900844 datasheet(51/118 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

900844

FUNCTIONAL DEVICE OPERATION

POWER STATES AND CONTROL

Figure 17. 900844 Internal Power Tree Block Diagram

As part of the turn on sequence, the 900844 enables a set of internal supplies that provide power to the rest of the circuitry:

1. VCOREREF: This is the main bandgap and reference voltage for all internal circuitries.

2. VCORE: This is the supply for the internal analog circuitry.

3. VCOREDIG: This is the supply for the internal digital circuitry.

Table 21 summarizes the voltage references on the 900844.

There is an internal node called the Best of Supply node (VBOS), which supplies the Real Time Clock and the Keep Alive

Registers. This ensures that power to these critical circuits is maintained for maximum life. VBOS represents the highest of the

VBAT and VCOINCELL input voltages. When VCOREDIG is > 1.2 V, an internal switch is closed, and the circuitry that was

powered from VBOS is now powered from VCOREDIG.

Table 21. 900844 Internal Power Supply Summary

Reference

Parameter

Target

VCOREREF

(Bandgap & Regulators Reference)

Output Voltage

1.2 V

Bypass Capacitor

100 nF typ.

VCOREDIG

(Digital Core Supply)

Output Voltage

1.5 V

Bypass Capacitor

2.2

μF typ.

VCORE

(Analog Core Supply)

Output Voltage

2.775 V

Bypass Capacitor

2.2

μF typ.

VBAT

VCOINCELL

VBOS

VCORERTC

Keep Alive

Bandgap

1.2V

CLOCK

RC/XTAL

Keep Alive

Registers

1.2V

0.9V

VPWR

VCOREREF

VCOREDIG

VCORE

UVDET

Closed when

VCOREDIG > 1.2V

1.5V

Digital Supply

1.2V

Reference Supply

2.775V

Analog Supply

ACTIVE

STATE

RTC

STATE

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