s-8460 Seiko Instruments Inc., s-8460 Datasheet - Page 9

• Manufacturer Part Number: s-8460
• Description: Step-up Or Down, Single-coil, Pwm Control Switching Regulator Controller
• Manufacturer: Seiko Instruments Inc.

Rev.2.1
STEP-UP OR DOWN, SINGLE-COIL, PWM CONTROL SWITCHING REGULATOR CONTROLLER
1. 4 Control Sequence
1. 5 Step-up and Step-down Selection Control
If the switches, SW1 and SW2, are turned on simultaneously, V
current flows. And if the switches, SW2 and SW3, are turned on simultaneously, the energy stored in the coil
flows to V
and SW2, and involving SW2 and SW3 both switches are turned off simultaneously to avoid useless current flowing
due to simultaneous turn-on of the switches.
The S-8460 automatically selects operation between step-up and step-down to maintain a constant output voltage
according to the relationship between the input voltage (V
Simple relationships that step-up operation work when input voltage ≤ output voltage and that step-down operation
work when input voltage ≥ output voltage do not hold. Step-up operation emerges when the output voltage is kept
constant by step-up operation, and step-down operation emerges when the output voltage is kept constant by step-
down operation according to the relationship between V
Figure 10 shows the turning point between step-up operation and step-down schematically for the case when the
output voltage is 3.3 V. In the area where the two slant lines are crossing and noted by “Step-up or down” the S-
8460 shows step-up operation or step-down operation.
appear alternately in this area, but that one of the two operations is selected and stable operation is carried out.
The voltage for the turning point between step-up and step-down varies slightly due to external parts and mounting
conditions.
_00
Figure 10 Graphic Scheme for Automatic Selection of Step-up and Step-down
V
SS
IN
and is wasted. The S-8460 thus controls the switches in such a way that in operations involving SW1
Parasitic diode
SW1
18
3.3
2.2
0.1
Step-up or
down
1.0
Step-down operation
SW2
Seiko Instruments Inc.
Step-up operation
I
OUT
Figure 9
10.0
(mA)
IN
, V
100.0
OUT
Not that step-up operation and step-down operation
IN
), output voltage (V
, and I
V
OUT
SW3
IN
= 3.3 V
and V
1 000.0
OUT
Outpu t voltage
.
SD1
SS
are short-circuited and large useless
OUT
C
), and output current (I
OUT
V
OUT
S-8460
OUT
9
).