參數(shù)資料
型號: ISL4241E
廠商: Intersil Corporation
英文描述: QFN Packaged, +/-15kV ESD Protected, +2.7V to +5.5V, 10Nanoamp, 250kbps, RS-232 Transmitters/Receivers
中文描述: QFN封裝,/ - 15kV的ESD保護,2.7V至5.5V,10Nanoamp,250kbps的和RS - 232發(fā)送器/接收器
文件頁數(shù): 9/13頁
文件大?。?/td> 377K
代理商: ISL4241E
9
On the ISL4241E, the powerdown control is via a simple
shutdown (SHDN) pin. Driving this pin high enables normal
operation, while driving it low forces the IC into it’s
powerdown state. Connect SHDN to V
CC
if the powerdown
function isn’t needed. Note that all the receiver outputs
remain enabled during shutdown (see Table 2). For the
lowest power consumption during powerdown, the receivers
should also be disabled by driving the EN input high (see
next section, and Figures 2 and 3).
The ISL4243E utilize 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 automatic powerdown circuitry. ISL4243E
inverting (standard) receiver outputs also disable when the
device is in manual powerdown, thereby eliminating the
possible current path through a shutdown peripheral’s input
protection diode (see Figures 2 and 3).
Connecting FORCEOFF and FORCEON together disables
the automatic powerdown feature, enabling them to function
as a manual SHUTDOWN input (see Figure 4).
With any of the above control schemes, the time required to
exit powerdown, and resume transmission is only 100
μ
s. A
mouse, or other application, may need more time to wake up
from shutdown. If automatic powerdown is being utilized, the
RS-232 device will reenter powerdown if valid receiver levels
aren’t reestablished within 30
μ
s of the ISL4243E powering
up. Figure 5 illustrates a circuit that keeps the ISL4243E
from initiating automatic powerdown for 100ms after
powering up. This gives the slow-to-wake peripheral circuit
time to reestablish valid RS-232 output levels.
INVALID Output (ISL4243E Only)
The INVALID output always indicates whether or not a valid
RS-232 signal (see Figure 6) is present at any of the receiver
inputs (see Table 2), 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 low after invalid levels have persisted on
all of the receiver inputs for more than 30
μ
s (see Figure 7).
INVALID switches back high 1
μ
s 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
FIGURE 4. CONNECTIONS FOR MANUAL POWERDOWN
WHEN NO VALID RECEIVER SIGNALS ARE
PRESENT
PWR
MGT
LOGIC
FORCEOFF
INVALID
CPU
I/O
FORCEON
ISL4243E
UART
FIGURE 5. CIRCUIT TO PREVENT AUTO POWERDOWN FOR
100ms AFTER FORCED POWERUP
ISL4243E
FORCEOFF
FORCEON
POWER
MANAGEMENT
UNIT
MASTER POWERDOWN LINE
1M
0.1
μ
F
FIGURE 6. DEFINITION OF VALID RS-232 RECEIVER LEVELS
0.3V
-0.3V
-2.7V
2.7V
INVALID LEVEL - POWERDOWN OCCURS AFTER 30
μ
s
VALID RS-232 LEVEL - ISL4243E IS ACTIVE
VALID RS-232 LEVEL - ISL4243E IS ACTIVE
INDETERMINATE - POWERDOWN MAY OR
MAY NOT OCCUR
INDETERMINATE - POWERDOWN MAY OR
MAY NOT OCCUR
ISL4241E, ISL4243E
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ISL4243E 制造商:INTERSIL 制造商全稱:Intersil Corporation 功能描述:QFN Packaged, ±15kV ESD Protected, +2.7V to +5.5V, 10Nanoamp, 250kbps, +2.7V to +5.5V, 10Nanoamp, 250kbps,