Optimizing Current Consumption

Current consumption, or more generally, energy usage, is a major concern for battery-powered products. Optimizing current consumption extends battery life and, consequently, improves product performance. The following topics are intended to help users optimize power consumption.

Static Power State
Bluetooth Low Energy State
Bluetooth State

Overview

There are three main factors that affect current consumption in a Bluetooth Audio SoC device.

The static power state of the SoC.
- The static power state of the SoC includes the power mode, DVFS, and the frequency of the CPU.
The amount of power transmitted.
- The amount of transmit power required includes transmit/receive power, which depends on the desired distance between the central and peripheral devices. The range is greatly influenced by environmental factors such as obstacles and the amount of 2.4 GHz traffic present. The first tip for power consumption optimization is to avoid transmitting more power than necessary.
The total amount of time that the Bluetooth is active.
- The amount of time that Bluetooth is active is determined by how often it needs to transmit or receive data and the duration of each transmission or reception. The first and most obvious tip is to keep the characteristics small. If 8 bits are sufficient, do not use a 32-bit integer.

In general, the power consumption of a Bluetooth Audio SoC device can be optimized by adjusting parameters related to advertising and connection states.

Note

The following test results are based on a specific board. All values are obtained from actual measurements performed using a specific image, and are only provided as an example. For detailed information about power consumption values, please refer to the data provided in the HDK.

Static Power State

Static power consumption affects the basic power consumption of the system.

Power Mode

The power modes of the platform include active mode, DLPS mode, power down mode, and ship mode. The platform must stay in an active state when Bluetooth is active. When Bluetooth is not active and in deep sleep mode, the platform can enter DLPS mode to reduce power consumption.

Note

In general, Bluetooth test scenarios will be carried out in active or DLPS mode.

RTL87x3E

Example:

Power Mode
Test Condition	Power Mode	Current (uA)
IC: 8773EFE VBAT: 3.7V	Active Mode	879
	DLPS Mode	29
	Power Down Mode	5.7
	Ship Mode	1.5

DVFS and CPU Frequency

DVFS can dynamically adjust voltage and frequency and has two modes: high-performance mode and low-performance mode. High-performance mode consumes more power than low-performance mode. However, when the frequency of the CPU or DSP exceeds a certain specific value, DVFS must switch to high-performance mode.

The frequency of the CPU can be set to different values within a certain range, and the higher the frequency, the more power is consumed. And when the CPU is in an idle state, the CPU can go into WFI to reduce power consumption.

Note

The following Bluetooth test scenario is as follows.

DVFS works in low-performance mode.
The CPU frequency is 40M and can enter WFI.
No DSP.

RTL87x3E

Example:

DVFS and CPU Frequency
Test Condition	DVFS	CPU State	CPU Frequency	Current (mA)
IC: 8773EFE VBAT: 3.7V	High Performance	WFI	625K	0.929
		Active	100M	4.169
			80M	3.340
			40M	2.024
	Low Performance	WFI	625K	0.879
		Active	40M	1.875
		Active	20M	1.397

RF Receive Power

The RF receive power is fixed.

RTL87x3E

Example:

Bluetooth Receive Power
Test Condition	State	Test Case	Packet Type	Current (mA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: Active Mode Measuring Time: 10s	Packet Receive (for MP)	BR	DH5	7.486
		EDR_2M	2DH5	7.490
		EDR_3M	3DH5	7.485

../../../../_images/rx_br_dh5.jpg — RX BR DH5

../../../../_images/rx_edr_2m_2dh5.jpg — RX EDR 2M 2DH5

../../../../_images/rx_edr_3m_3dh5.jpg — RX EDR 3M 3DH5

From the above results, there is no difference between the receive power consumption of BR and EDR.

Bluetooth Low Energy Receive Power
Test Condition	State	Test Case	PHY	Current (mA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: Active Mode Measuring Time: 10s	LE Packet Receive (for MP)	LE	LE 1M PHY	7.083
	LE Packet Receive (for MP)	LE	LE 2M PHY	7.746

../../../../_images/rx_le_1m_phy.jpg — RX LE 1M

../../../../_images/rx_le_2m_phy.jpg — RX LE 2M

From the above results, the receive power consumption of LE 2M PHY is greater than LE 1M PHY.

RF Transmit Power

The RF transmit power is adjustable, with the range as follows.

