BC447 Datasheet, PDF (20/36 Pages) ON Semiconductor – High Voltage Transistors

THS4271
THS4275
SLOS397E − JULY 2002 − REVISED JANUARY 2004
negative rail. The threshold voltages for power-on and
power-down are relative to the supply rails and given in the
specification tables. Above the Enable Threshold Voltage,
the device is on. Below the Disable Threshold Voltage, the
device is off. Behavior in between these threshold voltages
is not specified.
Note that this power-down functionality is just that; the
amplifier consumes less power in power-down mode. The
power-down mode is not intended to provide a high-
impedance output. In other words, the power-down
functionality is not intended to allow use as a 3-state bus
driver. When in power-down mode, the impedance looking
back into the output of the amplifier is dominated by the
feedback and gain setting resistors, but the output
impedance of the device itself varies depending on the
voltage applied to the outputs.
The time delays associated with turning the device on and
off are specified as the time it takes for the amplifier to
reach 50% of the nominal quiescent current. The time
delays are on the order of microseconds because the
amplifier moves in and out of the linear mode of operation
in these transitions.
Power-Down Reference Pin Operation
In addition to the power-down pin, the THS4275 also
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 ≤ MIDRAIL)
SUPPLY
VOLTAGE
(V)
REFERENCE PIN
VOLTAGE (V)
ENABLE DISABLE
LEVEL (V) LEVEL (V)
GND
≥ 1.8
≤1
±5
−2.5
≥ −0.7
≤ −1.5
−5
≥ −3.2
≤ −4
GND
≥ 1.8
≤1
5
1
≥ 2.8
≤2
2.5
≥ 4.3
≤ 3.5
In the above table, the threshold levels are derived by the
following equations:
REF + 1.8 V for enable
REF + 1 V for disable
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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).
POWER-DOWN THRESHOLD VOLTAGE LEVELS (REF > MIDRAIL)
SUPPLY
VOLTAGE
(V)
REFERENCE PIN
VOLTAGE (V)
ENABLE DISABLE
LEVEL (V) LEVEL (V)
Floating or 5
≥4
≤ 3.3
±5
2.5
≥ 1.5
≤ 0.8
1
≥0
≤ −0.7
Floating or 5
≥ 3.3
≤ 3.3
5
4
≥3
≤ 2.3
3.5
≥ 2.5
≤ 1.8
In the above table, the threshold levels are derived by the
following equations:
REF − 1 V for enable
REF − 1.7 V for disable
Note that in order to maintain these threshold levels, the
reference pin can be any voltage between (Vs+/2) + 1 V to
Vs+.
The recommended mode of operation is to tie the
reference pin to midrail, thus setting the threshold levels to
midrail +1 V and midrail +1.8 V.
NO. OF CHANNELS
Single (8-pin)
PACKAGES
THS4275D, THS4275DGN, and
THS4275DRB
Power Supply Decoupling Techniques and
Recommendations
Power supply decoupling is a critical aspect of any
high-performance amplifier design process. Careful
decoupling provides higher quality ac performance (most
notably improved distortion performance). The following
guidelines ensure the highest level of performance.
1. Place decoupling capacitors as close to the power
supply inputs as possible, with the goal of minimizing
the inductance of the path from ground to the power
supply.
2. Placement priority should put the smallest valued
capacitors closest to the device.
3. Use of solid power and ground planes is
recommended to reduce the inductance along power
supply return current paths, with the exception of the
areas underneath the input and output pins.
4. Recommended values for power supply decoupling
include a bulk decoupling capacitor (6.8 to 22 µF), a
mid-range decoupling capacitor (0.1 µF) and a high
frequency decoupling capacitor (1000 pF) for each
supply. A 100-pF capacitor can be used across the
supplies as well for extremely high frequency return
currents, but often is not required.