S-8521E18MC-BLD-T2 Seiko Instruments, S-8521E18MC-BLD-T2 Datasheet - Page 9

• Manufacturer Part Number: S-8521E18MC-BLD-T2
• Description: DC/DC Switching Regulators 1.8V Step-Dn PWM/PFM
• Manufacturer: Seiko Instruments

Specifications of S-8521E18MC-BLD-T2

• Output Voltage: 1.8 V
• Mounting Style: SMD/SMT
• Package / Case: SOT-23-5
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Rev.7.4
2. Power-Off Pin (ON/OFF Pin)
3. Soft-Start Function
4. Overload Protection Circuit (A, C, E Series)
voltage appears through the EXT pin, prodding the switching transistor to go off. All the internal circuits
stop working, and substantial savings in current consumption are thus achieved.
internally, please avoid operating the pin in a floating state. Also, try to refrain from applying a voltage of
0.3 V to 1.8 V to the pin, lest the current consumption increase. When this power-off pin is not used,
leave it coupled to the VIN pin.
The S-8520/21 Series comes with a built-in soft-start circuit. This circuit enables the output voltage to
rise gradually over the specified soft-start time, when the power is switched on or when the power-off pin
remains 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 (see Figure 5). Since this rush current depends on the input voltage and load conditions, we
recommend that you evaluate it by testing performance with the actual equipment.
The S-8520/21A, S-8520/21C Series, and S-8520/21E Series come with a built-in overload protection
circuit.
If the output voltage falls because of an overload, the maximum duty state (100 %) will continue. If this
100% duty state lasts longer than the prescribed overload detection time (T
circuit will hold the EXT pin at "H," thereby protecting the switching transistor and inductor. When the
overload protection circuit is functioning, the reference voltage circuit will be activated by means of a
This pin deactivates or activates the step-down operation.When the power-off pin is set to "L", the V
The power-off pin is configured as shown in Figure 4. Since pull-up or pull-down is not performed
_10
PWM Control & PWM/PFM Control Step-Down Switching Regulator-Controllers
Power-Off Pin
Figure 5 Waveforms of Output Voltage and Rush Current at Soft-Start
Rush current
S-8520A33MC (V
“H”
“L”
(0.5 A/div)
(1 V/div)
V
OUT
1.5 A
3 V
0 V
0 A
CR Oscillation
Seiko Instruments Inc.
Deactivated
Activated
IN
Power switched on
Circuit
:0 → 4.0 V)
Set value
Voltage
Output
V
t(1 ms/div)
SS
ON/OFF
Figure 4
PRO
), the overload protection
S-8520/8521 Series
V
V
IN
SS
IN
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