The Range of RF Transmit Power
Type	Min (dbm)	Max (dbm)
BR	-2	12
EDR_2M	-2	10
EDR_3M	-2	10
LE_1M	-2	12.5
LE_2M	-2	12.5

The power consumption increases as the transmit power setting increases.

RTL87x3E

Example:

Bluetooth BR Transmit Power
Test Condition	Continuous Transmit (for Certification)	Transmit Power (dbm)	Average Current (mA)	Max Current (mA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: Active Mode Measuring Time: 10s	BR Channel: 0 Packet Type: DH5 Payload Type: PRBS9	0	20.704	21.769
		4	26.609	27.696
		6	28.460	29.598
		10	35.161	36.293

../../../../_images/0db_br.jpg — 0dbm BR

../../../../_images/4db_br.jpg — 4dbm BR

../../../../_images/6db_br.jpg — 6dbm BR

../../../../_images/10db_br.jpg — 10dbm BR

Bluetooth EDR_2M Transmit Power
Test Condition	Continuous Transmit (for Certification)	Transmit Power (dbm)	Average Current (mA)	Max Current (mA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: Active Mode Measuring Time: 10s	EDR_2M Channel: 0 Packet Type: 2DH5 Payload Type: PRBS9	0	20.680	21.765
		4	26.431	27.534
		6	28.368	29.458
		10	34.630	36.030

Bluetooth EDR_3M Transmit Power
Test Condition	Continuous Transmit (for Certification)	Transmit Power (dbm)	Average Current (mA)	Max Current (mA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: Active Mode Measuring Time: 10s	EDR_3M Channel: 0 Packet Type: 3DH5 Payload Type: PRBS9	0	20.687	21.749
		4	26.428	27.554
		6	28.381	29.631
		10	34.602	35.822

Bluetooth LE_1M Transmit Power
Test Condition	Continuous Transmit (for Certification)	Transmit Power (dbm)	Average Current (mA)	Max Current (mA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: Active Mode Measuring Time: 10s	LE_1M Channel: 0 Packet Type: 3DH5 Payload Type: PRBS9	0	20.687	21.729
		4	26.557	27.614
		6	28.408	29.480
		10	35.062	36.171

As observed from the current diagram above, increasing the setting of transmit power will result in a larger maximum current value, which will increase power consumption.

The transmit power consumption of BR/EDR_2M/EDR_3M/LE_1M is basically the same.

Bluetooth Low Energy State

Bluetooth Low Energy includes the following states:

Advertising
Scan
Connection

Advertising

There are two main factors that affect the current consumption of advertising.

Advertising interval, range: 0x000020 to 0xFFFFFF, in units of 0.625ms.
- The power consumption decreases while the interval increases.
Advertising data length, range: 0 to 31.
- The power consumption increases while the length increases.

The following figure shows the current waveform of advertising.

../../../../_images/adv.jpg — Advertising

If low power mode is enabled (as in most of the examples), the SoC can enter DLPS mode automatically between advertising events.

../../../../_images/adv_dlps.jpg — Advertising DLPS

RTL87x3E

Test results of RTL87x3E.

Different Advertising Interval

Example:

Different Advertising Interval
Test Condition	Advertising Interval (ms)	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 15s Transmit Power: 0dbm Advertising Data Length: 31	100	495
	300	194
	500	125
	1000	82

../../../../_images/adv_interval_100.jpg — Advertising Interval 100ms

../../../../_images/adv_interval_1000.jpg — Advertising Interval 1000ms

Different Advertising Data Length

Example:

Different Advertising Data Length
Test Condition	Advertising Data Length	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 15s Transmit Power: 0dbm Advertising Interval: 100ms	0	342
	10	394
	20	439
	31	495

The larger the advertising data length, the greater the transmit duration.

../../../../_images/adv_data_len.jpg — Advertising Date Length

Scan

There are four parameters in scan, and three of them impact power consumption.

Scan interval, range: 0x0004 to 0xFFFF, in units of 0.625ms.
- The power consumption decreases while the interval increases.
Scan window, range: 0x0004 to 0xFFFF, in units of 0.625ms.
- The power consumption increases while the window increases.
Scan mode: When there is external advertising, the active scan consumes more power.
- Passive scan: No transmission is generated to reply when an external advertising is received.
- Active scan: Transmission is generated to reply when an external advertising is received.
Duplicate: This parameter has no effect on power consumption.
- Enable: Filter duplicate advertising, not report to host but still reply to advertising.
- Disable: Do not filter duplicate advertising and reply to advertising.

