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MSM6546/6546L

¡ Semiconductor

NOTES ON USE

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

The 0.9 V microcontroller 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 –1.3

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 to "0" causes twice the battery

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

the 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.