Description of Operation and Application
The ISL24003 are fabricated using a high voltage CMOS
process. They exhibit rail to rail input and output capability
and have very low power consumption. When driving a load
of 10K and 12pF, the buffers have a -3dB bandwidth of
10MHz and exhibit 9V/µs slew rate. The VCOM amplifier has
a -3dB bandwidth of 12MHz and exhibit 10V/µs slew rate.
Input, Output, and Supply Voltage Range
The ISL24003 are specified with a single nominal supply
voltage from 5V to 15V or a split supply with its total range
from 5V to 15V. Correct operation is guaranteed for a supply
range from 4.5V to 16.5V.
The input common-mode voltage range of the ISL24003
within 500mV beyond the supply rails. The output swings of
the buffers and VCOM amplifier typically extend to within
100mV of the positive and negative supply rails with load
currents of 5mA. Decreasing load currents will extend the
output voltage even closer to each supply rails.
Output Phase Reversal
The ISL24003 are immune to phase reversal as long as the
input voltage is limited from VS- -0.5V to VS+ +0.5V.
Although the device's output will not change phase, the
input's over-voltage should be avoided. If an input voltage
exceeds supply voltage by more than 0.6V, electrostatic
protection diode placed in the input stage of the device begin
to conduct and over-voltage damage could occur.
Output Drive Capability
The ISL24003 do not have internal short-circuit protection
circuitry. The buffers will limit the short circuit current to
120mA and the VCOM amplifier will limit the short circuit
current to 150mA if the outputs are directly shorted to the
positive or the negative supply. If the output is shorted
indefinitely, the power dissipation could easily increase such
that the part will be destroyed. Maximum reliability is
maintained if the output continuous current never exceeds
10mA for the buffers and 60mA for the VCOM amplifier.
These limits are set by the design of the internal metal
The Unused Buffers
It is recommended that any unused buffers should have their
inputs tied to ground plane.
With the high-output drive capability of the ISL24003, it is
possible to exceed the 125°C “absolute-maximum junction
temperature” under certain load current conditions.
Therefore, it is important to calculate the maximum junction
temperature for the application to determine if load
conditions need to be modified for the buffer to remain in the
safe operating area.
The maximum power dissipation allowed in a package is
determined according to:
• TJMAX = Maximum junction temperature
• TAMAX = Maximum ambient temperature
• θJA = Thermal resistance of the package
• PDMAX = Maximum power dissipation in the package
The maximum power dissipation actually produced by an IC
is the total quiescent supply current times the total power
supply voltage, plus the power in the IC due to the loads, or:
PDMAX = VS × IS + Σi × [(VS+ – VOUTi ) × ILOADi ] +
(VS+ – VOUT ) × ILA
when sourcing, and:
PDMAX = VS × IS + Σi × [(VOUTi – VS- ) × ILOADi ] +
(VOUT – VS- ) × ILA
• i = 1 to total number of buffers
• VS = Total supply voltage of buffer and VCOM
• ISMAX = Total quiescent current
• VOUTi = Maximum output voltage of the application
• VOUT = Maximum output voltage of VCOM
• ILOADi = Load current of buffer
• ILA = Load current of VCOM
If we set the two PDMAX equations equal to each other, we
can solve for the RLOAD's to avoid device overheat. The
package power dissipation curves provide a convenient way
to see if the device will overheat. The maximum safe power
dissipation can be found graphically, based on the package
type and the ambient temperature. By using the previous
equation, it is a simple matter to see if PDMAX exceeds the
device's power derating curves.
December 7, 2005