The following figure shows the current waveform of scan.

../../../../_images/ble_scan.jpg — Bluetooth Low Energy Scan

If low power mode is enabled (as in most of the examples), the SoC can enter DLPS mode automatically between scan events.

../../../../_images/ble_scan_dlps.jpg — Bluetooth Low Energy Scan DLPS

RTL87x3E

Test results of RTL87x3E.

Different Scan Interval

Example:

Different Scan Interval
Test Condition	Scan Interval (ms)	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 15s Transmit Power: 0dbm Scan Window: 2.5ms Scan Mode: Passive Duplicate: Disable	100	389
	300	153
	500	105
	1000	69

../../../../_images/scan_interval_100.jpg — Bluetooth Low Energy Scan Interval 100ms

../../../../_images/scan_interval_1000.jpg — Bluetooth Low Energy Scan Interval 1000ms

Different Scan Window

Example:

Different Scan Window
Test Condition	Scan Window (ms)	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 15s Transmit Power: 0dbm Scan Interval: 500ms Scan Mode: Passive Duplicate: Disable	2.5	105
	5	138
	10	204
	25	405

../../../../_images/scan_window.jpg — Bluetooth Low Energy Scan Window

Different Scan Mode

Example:

Different Scan Mode
Test Condition	Scan Mode	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 15s Transmit Power: 0dbm Scan Interval: 300ms Scan Window: 25ms Other Device Advertising Interval: 20ms Other Device Advertising Data Size: 23 Duplicate: Disable	Passive	645
	Active	665

The following figure shows the current waveform of Bluetooth Low Energy passive scan.

../../../../_images/ble_passive_scan.jpg — Bluetooth Low Energy Passive Scan

The following figure shows the current waveform of Bluetooth Low Energy active scan.

../../../../_images/ble_active_scan.jpg — Bluetooth Low Energy Active Scan

Connection

There are two main factors affecting the current consumption of connection.

Connection interval, range: 0x0006 to 0x0C80, in units of 1.25ms.
- The power consumption decreases while the interval increases.
Connection slave latency, range: 0x0000 to 0x01F3.
- If there is no data interaction when serving as a slave, how many intervals can be skipped. The power consumption decreases while the latency increases.

The following figure shows the current waveform of Bluetooth Low Energy connection.

../../../../_images/ble_connect.jpg — Bluetooth Low Energy Connect

If low power mode is enabled (as in most of the examples), the SoC can enter DLPS mode automatically between connection events.

../../../../_images/ble_connect_dlps.jpg — Bluetooth Low Energy Connect DLPS

RTL87x3E

Test results of RTL87x3E.

Different Connection Interval

Example:

Different Connection Interval
Test Condition	Connection Interval (ms)	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 15s Transmit Power: 0dbm Connection Slave Latency: 0	100	209
	300	96
	500	74
	1000	57

../../../../_images/connect_interval_100.jpg — Bluetooth Low Energy Connect Interval 100ms

../../../../_images/connect_interval_1000.jpg — Bluetooth Low Energy Connect Interval 1000ms

Different Connection Slave Latency

Example:

Different Connection Slave Latency
Test Condition	Connection Slave Latency	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 15s Transmit Power: 0dbm Connection Interval: 100ms	0	209
	1	124
	2	103
	3	90

The following figure shows the current waveform of Bluetooth Low Energy connection when setting the latency at 3.

../../../../_images/connect_latency_3.jpg — Bluetooth Low Energy Connect Latency 3

Bluetooth State

Bluetooth includes the following states:

Page Scan
Inquiry Scan
Sniff Mode
Page
Inquiry

Page Scan

There are four parameters in page scan, and three of them impact power consumption.

Page scan interval, range: 0x0012 to 0x1000, in units of 0.625ms, default 0x0800.
- The power consumption decreases while the interval increases.
Page scan window, range: 0x0011 to 0x1000, in units of 0.625ms, default 0x0012.
- The power consumption increases while the window increases.
Page scan type:
- Standard
- Interlace
  - During a standard scan, a device listens for the duration of the scan window (11.25ms default), while the generalized interlaced scan is performed as two back-to-back scan windows. Therefore, the interlace mode consumes more power.

Page timeout: how long to report a timeout error to the app when the connection is not possible. Therefore, the parameter has no influence on power consumption.

The following figure shows the current waveform of page scan.

