ISL3241E_14 Datasheet, PDF (8/16 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
Test Circuits and Waveforms (Continued)
SIGNAL
GENERATOR
EN
OR
FORCEOFF
V_CC
OR
R_IN
R
R_OUT
GND
FORCEON
OR SHDN
V_L
1kΩ
SW
C_L
V_L
GND
FORCEOFF
EN
t_PZH
R_OUT
50%
V_L
50%
0V
50%
OUTPUT HIGH
50%
50%
V_L
0V
t_PHZ
V_OH - 0.3V ^VOH
0V
PARAMETER
t_PHZ and t_PZH
t_PLZ and t_PZL
R_IN
GND
V_CC
FIGURE 3A. TEST CIRCUIT
SW
GND
V_L
R_OUT
t_PZL
t_PLZ
50%
OUTPUT LOW
V_L
V_OL + 0.3V _VOL
FIGURE 3B. MEASUREMENT POINTS
FIGURE 3. RECEIVER ENABLE AND DISABLE TIMES
Detailed Description
The ISL324xE operate from a single +2.7V to +3.6V supply,
guarantee a 250kbps minimum data rate, require only four
small external 0.1µF capacitors, feature low power
consumption, and meet all ElA RS-232 and V.28 specifications
even with V_CC = 3.0V. The circuit is divided into three sections:
The charge pump, the transmitters, and the receivers.
Charge-Pump
Intersil’s new ISL324xE devices utilize regulated on-chip dual
charge pumps as voltage doublers, and voltage inverters to
generate ±5.5V transmitter supplies from a V_CC supply as low
as 3.0V. This allows them to maintain RS-232 compliant output
levels over the ±10% tolerance range of 3.3V powered
systems. The efficient on-chip power supplies require only four
small, external 0.1µF capacitors for the voltage doubler and
inverter functions. The charge pumps operate discontinuously
(i.e., they turn off as soon as the V+ and V- supplies are
pumped up to the nominal values), resulting in significant
power savings.
Transmitters
The transmitters are proprietary, low dropout, inverting drivers
that translate logic input levels to EIA/TIA-232 output levels.
Coupled with the on-chip ±5.5V supplies, these transmitters
deliver true RS-232 levels over a wide range of single supply
system voltages.
All transmitter outputs disable and assume a high impedance
state when the device enters the power-down mode (see Table
2). These outputs may be driven to F12V when disabled.
The devices guarantee a 250kbps data rate for full load
conditions (3kΩ and 1000pF), V_CC ≥ 3.0V, with one transmitter
operating at full speed. Under more typical conditions of V_CC ≥
3.3V, R_L = 3kΩ and C_L = 200pF, one transmitter easily
operates at greater than 1Mbps.
The transmitter input switching threshold is set by the voltage
applied to the V_L pin, so tying V_L to a voltage lower than V_CC
reduces the Tx input V_IH and V_IL to values compatible with
logic ICs (e.g., UARTs and µcontrollers) powered by the V_L
voltage (see Figure 9 and Table 3). Transmitter inputs float if
left unconnected (there are no pull-up resistors), and may
cause supply current increases. Connect unused inputs to GND
for the best performance.
Receivers
All the ISL324xE devices contain standard inverting receivers
that three-state via the EN or FORCEOFF control lines.
Additionally, these products include noninverting “monitor”
receivers (denoted by the R_OUTB label) that are always active,
regardless of the state of any control lines. All the receivers
convert RS-232 signals to CMOS output levels, swinging
between GND and V_L, and accept inputs up to ±25V while
presenting the required 3kΩ to 7kΩ input impedance (see
Figure 4) even if the power is off (V_CC = 0V). The receivers’
Schmitt trigger input stage uses hysteresis to increase noise
immunity and decrease errors due to slow input signal
transitions.
V_L
R_XIN
-25V ≤ V_RIN ≤ +25V 5kΩ
R_XOUT
GND ≤ V_ROUT ≤ V_L
GND
FIGURE 4. INVERTING RECEIVER CONNECTIONS
The ISL3241E inverting receivers disable only when EN is
driven high. ISL3243E receivers disable during forced (manual)
powerdown, but not during automatic powerdown (see
Table 2).
8
FN6768.2
June 18, 2012