SM73301 Datasheet, PDF (18/22 Pages) Texas Instruments – RRIO, High Output Current & Unlimited Cap Load Op Amp in SOT23-5

TFT APPLICATIONS
Figure 8 below, shows a typical application where the
SM73301 is used as a buffer amplifier for the V_COM signal
employed in a TFT LCD flat panel:
FIGURE 8. V_COM Driver Application Schematic
30157661
Figure 9 shows the time domain response of the amplifier
when used as a V_COM buffer/driver with V_REF at ground. In this
application, the Op Amp loop will try and maintain its output
voltage based on the voltage on its non-inverting input
(V_REF) despite the current injected into the TFT simulated
load. As long as this load current is within the range tolerable
by the SM73301 (45mA sourcing and 65mA sinking for ±5V
supplies), the output will settle to its final value within less than
2µs.
30157665
FIGURE 9. V_COM driver performance scope photo
OUTPUT SHORT CIRCUIT CURRENT AND DISSIPATION
ISSUES
The SM73301 output stage is designed for maximum output
current capability. Even though momentary output shorts to
ground and either supply can be tolerated at all operating
voltages, longer lasting short conditions can cause the junc-
tion temperature to rise beyond the absolute maximum rating
of the device, especially at higher supply voltage conditions.
Below supply voltage of 6V, output short circuit condition can
be tolerated indefinitely.
With the Op Amp tied to a load, the device power dissipation
consists of the quiescent power due to the supply current flow
into the device, in addition to power dissipation due to the load
current. The load portion of the power itself could include an
average value (due to a DC load current) and an AC compo-
nent. DC load current would flow if there is an output voltage
offset, or the output AC average current is non-zero, or if the
Op Amp operates in a single supply application where the
output is maintained somewhere in the range of linear oper-
ation. Therefore:
P_TOTAL = P_Q + P_DC + P_AC
P_Q = I_S · V_S
Op Amp Quiescent Power
Dissipation
P_DC = I_O · (V_R - V_O)
P_AC = See Table 1 below
DC Load Power
AC Load Power
where:
I_S: Supply Current
V_S: Total Supply Voltage (V⁺ - V^−)
I_O: Average load current
V_O: Average Output Voltage
V_R: V⁺ for sourcing and V^− for sinking current
Table 1 below shows the maximum AC component of the load
power dissipated by the Op Amp for standard Sinusoidal, Tri-
angular, and Square Waveforms:
TABLE 1. Normalized AC Power Dissipated in the Output
Stage for Standard Waveforms
Sinusoidal
50.7 x 10^−3
P_AC (W.Ω/V²)
Triangular
46.9 x 10^−3
Square
62.5 x 10^−3
The table entries are normalized to V_S2/ R_L. To figure out the
AC load current component of power dissipation, simply mul-
tiply the table entry corresponding to the output waveform by
the factor V_S2/ R_L. For example, with ±15V supplies, a 600Ω
load, and triangular waveform power dissipation in the output
stage is calculated as:
P_AC= (46.9 x 10^−3) · [30²/600]= 70.4mW
Other Application Hints
The use of supply decoupling is mandatory in most applica-
tions. As with most relatively high speed/high output current
Op Amps, best results are achieved when each supply line is
decoupled with two capacitors; a small value ceramic capac-
17
www.national.com