ISL4244EIRZ Intersil, ISL4244EIRZ Datasheet - Page 10

• Manufacturer Part Number: ISL4244EIRZ
• Description: IC TXRX RS232 2.7-5.5V 32QFN
• Manufacturer: Intersil
• Type: Transceiverr

Specifications of ISL4244EIRZ

• 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: Lead free / RoHS Compliant

Power-down Functionality
The already low current requirement drops significantly
when the device enters power-down mode. In power-down,
supply current drops to 10nA, because the on-chip charge
pump turns off (V+ collapses to V
and the transmitter outputs tristate. Inverting receiver
outputs disable only in manual power-down; refer to Table 2
for details. This micro-power mode makes these devices
ideal for battery powered and portable applications.
Software Controlled (Manual) Power-down
These devices allow the user to force the IC into the low
power, standby state, and 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 power-down 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
power-down is desired, the user must strap FORCEON high
to disable the enhanced automatic power-down circuitry.
ISL4238E, ISL4244E, ISL4245 inverting (standard) receiver
outputs also disable when the device is in manual power-
down, 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 enhanced automatic power-down feature, enabling them
to function as a manual SHUTDOWN input (see Figure 4).
With any of the previous mentioned control schemes, the
time required to exit power-down, and resume transmission
is only 100µs.
FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN
POWERED
DOWN
UART
V
WAKE-UP
CC
LOGIC
TO
R
T
X
X
FORCEOFF = GND
TRANSITION
DETECTOR
V
OUT
R
= HI-Z
V
R
OUTB
T1
CC
OUT
10
IN
CC
, V- collapses to GND),
ISL4238E
ISL4244E
ISL4245
ISL4238E, ISL4244E, ISL4245E
R
T1
IN
OUT
When using both manual and enhanced automatic power-
down (FORCEON = 0), the ISL4238E, ISL4244E, ISL4245
won’t power up from manual power-down until both
FORCEOFF and FORCEON are driven high, or until a
transition occurs on a receiver or transmitter input. Figure 5
illustrates a circuit for ensuring that the ISL4238E,
ISL4244E, ISL4245 powers up as soon as FORCEOFF
switches high. The rising edge of the Master Power-down
signal forces the device to power up, and the ISL4238E,
ISL4244E, ISL4245 returns to enhanced automatic power-
down mode an RC time constant after this rising edge. The
time constant isn’t critical, because the ISL4238E,
ISL4244E, ISL4245 remains powered up for 30s after the
FORCEON falling edge, even if there are no signal
transitions. This gives slow-to-wake systems (e.g., a mouse)
plenty of time to start transmitting, and as long as it starts
transmitting within 30s both systems remain enabled.
INVALID Output
The INVALID output always indicates (see Table 2) whether or
not 30µs have elapsed with invalid RS-232 signals (see Figures
6 and 9) persisting on all of the receiver inputs, 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
FIGURE 4. CONNECTIONS FOR MANUAL POWER-DOWN
FIGURE 5. CIRCUIT TO ENSURE IMMEDIATE POWER UP
MANAGEMENT
POWER
CPU
UNIT
LOGIC
PWR
MGT
WHEN NO VALID RECEIVER SIGNALS ARE
PRESENT
WHEN EXITING FORCED POWER-DOWN
UART
MASTER POWER-DOWN LINE
I/O
FORCEOFF
FORCEON
INVALID
ISL4238E, ISL4244E, ISL4245
FORCEOFF
0.1µF
FORCEON
ISL4238E
ISL4244E
ISL4245
1MΩ
May 13, 2010
FN8038.5