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ISL83385E Datasheet(PDF) 6 Page - Intersil Corporation

Part No. ISL83385E
Description  15kV ESD Protected, 3V to 5.5V, /-1 Microamp, 250kbps, RS-232 Transmitters/Receivers
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Maker  INTERSIL [Intersil Corporation]
Homepage  http://www.intersil.com/cda/home
Logo INTERSIL - Intersil Corporation

ISL83385E Datasheet(HTML) 6 Page - Intersil Corporation

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6
(VCC = 0V). The receivers’ Schmitt trigger input stage uses
hysteresis to increase noise immunity and decrease errors
due to slow input signal transitions.
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 ISL83385E in new designs.
Powerdown Functionality
The already low current requirement drops significantly
when the device enters powerdown mode. In powerdown,
supply current drops to 1
µA, 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
The ISL83385E may be forced into its low power, standby
state via a simple shutdown (SHDN) pin (see Figure 2).
Driving this pin high enables normal operation, while driving
it low forces the IC into it’s powerdown state. The time
required to exit powerdown, and resume transmission is less
than 100
µs. Connect SHDN to VCC if the powerdown
function isn’t needed.
Capacitor Selection
These charge pumps only require 0.1
µF capacitors for the
full operational voltage range. Table 3 lists other acceptable
capacitor values for various supply voltage ranges. Do not
use values smaller than those listed in Table 3. Increasing
the capacitor values (by a factor of 2) reduces ripple on the
transmitter outputs and slightly reduces power consumption.
When using minimum required capacitor values, make sure
that capacitor values do not degrade excessively with
temperature. If in doubt, use capacitors with a larger nominal
value. The capacitor’s equivalent series resistance (ESR)
usually rises at low temperatures and it influences the
amount of ripple on V+ and V-.
Power Supply Decoupling
In most circumstances a 0.1
µF bypass capacitor is
adequate. In applications that are particularly sensitive to
power supply noise, decouple VCC to ground with a
capacitor of the same value as the charge-pump capacitor C1.
Connect the bypass capacitor as close as possible to the IC.
Transmitter Outputs when Exiting
Powerdown
Figure 3 shows the response of two transmitter outputs
when exiting powerdown mode. As they activate, the two
transmitter outputs properly go to opposite RS-232 levels,
with no glitching, ringing, nor undesirable transients. Each
transmitter is loaded with 3k
Ω in parallel with 2500pF. Note
that the transmitters enable only when the magnitude of the
supplies exceed approximately 3V.
RXOUT
GND
≤ VROUT ≤ VCC
5k
RXIN
-25V
≤ VRIN ≤ +25V
GND
VCC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
FIGURE 2. CONNECTIONS FOR MANUAL POWERDOWN
PWR
SHDN
CPU
I/O
ISL83385E
MGT
LOGIC
UART
TABLE 3. REQUIRED CAPACITOR VALUES
VCC
(V)
C1
(
µF)
C2, C3, C4
(
µF)
3.0 to 3.6
0.1
0.1
4.5 to 5.5
0.047
0.33
3.0 to 5.5
0.1
0.47
TIME (20
µs/DIV.)
T1
T2
2V/DIV
5V/DIV
VCC = +3.3V
SHDN
FIGURE 3. TRANSMITTER OUTPUTS WHEN EXITING
POWERDOWN
C1 - C4 = 0.1
µF
ISL83385E


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