CS47L35 datasheet(219/300 Pages) CIRRUS

219 / 300 page

DS1085F3

219

CS47L35

4.19 Charge Pumps, Regulators, and Voltage Reference

The MICBIAS generators are powered from MICVDD, which is generated by an internal charge pump and LDO, as shown

in Fig. 4-74.

Switchable outputs from the MICBIAS generators allow four separate reference/supply outputs to be independently

controlled. The MICBIAS regulators are enabled using the MICB1_ENA and MICB2_ENA bits. The MICBIAS output

switches are enabled using MICB1A_ENA, MICB1B_ENA, MICB2A_ENA, and MICB2B_ENA.

Note that, to enable any of the MICBIASnx outputs, both the output switch and the respective regulator must be enabled.

When a MICBIAS output is disabled, it can be configured to be floating or to be actively discharged. This is configured

using the MICBn_DISCH bits (for the MICBIAS regulators), and the MICBnx_DISCH bits (for the switched outputs). Each

discharge path is only effective when the respective regulator, or switched output, is disabled.

The MICBIAS generators can each operate in Regulator Mode or in Bypass Mode. The applicable mode is selected using

the MICBn_BYPASS bits.

In Regulator Mode (MICBn_BYPASS = 0), the output voltage is selected using the MICBn_LVL fields. In this mode,

MICVDD must be at least 200mV greater than the required MICBIAS output voltages. The MICBIAS outputs are powered

from the MICVDD pin and use the internal band-gap circuit as a reference.

In Regulator Mode, the MICBIAS regulators are designed to operate without external decoupling capacitors. The

regulators can be configured to support a capacitive load if required, using the MICBn_EXT_CAP bits. (This may be

appropriate for a DMIC supply.) It is important that the external capacitance is compatible with the applicable MICBn_EXT_

CAP setting. The compatible load conditions are detailed in Table 3-11.

In Bypass Mode (MICBn_BYPASS = 1), the respective outputs (MICBIASnx), when enabled, are connected directly to

MICVDD. This enables a low power operating state. Note that the MICBn_EXT_CAP settings are not applicable in Bypass

Mode—there are no restrictions on the external MICBIAS capacitance in Bypass Mode.

The MICBIAS generators incorporate a pop-free control circuit to ensure smooth transitions when the MICBIAS outputs

are enabled or disabled in Bypass Mode; this feature is enabled using the MICBn_RATE bits.

The MICBIAS generators are shown in Fig. 4-74. The MICBIAS control fields are described in Table 4-112.

The maximum output current for each MICBIAS regulator is noted in Table 3-11. This limit must be observed for each pair

of MICBIASnx outputs, especially if more than one microphone is connected to a single regulator. Note that the maximum

output current differs between Regulator Mode and Bypass Mode.

4.19.4 Voltage-Reference Circuit

The CS47L35 incorporates a voltage-reference circuit, powered by AVDD. This circuit ensures the accuracy of the

LDO-regulator and MICBIAS voltage settings.

4.19.5 Block Diagram and Control Registers

The charge-pump and regulator circuits are shown in Fig. 4-74. Note that decoupling capacitors and flyback capacitors

are required for these circuits. Refer to Section 5.1 for recommended external components.

CS47L35 Datasheet(PDF) 219 Page - Cirrus Logic