../../../../_images/page_scan.jpg — Bluetooth Page Scan

If low power mode is enabled (as in most of the examples), the SoC can enter DLPS mode automatically between page scan events.

../../../../_images/page_scan_dlps.jpg — Bluetooth Page Scan DLPS

RTL87x3E

Test results of RTL87x3E.

Different Page Scan Interval

Example:

Different Page Scan Interval
Test Condition	Page Scan Interval (ms)	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 30s Transmit Power: 6dbm Page Scan Window: 11.25ms Page Scan Type: Interlace Page Timeout: 10240ms	300	575
	600	305
	1280	162
	2560	93

../../../../_images/page_scan_interval_300.jpg — Bluetooth Page Scan Interval 300ms

../../../../_images/page_scan_interval_2560.jpg — Bluetooth Page Scan Interval 2560ms

Different Page Scan Window

Example:

Different Page Scan Window
Test Condition	Page Scan Window (ms)	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 30s Transmit Power: 6dbm Page Scan Interval: 1280ms Page Scan Type: Interlace Page Timeout: 10240ms	11.25	162
	20	249
	25	299
	30	368

../../../../_images/page_scan_window.jpg — Bluetooth Page Scan Window

Different Page Scan Type

Example:

Different Page Scan Type
Test Condition	Page Scan Type	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 30s Transmit Power: 6dbm Page Scan Interval: 1280ms Page Scan Window: 11.25ms Page Timeout: 10240ms	Interlace	162
	Standard	104

The following figure shows the current waveform of interlace page scan.

../../../../_images/page_scan_interlace.jpg — Bluetooth Interlace Page Scan

The following figure shows the current waveform of standard page scan.

../../../../_images/page_scan_standard.jpg — Bluetooth Standard Page Scan

Inquiry Scan

There are three main factors that affect current consumption of inquiry scan.

Inquiry scan interval, range: 0x0012 to 0x1000, in units of 0.625ms, default 0x1000.
- The power consumption decreases while the interval increases.
Inquiry scan window, range: 0x0011 to 0x1000, in units of 0.625ms, default 0x0012.
- The power consumption increases while the window increases.
Inquiry scan type:
- Standard
- Interlace
  - During a standard scan, a device listens for the duration of the scan window (11.25ms default), while the generalized interlaced scan is performed as two back-to-back scan windows. Therefore, the interlace mode consumes more power.

Note

Since inquiry scan will generate a transmission when it finds another device, the following test results will have higher power consumption than testing in a shielded room.

The following figure shows the current waveform of inquiry scan.

../../../../_images/inquiry_scan.jpg — Bluetooth Inquiry Scan

If low power mode is enabled (as in most of the examples), the SoC can enter DLPS mode automatically between inquiry scan events.

../../../../_images/inquiry_scan_dlps.jpg — Bluetooth Inquiry Scan DLPS

RTL87x3E

Test results of RTL87x3E.

Different Inquiry Scan Interval

Example:

Different Inquiry Scan Interval
Test Condition	Inquiry Scan Interval (ms)	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 30s Transmit Power: 6dbm Inquiry Scan Window: 11.25ms Inquiry Scan Type: Interlace	300	607
	600	328
	1280	180
	2560	105

../../../../_images/inquiry_scan_300.jpg — Bluetooth Inquiry Scan Interval 300ms

../../../../_images/inquiry_scan_2560.jpg — Bluetooth Inquiry Scan Interval 2560ms

Different Inquiry Scan Window

Example:

Different Inquiry Scan Window
Test Condition	Inquiry Scan Window (ms)	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 30s Transmit Power: 6dbm Inquiry Scan Interval: 2560ms Inquiry Scan Type: Interlace	11.25	105
	20	147
	25	174
	30	201

../../../../_images/inquiry_scan_window.jpg — Bluetooth Inquiry Scan Window

Different Inquiry Scan Type

Example:

Different Inquiry Scan Type
Test Condition	Inquiry Scan Type	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 30s Transmit Power: 6dbm Inquiry Scan Interval: 2560ms Inquiry Scan Window: 11.25ms	Interlace	105
	Standard	70

The following figure shows the current waveform of interlace inquiry scan.

../../../../_images/interlace_inquiry_scan.jpg — Bluetooth Interlace Inquiry Scan

The following figure shows the current waveform of standard inquiry scan.

../../../../_images/standard_inquiry_scan.jpg — Bluetooth Standard Inquiry Scan

Sniff Mode

There are three main factors that affect current consumption of sniff mode.

