s-8460 Seiko Instruments Inc., s-8460 Datasheet - Page 7

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

Rev.2.1
Operation
1. Step-up or Step-down DC-DC Converter
STEP-UP OR DOWN, SINGLE-COIL, PWM CONTROL SWITCHING REGULATOR CONTROLLER
1. 1 Basic Operation
The S-8460 automatically selects step-up operation or step-down operation to hold the output voltage constant
according to the input voltage (V
can be constructed using the S-8460, since the S-8460 works as a switching regulator for both step-up and step-
down operation.
Figure 6 shows the block diagram of the S-8460.
Internal circuits operate on the internal voltage (V
V
output voltage of the pre-driver circuit for EXT1 lies between the BST pin voltage V
where the BST pin voltage V
SW1 to SW3, thus become V
IN
_00
is 4.5 V or more, the voltage is stepped down to 4.5 V and when V
BST
EXT1
LX
EXT2
VL
ON / OFF
L
BST
, which drives these external MOS FETs.
IN
is normally V
), output voltage (V
Seiko Instruments Inc.
VIN
LX
Figure 6
L
+ V
) except pre-driver circuit for EXT1 and ON/OFF circuit. When
VSS
step-down selection
PWM step-up and
OUT
L
. The gate to source voltages for all external MOS FETs,
), and output current (I
DVSS
Oscillation
Voltage
source
protection
Overload
circuit
CPRO
Reference voltage
IN
with soft-start
is lower than 4.5 V, V
CSS
+
−
OUT
). A high-efficient power supply
BST
EXT3
FB
and the LX pin voltage V
L
is set to V
S-8460
IN
. The
7
LX