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ISL83384ECA-T

P1-P3P4-P6P7-P9
4
FN6017.3
March 15, 2005
Detailed Description
The ISL83384E 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 ISL83384E utilizes regulated on-chip dual
charge pumps as voltage doublers, and voltage inverters to
generate 5.5V transmitter supplies from a V
CC
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 V
CC
range. 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), V
CC
3.0V, with one
transmitter operating at full speed. Under more typical
conditions of V
CC
3.3V, R
L
= 3k, and C
L
= 250pF, one
transmitter easily operates at 900Kbps.
Transmitter inputs float if left unconnected (there are no pull-
up resistors), and may cause I
CC
increases. Connect
unused inputs to GND for the best performance.
Receivers
The ISL83384E contains standard inverting receivers that
three-state via the SHDN
control line. Receivers driving
powered down peripherals must be disabled to prevent
current flow through the peripheral’s protection diodes (see
Figures 2 and 3).
Transmitter Propagation Delay Transmitter Input to
Transmitter Output,
C
L
= 1000pF
t
PHL
Full - 0.6 3.5 s
t
PLH
Full - 0.7 3.5 s
Receiver Propagation Delay Receiver Input to Receiver
Output, C
L
= 150pF
t
PHL
Full - 0.2 1 s
t
PLH
Full - 0.3 1 s
Transmitter Output Enable Time From SHDN Rising Edge to T
OUT
= 3V 25 - 50 - s
Transmitter Output Disable Time From SHDN Falling Edge to T
OUT
= 5V 25 - 600 - ns
Transmitter Skew t
PHL
- t
PLH
(Note 3) 25 - 100 - ns
Receiver Skew t
PHL
- t
PLH
25 - 100 - ns
Transition Region Slew Rate R
L
= 3kto 7k
Measured From 3V to -3V or
-3V to 3V
V
CC
= 3.3V, C
L
= 150pF to
2500pF
25 4 - - V/s
V
CC
= 4.5V, C
L
= 150pF to
2500pF
25 6 - - V/s
ESD PERFORMANCE
RS-232 Pins (T
OUT
, R
IN
) Human Body Model 25 - 15 - kV
IEC61000-4-2 Contact Discharge 25 - 8-kV
IEC61000-4-2 Air Gap Discharge 25 - 15 - kV
All Other Pins Human Body Model 25 - 3-kV
NOTE:
3. Transmitter skew is measured at the transmitter zero crossing points.
Electrical Specifications Test Conditions: V
CC
= 3V to 5.5V, C
1
- C
4
= 0.1F; Unless Otherwise Specified.
Typicals are at T
A
= 25°C (Continued)
PARAMETER TEST CONDITIONS
TEMP
(°C) MIN TYP MAX UNITS
TABLE 2. POWERDOWN AND ENABLE LOGIC TRUTH TABLE
SHDN
INPUT
TRANSMITTER
OUTPUTS
RECEIVER
OUTPUTS MODE OF OPERATION
H Active Active Normal Operation
L High-Z High-Z Manual Powerdown
ISL83384E
5
FN6017.3
March 15, 2005
All the receivers convert RS-232 signals to CMOS output
levels and accept inputs up to 30V while presenting the
required 3k to 7k input impedance (see Figure 1) even if
the power is off (V
CC
= 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 V
CC
= 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 ISL83384E.
Low Power, Pin Compatible Replacement
Pin compatibility with existing 5V products (e.g., MAX222),
coupled with the wide operating supply range, make the
ISL83384E a potential lower power, higher performance
drop-in replacement for existing 5V applications. As long as
the 5V RS-232 output swings are acceptable, and
transmitter pull-up resistors aren’t required, the ISL83384E
should work in most 5V applications.
When replacing a device in an existing 5V application, it is
acceptable to terminate C
3
to V
CC
as shown on the “Typical
Operating Circuit”. Nevertheless, terminate C
3
to GND if
possible, as slightly better performance results from this
configuration.
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 V
