CSR86xx Hardware design guideline

Designing with CSR8600
Hardware design guidelines
Seaman.Zhang
March 2013

Introduction
? Key Functional Blocks
– Power Supplies ? Power supplies available and how to use them ? VREGENABLE and RESET ? Routing Guidelines for the power supplies – RF ? Interfacing and Layout Guidelines ? Latest Patch should improve a2dp rangeLatest Patch should improve a2dp range – Audio ? Microphone and line in ? Speaker out ? Alternative audio IO – IO ? Power domains and usage suggestions
. Confidential ? Cambridge Silicon Radio Limited 2012
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Power Supplies
FOR INTERNAL USE ONLY

Power Architecture – possible power supply configurations / use cases
1. Li-Ion battery and both SMPS
– – – – – Main headset use case Best efficiency Lower BOM cost than mode 1 Worse efficiency than mode 1 Cannot use low impedance audio loads as the 1V8 SMPS cannot provide enough current Lower BOM cost than mode 1 Worse efficiency than mode 1 Slightly higher quiescent current than mode 2 Can use all features of the chip including low impedance audio loads USB dongles
2. Li-Ion battery and just the 1V8 SMPS
3. Li-Ion battery and the SMPS in dual 1V8 mode
– – – – –
4. No battery, powered from external 5V supply 5. No battery, powered from external 3V3 supply 6. No battery, powered from external 1V8 supply
. Confidential ? Cambridge Silicon Radio Limited 2012
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Charger – internal mode
? No trimming required
– pre-trimmed by CSR
? High current
– up to 200mA – in 10mA steps
? Separate VBAT_SENSE
– eliminates ? of resistive losses – connect close to battery cell
? Chip can power down with VCHG
present
– About 80uA of current consumption in this mode
? Current programmable from the VM application
– turn current down at high temperatures to protect the battery
? Wide input voltage range
– 4.25V – 5.75V average
? 4.0V – 6.0V transients
. Confidential ? Cambridge Silicon Radio Limited 2012
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Charger – external mode
? Replaces boost charge mode
– no external current source – single inexpensive PNP Bipolar Transistor (such as BCX-51)
? In excess of 500mA possible
– correct heat dissipation is critical – current only limited by gain of the BJT – lack of PNP transistor gain limits current at low VCHG and high VBAT voltages
? VM app can choose mode (internal vs external)
– switch to internal mode when battery gets too hot – switch back to external mode when battery cools down
. Confidential ? Cambridge Silicon Radio Limited 2012
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Bypass regulator
? Internal 3V3 regulator
– no external active components for USB operation – designed to power the whole chip
? Battery not required
– chip can operate without a battery – useful for USB dongle type designs
? Charger disabled at boot
– VM can decide whether and when to start charging (and in what mode) – optionally firmware can switch charger on after boot (PSKEY_CHARGER_AUTO_ENABLE)
. Confidential ? Cambridge Silicon Radio Limited 2012
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SMPS - dual mode (most power efficient)
? 2 LX inductors
– 4.7μH – small size (0805) – must be low ESR (sub 1?, 0.1R ? 0.5R recommended)
? Switch selects
external power or VBAT
– critical transitions are automatic – non-critical transitions are 4MHz switching freq configurable – can be fine tuned using PSKEY_SMPS_FREQ_OFFSET – correct PCB routing is critical
. Confidential ? Cambridge Silicon Radio Limited 2012
?
? 2.2μF decoupling capacitors
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SMPS - single
? only 1 LX inductor
– but current from1V8 SMPS is restricted to internal chip use only
? For lower power systems
– Example: USB dongle with no analogue audio
? 1V35 generated by AUX LDO / ANA LDO regulator
– enable LDOs in PSKEY_PSU_ENABLES
. Confidential ? Cambridge Silicon Radio Limited 2012
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SMPS - parallel mode
? Both SMPS regulators
running
– power transistors wired in parallel
? Only 1 LX inductor
– higher current – no power consumption restrictions
? Make sure inductor can
handle the peak currents
– Max DC load + 50mA + margin for <10% inductance loss – Not the self heating rating!
? For cost sensitive mains powered applications
– increase in battery size (and cost) outweighs size (and cost) of the inductor for battery powered devices
. Confidential ? Cambridge Silicon Radio Limited 2012
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Linear regulators – both SMPS regulators used
? AUX LDO
– left unused
? ANA LDO
– left unused
? DIG LDO
– powered from 1V35 rail
. Confidential ? Cambridge Silicon Radio Limited 2012
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Linear regulators – 1V8 SMPS and ANA LDO regulators used
? AUX LDO
– required for AUX circuits
? ANA LDO
– generates 1V35 rail for BT and audio
? DIG LDO
– powered from 1V8 rail
. Confidential ? Cambridge Silicon Radio Limited 2012
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VREGENABLE and RESET(Headset)
A headset product is typically powered by a rechargeable battery connected to the VBAT input of the CSR8600, with a push button or slider switch controlling the VREGENABLE line.
? An external reset circuit is not ? ?
usually required. VREGENABLE should be connected to a push button or slider switch. RST can be left unconnected or driven by an external circuit.
. Confidential ? Cambridge Silicon Radio Limited 2012
Page 13

