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AS3542 3v2
Data Sheet, Strictly Confidential - D e ta i l e d D e s c r i p t i o n - P o w e r M a n a g e m e n t F u n c t i o n s
9 Detailed Description - Power Management Functions
9.1
Low Drop Out Regulators
9.1.1 General
These LDOs are designed to supply sensitive analogue circuits, audio devices, AD and DA converters, micro-control-
ler and other peripheral devices. The design is optimized to deliver the best compromise between quiescent current
and regulator performance for battery powered devices.
Stability is guaranteed with ceramic output capacitors of 1
μ
F +/-20% (X5R) or 2.2
μ
F +100/-50% (Z5U). The low ESR of
these caps ensures low output impedance at high frequencies. Regulation performance is excellent even under low
dropout conditions, when the power transistor has to operate in linear mode. Power supply rejection is high enough to
suppress high ripple on the battery at the output. The low noise performance allows direct connection of noise sensi-
tive circuits without additional filtering networks. The low impedance of the power device enables the device to deliver
up to 150mA even at nearly discharged batteries without any decrease of performance.
Figure 19. LDO Block Diagram
9.1.2 LDO1
This LDO generates the audio supply voltage used for the AFE itself.
Input voltage is VDD17IN
Output voltage is VDD17 (typ. 1.7V)
Driver strength: 50mA
It is set to a default output voltage of 1.7V, 50mA
max
. It supplies the analog audio blocks of the AFE. Additional external
loads are possible but most not exceed the supply ratings in total together with the operating internal blocks. Further
the external load must not induce noise to the sensitive AVDD17 supply pin.
9.1.3 LDO2
This LDO generates the digital and audio supply voltage used for the AFE itself.
Input Voltage is BVDD
Output Voltage is VDD27 (typ. 2.7V)
Driver strength: 100mA
It is set to a default output voltage of 2.7V, 100mA
max
. It supplies the digital part of the AFE as well as all audio
switches and multiplexers. Additional external loads are possible but most not exceed the supply ratings in total
together with the operating internal blocks. Further the external load must not induce noise to the AVDD27 supply pin
but is not as critical as AVDD17.