EM6821 datasheet(7/68 Pages) EMMICRO

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EM6821

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3. Power Supply

The EM6821 is supplied by a single external power supply between VDD (Vbat) and VSS (Ground). A built-in

voltage regulator generates Vreg providing regulated voltage for the oscillator and the internal logic. The output

drivers are supplied directly from the external supply VDD. The internal power configuration is shown below in

Figure 5.

To supply the internal core logic it is possible to use either the internal voltage regulator (Vreg < VDD) or Vbat

directly ( Vreg = VDD). The selection is done by metal 1 mask option. By default the voltage regulator is used.

Refer to chapter 18.1.5 for the metal mask selection.

The internal voltage regulator is chosen for high voltage systems. It saves power by reducing the internal core

logic’s power supply to an optimum value. However, due to the inherent voltage drop over the regulator the

minimal VDD is restricted to 1.4 V .

A direct Vbat connection can be selected for systems running on a 1.5 V battery. The internal 1 KOhm resistor

together with the external capacitor on Vreg is filtering the VDD supply to the internal core. In this case the

minimum VDD can be as low as 1.2 V.

Figure 5. Internal Power Supply

R ef. Logic

Term inal

Vreg

T erm inal

V bat

R ef. LC D

A ll P ad

input &

output

buffers,

SV LD

C ore Logic,

LC D Logic,

O scillator

V oltage m ultiplier,

LC D outputs

M1 B

M1 A

1kO hm

MV reg

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