ISL4244EIR Intersil, ISL4244EIR Datasheet - Page 11

• Manufacturer Part Number: ISL4244EIR
• Description: IC 3DRVR/5RCVR RS232 3V 32-QFN
• Manufacturer: Intersil
• Type: Transceiverr

Specifications of ISL4244EIR

• Number Of Drivers/receivers: 3/5
• Protocol: RS232
• Voltage - Supply: 2.7 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 32-VQFN Exposed Pad, 32-HVQFN, 32-SQFN, 32-DHVQFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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 high 1µs after detecting a valid RS-232
level on a receiver input. INVALID operates in all modes
(forced or automatic power-down, or forced on), so it is also
useful for systems employing manual power-down circuitry.=
Enhanced Automatic Power-down
Even greater power savings is available by using these devices
which feature an enhanced automatic power-down function.
When the enhanced power-down logic determines that no
transitions have occurred on any of the transmitter nor receiver
inputs for 30 seconds, the charge pump and transmitters
power-down, thereby reducing supply current to
ISL4238E, ISL4244E, ISL4245 automatically powers back up
whenever it detects a transition on one of these inputs. This
automatic power-down feature provides additional system
power savings without changes to the existing operating
system.
Enhanced automatic power-down operates when the
FORCEON input is low, and the FORCEOFF input is high.
Tying FORCEON high disables automatic power-down, but
manual power-down is always available via the overriding
FORCEOFF input. Table 2 summarizes the enhanced
automatic power-down functionality.
Figure 7 illustrates the enhanced power-down control logic.
Note that once the ISL4238E, ISL4244E, ISL4245 enters
power-down (manually or automatically), the 30 second
timer remains timed out (set), keeping the ISL4238E,
ISL4244E, ISL4245 powered down until FORCEON
transitions high, or until a transition occurs on a receiver or
transmitter input.
FIGURE 6. DEFINITION OF VALID RS-232 RECEIVER LEVELS
-0.3V
-2.7V
2.7V
0.3V
INVALID LEVEL - INVALID = 0
VALID RS-232 LEVEL - INVALID = 1
VALID RS-232 LEVEL - INVALID = 1
INDETERMINATE
INDETERMINATE
11
ISL4238E, ISL4244E, ISL4245E
10nA
. The
The INVALID output signal switches low to indicate that invalid
levels have persisted on all of the receiver inputs for more than
30µs (see Figure 9), but this has no direct effect on the state of
the ISL4238E, ISL4244E, ISL4245 (see the next sections for
methods of utilizing INVALID to power down the device).
The time to recover from automatic power-down mode is
typically 100µs.
Emulating Standard Automatic Power-down
If enhanced automatic power-down isn’t desired, the user can
implement the standard automatic power-down feature (mimics
the function on the ISL4243E) by connecting the INVALID
output to the FORCEON and FORCEOFF inputs, as shown in
Figure 8. After 30µs of invalid receiver levels, INVALID switches
low and drives the ISL4238E, ISL4244E, ISL4245 into a forced
power-down condition. INVALID switches high as soon as a
receiver input senses a valid RS-232 level, forcing the
ISL4238E, ISL4244E, ISL4245 to power on. See the “INVALID
DRIVING FORCEON AND FORCEOFF” section of Table 2 for
an operational summary. This operational mode is perfect for
handheld devices that communicate with another computer via
a detachable cable. Detaching the cable allows the internal
receiver pull-down resistors to pull the inputs to GND (an invalid
RS-232 level), causing the 30µs timer to time-out and drive the
IC into power-down. Reconnecting the cable restores valid
levels, causing the IC to power back up.
T_IN
R_IN
FIGURE 7. ENHANCED AUTOMATIC POWER-DOWN LOGIC
FIGURE 8. CONNECTIONS FOR AUTOMATIC POWER-DOWN
CPU
DETECT
DETECT
EDGE
EDGE
WHEN NO VALID RECEIVER SIGNALS ARE
PRESENT
FORCEON
UART
I/O
INVALID
FORCEOFF
30sec
TIMER
FORCEON
R
S
ISL4238E
ISL4244E
ISL4245
FORCEOFF
AUTOPWDN
May 13, 2010
FN8038.5