The switching point is a function of the VL voltage.
FORCEON Active high input to override automatic powerdown circuitry thereby keeping transmitters active (FORCEOFF must be high). The
switching point is a function of the VL voltage.
PD Exposed Thermal Pad. Connect to GND.
ISL4270E
FN6041 Rev 2.00 Page 3 of 13
June 16, 2010
Typical Operating Circuit
27
VCC
T1OUT
T2OUT
T3OUT
T1IN
T2IN
T3IN
T1
T2
T3
0.1F
+0.1F
+
0.1F
5
6
23
22
10 21
29
31
30
4
V+
V-
C1+
C1-
C2+
C2-
+
0.1F
2
3
R1OUT R1IN
20
5k
R2OUT R2IN
19
13
5k
R3OUT R3IN
18
12
5k
14
C1
C2
+C3
C4
FORCEON
FORCEOFF
11
GND
28
+3.3V +0.1F
26
VCC
TTL/CMOS
LOGIC LEVELS
RS-232
LEVELS
RS-232
LEVELS
R1
R2
R3
7
INVALID
TO POWER
CONTROL LOGIC
VL
15
LOGIC VCC +
0.1F
ISL4270E
FN6041 Rev 2.00 Page 4 of 13
June 16, 2010
Absolute Maximum Ratings Thermal Information
VCC to Ground. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6V
VL to Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 7V
V+ to Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 7V
V- to Ground. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +0.3V to -7V
V+ to V- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14V
Input Voltages
TIN, FORCEON, FORCEOFF . . . . . . . . . . . . . . . . . . -0.3V to 6V
RIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25V
Output Voltages
TOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.2V
ROUT
, INVALID. . . . . . . . . . . . . . . . . . . . . . . . -0.3V to (VL +0.3V)
Short Circuit Duration
TOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Continuous
ESD Rating . . . . . . . . . . . . See “ESD PERFORMANCE” on page5
Thermal Resistance (Typical, Notes 1, 2) JA (°C/W) JC (°C/W)
32 Ld QFN Package. . . . . . . . . . . . . . . 30 2.2
Moisture Sensitivity (see Technical Brief TB363)
QFN Package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Level 1
Maximum Junction Temperature (Plastic Package) . . . . . . . 150oC
Maximum Storage Temperature Range . . . . . . . . . . -65oC to 150oC
Pb-Free Reflow Profile. . . . . . . . . . . . . . . . . . . . . . . . .see link below
http://www.intersil.com/pbfree/Pb-FreeReflow.asp
Operating Conditions
Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . -40oC to 85oC
CAUTION: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to such conditions may adversely impact product reliability and
result in failures not covered by warranty.
NOTES:
1. JA is measured in free air with the component mounted on a high effective thermal conductivity test board with “direct attach” features. See
Tech Brief TB379, and Tech Brief TB389.
2. For JC, the “case temp” location is the center of the exposed metal pad on the package underside.
Electrical Specifications Test Conditions: VCC = 3V to 5.5V, C1 - C4 = 0.1µF, VL = VCC; Unless Otherwise Specified.
