ISL3241E Datasheet, PDF (11/16 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
receiver output high voltage, to values compatible with the
logic device’s I/O levels. Tailoring the ISL324XE’s logic pin
input switching points and output levels to the supply voltage
of the UART, ASIC, or µcontroller eliminates the need for a
level shifter/translator between the two ICs.
TABLE 3. V_IH AND V_IL vs V_L FOR V_CC = 3.3V
V_L (V)
1.6
V_IH (V)
0.85
V_IL (V)
0.8
1.8
0.95
0.9
2.5
1.25
1.2
V_L may range from 1.6V to V_CC, and Table 3 indicates the
ISL324xE’s typical V_IH and V_IL levels for several V_L values.
Note that the V_L supply current increases significantly when
V_L exceeds V_CC (see Figure 20).
If logic translation isn’t required, connect V_L to V_CC.
V_CCI = +3.3V
V_CCL = +1.8V
T_IN
V_IH ≥ 2V
V_OH ≤ 1.8V
T_XD
GND
V_OH ≥ 3V
R_OUT
RXD
INPUT
DIODE
GND
RS-232 IC WITH NO
VL PIN
UART/PROCESSOR
V_CCI = +3.3V
V_CCL = +1.8V
GND
V_L
T_IN ^{VIH ≤ 1V}
T_XD
V_OH ≤ 1.8V
R_OUT ^{VOH ≤ 1.8V}
R_XD
INPUT
DIODE
GND
ISL324xE
UART/PROCESSOR
FIGURE 9. USING V_L PIN TO ADJUST LOGIC LEVELS
INVALID Output (ISL3243E Only)
The INVALID output always indicates whether or not a valid
RS-232 signal (see Figure 10) 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).
2.7V
VALID RS-232 LEVEL - ISL3243E IS ACTIVE
INDETERMINATE - POWERDOWN MAY OR
MAY NOT OCCUR
0.3V
-0.3V
INVALID LEVEL - POWER-DOWN OCCURS AFTER 20μs
INDETERMINATE - POWERDOWN MAY OR
MAY NOT OCCUR
-2.7V
VALID RS-232 LEVEL - ISL3243E IS ACTIVE
FIGURE 10. DEFINITION OF VALID RS-232 RECEIVER LEVELS
INVALID switches low after invalid levels have persisted on
all of the receiver inputs for more than 20µs (see Figure 11).
INVALID switches back 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. When automatic powerdown is utilized, INVALID = 0
indicates that the ISL3243E is in powerdown mode.
RECEIVER
INPUTS
INVALID
} _REGION
TRANSMITTER
OUTPUTS
INVALID
OUTPUT
V_L
t_INVL
0
AUTOPWDN
V+
V_CC
0
V-
t_INVH
PWR UP
FIGURE 11. AUTOMATIC POWERDOWN AND INVALID
TIMING DIAGRAMS
Automatic Power-down (ISL3243E Only)
Even greater power savings is available by using the
ISL3243E which features an automatic power-down
function. When no valid RS-232 voltages (see Figure 11) are
sensed on any receiver input for 20µs, the charge pump and
11
FN6768.1
May 13, 2010