VREGENABLE and RESET(USB Dongle)
A USB dongle is only powered when it is plugged into a USB port and does not need a switch to control the power. VREGENABLE should be left unconnected as the USB supply connected to the VCHG input will enable the IC correctly.
. Confidential ? Cambridge Silicon Radio Limited 2012
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VREGENABLE and RESET(3.3 V Powered Module)
If the CSR8600 is powered with an external 3.3 V supply connected to the VBAT line, VREGENABLE must be driven high after the IC has powered up otherwise the device may not initialise properly.
? VREGENABLE should not just be
pulled up to VBAT directly. VREGENABLE must be held low during power up and brought high once the VBAT supply is stable.
? VREGENABLE should be connected
to an external reset or a reset circuit.
? RESET may be connected to the
VREGENABLE if an external reset is not required.
. Confidential ? Cambridge Silicon Radio Limited 2012
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Microphone bias
? Current not programmable
– regulator consumes microphone current + ~400μA
? Only two discrete voltage levels (1.8V and 2.6V)
– exact voltage level has little impact on microphone gain = no need for 16 voltage levels
? Designed to drive 1 or 2 microphones ? Low noise (5μVrms)
– 4x improvement in noise power over BC5MM
? No external decoupling capacitor needed
– saves PCB space and cost
. Confidential ? Cambridge Silicon Radio Limited 2012
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Power Supply routing and decoupling
FOR INTERNAL USE ONLY

Correct Wiring of Decoupling Capacitors
Chip pin VCC GND ? Capacitor decouples power to ?
the chip Capacitor prevents noise coupling back to power plane
Chip pin
VCC GND
? Power plane is decoupled, not ?
the chip Sometime you have no choice (lack of PCB space)
– Make PCB tracks wide
. Confidential ? Cambridge Silicon Radio Limited 2012
Page 18

Looking at Circuits from a PCB Perspective
Schematic view of a circuit VCC VCC VCC Reality
Driver
signal
Load
GND
Driver
signal
Load
? Schematics are counterintuitive - current paths are not obvious ? Signal return path will create a current loop
. Confidential ? Cambridge Silicon Radio Limited 2012
Page 19

Choosing the Right Decoupling Capacitor Value
? Use the appropriate
capacitor for the frequency to be decoupled
– 15p is effective around RF – Small parasitics in layout are significant at RF frequencies
0402 Capacitor Impedance vs. Frequency
15p COG 10n X7R 100n X7R
? Refer to reference
designs for values
2.2u X5R
2.4GHz Generated using Murata’s Chip S Parameter & Impedance Library
. Confidential ? Cambridge Silicon Radio Limited 2012
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