Typicals are at TA = 25oC, VCC = VL = 3.3V
PARAMETER TEST CONDITIONS
TEMP
(oC)
MIN
(Note 4) TYP
MAX
(Note 4) UNITS
DC CHARACTERISTICS
Supply Current, Automatic
Powerdown
All RIN Open, FORCEON = GND, FORCEOFF =V
CC 25 - 0.3 5 A
Supply Current, Powerdown FORCEOFF =GND 25 - 0.3 5 A
Supply Current,
Automatic Powerdown Disabled
All Outputs Unloaded, FORCEON = FORCEOFF =V
CC,
VCC = 3.15V
25 - 0.3 1 mA
LOGIC AND TRANSMITTER INPUTS
Input Logic Threshold Low TIN, FORCEON, FORCEOFF VL = 3.3V or 5V Full - - 0.8 V
VL = 2.5V Full - - 0.6 V
Input Logic Threshold High TIN, FORCEON, FORCEOFF VL = 5V Full 2.4 - - V
VL = 3.3V Full 2.0 - - V
VL = 2.5V Full 1.4 - - V
VL = 1.8V 25 - 0.9 - V
Transmitter Input Hysteresis 25 - 0.5 - V
Input Leakage Current TIN, FORCEON, FORCEOFF Full - 0.01 1.0 A
RECEIVER OUTPUTS
Output Voltage Low IOUT = 1.6mA Full - - 0.4 V
Output Voltage High IOUT = -1.0mA Full VL - 0.6 VL - 0.1 - V
RECEIVER INPUTS
Input Voltage Range Full -25 - 25 V
Input Threshold Low VCC = VL = 5.0V 25 0.8 1.5 - V
VCC = VL = 3.3V 25 0.6 1.2 - V
Input Threshold High VCC = VL = 5.0V 25 - 1.8 2.4 V
VCC = VL = 3.3V 25 - 1.5 2.4 V
Input Hysteresis 25 - 0.5 - V
Input Resistance 25357k
ISL4270E
FN6041 Rev 2.00 Page 5 of 13
June 16, 2010
TRANSMITTER OUTPUTS
Output Voltage Swing All Transmitter Outputs Loaded with 3k to Ground Full 5.0 5.4 - V
Output Resistance VCC = V+ = V- = 0V, Transmitter Output = 2V Full 300 10M -
Output Short-Circuit Current VOUT = 0V Full - 35 60 mA
Output Leakage Current VOUT =12V, VCC = 0V or 3V to 5.5V
Automatic Powerdown or FORCEOFF =GND
Full - - 25 A
ENHANCED AUTOMATIC POWERDOWN (FORCEON = GND, FORCEOFF = VCC)
Receiver Input Thresholds to
INVALID High
See Figure 4 Full -2.7 - 2.7 V
Receiver Input Thresholds to
INVALID Low
See Figure 4 Full -0.3 - 0.3 V
INVALID Output Voltage Low IOUT = 1.6mA Full - - 0.4 V
INVALID Output Voltage High IOUT = -1.0mA Full VL - 0.6 - - V
Receiver Positive or Negative
Threshold to INVALID High Delay
(tINVH)
See Figure 7 25 - 1 - s
Receiver Positive or Negative
Threshold to INVALID Low Delay
(tINVL)
See Figure 7 25 - 30 - s
Receiver or Transmitter Edge to
Transmitters Enabled Delay (tWU)
Note 3, See Figure 7 25 - 100 - s
Receiver or Transmitter Edge to
Transmitters Disabled Delay
(tAUTOPWDN)
Note 3, See Figure 7 Full 15 30 60 sec
TIMING CHARACTERISTICS
Maximum Data Rate RL=3kCL= 1000pF, One Transmitter Switching Full 250 500 - kbps
Receiver Propagation Delay Receiver Input to Receiver
Output, CL= 150pF
tPHL 25 - 0.15 - s
tPLH 25 - 0.15 - s
Time to Exit Powerdown TX | VOUT | 3.7V 25 - 100 - s
Transmitter Skew tPHL - tPLH 25 - 100 - ns
Receiver Skew tPHL - tPLH 25 - 50 - ns
Transition Region Slew Rate VCC =3.3V,
RL=3kto 7k
Measured From 3V to -3V or -3V
to 3V
CL = 150pF to 1000pF 25 6 18 30 V/s
CL = 150pF to 2500pF 25 4 13 30 V/s
ESD PERFORMANCE
RS-232 Pins (TOUT
, RIN) Human Body Model 25 - 15 - kV
IEC61000-4-2 Air Gap Discharge 25 - 15 - kV
IEC61000-4-2 Contact Discharge 25 - 8-kV
NOTES:
3. An “edge” is defined as a transition through the transmitter or receiver input thresholds.
4. Parameters with MIN and/or MAX limits are 100% tested at +25°C, unless otherwise specified. Temperature limits established by characterization
and are not production tested.
