MAX3325CAI-T Maxim Integrated, MAX3325CAI-T Datasheet - Page 8

• Manufacturer Part Number: MAX3325CAI-T
• Description: RS-232 Interface IC
• Manufacturer: Maxim Integrated
• Series: MAX3325r

Specifications of MAX3325CAI-T

• Data Rate: 250 Kbps
• Operating Supply Voltage: 3 V to 3.6 V
• Supply Current: 2 mA
• Operating Temperature Range: - 40 C to + 85 C
• Number Of I/os: 2 / 2
• Propagation Delay Time Ns: 300 ns

3V Dual RS-232 Transceiver with
LCD Supply and Contrast Controller
The MAX3325’s internal power supply consists of a reg-
ulated dual charge pump that provides output voltages
of +5.5V (doubling charge pump) and -5.5V (inverting
charge pump) over the 3.0V to 3.6V V
charge pump operates in discontinuous mode; if the
output voltages are less than 5.5V, the charge pump is
enabled; if the output voltages exceed 5.5V, the charge
pump is disabled. Each charge pump requires a flying
capacitor (C1, C2) and a reservoir capacitor (C3, C4)
to generate the V+ and V- supplies (Figure 1).
The transmitters are inverting level translators that con-
vert logic levels to ±5.0V EIA/TIA-232 levels. The
MAX3325 transmitters guarantee a 250kbps data rate
with worst-case loads of 3kΩ in parallel with 1000pF,
providing compatibility with PC-to-PC communication
software (such as LapLink™).
The MAX3325’s transmitters are disabled and the out-
puts are forced into a high-impedance state when the
RS-232 circuitry is in shutdown (SD232 = low). The
MAX3325 permits the outputs to be driven up to ±13V
in shutdown.
The transmitter inputs do not have pull-up resistors.
Connect unused inputs to GND or V
The receivers convert RS-232 signals to logic output
levels. The V
The receiver outputs are always active, regardless of
the shutdown state.
The MAX3325 has a regulated +5V output suitable for
powering +5V LCD modules or other circuits. The out-
put of the boost charge pump is regulated with an LDO
linear regulator. The REG output sources up to 11mA of
current to external circuitry.
The LCD output provides a flexible output voltage to
adjust the contrast of LCD modules. The output voltage
range is determined by the external circuitry connected
to LCD, FB, DAC, REF+ (or REF-, depending on con-
trast polarity). Additionally, the TEMP output can be
used to automatically compensate the contrast adjust-
ment for temperature variance.
The LCD output is a linear regulator powered by the neg-
ative charge pump. It is capable of sinking up to 3mA of
current. Although the LCD regulator can be adjusted to
LapLink is a trademark of Traveling Software.
8
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Dual Charge-Pump Voltage Converter
L
pin controls the logic output high voltage.
Positive Voltage Regulator
Detailed Description
Adjustable LCD Supply
RS-232 Transmitters
RS-232 Receivers
DD
.
DD
range. The
positive voltages, it is not capable of sourcing current. A
minimum output current of 100µA is required.
The MAX3325’s DAC output is an unbuffered inverted
R2R structure with an output voltage range of 0 to
+1.2V. The DAC output impedance is typically 50kΩ,
and can be connected through a series resistor to the
FB input of the LCD regulator. An internal power-on
reset circuit sets the DAC to midscale on power-up.
The DAC code is controlled by UP and DOWN to adjust
the contrast of the LCD module. These inputs are
intended to interface to digital signals, but do not
include debounce circuitry. See the Applications sec-
tion. See Table 1 for the truth table.
The MAX3325’s TEMP output is used to minimize devia-
tion in LCD contrast level due to temperature changes.
The TEMP output is capable of sinking or sourcing up
to 22µA to the external resistor network.
Supply current falls below 1µA in shutdown mode
(SDLCD = SD232 = low). When shut down, the device’s
charge pumps are shut off, V+ is pulled down to V
V- is pulled to ground, and the transmitter outputs are
disabled (high impedance). The LCD section is also
powered down. The REG, LCD, and both reference out-
puts become high impedance. The time required to exit
shutdown is typically 100µs, as shown in the Typical
Operating Characteristics . However, the TEMP output
requires 50ms to fully stabilize. Connect SDLCD and
SD232 to V
Table 2.
Table 1. DAC Truth Table
Table 2. Shutdown Truth Table
X = Don’t care
SDLCD
UP
0
1
X
0
1
DD
SD232
DOWN
0
X
1
0
1
if the shutdown mode is not used. See
Low-power shutdown mode
LCD bias and REG outputs enabled
RS-232 transmitters enabled
DAC set to midscale
DAC register decrements 1 count
DAC register increments 1 count
Temperature Compensation
FUNCTION
FUNCTION
DAC Control Inputs
Shutdown Mode
6-Bit DAC
DD
,