G-
T
W
-00
08947.1.2
SMPS_1V8_SENSE
LX_1V8
1.8V Switch-mode
Regulator
SENSE
LX
L1
4.7µH
C3
2.2µF
1.8V Supply Rail
VSS_SMPS_1V8
SMPS_1V35_SENSE
LX_1V35
1.35V Switch-
mode Regulator
SENSE
LX
VSS_SMPS_1V35
VBAT
3V3_USB
C1
2.2µF
C2
2.2µF
Figure 10.5: 1.8V and 1.35V Switch-mode Regulators Outputs Parallel Configuration
Ensure the series resistance of the tracks is minimised between the regulator input VBAT and 3V3_USB, ground
terminals, the filter and decoupling components, and the external voltage source to maintain high-efficiency power
conversion and low supply ripple.
Ensure a solid ground plane between C1, C2, C3, VSS_SMPS_1V8 and VSS_SMPS_1V35.
Also minimise the collective parasitic capacitance on the track between LX_1V8, LX_1V35 and the inductor L1, to
maximise efficiency.
For the regulator to meet the specifications in Section 13.3.1.2 requires a total resistance of <1.0Ω (<0.5Ω
recommended) for the following:
■
The track between the battery and VBAT.
■
The track between LX_1V8, LX_1V35 and the inductor.
■
The inductor L1, ESR.
■
The track between the inductor, L1, and the sense point on the 1.80V supply rail.
The following enable the 1.80V switch-mode regulator:
■
VREGENABLE pin
■
The CSR8640 BGA firmware with reference to PSKEY_PSU_ENABLES
■
VCHG pin
The switching frequency is adjustable by setting an offset from 4.00MHz using PSKEY_SMPS_FREQ_OFFSET.
When the 1.80V switch-mode regulator is not required, leave unconnected:
■
The regulator input VBAT and 3V3_USB
■
The regulator output LX_1V8
10.4
Bypass LDO Linear Regulator
The integrated bypass LDO linear regulator is available as a 3.30V supply rail and is an alternative supply rail to the
battery supply. This is especially useful when the battery has no charge and the CSR8640 BGA needs to power up.
The input voltage should be between 4.75 / 3.10V and 5.25V.
Note:
The integrated bypass LDO linear regulator can operates down to 3.0V with a reduced performance.
Advance Information
This material is subject to CSR's non-disclosure agreement
© Cambridge Silicon Radio Limited 2011
Page 65 of 110
CS-209182-DSP1
CSR8640 BGA
Data Sheet
