SM1350 series

NIPPON PRECISION CIRCUITS—9

Melody Output Circuit

The volume control circuit comprises a P-channel

current-summing D/A converter, a built-in constant-

current source and an external variable resistor. The

circuit is set for either BTL output or A-class output

by master-slice option.

BTLoutput

The BTL output comprises a pair of 9-bit D/A

converters and 4 external transistors (2

× NPN + 2 ×

PNP) to drive a speaker.

A-class output circuit

The A-class output circuit comprises a single 10-bit

D/A converter with current output on SP. The D/A

converter MSB is set ON immediately after the

oscillator starts, and the current output that results is

the center point above and below which the converter

current output varies in response to the waveform

amplitude. The SP output is current-to-voltage

converted for connection to audio equipment or

amplifiers. In A-class output mode, the 4 sound

generator waveforms are time multiplexed, so an

integrating circuit must be connected between SP

and the amplifier to recover the signal.

Figure 4. BTL output circuit

VDD

VSS

VOL

MSB

MSBN

SP

SPN

VSS

SPEAKER

C

Note: Refer to the "TIMING DIAGRAMS" section to confirm melody timing specifics.

Figure 5. A-class output circuit

VDD

VSS

VOL

SP

BUSYN

AMP

SPEAKER