Sniff mode interval, range: 0x0002 to 0xFFFE, in units of 0.625ms.
- The power consumption decreases while the interval increases.
Sniff mode attempt, range: 0x0001 to 0x7FFF, in units of 1.25ms.
- The power consumption increases while the sniff mode attempt increases.
Sniff mode timeout, range: 0x0000 to 0x7FFF, in units of 1.25ms.
- The power consumption increases while the sniff mode timeout increases.

../../../../_images/sniff_mode_slave_attempt_timeout.jpg — Bluetooth Sniff Mode Slave Attempt Timeout

A slot has an interval of 0.625ms and normally contains a transmission or a reception. The interval of an attempt is 1.25ms, so one attempt contains two slots. Timeout is the slots that are required to be waited when data is received. During the attempt period, the master will generate a transmission in each attempt. Therefore, the slave will generate a reception and then generate a transmission to reply.

Note

When the attempt or timeout is set to a large value, it will affect the situation of multi-link. Therefore, in the SoC, if the attempt or timeout exceeds 10, the attempt will be set to 4 and the timeout will be set to 2.

The following figure shows the current waveform of sniff mode.

../../../../_images/sniff_mode.jpg — Bluetooth Sniff Mode

If low power mode is enabled (as in most of the examples), the SoC can enter DLPS mode automatically between sniff mode events.

../../../../_images/sniff_mode_dlps.jpg — Bluetooth Sniff Mode DLPS

RTL87x3E

Test results of RTL87x3E.

Different Sniff Mode Interval

Example:

Different Sniff Mode Interval
Test Condition	Sniff Mode Interval (ms)	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 30s Transmit Power: 6dbm Sniff Mode Attempt: 2 Sniff Mode Timeout: 5ms	100	364
	250	167
	500	100
	1000	71

../../../../_images/sniff_mode_interval_100.jpg — Bluetooth Sniff Mode Interval 100ms

../../../../_images/sniff_mode_interval_1000.jpg — Bluetooth Sniff Mode Interval 1000ms

Different Sniff Mode Attempt

Example:

Different Sniff Mode Attempt
Test Condition	Sniff Mode Attempt	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 30s Transmit Power: 6dbm Sniff Mode Interval: 500ms Sniff Mode Timeout: 5ms	2	100
	4	129
	6	159
	8	188

The following figure shows the current waveform of sniff mode when setting attempt at 2.

../../../../_images/sniff_mode_attempt_2.jpg — Bluetooth Sniff Mode Attempt 2

The following figure shows the current waveform of sniff mode when setting attempt at 4.

../../../../_images/sniff_mode_attempt_4.jpg — Bluetooth Sniff Mode Attempt 4

Different Sniff Mode Timeout

Example:

Different Sniff Mode Timeout
Test Condition	Sniff Mode Timeout (ms)	Current (uA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: DLPS Mode Measuring Time: 30s Transmit Power: 6dbm Sniff Mode Interval: 500ms Sniff Mode Attempt: 2	0	99
	5	100
	10	99
	15	129
	25	129
	35	129
	100	129

The following figure shows the current waveform of sniff mode when setting timeout at 0ms/5ms/10ms.

../../../../_images/sniff_mode_timeout_0.jpg — Bluetooth Sniff Mode Timeout 0

The following figure shows the current waveform of sniff mode when setting timeout at 15ms/25ms/35ms/100ms.

../../../../_images/sniff_mode_timeout_15.jpg — Bluetooth Sniff Mode Timeout 15

From the above results, when timeout is less than 10 (in units of 1.25ms), it has little influence on power consumption. When timeout exceeds 10, the power consumption becomes higher because the SoC forces attempt to be set to 4 and timeout to be set to 2.

Page and Inquiry

Page and inquiry have no parameters affecting power consumption.

RTL87x3E

Test results of RTL87x3E.

Page

Example:

Page
Test Condition	Type	Current (mA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: Active Mode Measuring Time: 5s Transmit Power: 6dbm	Page	7.00

../../../../_images/page.jpg — Bluetooth Page

Inquiry

Example:

Inquiry
Test Condition	Type	Current (mA)
IC: 8773EFE VBAT: 3.7V CPU: 40M DVFS: Low Performance Power Mode: Active Mode Measuring Time: 5s Transmit Power: 6dbm	Inquiry	7.36

../../../../_images/inquiry.jpg — Bluetooth Inquiry