Electrical Specifications Test Conditions: VCC = 3V to 5.5V, C1 - C4 = 0.1µF, VL = VCC; Unless Otherwise Specified.
Typicals are at TA = 25oC, VCC = VL = 3.3V (Continued)
PARAMETER TEST CONDITIONS
TEMP
(oC)
MIN
(Note 4) TYP
MAX
(Note 4) UNITS
ISL4270E
FN6041 Rev 2.00 Page 6 of 13
June 16, 2010
Detailed Description
The ISL4270E operates from a single +3V to +5.5V supply,
guarantees a 250kbps minimum data rate, requires only four
small external 0.1F capacitors, features low power
consumption, and meets all ElA RS-232C and V.28
specifications. The circuit is divided into three sections: The
charge pump, the transmitters, and the receivers.
Charge-Pump
Intersil’s new ISL4270E utilizes regulated on-chip dual
charge pumps as voltage doublers, and voltage inverters to
generate 5.5V transmitter supplies from a VCC supply as
low as 3.0V. This allows these devices to maintain RS-232
compliant output levels over the 10% tolerance range of
3.3V powered systems. The efficient on-chip power supplies
require only four small, external 0.1F capacitors for the
voltage doubler and inverter functions over the full VCC
range; other capacitor combinations can be used as shown
in Table 3. The charge pumps operate discontinuously (i.e.,
they turn off as soon as the V+ and V- supplies are pumped
up to the nominal values), resulting in significant power
savings.
Transmitters
The transmitters are proprietary, low dropout, inverting
drivers that translate TTL/CMOS inputs to EIA/TIA-232
output levels. Coupled with the on-chip 5.5V supplies,
these transmitters deliver true RS-232 levels over a wide
range of single supply system voltages.
All transmitter outputs disable and assume a high
impedance state when the device enters the powerdown
mode (see Table 2). These outputs may be driven to 12V
when disabled.
All devices guarantee a 250kbps data rate for full load
conditions (3k and 1000pF), VCC 3.0V, with one
transmitter operating at full speed. Under more typical
conditions of VCC 3.3V, RL=3k, and CL= 250pF, one
transmitter easily operates at 1.25Mbps.
The transmitter input threshold is set by the voltage applied
to the VL supply pin. Transmitter inputs float if left
unconnected (there are no pull-up resistors), and may cause
ICC increases. Connect unused inputs to GND for the best
performance.
Receivers
The ISL4270E contains standard inverting receivers that
convert RS-232 signals to CMOS output levels and accept
inputs up to 25V while presenting the required 3k to 7k
input impedance (see Figure 1) even if the power is off
(VCC = 0V). The receivers’ Schmitt trigger input stage uses
hysteresis to increase noise immunity and decrease errors
due to slow input signal transitions. Receiver outputs swing
from GND to VL, and do not tristate in powerdown (see
Table 2).
Low Power Operation
This 3V device requires a nominal supply current of 0.3mA,
even at VCC = 5.5V, during normal operation (not in
powerdown mode). This is considerably less than the 11mA
current required by comparable 5V RS-232 devices, allowing
users to reduce system power simply by replacing the old
style device with the ISL4270E in new designs.
Powerdown Functionality
The already low current requirement drops significantly
when the device enters powerdown mode. In powerdown,
supply current drops to 1A, because the on-chip charge
pump turns off (V+ collapses to VCC, V- collapses to GND),
and the transmitter outputs tristate. This micro-power mode
makes these devices ideal for battery powered and portable
applications.
Software Controlled (Manual) Powerdown
This device allows the user to force the IC into the low
power, standby state, and utilizes a two pin approach where
the FORCEON and FORCEOFF inputs determine the IC’s
mode. For always enabled operation, FORCEON and
FORCEOFF are both strapped high. To switch between
active and powerdown modes, under logic or software
control, only the FORCEOFF input need be driven. The
FORCEON state isn’t critical, as FORCEOFF dominates
over FORCEON. Nevertheless, if strictly manual control over
powerdown is desired, the user must strap FORCEON high
to disable the enhanced automatic powerdown circuitry.
