THS4531A_15 Datasheet, PDF (26/59 Pages) Texas Instruments – THS4531A Ultra Low-Power, Rail-to-Rail Output, Fully Differential Amplifier

THS4531A
SLOS823B – DECEMBER 2012 – REVISED JUNE 2015
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Feature Description (continued)
To properly interface to 1.8-V logic with minimal increase in additional current draw, a logic-level translator like
the SN74AVC1T45 device can be used.
Alternatively, the same function can be achieved using a diode and pullup resistor as shown in Figure 69.
3V
1.8V
Controller
VS+
RPU
THS4531A
D
PD
Figure 69. THS4531A Power Down Interface to 1.8-V Logic Microcontroller
The voltage at the power down pin will be a function of the supply voltage, input logic level, and diode drop. As
long as the diode is forward biased, the power down voltage is calculated using Equation 3.
V_PD = V_L + V_f
where
• V_L is the logic level voltage.
• V_f is the forward voltage drop across the diode.
(3)
This means for 1.8-V logic, the forward voltage of the diode should be greater than 0.3 V but less than 0.7 V to
keep the power down logic level above 2.1 V and less than 0.7 V respectively.
For example, if 1N914 is selected as the diode with a forward voltage of approximately 0.4 V, the translated logic
voltages will be 0.4 V for disabled operation and 2.2 V for enabled operation.
Use Equation 4 to calculate the additional current draw.
i_PD
V_CC
=
- (V_L
R_PU
+ V_f
)
(4)
Equation 2 shows that larger values of RPU result in a smaller additional current. A reasonable value of RPU is
500 kΩ where an additional current draw of 5.2 µA is expected while the device is in operation and 1.6 µA when
disabled.
8.4 Device Functional Modes
The THS4531A has two functional modes: full-power mode and power-down mode. The power-down mode
reduces the quiescent current of the device to 500 nA from a typical value of 290 µA with a 5-V supply.
With a turnon time of only 600 ns and a turnoff time of 15 ns, the power-down mode can be used to greatly
reduce the average power consumption of the device without sacrificing system performance.
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