ICL3207_05 Datasheet, PDF (7/11 Pages) Intersil Corporation – Low Power, +3V to +5.5V, 250kbps, RS-232 Transmitters/Receivers

ICL3207, ICL3217
2.7V
0.3V
-0.3V
-2.7V
VALID RS-232 LEVEL - ICL3217 IS ACTIVE
INDETERMINATE - POWERDOWN MAY OR
MAY NOT OCCUR
INVALID LEVEL - POWERDOWN OCCURS AFTER 30µs
INDETERMINATE - POWERDOWN MAY OR
MAY NOT OCCUR
VALID RS-232 LEVEL - ICL3217 IS ACTIVE
FIGURE 4. DEFINITION OF VALID RS-232 RECEIVER
LEVELS
RECEIVER
INPUTS
} INVALID
REGION
TRANSMITTER
OUTPUTS
AUTOPWDN
V+
V_CC
0
V-
PWR UP (t_WU)
FIGURE 5. AUTOMATIC POWERDOWN TIMING DIAGRAM
This automatic powerdown feature provides additional
system power savings without changes to the existing
operating system or hardware.
Utilizing power management circuitry, to power down the
rest of the communication circuitry (e.g., the UART) when
the ICL3217 powers down, produces even greater power
savings. Connecting a transition detector to the V- pin (see
Figure 3) is an easy way for the power management logic to
determine when the ICL3217 enters and exits powerdown.
Capacitor Selection
The charge pumps require 0.1µF, or greater, capacitors for
3.3V operation. With 0.1µF capacitors, five percent tolerance
supplies (e.g., 3.14V minimum) deliver greater than ±5V
transmitter swings at full data rate, while ten percent
tolerance supplies (e.g., 2.97V minimum) deliver ±4.95V
transmitter swings. If greater than ±5V transmitter swings
are required with a ten percent tolerance 3.3V supply,
0.22µF capacitors are recommended (see Table 3). Existing
5V applications typically utilize either 0.1µF or 1µF
capacitors, and the ICL32X7E works well with either value.
New 5V designs should use 0.22µF capacitors for the best
results. For other supply voltages refer to Table 3 for
capacitor values. 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. C₂, C₃, and C₄ can be
increased without increasing C₁’s value, however, do not
increase C₁ without also increasing C₂, C₃, and C₄ to
maintain the proper ratios (C₁ 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-.
TABLE 3. REQUIRED CAPACITOR VALUES
V_CC (V)
3.15 to 3.6
C₁ (µF)
0.1
C₂, C₃, C₄ (µF)
0.1
3.0 to 3.6
0.22
0.22
4.5 to 5.5
0.1 to 1.0
0.1 to 1.0
3.0 to 5.5
0.22
0.22
Power Supply Decoupling
In most circumstances a 0.1µF 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 C₁. Connect the bypass
capacitor as close as possible to the IC.
Transmitter Outputs when Exiting
Powerdown
Figure 6 shows the response of two ICL3217 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 3kΩ in parallel with 2500pF.
Note that the transmitters enable only when the magnitude
of the supplies exceed approximately 3V.
.
5V/DIV
RX_IN
T1
2V/DIV
T2
V_CC = +3.3V
C1 - C4 = 0.1µF
TIME (20µs/DIV.)
FIGURE 6. TRANSMITTER OUTPUTS WHEN EXITING
POWERDOWN (ICL3217ONLY)
7