s-8460 Seiko Instruments Inc., s-8460 Datasheet - Page 8

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

8
STEP-UP OR DOWN, SINGLE-COIL, PWM CONTROL SWITCHING REGULATOR CONTROLLER
S-8460
1. 2 Step-up Operation
1. 3 Step-down Operation
Step-up operation is carried out by setting SW1 : ON, SW2 : OFF, and toggling SW3. The voltage V
needed at the BST pin to turn SW1 on. For this purpose, the BST pin voltage (C
by the switch combination SW1 : OFF, SW2 : ON for approximately 200 ns just after SW3 is turned off, and the
BST pin is then bootstrapped to V
SW2 is turned on after SW1 is turned off and SW1 is turned on after SW2 is turned off to avoid the large current to
flow between V
are turned off, current flows to V
allowed to flow through the parasitic diode. In this case, a Schottky diode must be connected parallel to the MOS
FET.
Step-down operation is carried out by synchronous switching of SW1 and SW2, and keeping SW3 open.
The BST pin voltage is kept at V
down operation.
V
V
IN
Parasitic diode
IN
Parasitic diode
IN
and V
SW1
SW1 ON/OFF
SS
if SW1 and SW2 are turned on simultaneously. When the two switches, SW1 and SW2,
LX1
IN
IN
OUT
+ V
+ V
L
through the parasitic diode of SW2. In some MOS FETs current is not
L
, since the switches, SW1 and SW2, repeat toggling in each period in step-
SW2
ON/OFF
SW2
by SW1 : ON, SW2 : OFF.
Seiko Instruments Inc.
Figure 7
Figure 8
SW3
OFF
SW3
ON/OFF
SD1
SD1
BST
C
) is charged to the V
C
OUT
OUT
V
V
OUT
OUT
Rev.2.1
IN
L
voltage
+ V
_00
L
is