CC
, V- collapses to GND),
and the transmitter and receiver outputs three-state. This
micro-power mode makes these devices ideal for battery
powered and portable applications.
Software Controlled (Manual) Powerdown
The ISL83384E may be forced into its low power, standby
state via a simple shutdown (SHDN
) pin (see Figure 4).
Driving this pin high enables normal operation, while driving
it low forces the IC into its powerdown state. The time
required to exit powerdown, and resume transmission is less
than 50s. Connect SHDN
to V
CC
if the powerdown function
isn’t needed.
R
XOUT
GND V
ROUT
V
CC
5k
R
XIN
-25V V
RIN
+25V
GND
V
CC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
PERIPHERAL
OLD
V
CC
POWERED
GND
SHDN
= GND
V
CC
Rx
Tx
V
CC
CURRENT
V
OUT
=
V
CC
FLOW
RS-232 CHIP
DOWN
UART
FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN
ISL83384E
TRANSITION
DETECTOR
R
X
T
X
V
CC
V
CC
TO
V
OUT
=
HI-Z
WAKE-UP
LOGIC
POWERED
DOWN
UART
V-
FIGURE 4. CONNECTIONS FOR MANUAL POWERDOWN
PWR
SHDN
CPU
I/O
ISL83384E
MGT
LOGIC
UART
ISL83384E
6
FN6017.3
March 15, 2005
Capacitor Selection
The charge pumps require 0.1F or greater capacitors for
operation with 3.3V V
CC
5.5V. Increasing the capacitor
values (by a factor of 2) reduces ripple on the transmitter
outputs and slightly reduces power consumption. C
2
, C
3
,
and C
4
can be increased without increasing C
1
’s value,
however, do not increase C
1
without also increasing C
2
, C
3
,
and C
4
to maintain the proper ratios (C
1
to the other
capacitors).
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-.
Operation Down to 2.7V
ISL83384E transmitter outputs meet RS-562 levels (3.7V),
at the full data rate, with V
CC
as low as 2.7V. RS-562 levels
typically ensure interoperability with RS-232 devices.
Power Supply Decoupling
In most circumstances a 0.1F bypass capacitor is
adequate. In applications that are particularly sensitive to
power supply noise, decouple V
CC
to ground with a
capacitor of the same value as the charge-pump capacitor C
1
.
Connect the bypass capacitor as close as possible to the IC.
Transmitter Outputs when Exiting
Powerdown
Figure 5 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in parallel with 2500pF. Note
that the transmitters enable only when the magnitude of the
supplies exceed approximately 3V.
High Data Rates
The ISL83384E maintains the RS-232 5V minimum
transmitter output voltages even at high data rates. Figure 6
details a transmitter loopback test circuit, and Figure 7
illustrates the loopback test result at 120Kbps. For this test,
all transmitters were simultaneously driving RS-232 loads in
parallel with 1000pF, at 120Kbps. Figure 8 shows the
loopback results for a single transmitter driving 1000pF and
an RS-232 load at 250Kbps. The static transmitter was also
loaded with an RS-232 receiver.
TIME (20s/DIV)
T1
T2
2V/DIV
5V/DIV
V
CC
= +3.3V
SHDN
FIGURE 5. TRANSMITTER OUTPUTS WHEN EXITING
POWERDOWN
C1 - C4 = 0.1F
FIGURE 6. TRANSMITTER LOOPBACK TEST CIRCUIT
FIGURE 7. LOOPBACK TEST AT 120Kbps
ISL83384E
V
CC
C
1
C
2
C
4
C
3
+
+
+
+
1000pF
V+
V-
5K
T
IN
R
OUT
C1+
C1-
C2+
C2-
R
IN
T
OUT
+
V
CC
0.1F
V
CC
SHDN
T1
IN
T1
OUT
R1
OUT
5s/DIV
V
CC
= +3.3V
5V/DIV
C1 - C4 = 0.1F
ISL83384E
P1-P3P4-P6P7-P9

ISL83384ECA-T

Mfr. #:
Buy ISL83384ECA-T
Manufacturer:
Renesas / Intersil
Description:
IC TXRX 2/2 FULL RS232 20SSOP
Lifecycle:
New from this manufacturer.
Delivery:
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