
12
EPSON
S1C88409 TECHNICAL MANUAL
CHAPTER 2: POWER SUPPLY
2.1 Operating Voltage
Table 2.1.1 shows the operating voltage of the
S1C88409.
Using a low voltage for VDD according to operat-
ing speed needs can reduce power consumption.
Table 2.1.1 Correspondence between operating voltage
and operating frequency
Operatable voltage range (VDD)
1.8 V to 5.5 V
2.6 V to 5.5 V
3.5 V to 5.5 V
4.5 V to 5.5 V
Max. clock frequency (OSC3)
1.1 MHz
4.4 MHz
6.6 MHz
8.8 MHz
Note: I/O signal levels (high and low) that are
described in this manual show the following
voltage level if not otherwise noted.
High level = VDD
Low level = VSS
2.2 Internal Power Supply Circuit
The S1C88409 has the built-in power supply circuit
shown in Figure 2.2.1. The power supply circuit
generates the voltage VD1 for the internal circuits
by supplying a voltage within the range men-
tioned above between the VDD (+) and VSS (GND)
terminals.
VD1 voltage can be selected from among four
types: 4.2 V (Max. 8.8 MHz), 3.2 V (Max. 6.6 MHz),
2.4 V (Max. 4.4 MHz) and 1.6 V (Max. 1.1 MHz).
It should be selected by a program to switch
according to the supply voltage and oscillation
frequency.
Refer to Section 5.4, "Oscillation Circuit" for
switching VD1.
Note: Be sure not to use the VD1 terminal output
for driving external circuits.
CHAPTER
2POWER SUPPLY
This section explains the operating voltage and the configuration of the internal power supply circuit of
the S1C88409.
2.3 Heavy Load Protection Mode
The S1C88409 has a heavy load protection function
for stable operation even when the supply voltage
fluctuates by driving a heavy load. The heavy load
protection mode becomes valid when the periph-
eral circuits are in the following status:
(1) The OSC3 oscillation circuit is switched ON
(OSCC = "1" and not in SLEEP)
(2) The buzzer output is switched ON
(BZON = "1" or BZSHT = "1")
SLEEP status
Heavy load
protection mode
OSCC
BZON
BZSHT
Fig. 2.3.1 Configuration of heavy load protection mode
control circuit
For details of the OSC3 oscillation circuit and
buzzer output, refer to Section 5.4, "Oscillation
Circuit" and Section 5.15, "Sound Generator",
respectively.
VD1
VDD
VD1
VSS
Voltage regulator
External
power
supply
Oscillation circuit
OSC1–OSC4
Internal voltage
setting circuit
Internal circuits
Fig. 2.2.1 Configuration of power supply circuit