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Power Management Unit

BCM20705 Data Sheet

BROADCOM CONFIDENTIAL

Broadcom®

Bluetooth Transceiver and Baseband Processor

November 13, 2014 • MCS20705-DS104-R

Page 19

Power Management Unit

The Power Management Unit (PMU) provides power management features that can be invoked through power

management registers or packet handling in the baseband core. This section contains descriptions of the PMU

features.

RF Power Management

The BBC generates power-down control signals for the transmit path, receive path, PLL, and power amplifier to

the 2.4 GHz transceiver. The transceiver then processes the power-down functions, accordingly.

Host Controller Power Management

The host can place the device in a sleep state, in which all nonessential blocks are powered off and all

nonessential clocks are disabled. Power to the digital core is maintained so that the state of the registers and

RAM is not lost. In addition, the LPO clock is applied to the internal sleep controller so that the chip can wake

automatically at a specified time or based on signaling from the host. The goal is to limit the current consumption

to a minimum, while maintaining the ability to wake up and resume a connection with minimal latency.

If a scan or sniff session is enabled while the device is in Sleep mode, the device automatically will wake up for

the scan/sniff event, then go back to sleep when the event is done. In this case, the device uses its internal LPO-

based timers to trigger the periodic wake up. While in Sleep mode, the transports are idle. However, the host

can signal the device to wake up at any time. If signaled to wake up while a scan or sniff session is in progress,

the session continues but the device will not sleep between scan/sniff events. Once Sleep mode is enabled, the

wake signaling mechanism can also be thought of as a sleep signaling mechanism, since removing the wake

status will often cause the device to sleep.

In addition to a Bluetooth device wake signaling mechanism, there is a host wake signaling mechanism. This

feature provides a way for the Bluetooth device to wake up a host that is in a reduced power state.

There are two mechanisms for the device and the host to signal wake status to each other:

When running in SPI mode, the BCM20705 has a mode where it enters Sleep mode when there is no activity

on the SPI interface for a specified (programmable) amount of time. Idle mode is detected when the SPI_CSN

is left deasserted. Whether to sleep on an idle interface and the amount of time to wait before entering Sleep

mode can be programed by the host. Once the BCM20705 enters sleep, the host can wake it by asserting

SPI_CSN. If the host decides to sleep, the BCM20705 will wake up the host by asserting SPI_INT when it has

data for it.

USB

When running in USB mode, the device supports the USB version

2.0 full-speed specification, suspend/resume signaling, as well as

remote wake-up signaling for power control.

Bluetooth WAKE (BT_WAKE) and

Host WAKE (and HOST_WAKE)

signaling

The BT_WAKE pin (GPIO_0) allows the host to wake the BT device,

and HOST_WAKE (GPIO_1) is an output that allows the BT device

to wake the host.

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