S-8520A20MC-AVFT2X Datasheet, PDF (14/44 Pages) Seiko Instruments Inc – SWITCHING REGULATOR CONTROLLER

STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8520/8521 Series
Rev.9.0_01
2. Soft start function
The
S-8520/8521
Series
has
a
built-in
soft
start-circuit.
This
circuit
enables
the output
______
voltage
(VOUT)
to
rise
gradually over the specified soft start time (t), when power-on or when the ON/OFF pin is at the “H” level. This
prevents the output voltage from overshooting.
However, the soft-start function of this IC is not able to perfectly prevent a rush current from flowing to the load
(Refer to Figure 8). Since this rush current depends on the input voltage and load conditions, Perform sufficient
evaluation with actual device for design.
3V
V_OUT
[1 V/div]
0V
S-8520A33MC (V_IN: 0 V→4.0 V)
1.5 A
Rush current
[0.5 A/div]
0A
t [1 ms/div]
Figure 8 Waveforms of output voltage and rush current at soft start
_______
3. ON/OFF pin (Shutdown pin)
______
The ON/OFF pin stops or starts step-up operation.
______
Setting the ON/OFF pin to the “L” level stops operation of all the internal circuits and reduces current consumption
significantly. The EXT pin’s voltage is set to the VIN voltage level so that the switching transistor is turned off.
______
Do not use the ON/OFF pin in a floating state because it has the structure shown in Figure 9 and is not pulled up
______
or pulled down internally. Do not apply a voltage of between 0.3 V and 1.8 V to the ON/OFF pin because applying
______
such a voltage increases the current consumption. When not using the ON/OFF pin, connect it to the VIN pin.
______
ON/OFF pin
“H”
“L”
Table 8
CR Oscillation Circuit
Operation
Stop
VIN
Output voltage
Set value
VSS
______
ON/OFF
Figure 9
VSS
14