S-8540 Datasheet, PDF (19/36 Pages) Seiko Instruments Inc – STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER

STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00
S-8540/8541 Series
„ Precautions
y Install the external capacitors, diode, coil, and other peripheral components as close to the IC as possible,
and make a one-point grounding.
When the input voltage is 9 to 10 V, V_OUT may vary largely according to the grounding method.
When it is difficult to make one-point grounding, use two grounds: one for V_IN, C_IN, and SD GND, and the
other for V_OUT, V_CVREF, and IC GND.
y Characteristics ripple voltage and spike noise occur in IC containing switching regulators. Moreover rush
current flows at the time of a power supply injection. Because these largely depend on the inductor, the
capacitor and impedance of power supply used, fully check them using an actually mounted model.
y If the input voltage is high and output current is low, pulses with a low duty ratio may appear, and then the
0% duty ratio continues for several clocks. In this case the operation changes to the pseudo pulse
frequency modulation (PFM) mode, but the ripple voltage hardly increases.
y If the input power supply voltage is lower than 1.0 V, the IC operation is unstable and the external switch
may be turned on.
If input power supply voltage is 10.0 V or higher, the circuit operation is unstable and the IC may be
damaged.
The input voltage must be in the standard range (2.5 to 10.0 V).
y The current limit circuit of the IC limits current by detecting a voltage difference of external resistor R_SENSE.
In choosing the components, make sure that overcurrent will not surpass the allowable dissipation of the
switching transistor and the inductor.
y Make sure that dissipation of the switching transistor will not surpass the allowable power dissipation of the
package (especially at high temperature).
y Do not apply an electrostatic discharge to this IC that exceeds the performance ratings of the built-in
electrostatic protection circuit.
y Seiko Instruments Inc. shall bear no responsibility for any patent infringement by a product that includes an
IC manufactured by Seiko Instruments Inc. in relation to the method of using the IC in that product, the
product specifications, or the destination country.
Seiko Instruments Inc.
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