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PDF S-8540 Data sheet ( Hoja de datos )
| Número de pieza | S-8540 | |
| Descripción | (S-8540 / S-8541) 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER | |
| Fabricantes | Seiko Instruments | |
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STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE
SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series
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
• Output voltage
• Output voltage precision
• Feed back type for output voltage (FB)
• External components:
• Built-in PWM/PFM switchover control
circuit (S-8541 series)
• Current limit circuit
• Soft-start
• Shutdown function
• Small package
• Lead-free products
600 kHz (A, B types)
300 kHz (C, D types)
1.5 to 6.0 V, selectable in 0.1V steps (A, C types)
±2.0%
a transistor, a coil, a diode, and capacitors
Duty ratio: 29% (PFM control)
29 to 100% (PWM control)
Current is set by an external resistor RSENSE.
Time is set by a capacitor CSS and a resistor RSS.
8-Pin MSOP
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
Package Name
8-Pin MSOP
Package
FN008-A
Drawing Code
Tape
FN008-A
Reel
FN008-A
Seiko Instruments Inc.
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www.DataShSeeTt4EUP.-cDomOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00
S-8540/8541 Series
Pin Configuration
8-Pin MSOP
TOP view
1
2
3
4
8
7
6
5
Figure 3
Table 3
Pin No. Pin Name
Pin Description
1 VSS GND pin
2 EXT Connection pin for external transistor
3 VIN IC power supply pin
4
CVREF
Bypass capacitor connection pin for
reference voltage source
Shutdown pin
5
Soft-start capacitor connection pin
ON/ OFF • Normal operation (step-down operation)
• All circuit halts (no step-down operation)
6
NC*1
FB
None connected (A, C types)
Feed back pin (B, D types)
7 VOUT Output voltage pin
8 SENSE Current limit detection pin
*1. The NC pin is electrically open.
The NC pin can be connected to VIN and VSS.
Seiko Instruments Inc.
5
5 Page 
www.DataShSeeTt4EUP.-cDomOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00
S-8540/8541 Series
2. Soft-start function
The S-8540/8541 series has a built-in soft-start circuit. This circuit enables the output voltage to rise
gradually over the specified soft-start time to suppress the overshooting of the output voltage and the
rush current from the power source when the power is switched on or the power-off pin is set to "H"
The soft-start function of this IC, however, can not suppress rush current to the load completely (Refer
to Figure 9) . The rush current is affected by the input voltage and the load. Please evaluate the rush
current under the actual test condition.
S-8540A33FN (VIN = VON / OFF = 0 → 5 V)
3.0 V
V OU T
(1 V/div)
0V
1A
Rush current
(0.5 A/div)
0A
time (1 ms/div)
Figure 9 Waveforms of output voltage and rush current at soft-start
The soft-start function of the IC is achieved by raising internal reference voltage gradually, which is
caused by the raising of shutdown pin voltage through RC components (RSS and CSS) connected to
shutdown pin.
A soft-start time (tSS) is changed by RSS, CSS and the input voltage V ON/OFF to RSS.
tSS is calculated from the following formula:
tSS [ms]=R [kΩ] × C [μF] × In (V ON/OFF [V] / (V ON/OFF [V] − 1.8))
e.g. When RSS = 220 kΩ, CSS = 0.047 μF, V ON/OFF = 2.7 V , then tSS = 11.4 ms.
Seiko Instruments Inc.
11
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| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet S-8540.PDF ] | |
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