UCB1510DB 데이터 시트보기 (PDF) - Philips Electronics

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UCB1510DB

AC97 digital modem codec

Philips Electronics 

Philips Semiconductors

UCB1510

AC97 digital modem codec

9. On-chip reference circuit

The UCB1510 contains an on chip reference voltage source, which generates the

bias currents and the virtual analog ground. Alternatively the UCB1510 can be driven

from an external reference voltage source.

Bias ENA

vref_external

ena

internal

bandgap

reference

Vbg

voltage

circuitry

vref_bypass

&

&

Fig 5. Block diagram of the reference circuit.

internal

analog

ground

VREFBYP

Two bits in the control register 0x5A determine the mode of operation of this

reference voltage circuit. vref_bypass connects the internal reference voltage to the

VREFBYP pin, while vref_external disables the internal reference voltage and

switches the UCB1510 into the external voltage reference mode.

If the internal reference voltage is connected to the VREFBYP pin, an external

capacitor could be connected to filter this reference voltage. When choosing a

capacitor, the internal impedance (around 50 kΩ) should be taken into account.

If vref_external is set, an external voltage reference connected to the VREFBYP pin

is used as the voltage reference by UCB1510.

10. Power supply strategy

Since all the control logic of the UCB1510 is powered by the VDDD, power should

always be present on this pin for interrupts to be possible. VDDA needs not be present

all the time although it is recommended to use the control bits to turn OFF the analog

sections.

9397 750 06856

Preliminary specification

Rev. 01 — 4 February 2000

© Philips Electronics N.V. 2000. All rights reserved.

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