s-8460 Seiko Instruments Inc., s-8460 Datasheet - Page 10

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

10
STEP-UP OR DOWN, SINGLE-COIL, PWM CONTROL SWITCHING REGULATOR CONTROLLER
S-8460
2. Soft-Start Function
3. ON/OFF Pin (Shutdown Pin)
1. 6 PWM Control
The S-8460 is a DC-DC converter using a pulse width modulation method (PWM) and features a low current
consumption. In conventional PFM DC-DC converters, pulse are skipped when the output load current is low,
causing a fluctuation in the ripple frequency of the output voltage, resulting in an increase in the ripple voltage.
The switching frequency does not change, although the pulse width changes from 0 to 83% at step-up operation
and 0 to 78% in step-up operation. When the pulse width is 0% (when there is no load or the input voltage is
high), current consumption is low since pulses are skipped.
The S-8460 has a built-in soft-start circuit. This circuit enables the output voltage to rise gradually over the
specified soft-start time to suppress the overshooting of the output voltage when the power is switched on or the
ON/OFF pin is changed from “L” to “H”.
The soft-start time (t
The time needed for the output voltage (V
approximately expressed by the following equation.
The value for C
time. If the soft-start time is short, possibility for output overshoot, input current rush, and malfunction of the IC
increases.
When the ON/OFF pin is set to “L”, the EXT1 pin voltage becomes equal to the L
EXT2 and EXT3 pins becomes V
the internal circuit and suppresses the current consumption down to approximately 0.5 μA. The power supply
(V
side V
The ON/OFF pin is configured as shown in Figure 12 and is not either pulled up or pulled down. So, do not use it
with it in a floating state. When the ON/OFF pin is not used, connect it to the VIN pin.
L
), the CSS pin, and CPRO pin become V
OUT
is thus possible when the S-8460 is in halt state.
SS
should be selected to give enough margin to the soft-start time against the power supply rise
SS
) can be set by an external capacitor (C
100
90
80
70
60
50
40
30
20
10
0
0
SS
level to turn the external MOS FET off. At the same time, the S-8460 stops all
Figure 11 Soft-Start Time
t
SS
5000
Seiko Instruments Inc.
(ms) = 0.0026 × C
External capacitor (C
SS
OUT
level. Electrical isolation between power input side V
) to reach 95% of the setting value of the output voltage is
10000
SS
SS
(pF)
).
SS
) [pF]
15000
20000
X
voltage and the voltage of the
Rev.2.1
IN
and output
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