Datasheet

Power-Down Reference Pin Operation
3-5
THS4221 and THS4225 EVM Applications
3.4 Power-Down Reference Pin Operation
In addition to the power-down pin, the THS4225 EVM features a reference pin
(REF) which allows the user to control the enable or disable power-down
voltage levels applied to the PD pin. Operation of the reference pin as it relates
to the power-down pin is described below.
In most split-supply applications, the reference pin is connected to ground. In
some cases, the user may want to connect it to the negative or positive supply
rail. In either case, the user needs to be aware of the voltage level thresholds
that apply to the power-down pin. The tables below show examples and
illustrate the relationship between the reference voltage and the power-down
thresholds.
Power-Down Threshold Voltage Levels (REF 3 Midrail)
Supply Voltage
(V)
Reference Pin
Voltage (V)
Enable Level
(V)
Disable Level
(V)
GND ≥1.8 ≤1
±5
−2.5 ≥−0.7 ≤−1.5
±5
−5 ≥−3.2 ≤−4
GND ≥1.8 ≤1
5
1 ≥2.8 ≤2
5
2.5 ≥4.3 ≤3.5
3.3 GND ≥1.8 ≤1
In the above table, the threshold levels are derived by the following equations:
REF + 1.8 V for enable
REF + 1 V for disable
Note that in order to maintain these threshold levels, the reference pin can be
any voltage between Vs– or GND up to Vs/2 (midrail).
For 3.3-V operation, the reference pin must be connected to the most negative
rail (for single supply this is GND).