Datasheet
SLOS310B − DECEMBER 2000 − REVISED SEPTEMBER 2006
12
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
V
DD
/2 bypass capacitor, C
B
The V
DD
/2 bypass capacitor, C
B
, is the most critical capacitor and serves several important functions. During
start-up or recovery from shutdown mode, C
B
determines the rate at which the amplifier starts up. The second
function is to reduce noise produced by the power supply caused by coupling into the output drive signal. This
noise is from the mid-rail generation circuit internal to the amplifier, which appears as degraded PSRR and THD
+ N. The capacitor is fed from two internal 500-kΩ potential-dividing resistors. To keep the start-up bounce as
low as possible, the relationship shown in equation 4 should be maintained. This ensures the input capacitor
is fully charged before the bypass capacitor is fully charged and the amplifier starts up.
10
ǒ
C
B
250 kW
Ǔ
v
1
ǒ
R
F
) R
S
Ǔ
C
S
As an example, consider a circuit where C
B
is 2.2 µF, C
S
is 0.47 µF, R
F
is 50 kΩ, and R
S
is 10 kΩ. Inserting these
values into equation 4 produces the following:
18.2 ≤ 35.5
which satisfies the rule. For bypass capacitor, C
B
, 0.1-µF to 2.2-µF ceramic or tantalum low-ESR capacitors
are recommended for the best stability and noise performance.
using low-ESR capacitors
Low-ESR capacitors are recommended. A real (as opposed to ideal) capacitor can be modeled simply as a
resistor in series with an ideal capacitor. The voltage drop across this resistor minimizes the beneficial effects
of the capacitor in the circuit. The lower the equivalent value of this resistance, the more the real capacitor
behaves like an ideal capacitor.
shutdown function
The TLV4120 has a shutdown terminal for conserving power in energy sensitive applications. When the
shutdown terminal is pulled high the amplifier is disabled, placing the outputs into a high impedance state and
reducing the supply current to the order of microamperes.
To enable the amplifier, the shutdown terminal must be pulled low. If open drain logic is used, pull-up resistors
must be employed to ensure proper and known shutdown status. It is not recommended that the shutdown input
is left to float, as the device could inadvertently shutdown.