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MSM6545/6575/6545L/6575L

¡ Semiconductor

NOTES ON USE

Power Supply for 0.9 V Microcontroller Series (Backup Flag and Constant-Voltage Circuit)

The 0.9 V devices have a built-in constant-voltage circuit. The output of this constant-voltage

circuit powers the microcontroller's internal logic circuits. Setting a backup flag (BUF) allows

the input of the constant voltage circuit to be switched to either the battery or the output

generated in the voltage converter, based on the battery voltage. A battery voltage of 1.5 V or

3.0 V can be selected.

current consumed by the internal logic to be limited, irrespective of the battery voltage.

However, if the input of the constant voltage circuit is below this set value (approximately –

the internal voltage (output from the constant voltage circuit) falls to 0.9 V. Setting the backup

flag allows a larger operating voltage margin despite changes in internal voltage due to noise.

For example, for the 1.5 V specification, setting the backup flag at "0" supplies twice the battery

voltage to the constant voltage circuit. Thus, even if the battery voltage falls to 0.9 V, the output

internal logic circuits, because 1.8 V is applied to the input of the constant-voltage circuit.

Figures 1 to 4 show the internal status depending on the backup flag settings for the battery, as

well as status features.

XTAL

(0 V)

(–1.5 V)

(–3.0 V)

(–4.5 V)

(About–1.3 V)

LCD driver*

Voltage converter

Backup flag

(BUF)

Constant voltage circuit

VR

Internal logic

XT

XTB

LCD driver.