A21SP16 datasheet(29/37 Pages) STMICROELECTRONICS

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A21SP16

Application information

5.5

Decoupling of the circuit

A power supply capacitor, referred to as CS, is needed to correctly bypass the A21SP16.

The A21SP16 has a typical switching frequency at 250 kHz and output fall and rise time

about 5 ns. Due to these very fast transients, careful decoupling is mandatory.

A 1 µF ceramic capacitor is enough, but it must be located very close to the A21SP16 in

order to avoid any extra parasitic inductance created an overly long track wire. In relation

with dI/dt, this parasitic inductance introduces an overvoltage that decreases the global

efficiency and, if it is too high, may cause a breakdown of the device.

In addition, even if a ceramic capacitor has an adequate high frequency ESR value, its

current capability is also important. A 0603 size is a good compromise, particularly when a

 load is used.

Another important parameter is the rated voltage of the capacitor. A 1 µF/6.3 V capacitor

used at 5 V, loses about 50% of its value. In fact, with a 5 V power supply voltage, the

decoupling value is about 0.5 µF instead of 1 µF. As CS has particular influence on the

THD+N in the medium-high frequency region, this capacitor variation becomes decisive. In

addition, less decoupling means higher overshoots, which can be problematic if they reach

the power supply AMR value (6 V).

5.6

Wake-up time (tWU)

When the standby is released to set the device ON, there is a wait of about 5 ms. The

A21SP16 has an internal digital delay that mutes the outputs and releases them after this

time in order to avoid any pop noise.

5.7

Shutdown time (tSTBY)

When the standby command is set, the time required to put the two output stages into high

impedance and to put the internal circuitry in shutdown mode, is about 5 ms. This time is

used to decrease the gain and avoid any pop noise during shutdown.

5.8

Consumption in shutdown mode

Between the shutdown pin and GND there is an internal 300 k

 resistor. This resistor forces

the A21SP16 to be in standby mode when the standby input pin is left floating.

However, this resistor also introduces additional power consumption if the shutdown pin

voltage is not 0 V.

For example, with a 0.4 V standby voltage pin, Table 3: Operating conditions on page 3,

shows that you must add 0.4 V/300 k

 = 1.3 µA in typical (0.4 V/273 k = 1.46 µA in

maximum) to the shutdown current specified in Table 5 on page 5.

5.9

Single-ended input configuration

It is possible to use the A21SP16 in a single-ended input configuration. However, input

coupling capacitors are needed in this configuration. The schematic in Figure 61 shows a

single-ended input typical application.

A21SP16 Datasheet(PDF) 29 Page - STMicroelectronics

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