FN4805.21 March 1, 2006 Automatic powerdown operates when the FORCEON input is low, and the FORCEOFF input is high. Tying FORCEON high disables" />
參數(shù)資料
型號: ICL3222IA
廠商: Intersil
文件頁數(shù): 5/28頁
文件大?。?/td> 0K
描述: IC 2DRVR/2RCVR RS232 3V 20-SSOP
標準包裝: 66
類型: 收發(fā)器
驅(qū)動器/接收器數(shù): 2/2
規(guī)程: RS232
電源電壓: 3 V ~ 5.5 V
安裝類型: 表面貼裝
封裝/外殼: 20-SSOP(0.209",5.30mm 寬)
供應(yīng)商設(shè)備封裝: 20-SSOP
包裝: 帶卷 (TR)
13
FN4805.21
March 1, 2006
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 automatic powerdown functionality.
Devices with the automatic powerdown feature include an
INVALID output signal, which switches low to indicate that
invalid levels have persisted on all of the receiver inputs for
more than 30
s (See Figure 7). 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. When automatic
powerdown is utilized, INVALID = 0 indicates that the
ICL32XX is in powerdown mode.
The time to recover from automatic powerdown mode is
typically 100
s.
Receiver ENABLE Control (ICL3221/22/23/41 Only)
Several devices also feature an EN input to control the
receiver outputs. Driving EN high disables all the inverting
(standard) receiver outputs placing them in a high
impedance state. This is useful to eliminate supply current,
due to a receiver output forward biasing the protection diode,
when driving the input of a powered down (VCC = GND)
peripheral (See Figure 2). The enable input has no effect on
transmitter nor monitor (ROUTB) outputs.
Capacitor Selection
The charge pumps require 0.1
F capacitors for 3.3V
operation. 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-.
Power Supply Decoupling
In most circumstances a 0.1
F 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.
Operation Down to 2.7V
ICL32XX transmitter outputs meet RS-562 levels (±3.7V), at
full data rate, with VCC as low as 2.7V. RS-562 levels
typically ensure interoperability with RS-232 devices.
Transmitter Outputs when Exiting
Powerdown
Figure 8 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.
FIGURE 6. DEFINITION OF VALID RS-232 RECEIVER LEVELS
0.3V
-0.3V
-2.7V
2.7V
INVALID LEVEL - POWERDOWN OCCURS AFTER 30ms
VALID RS-232 LEVEL - ICL32XX IS ACTIVE
INDETERMINATE - POWERDOWN MAY OR
MAY NOT OCCUR
RECEIVER
INPUTS
TRANSMITTER
OUTPUTS
INVALID
OUTPUT
V+
VCC
0
V-
VCC
0
tINVL
tINVH
INVALID
REGION
}
FIGURE 7. AUTOMATIC POWERDOWN AND INVALID
TIMING DIAGRAMS
AUTOPWDN
PWR UP
TABLE 3. REQUIRED CAPACITOR VALUES
VCC
(V)
C1
(
F)
C2, C3, C4
(
F)
3.0 to 3.6
0.1
4.5 to 5.5
0.047
0.33
3.0 to 5.5
0.1
0.47
ICL3221, ICL3222, ICL3223, ICL3232, ICL3241, ICL3243
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