S-8540/8541 Series
www.sii-ic.com
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM
SWITCHABLE SWITCHING REGULATOR CONTROLLER
© Seiko Instruments Inc., 2000-2010 Rev.4.0_00
Seiko Instruments Inc. 1
The S-8540/8541 Series is a family of CMOS step-down switching regulator controllers with PWM control (S-
8540 Series) and PWM/PFM switchover control (S-8541 Series). These devices consist of a reference voltage
source, oscillation circuit, an error amplifier, phase compensation circuit, PWM control circuit, current limit
circuit. A high efficiency and large current switching regulator is realized with the help of small external
components due to the high oscillation frequency, 300 kHz and 600 kHz.
The S-8540 Series provides low-ripple voltage, high efficiency, and excellent transient characteristics which
come from the PMW control circuit capable of varying the duty ratio linearly from 0 to 100%, the optimized error
amplifier, and the phase compensation circuit.
The S-8541 Series operates under PWM control when the duty ratio is 29% or higher and operates under PFM
control when the duty ratio is less than 29% to ensure high efficiency over all load range.
These controllers serve as ideal main power supply units for portable devices due to the high oscillation
frequencies together with the small 8-Pin MSOP package.
Features
• Oscillation frequency
600 kHz (A, B types)
300 kHz (C, D types)
• Output voltage
1.5 to 6.0 V, selectable in 0.1V steps (A, C types)
• Output voltage precision ±2.0%
• Feed back type for output voltage (FB)
• External components:
a transistor, a coil, a diode, and capacitors
• Built-in PWM/PFM switchover control
circuit (S-8541 series)
Duty ratio: 29% (PFM control)
29 to 100% (PWM control)
• Current limit circuit
Current is set by an external resistor R
SENSE
.
• Soft-start
Time is set by a capacitor C
SS
and a resistor R
SS
.
• Shutdown function
• Lead-free, halogen-free
*1
*1. Refer to “ Product Name Structure” for details.
Applications
• Power supplies for PDAs, electric organizers, and portable devices.
• Power supplies for audio equipment such as portable CD players and headphone stereos.
• Main or sub Power supplies for notebook computers and peripheral equipment.
Package
• 8-Pin MSOP