Connecting FORCEOFF and FORCEON together disables
the enhanced automatic powerdown feature, enabling them
to function as a manual SHUTDOWN input (see Figure 2).
With any of the above control schemes, the time required to
exit powerdown, and resume transmission is only 100s.
When using both manual and enhanced automatic
powerdown (FORCEON = 0), the ISL4270E won’t power up
from manual powerdown until both FORCEOFF and
FORCEON are driven high, or until a transition occurs on a
receiver or transmitter input. Figure 3 illustrates a circuit for
ensuring that the ISL4270E powers up as soon as
FORCEOFF switches high. The rising edge of the Master
Powerdown signal forces the device to power up, and the
ISL4270E returns to enhanced automatic powerdown
RXOUT
GND VROUT VL
5k
RXIN
-25V VRIN +25V
GND
VL
FIGURE 1. RECEIVER CONNECTIONS
ISL4270E
FN6041 Rev 2.00 Page 7 of 13
June 16, 2010
mode an RC time constant after this rising edge. The time
constant isn’t critical, because the ISL4270E remains
powered up for 30 seconds after the FORCEON falling edge,
even if there are no signal transitions. This gives slow-to-
wake systems (e.g., a mouse) plenty of time to start
transmitting, and as long as it starts transmitting within 30
seconds both systems remain enabled.
VL Logic Supply Input
Unlike other RS-232 interface devices where the CMOS
outputs swing between 0 and VCC, the ISL4270E features a
separate logic supply input (VL; 1.8V to 5V, regardless of
VCC) that sets VOH for the receiver and INVALID outputs.
Connecting VL to a host logic supply lower than VCC,
prevents the ISL4270E outputs from forward biasing the
input diodes of a logic device powered by that lower supply.
Connecting VL to a logic supply greater than VCC ensures
that the receiver and INVALID output levels are compatible
even with the CMOS input VIH of AC, HC, and CD4000
devices. Note that the VL supply current increases to 100A
with VL= 5V and VCC = 3.3V (see Figure 16). VL also
powers the transmitter and logic inputs, thereby setting their
switching thresholds to levels compatible with the logic
supply. This separate logic supply pin allows a great deal of
flexibility in interfacing to systems with different logic
supplies. If logic translation isn’t required, connect VL to the
ISL4270E VCC.
TABLE 2. POWERDOWN LOGIC TRUTH TABLE
RCVR OR XMTR
EDGE WITHIN 30
SEC?
FORCEOFF
INPUT
FORCEON
INPUT
TRANSMITTER
OUTPUTS
RECEIVER
OUTPUTS
RS-232 LEVEL
PRESENT AT
RECEIVER INPUT?
INVALID
OUTPUT MODE OF OPERATION
NO H H Active Active NO L Normal Operation (Enhanced
Auto Powerdown Disabled)
NO H H Active Active YES H
YES H L Active Active NO L Normal Operation (Enhanced
Auto Powerdown Enabled)
YES H L Active Active YES H
NO H L High-Z Active NO L Powerdown Due to Enhanced
Auto Powerdown Logic
NO H L High-Z Active YES H
X L X High-Z Active NO L Manual Powerdown
X L X High-Z Active YES H
INVALID DRIVING FORCEON AND FORCEOFF (EMULATES AUTOMATIC POWERDOWN)
X NOTE 5 NOTE 5 Active Active YES H Normal Operation
X NOTE 5 NOTE 5 High-Z Active NO L Forced Auto Powerdown
NOTES:
5. Input is connected to INVALID Output.
FIGURE 2. CONNECTIONS FOR MANUAL POWERDOWN
PWR
FORCEOFF, FORCEON
CPU I/O
ISL4270E
MGT
LOGIC
UART
VL
I/O CHIP
POWER SUPPLY
VCC
INVALID
FIGURE 3. CIRCUIT TO ENSURE IMMEDIATE POWER UP
WHEN EXITING FORCED POWERDOWN
FORCEOFF FORCEON
POWER MASTER POWERDOWN LINE
1M
0.1F
MANAGEMENT
UNIT
ISL4270E
ISL4270E
FN6041 Rev 2.00 Page 8 of 13
June 16, 2010
INVALID Output
The INVALID output always indicates (see Table 2) whether
or not 30s have elapsed with invalid RS-232 signals (see
Figures 4 and 7) persisting on all of the receiver inputs,
giving the user an easy way to determine when the interface
block should power down. Invalid receiver levels occur
whenever the driving peripheral’s outputs are shut off
(powered down) or when the RS-232 interface cable is
disconnected. In the case of a disconnected interface cable
where all the receiver inputs are floating (but pulled to GND
by the internal receiver pull down resistors), the INVALID
logic detects the invalid levels and drives the output low. The
power management logic then uses this indicator to power
down the interface block. Reconnecting the cable restores
valid levels at the receiver inputs, INVALID switches high,
and the power management logic wakes up the interface
block. INVALID can also be used to indicate the DTR or
RING INDICATOR signal, as long as the other receiver
inputs are floating, or driven to GND (as in the case of a
powered down driver).
INVALID switches high 1s after detecting a valid RS-232
level on a receiver input. INVALID operates in all modes
(forced or automatic powerdown, or forced on), so it is also
useful for systems employing manual powerdown circuitry.
Enhanced Automatic Powerdown
Even greater power savings is available by using the
enhanced automatic powerdown function. When the
enhanced powerdown logic determines that no transitions
have occurred on any of the transmitter nor receiver inputs
for 30 seconds, the charge pump and transmitters
powerdown, thereby reducing supply current to 1A. The
ISL4270E automatically powers back up whenever it detects
a transition on one of these inputs. This automatic
powerdown feature provides additional system power
savings without changes to the existing operating system.
Enhanced automatic powerdown operates when the
FORCEON input is low, and the FORCEOFF input is high.
Tying FORCEON high disables automatic powerdown, but
manual powerdown is always available via the overriding
FORCEOFF input. Table 2 summarizes the enhanced
automatic powerdown functionality.
Figure 5 illustrates the enhanced powerdown control logic.
Note that once the ISL4270E enters powerdown (manually
or automatically), the 30 second timer remains timed out
(set), keeping the ISL4270E powered down until FORCEON
transitions high, or until a transition occurs on a receiver or
transmitter input.
As stated previously, the INVALID output switches low
whenever invalid levels have persisted on all of the receiver
inputs for more than 30s (see Figure 7), but this has no
direct effect on the state of the ISL4270E (see the next
sections for methods of utilizing INVALID to power down the
device).
The time to recover from automatic powerdown mode is
typically 100s.
Emulating Standard Automatic Powerdown
If enhanced automatic powerdown isn’t desired, the user can
implement the standard automatic powerdown feature
(mimics the function on the ICL3221E/23E/43E) by
connecting the INVALID output to the FORCEON and
FORCEOFF inputs, as shown in Figure 6. After 30s of
invalid receiver levels, INVALID switches low and drives the
ISL4270E into a forced powerdown condition. INVALID
switches high as soon as a receiver input senses a valid
RS-232 level, forcing the ISL4270E to power on. See the
FIGURE 4. DEFINITION OF VALID RS-232 RECEIVER LEVELS
0.3V
-0.3V
-2.7V
2.7V
INVALID LEVEL - INVALID = 0
VALID RS-232 LEVEL - INVALID = 1
VALID RS-232 LEVEL - INVALID = 1
INDETERMINATE
INDETERMINATE
FIGURE 5. ENHANCED AUTOMATIC POWERDOWN LOGIC
30s
TIMER
S
R
FORCEOFF
AUTOPWDN
FORCEON
R_IN
T_IN EDGE
DETECT
EDGE
DETECT
FIGURE 6. CONNECTIONS FOR AUTOMATIC POWERDOWN
WHEN NO VALID RECEIVER SIGNALS ARE
PRESENT
FORCEOFF
INVALID
CPU
I/O
FORCEON
ISL4270E
UART