ISL3241E Datasheet, PDF (10/16 Pages) Intersil Corporation – QFN Packaged, ±15kV ESD Protected, +2.7V to +3.6V, 250kbps, RS-232 Transmitters/Receivers with Separate Logic Supply Pin

ISL3241E, ISL3243E
V_CCL
TRANSITION
DETECTOR
TO
WAKE-UP
LOGIC
V_CC
R2_OUTB
R_X
POWERED
DOWN
UART
T_X
V_OUT = HI-Z
R2_OUT
T1_IN
V_CCI
V_L
V_CC
ISL324XE
R2_IN
FORCEOFF = GND
OR
SHDN = GND, EN = V_L
T1_OUT
FIGURE 6. DISABLED RECEIVERS PREVENT POWER DRAIN
Software Controlled (Manual) Powerdown
The devices in this family provide pins that allow the user to
force the IC into the low power, standby state.
On the ISL3241E, 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_L if the powerdown
function isn’t needed. Note that all the receiver outputs
remain controlled by EN 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 5 and 6).
The ISL3243E utilizes 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. ISL3243E
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 5 and 6).
Connecting FORCEOFF and FORCEON together disables
the automatic powerdown feature, enabling them to function
as a manual SHUTDOWN input (see Figure 7).
PWR
MGT
LOGIC
FORCEOFF
FORCEON
V_CCL ^INVALID
V_L
V_CC
CPU
I/O
UART
V_CCI
V_CC
ISL3243E
FIGURE 7. CONNECTIONS FOR MANUAL POWERDOWN
WHEN NO VALID RECEIVER SIGNALS ARE
PRESENT
With any of the above control schemes, the time required to
exit powerdown, and resume transmission is only 20µs. A
mouse, or other application, may need more time to wake up
from shutdown. If automatic power-down is being utilized,
the RS-232 device will reenter power-down if valid receiver
levels aren’t reestablished within 20µs of the ISL3243E
powering up. Figure 8 illustrates a circuit that keeps the
ISL3243E from initiating automatic power-down for 100ms
after powering up. This gives the slow-to-wake peripheral
circuit time to reestablish valid RS-232 output levels.
POWER
MANAGEMENT
UNIT
MASTER POWERDOWN LINE
0.1µF
1MΩ
FORCEOFF FORCEON
ISL3243E
FIGURE 8. CIRCUIT TO PREVENT AUTO POWERDOWN FOR
100ms AFTER FORCED POWERUP
V_L Logic Supply Input
Note: Power-up V_CC before powering up the V_L supply.
The ISL324xE feature a V_L pin that powers the logic input
and output pins. These pins interface with “logic” devices
such as UARTs, ASICs, and μcontrollers, and today most of
these devices use power supplies significantly lower than
3.3V. Thus, the logic device’s low V_OH might not exceed the
V_IH of a 3.3V powered ISL324xE logic input, or a 3.3V
receiver output high level might overdrive and damage the
input diodes on an input of a 1.8V powered logic device, as
shown in Figure 9. Connecting the V_L pin to the power
supply of the logic device (see Figure 9) reduces the
ISL324xE’s logic input switching points, and limits the
10
FN6768.1
May 13, 2010