S8520 datasheet(15/44 Pages) SII

Part #	S8520

Description	STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER

Download	44 Pages

Scroll/Zoom	100%

Manufacturer	SII [Seiko Instruments Inc]

Direct Link	http://www.sii.co.jp

Logo

15 / 44 page

STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER

Rev.9.0_01

S-8520/8521 Series

15

4. Overload protection circuit (A, C, E types)

The A, C and E types of the S-8520/8521 Series have a built-in overload protection circuit.

If the output voltage drops under the overload status, the maximum duty status (100%) continues. If this 100% duty

status lasts longer than the overload detection time (tpro), the circuit keeps the EXT pin at “H” to protect the

switching transistor and inductor. When the overload protection circuit is functioning, the soft start works in the IC

for the reference voltage, and the reference voltage rises slowly from 0 V. The reference voltage and the feedback

voltage obtained by dividing the output voltage are compared to each other. While the reference voltage is low, the

EXT pin keeps “H” and oscillation stops. If the reference voltage rises and exceeds the feedback voltage, oscillation

restarts.

After oscillation is restarted, if a load is heavy and the EXT pin keeps the “L” level longer than the overload

detection time (tpro), the circuit operates again, and the IC enters the intermittent operation mode by repeating the

action described above. Once the overload state is off, the IC restarts the normal operation.

Waveforms

at EXT pin

Protection circuit ON

[tss

× 0.3]

Overload detection time (tpro)

Figure 10 Waveforms at EXT pin when the overload protection circuit operates

5. 100% duty cycle

The S-8520/8521 Series operates with a maximum duty cycle of 100%. When using the B, D and F types products,

which do not have the overload protection circuit, the switching transistor keeps ON continually to supply current to

the load, even in cases where the input voltage drops to the set value of output voltage or less. The output voltage

in this case is; the voltage subtracting both of the inductance’s DC resistance and the voltage drop by the switching

resistor’s ON-resistance, from the input voltage.

The A, C and E types that have the overload protection circuit cannot be used for continually supplying current to

the load, as described above, because these types enter the intermittent operation mode by the overload protection

circuit’s operation, when 100% duty lasts longer than the overload detection time (tpro).

Similar Part No. - S8520

Manufacturer	Part #	Datasheet	Description
Vishay Siliconix	S852T	179Kb / 8P	Silicon NPN Planar RF Transistor Rev. 1.4, 02-May-05
	S852T	281Kb / 8P	Silicon NPN Planar RF Transistor Rev. 1.5, 08-Sep-08
	S852T	281Kb / 8P	Silicon NPN Planar RF Transistor Rev. 1.5, 08-Sep-08
	S852T	282Kb / 8P	Silicon NPN Planar RF Transistor Rev. 1.5, 08-Sep-08
	S852T-GS08	282Kb / 8P	Silicon NPN Planar RF Transistor Rev. 1.5, 08-Sep-08

Manufacturer	Part #	Datasheet	Description
ABLIC Inc.	S-8520	612Kb / 44P	STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER Rev.9.0_02
Seiko Instruments Inc	S8540	2Mb / 36P	STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
	S-8540	445Kb / 36P	STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
	S8340	3Mb / 55P	STEP-UP, 600 kHz, PWM CONTROL OR PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
	S-8365AAABA-M5T1Y2	3Mb / 63P	PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
	S-8355K18MC-NADT2X	3Mb / 72P	PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
	S8353	2Mb / 49P	STEP-UP, PWM CONTROL or PWM / PFM SWITCHABLE BUILT-IN TRANSISTOR SWITCHING REGULATOR
ABLIC Inc.	S-8353	567Kb / 49P	STEP-UP, PWM CONTROL or PWM / PFM SWITCHABLE BUILT-IN TRANSISTOR SWITCHING REGULATOR Rev.3.0_02
Seiko Instruments Inc	S-8520	2Mb / 34P	PWM CONTROL & PWM/PFM CONTROL STEP-DOWN SWITCHING REGULATOR-CONTROLLERS
Seiko Instruments Inc	S8355	3Mb / 72P	STEP-UP, SUPER-SMALL PACKAGE, 600 kHz, PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER