Rev.3.2_00
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE
SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series
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 RSENSE.
• Soft-start Time is set by a capacitor CSS and a resistor RSS.
• Shutdown function
• Small package 8-Pin MSOP
• Lead-free products
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 Drawing Code
Package Tape Reel
8-Pin MSOP FN008-A FN008-A FN008-A
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
2 Seiko Instruments Inc.
Block Diagrams
1. A, C types (fixed output voltage)
VSS
VOUT
SD PWM or
PWM / PFM
switching
Ph
ase
compensation
circuit
Triangular wave
oscillation circuit
VIN
L
EXT
Voltage/current
referen ce
Shut down soft start
circuit
VIN
Pch Power
MOS FET
Power for IC
RSENS
E
SENSE
PWM comparator
Error amplifier
CIN
COUT
VRE F=1.0 V
125 mV
CVREF
C
V
L
ON/OFF VON/OFF
CSS
RSS
Figure 1
2. B, D types (feed back)
VSS
VOUT
SD PWM or
PWM / PFM
switchin
g
Phase
compensation
circuit
Triangular wave
oscillation circuit
VIN
L
EXT
Voltage/current
reference
Shut down soft start
circuit
VIN
Pch Power
MO S FET
Power for IC
RSENSE
SENSE
PWM comparato
Error amplifier
FB
CFB
RB
CIN
COUT
VRE F=1.0 V
125 mV
CVREF
C
V
L
ON/OFF VON/OFF
CSS
RSS
VOUT
RA
Figure 2
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 3
Product Name Structure
• The control types, product types, and output voltage for the S-8540/8541 series can be selected at the
user’s request. Please refer to the “1. Product name” for the definition of the product name and “2.
Product Name List” for the full product names.
1. Product name
S-854X X XX FN - XXX T2 G
P roduct t ype
A: Fixed o utput vo ltage , fosc = 60 0 kH z
B: Feed back type, fosc = 600kHz
C: Fixed output voltage, fosc = 300 kHz
D: Feed back type, fosc = 300 kHz
Output voltage*3
15 to 60
(e.g . W hen t he ou tput v ol tage is 1. 5 V, it is expressed as 15.)
C
ontrol system
0: PWM c ontr ol
1: PWM / P FM sw it ching cont rol
P a c kage c od e
FN: 8-Pin MSOP
P roduct c ode
*2
IC di r ect ion in t a
p
e s
p
ecifications
*1
*1. Refer to the taping specifications at the end of this book.
*2. Refer to the “2. Product name list”.
*3. 00: Feed back type
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
4 Seiko Instruments Inc.
2. Product name list
2.1 A, B types (oscillation frequency: 600 kHz)
Table 1
Output Voltage (V) S-8540XXXFN Series S-8541XXXFN Series
1.5 S-8540A15FN-IAAT2G −
1.6 − S-8541A16FN-IGBT2G
1.8 S-8540A18FN-IADT2G S-8541A18FN-IGDT2G
2.5 S-8540A25FN-IAKT2G S-8541A25FN-IGKT2G
3.3 S-8540A33FN-IAST2G S-8541A33FN-IGST2G
5.0 S-8540A50FN-IBBT2G −
Feed back (1.5 to 6.0) S-8540B00FN-IMAT2G S-8541B00FN-IMDT2G
Remark Please consult the SII marketing department for products with an output voltage
other than those specified above.
2.2 C,D types (oscillation frequency: 300 kHz)
Table 2
Output Voltage (V) S-8540XXXFN Series S-8541XXXFN Series
1.8 S-8540C18FN-ICDT2G S-8541C18FN-IIDT2G
2.5 S-8540C25FN-ICKT2G S-8541C25FN-IIKT2G
3.2 − S-8541C32FN-IIRT2G
3.3 S-8540C33FN-ICST2G S-8541C33FN-IIST2G
Feed back (1.5 to 6.0) S-8540D00FN-IMBT2G S-8541D00FN-IMET2G
Remark Please consult the SII marketing department for products with an output voltage
other than those specified above.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 5
Pin Configuration
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
5 ON/OFF
Shutdown pin
Soft-start capacitor connection pin
• Normal operation (step-down operation)
• All circuit halts (no step-down operation)
NC*1 None connected (A, C types)
6 FB Feed back pin (B, D types)
8-Pin MSOP
TOP view
1
2
3
4
5
6
7
8
Figure 3
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.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
6 Seiko Instruments Inc.
Absolute Maximum Ratings
Table 4 (Ta = 25 °C unless otherwise specified)
Item Symbol Absolute Maximum Ratings Unit
VIN pin voltage VIN V
SS − 0.3 to VSS + 12 V
CVREF pin voltage VCVREF V
SS − 0.3 to VIN + 0.3 V
ON/OFF pin voltage VON/OFF VSS − 0.3 to VSS + 12 V
FB pin voltage*1 V
FB V
SS − 0.3 to VSS + 12 V
VOUT pin voltage VOUT V
SS − 0.3 to VSS + 12 V
SENSE pin voltage VSENSE V
SS − 0.3 to VSS + 12 V
EXT pin voltage VEXT V
SS − 0.3 to VIN + 0.3 V
EXT pin current IEXT ± 100 mA
300 (When not mounted on board) mW
Power dissipation PD 500*2 mW
Operating ambient temperature Topr − 40 to + 85 °C
Storage temperature Tstg − 40 to + 125 °C
*1. Feed back type (B, D types)
*2. When mounted on board
[Mounted board]
(1) Board size : 114.3 mm × 76.2 mm × t1.6 mm
(2) Board name : JEDEC STANDARD51-7
Caution The absolute maximum ratings are rated values exceeding which the product could suffer
physical damage. These values must therefore not be exceeded under any conditions.
(1) When mounted on board (2) When not mounted on board
0 50 100
150
400
200
0
Power dissipation P
D
(mW)
Ambient temperature Ta (°C)
500
300
100
600
050 100
150
200
100
0
Power dissipation
P
D
(mW)
Ambient temperature Ta (°C)
250
150
50
300
350
Figure 4 Power Dissipation of Package
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 7
Electrical Characteristics
1. S-8540/8541 Series A, C types Table 5
(Ta = 25 °C, unless otherwise specified)
Parameter Symbol Conditions Min. Typ. Max. Units
Measure-
ment
Circuit
Output voltage
*1
V
OUT (E)
V
IN
= V
OUT (S)
×
1.5
I
OUT
= 120 mA V
OUT (S)
×
0.980 V
OUT (S)
V
OUT (S)
×
1.020 V 2
Input voltage V
IN
−
2.5
−
10.0 V 1
S-8540/8541Axx
−
180 300
Current consumption 1 I
SS1
V
IN
= V
OUT (S)
×
1.5
100 % duty ratio S-8540/8541Cxx
−
140 240
μ
A 1
Current consumption
during shutdown I
SSS
V
ON/OFF
= 0 V
V
OUT
= V
OUT (S)
×
0.95
−
−
1.0
μ
A 1
I
EXTH
V
IN
= 10 V, V
EXT
= V
IN
−
0.2 V
−
32
−
48
−
mA 1
EXT pin output current I
EXTL
V
IN
= 10 V, V
EXT
= 0.2 V 45 66
−
mA 1
Line regulation
Δ
V
OUT1
V
OUT (S)
×
1.1
≤
V
IN
≤
10 V, I
OUT
= 120 mA
−
30 60 mV 2
Load regulation
Δ
V
OUT2
V
IN
= V
OUT (S)
×
1.5, 10
μ
A
≤
I
OUT
≤
150 mA
−
30 60 mV 2
Output voltage temperature
coefficient
Δ
Δ
V
Ta V
OUT
OUT
•
V
IN
= V
OUT (S)
×
1.5, I
OUT
= 120 mA
−
40
≤
Ta
≤
+
85 °C
−
±
100
−
ppm/
°C 2
S-8540/8541Axx 510 600 690 2
Oscillation frequency f
OSC
Measure waveform at the EXT
pin. S-8540/8541Cxx 255 300 345
kHz
Maximum duty ratio MaxDuty Measure waveform at the EXT pin. 100
−
−
%
2
PWM/PFM-control switch
duty ratio
*2
PFMDuty V
IN
= V
OUT (S)
×
1.5, no load 19 29 39
%
2
Current limit detection
voltage V
SENSE
V
IN
= V
OUT (S)
×
1.5,
Measure waveform at the EXT pin. 100 125 150 mV 1
SENSE pin input current I
SENSE
V
IN
= V
OUT (S)
×
1.5, V
SENSE
= V
IN
−
0.1 V 6.7 11.2 16.8
μ
A 1
V
SH
V
IN
= V
OUT (S)
×
1.5, Judge V
OUT(S)
×
0.98. 2.3
−
−
V 2 Shutdown pin
input voltage V
SL
V
IN
= V
OUT (S)
×
1.5, Judge CVREF pin "L".
−
−
0.3 V 1
I
SH
V
IN
= V
OUT (S)
×
1.5, V
ON/OFF
= V
OUT
−
0.1
−
0.1
μ
A 1 Shutdown pin
input leakage current I
SL
V
IN
= V
OUT (S)
×
1.5, V
ON/OFF
= 0 V
−
0.1
−
0.1
μ
A 1
Soft-start time t
SS
Time until V
OUT (E)
reaches 90% or higher of the V
OUT(S)
7.0 12.0 17.0 ms 2
Efficiency EFFI
−
−
90
−
%
2
External components
Coil (L) :Sumida Corporation. CDRH6D28-100
Diode (SD) :
Matsushita Electric Inducstrial Co., Ltd.
MA2Q737 (Schottky diode)
Output capacitor (COUT) :Nichicon Corporation F93 (16 V, 47 μF, tantalum)
Input capacitor (CIN) :Nichicon Corporation F93 (16 V, 47 μF, tantalum)
Transistor (PSW) :Toshiba Corporation 2SA1213
Base resistor (Rb) :100 mΩ
Base capacitor (Cb) :2200 pF
CVL :1.0 μF
CSS :0.047 μF
RSS :220 kΩ
RSENSE :100 mΩ
Condition: Recommended parts are used unless otherwise specified.
VIN =VOUT (S) ×1.5 V, IOUT = 120 mA (When VOUT (S) ≤ 1.6 V, then VIN = 2.5 V)
*1. VOUT (S) : Specified output voltage value, VOUT (E) : Actual output voltage value
*2. Applied to the S-8541 series only
Caution 1. Line regulation and load regulation may change greatly due to GND wiring when VIN is high.
2. In the S-8540 series (PWM control), a state in which the duty ratio 0% continues for several
clocks may occur when the input voltage is high and the output current is low. In this case,
the operation changes to the pseudo PFM mode, but the ripple voltage hardly increases.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
8 Seiko Instruments Inc.
2. S-8540/8541 Series B, D types Table 6
(Ta = 25 °C,unless otherwise specified)
Parameter Symbol Conditions Min. Typ. Max. Units
Measure-
ment
Circuit
Output voltage
*1, *2
V
OUT (E)
V
IN
= 4.5 V
I
OUT
= 120 mA V
OUT (S)
×
0.980 V
OUT (S)
= 3.000 V
OUT (S)
×
1.020 V 4
Input voltage V
IN
−
2.5
−
10.0 V 3
S-8540/8541B00
−
180 300
Current consumption 1 I
SS1
V
IN
= 4.5 V
100
%
duty ratio S-8540/8541D00
−
140 240
μ
A 3
Current consumption
during shutdown I
SSS
V
ON/OFF
= 0 V
V
OUT
= V
OUT (S)
×
0.95
−
−
1.0
μ
A 3
I
EXTH
V
IN
= 10 V, V
EXT
= V
IN
−
0.2 V
−
32
−
48
−
mA 3
EXT pin output current I
EXTL
V
IN
= 10 V, V
EXT
= 0.2 V 45 66
−
mA 3
Line regulation
Δ
V
OUT1
3.3
≤
V
IN
≤
10 V, I
OUT
= 120 mA
−
30 60 mV 4
Load regulation
Δ
V
OUT2
10
μ
A
≤
I
OUT
≤
150 mA
−
30 60 mV 4
Output voltage
temperature coefficient
Δ
Δ
V
Ta V
OUT
OUT
•
V
IN
= V
OUT (S)
×
1.5, I
OUT
= 120 mA
−
40
≤
Ta
≤
+
85°C
−
±
100
−
ppm/
°C 4
Measure waveform at S-8540/8541B00 510 600 690
Oscillation frequency f
OSC
the EXT pin. S-8540/8541D00 255 300 345 kHz 4
Maximum duty ratio MaxDuty Measure waveform at the EXT pin. 100
−
−
%
4
PWM/PFM-control switch
duty ratio
*3
PFM Duty V
IN
= V
OUT (S)
×
1.5 V, no load 19 29 39
%
4
Current limit detection
voltage V
SENSE
V
IN
= 4.5 V, Measure waveform at the EXT pin. 100 125 150 mV 3
SENSE pin input current I
SENSE
V
IN
= 4.5 V, V
SENSE
= V
IN
−
0.1 V 6.7 11.2 16.8
μ
A 3
V
SH
V
IN
= 4.5 V, Judge V
OUT (S)
×
0.98. 2.3
−
−
V 4
Shutdown pin
input voltage V
SL
V
IN
= 4.5 V, Judge CVREF pin "L".
−
−
0.3 V 3
I
SH
V
IN
= 4.5 V, V
ON/OFF
= V
OUT
−
0.1
−
0.1
μ
A 3
Shutdown pin
input leakage current I
SL
V
IN
= 4.5 V, V
ON/OFF
= 0 V
−
0.1
−
0.1
μ
A 3
Soft-start time t
SS
Time until V
OUT (E)
reaches 90
%
or higher of the
V
OUT (S)
7.0 12.0 17.0 ms 4
Efficiency EFFI
−
−
90
−
%
4
External components:
Coil (L) :Sumida Corporation CDRH6D28-100
Diode (SD) :Matsushita Electric Inducstrial Co., Ltd. MA2Q737 (Schottky diode)
Output capacitor (C
OUT
) :Nichicon Corporation F93 (16 V, 47
μ
F, tantalum)
Input capacitor (C
IN
) :Nichicon Corporation F93 (16 V, 47
μ
F, tantalum)
Transistor (P
SW
) :Toshiba Corporation 2SA1213
Base resistor (R
b
) :100 m
Ω
Base capacitor (C
b
) :2200 pF
C
VL
:1.0
μ
F
C
SS
:0.047
μ
F
R
SS
:220 k
Ω
R
SENSE
:100 m
Ω
R
A
:200 k
Ω
R
B
:100 k
Ω
C
FB
:50 pF
Condition: Connect recommended parts unless otherwise specified. V
IN
=4.5 V, I
OUT
=120 mA
*1.
V
OUT (S)
: Specified output voltage value, V
OUT (E)
: Actual output voltage value
*2.
The typical value (specified output voltage value) is V
OUT (S)
= 1
+
R
A
/R
B
= 3.0 V. See “Output Voltage adjustment”.
*3.
S-8541 series only
Caution 1. Line regulation and load regulation may change greatly due to GND wiring when VIN is high.
2. In the S-8540 series (PWM control), a state in which the duty ratio 0% continues for several
clocks may occur when the input voltage is high and the output current is low. In this case,
the operation changes to the pseudo PFM mode, but the ripple voltage hardly increases.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 9
Measurement Circuits
1.
VSS
ON/OFF
EXT
SENSE
VOUT VIN
CVREF
A
A
A
A
A
A
CV
L
CIN
Figure 5
2.
L
SD
PSW
Cb
Rb
VIN CIN
CVREF
RSENSE
CSS
COUT
RSS
VON/OFF
+
+
VSS
ON/OFF
EXT
SENSE
VOUT VIN
CVL
Figure 6
3.
A
A
A
A
A
A
CVREF
CIN
VSS
ON/OFF
EXT
FB
SENSE
VOUT VIN CVL
RFB1
RFB2
CFB
Figure 7
4.
LSD
PSW
Cb
Rb
VIN CIN
CVREF
RFB2 RSENSE
CFB RFB1
C
SS
COUT
RSS
VON/OFF
+
+ VSS
ON/OFF
EXT
FB
SENSE
VOUT VIN
C
VL
Figure 8
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
10 Seiko Instruments Inc.
Operation
1. Switching control method
1. 1 PWM control (S-8540 Series)
The S-8540 series consists of pulse width modulation (PWM) DC/DC converters. In conventional
pulse frequency modulation (PFM) DC/DC converters, pulses are skipped when they operate at low
output load current, causing the variation in the ripple frequency and the increase in the ripple voltage of
the output voltage both of which constitute inherent drawbacks to those converters.
In the S-8540 series the pulse width varies in the range from 0 to 100% according to the load current,
yet ripple voltage produced by the switching can easily be removed by a filter since the switching
frequency is always constant. These converters thus provide a low-ripple voltage over wide range of
input voltage and load current. And it will be skippped to be low current consumption when the pulse
width is 0% or it is no load, input current voltage is high.
1. 2 PWM/PFM switchover control (S-8541 Series)
The S-8541 series is a DC-DC converter that automatically switches between a pulse width modulation
method (PWM) and a pulse frequency modulation method (PFM), depending on the load current, and
features low current consumption.
The S-8541 series operates under PWM control with the pulse width duty changing from 29 to 100%
when the output load current is high. On the other hand, when the output current is low, the S-8541
series operates under PFM control with the pulse width duty fixed at 29%, and pulses are skipped
according to the load current. The oscillation circuit thus oscillates intermittently so that the resultant
lower self current consumption prevents a reduction in the efficiency when the load current is low. The
switching point from PWM control to PFM control depends on the external devices (coil, diode, etc.),
input voltage, and output voltage. This series is an especially efficient DC-DC converter at an output
current of around 100 μA.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 11
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.
t ime (1 ms/div)
VOU T
(1 V/div)
Rush current
(0.5 A/div)
0 V
3.0 V
0 A
1 A
S-8540A33FN (VIN = VON / OFF = 0 → 5 V)
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 VON/OFF to RSS.
tSS is calculated from the following formula:
tSS [ms]=R [kΩ] × C [μF] × In (VON/OFF [V] / (VON/OFF [V] − 1.8))
e.g. When RSS = 220 kΩ, CSS = 0.047 μF, VON/OFF = 2.7 V , then tSS = 11.4 ms.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
12 Seiko Instruments Inc.
3. ON/OFF pin (shutdown pin)
This pin deactivates or activates the step-down operation.
When the OFF/ON pin is set to "L", the VIN 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.
The OFF/ON pin is configured as shown in Figure 10. Since pull-up or pull-down is not performed
internally, please avoid operating the pin in a floating state. Also, try to refrain from applying a voltage of
0.3 to 1.8 V to the pin, lest the current consumption increase. When this OFF/ON pin is not used,
leave it coupled to the VIN pin.
Table 7
OFF/ON Pin CR Oscillation Circuit Output Voltage
“H” Activated Set value
“L” Deactivated OPEN
ON/OFF
VIN
VSS
Figure 10
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 13
4. Current limit circuit
The S-8540/8541 series contains a current limit circuit.
The current limit circuit is designed to prevent thermal destruction of external transistors due to overload
or magnetic saturation of the coil.
The current limit circuit can be enabled by inserting a SENSE resistor (RSENSE) between the external coil
and the output pin VOUT, and connecting the node for the SENSE resistor and the coil to the SENSE
pin.
A current limit comparator in the IC is used to check whether the voltage between the SENSE pin and
VOUT pin reaches the current limit detection voltage (VSENSE = 125 mV (typ.) ). The current flowing
through the external transistor is limited by turning it off during the left time of the oscillation period after
detection. The transistor is turned on again at the next clock and current limit detection resumes. If
the overcurrent state still persists, the current limit circuit operates again, and the process is repeated.
If the overcurrent state is eliminated, the normal operation resumes. Slight overshoot occurs in the
output voltage when the overcurrent state is eliminated.
Current limit setting value (ILimit) is calculated by the following formula:
ILimit = Rsense mV) 125 ( Vsense =
If the change with time of the current flowing through the sense resistor is higher than the response
speed of the current limit comparator in the IC, the actual current limit value becomes higher than the
ILimit (current limit setting value) calculated by the above formula. When the voltage difference between
VIN pin and VOUT pin is large, the actual current limit value increases since the change with time of the
current flowing through the sense resistor becomes large.
4. 1 VIN vs. Ipeak in the overcurrent state
VIN vs. Ipeak
0.0
0.5
1.0
1.5
2.0
2.5
3.0
2.5 4.0 5.5 7.0 8.5 10.0
VIN (V)
Ipeak (A)
(IC: S- 8 540A 33FN, coil: CDRH6D28-100, RSENSE: 100 mΩ)
1.25 A
Figure 11 lpeak change by input voltage
When the output voltage is approximate 1.0 V or less, the load short-circuit protection does not work,
since the current limit circuit does not operate.
When the current limit circuit is not used, remove the SENSE resistor and connect the SENSE pin to the
VSS or VOUT pin.
5. 100% duty cycle
The S-8540/8541 series operates up to the maximum duty cycle of 100%. The switching transistor is
kept on continuously to supply current to the load, when the input voltage falls below the preset output
voltage value. The output voltage in this case is equal to the subtraction of lowering causes by DC
resistance of the coil and on resistance of the switching FET from the input voltage.
Even when the duty cycle is 100%, the current limit circuit works when overcurrent flows.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
14 Seiko Instruments Inc.
Selection of Series Products and Associated External Components
1. Selecting a product
The S-8540/8541 series is classified into eight types according to the way of control (PWM and
PWM/PFM switching), the oscillation frequencies, and output voltage settings (fixed and feed back).
Please select the type that suits your needs best by taking the advantage described below into account.
1. 1 Control method:
Two different control methods are available: PWM control (S-8540 series) and PWM/PFM switching
control (S-8541 series).
1. 2 Oscillation frequencies:
The oscillation frequencies are selectable in 600 kHz (A and B types) or 300 kHz (C and D types).
Because of their high oscillation frequency, the products in the A and B types allow the use of small
size inductors since the peak current decreases when the same load current flows. In addition, they
can also be used with small output capacitors. These outstanding features make the A and B types
ideal for downsized devices.
On the other hand, the C and D types, having lower oscillation frequency, are characterized by small
self-consumption current and excellent efficiency under light load.
1. 3 Output voltage setting:
Two different types are available: fixed output (A and C types) and feed back type (B and D types).
Table 8 provides a rough guide for selecting a product depending on the requirements of the
application. Choose the product that has the best score ({).
Table 8
S-8540 S-8541
A B C D A B C D
The set output voltage is fixed (1.5 to 6.0 V)
Set an output voltage freely (1.5 to 6.0 V)
The efficiency at light load (less than 10 mA) is
important.
{ { { {
The efficiency at 100 mA or more is important. { { { {
Low-ripple voltage is important. { { { {
Use of small external parts is Important. ~ ~ ~ ~
Remark : Indispensable condition
{ : Superiority of requirement
~ : Particularly superiority of requirement
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 15
2. Inductor
The inductance value (L) greatly affects the maximum output current (IOUT) and the efficiency (η).
The peak current (IPK) increases by decreasing L and the stability of the circuit improves and IOUT
increases. If L is made even smaller, the efficiency falls causing a decline in the current drive capacity
for the switching transistor, and IOUT decreases.
The loss of IPK by the switching transistor decreases by increasing L and the efficiency becomes
maximum at a certain L value. Increasing L further decreases the efficiency due to the loss of coil DC
resistance. IOUT also decreases.
When the inductance is large in an S-8540/8541 series product, the output voltage may grow unstable
in some cases, depending on the conditions of the input voltage, output voltage, and the load current.
Perform sufficient evaluation under the actual condition and decide an optimum inductance.
The recommended inductances are 10 μH for A, B types and 22 μH for C, D types.
When choosing an inductor, attention to its allowable current should be paid since the current over the
allowable value will cause magnetic saturation in the inductor, leading to a marked decline in efficiency.
An inductor should therefore be selected so as not IPK to surpass its allowable current. The peak current
(IPK) is represented by the following equation in non-continuous operation mode:
INOSC
OUTINOUT
OUTPK VLf2 )V(VV
II ×××
−×
+=
Where fOSC is the oscillation frequency.
3. Diode
The diode to be externally coupled to the IC should be a type that meets the following conditions:
• The forward voltage is low (Schottky barrier diode recommended).
• The switching speed is high (50 ns max.).
• The reverse direction voltage is higher than VIN.
• The current rating is larger than IPK.
4. Capacitors
4. 1 Capacitors (CIN, COUT)
The capacitor inserted in the input side (CIN) serves to reduce the power impedance and to average
the input current for better efficiency. The CIN value should be selected according to the impedance of
the power supply. It should be 47 to 100 μF, although the actual value depends on the impedance of
the power source used and load current value.
For the output side capacitor (COUT), select a large capacitance with low ESR (Equivalent Series
Resistance) to smoothen the ripple voltage. When the input voltage is extremely high or the load
current is extremely large, the output voltage may become unstable. In this case the unstable area
will become narrow by selecting a large capacitance for an output side capacitor. A tantalum
electrolytic capacitor is recommended since the unstable area widens when a capacitor with a large
ESR, such as an aluminum electrolytic capacitor, or a capacitor with a small ESR, such as a ceramic
capacitor, is chosen. The range of the capacitance should generally be 47 to 100 μF.
4. 2 Internal power source stabilization capacitor (CVL)
The main circuits of the IC work on an internal power source connected to the CVREF pin. The CVL
is a bypass capacitor for stabilizing the internal Power source. CVL should be a 1 μF ceramic
capacitor and wired in a short distance and at a low impedance.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
16 Seiko Instruments Inc.
5. External transistor
The S-8540/8541 series can work with an enhancement (Pch) MOS FET or a bipolar (PNP) transistor as
an external transistor.
5. 1 Enhancement (Pch) MOS FET
The EXT pin can directly drive the Pch MOS FET with a gate capacity of approximate 1200 pF.
When a Pch MOS FET is chosen, efficiency will be 2 to 3 % higher than that achieved by a PNP
bipolar transistor since the MOS FET switching speed is faster than that of the bipolar transistor and
power loss due to the base current is avoided.
The important parameters in selecting a Pch MOS FET are the threshold voltage, breakdown voltage
between gate and source, breakdown voltage between drain and source, total gate capacity, on-
resistance, and the current ratings.
The EXT pin swings from voltage VIN to VSS. When the input voltage is low, a MOS FET with a low
threshold voltage has to be used so that the MOS FET will turn on as required. When, conversely, the
input voltage is high, select a MOS FET whose gate-source breakdown voltage is higher than the
input voltage by at least several volts.
Immediately after the power is turned on, or the power is turned off (that is, when the step-down
operation is terminated), the input voltage is applied across the drain and the source of the MOS FET.
The transistor therefore needs to have drain-source breakdown voltage that is also several volts
higher than the input voltage.
The total gate capacity and the on-resistance affect the efficiency.
The power loss for charging and discharging the gate capacity by switching operation will affect the
efficiency at low load current region more when the total gate capacity becomes larger and the input
voltage becomes higher. If the efficiency at low load is a matter of concern, select a MOS FET with a
small total gate capacity.
In regions where the load current is high, the efficiency is affected by power loss caused by the on-
resistance of the MOS FET. If the efficiency under heavy load is particularly important in the
application, choose a MOS FET having on-resistance as low as possible.
As for the current rating, select a MOS FET whose maximum continuous drain current rating is higher
than IPK.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 17
5. 2 Bipolar (PNP) transistor
Figure 12 shows a circuit diagram using Toshiba Corporation 2SA1213-Y for the bipolar transistor
(PNP). Using a bipolar transistor, the driving capacity for increasing the output current is determined
by the hFE value and the Rb value.
VIN EXT
2SA1213-Y
VIN
R
b
Cb
Figure 12
The Rb value is given by the following equation:
EXTL
IN
I0.4
I0.7V
Rb
b−
−
=
Calculate the necessary base current Ib using the hFE value of the bipolar transistor from the relation,
Ib = IPK/hFE, and select a smaller value for Rb which is calculated from the above equation.
A small Rb value will certainly contribute to increase the output current, but it will also decrease the
efficiency. Determine the optimum value through experiment since the base current flows as pulses
and voltage drop may takes place due to the wiring resistance and so on.
In addition, if speed-up capacitor Cb is inserted in parallel with resistance Rb, as shown in Figure 12,
the switching loss will be reduced, leading to a higher efficiency.
by using the following equation :
0.7fR2 1
COSC
b
b×××
≤
π
Select a Cb value after performing sufficient evaluation since the optimum Cb value differs depending
upon the characteristics of the bipolar transistor.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
18 Seiko Instruments Inc.
Standard Circuits
1. Fixed output voltage (Pch MOS FET)
+
−
−
+
−
+
L
SD
RSENSE
Tr
V
IN
C
IN
SENS
E
VREF
=
1.0 V
PWM, PWM/PFM
swi tching control
circuit
Shutdown soft sta rt
circuit
125mV
Error ampl ifier
PWM comparator
Triangular wave
oscillation c ircuit
P hase
compe nsation
circuit
P o w er fo r IC
V
IN
EXT
COUT
V
S
S
V
OUT
CV REF
VON/OFF
ON/OFF
One po i nt gr oun d
Voltage/ cu rrent
reference
Figure 13
2. Feed back type (Pch MOS FET)
L
SD
R
SENSE
Tr
V
IN
CIN
SENSE
+
−
VREF=1.0 V
125m V
V
IN
EXT
+
−
+
−
COUT
V
S
S
V
OUT
CFB
RB
RA
FB
PW M, PW M/PFM
switching control
circuit
Shutdown soft star t
circuit
Error amplifier
PWM c o m p arator
Tri a ng ular wav e
oscillation circuit
Phase
comp ensation
circuit
Po we r fo r IC
V
oltage/current
r
eferenc e
CVREF
V
ON/OFF
ON/OFF
One poi n t gr ou n d
Figure 14
Caution The above connection diagram and constant will not guarantees successful operation.
Perform through evaluation using the actual application to set the constant.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 19
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, VOUT may vary largely according to the grounding method.
When it is difficult to make one-point grounding, use two grounds: one for VIN, CIN, and SD GND, and the
other for VOUT, VCVREF, 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 RSENSE.
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.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
20 Seiko Instruments Inc.
Application Circuits
1. External adjustment of output voltage
The output voltage can be adjusted or changed in the output voltage setting range (1.5 to 6.0 V) by
adding external resistors (RA, RB) and a capacitor (CFB) in the S-8540/8541B00AFN and S-
8540/8541D00AFN, as shown in Figure 15. Temperature gradient can be given by inserting a
thermistor in series to RA and RB.
L
SD
R
SENSE
Tr
V
IN
C
IN
SENSE
+
−
VREF=1.0 V
125m V
V
IN
EXT
+
−
+
−
COUT
V
S
S
V
OUT
CFB
RB
RA
FB
PW M, PW M/PFM
switching control
circuit
Shutdown soft start
circuit
Error amplifier
PWM c o m p arator
Tri a ng ular wav e
oscillation circuit
Phase
comp ensation
circuit
Po we r fo r IC
V
oltage/current
r
eferenc e
CVREF
V
ON/OFF
ON/OFF
One poi n t gr ou n d
Figure 15
Caution The above connection diagram and constant will not guarantees successful operation.
Perform through evaluation using the actual application to set the constant.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 21
RA, RB must be RA + RB ≤ 2 MΩ and the ratio of RA to RB should be set so that the FB pin is 1.0 V. Add a
capacitor (CFB) in parallel to RA to prevent unstable operation like output oscillation.
Set the CFB so that f = 1/(2 × πCFB × RA) is 0.1 to 20 kHz (normally 10 kHz).
e.g. When VOUT = 3.0 V, RA = 200 kΩ, RB = 100 kΩ, then CFB = 100 pF.
The precision of output voltage (VOUT) determined by RA, RB is affected by the precision of the voltage at
the FB pin (1 V ± 2.0%), the precision of RA and RB, current input to the FB pin, and IC power supply
voltage VDD.
Suppose that the FB pin input current is 0 nA, and that the maximum absolute values of the external
resistors RA and RB are RA max. and RB max, and the minimum absolute values of the external resistors
RA and RB are RA min. and RB min., and that the output voltage shift due to the VDD voltage
dependency is ΔV, the minimum value VOUT min. and maximum value VOUT max. of the output voltage
VOUT variation is calculated by the following formula:
VOUTmin. = (1 +max.R min.R
B
A) × 0.98 − ΔV [V]
VOUTmax. = (1 +Rmax.
R min.
A
B) × 1.02 + ΔV [V]
The precision of the output voltage VOUT cannot be made lower than the precision of the IC output voltage
without adjustment of external resistors RA and RB. The lower the RA/RB, the less it is affected by the
absolute value precision of the external resistors RA and RB. The lower the RA and RB, the less it is
affected by the FB pin input current.
To suppress the influence of FB pin input current on the variation of output voltage VOUT, the external
resistor RB value must be made sufficiently lower than the input impedance of the FB pin, 1 V/50 nA =
20 MΩ max.
Waste current flows through external resistors RA and RB. When it is not a negligible value with respect
to load current in actual use, the efficiency decreases. The RA and RB values of the external resistors
must therefore be made sufficiently high.
Evaluation of the influence of the noise is needed in the actual condition If the RA and RB values of
resistors are high (1 MΩ or higher) since they are susceptible to external noise.
The output voltage VOUT precision and the waste current are in a trade-off relation. They must be
considered according to application requests.
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
22 Seiko Instruments Inc.
Typical Characteristics
1. Examples of major parameters characteristics
(1) ISS1 − VIN S-8540/8541(300 kHz) (2) ISS1 − VIN S-8540/8541(600 kHz)
0
50
100
150
200
250
2.5 4.0 5.5 7.0 8.5 10.0
V
IN (V)
ISS1 (μA)
25°C 85°C
Ta=−40°C
0
50
100
150
200
250
2.5 4.0 5.5 7.0 8.5 10.0
V
IN (V)
ISS1
(
μ
A
)
25°C
85°C
Ta=−40°C
(3) fOSC − VIN S-8540/8541(300 kHz)
240
260
280
300
320
340
360
2.5 4.0 5.5 7.0 8.5 10.0
V
IN (V)
fOSC (kHz)
25°C
85°C
Ta=−40°C
(4) fOSC − VIN S-8540/8541(600 kHz)
480
520
560
600
640
680
720
2.5 4.0 5.5 7.0 8.5 10.0
VIN (V)
fOSC (kHz)
25°C
85°C
Ta=−40°C
(5) IEXTH − VIN S-8540/8541
0
20
40
60
80
100
2.5 4.0 5.5 7.0 8.5 10.0
V
IN (V)
IEXTH (mA)
25°C
85°C
Ta=−40°C
(6) IEXTL − VIN S-8540/8541
0
20
40
60
80
100
2.5 4.0 5.5 7.0 8.5 10.0
V
IN (V)
IEXTL (mA)
25°C 85°C
Ta
=
−
40°C
(7) VSH − VIN S-8540/8541 (8) VSL − VIN S-8540/8541
1.7
1.8
1.9
2.0
2.1
2.2
2.3
2.5 4.0 5.5 7.0 8.5 10.0
V
IN (V)
VSH (V)
25°C
85°C
Ta=−40°C
0.3
0.4
0.5
0.6
0.7
0.8
0.9
2.5 4.0 5.5 7.0 8.5 10.0
V
IN (V)
VSL (V)
25°C
85°C
Ta=−40°C
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 23
(9) tSS − VIN
8
9
10
11
12
13
14
15
16
2.5 4.0 5.5 7.0 8.5 10.0
V
IN (V)
tSS (ms)
25°C 85°C
Ta=−40°C
(10) VOUT − VIN 1.8 V PWM/PFM 600 kHz (11) VOUT − VIN 3.3 V PWM/PFM 600 kHz
1.75
1.77
1.79
1.81
1.83
1.85
2.5 4 5.5 7 8.5 10
VIN (V)
VOUT(V)
100 mA 400 mA
IOUT=0.1 mA
3.20
3.25
3.30
3.35
3.40
2.5 4.0 5.5 7.0 8.5 10.0
VIN (V)
VOUT(V)
IOUT=0.1 mA 100 mA
400 mA
(12) VOUT − VIN 3.3 V PWM 600 kHz (13) VOUT − VIN 3.3 V PWM/PFM 300 kHz
3.20
3.25
3.30
3.35
3.40
2.5 4.0 5.5 7.0 8.5 10.0
V
IN (V)
V OUT
(V)
I
OUT =0.1 mA 100 mA
400 mA
3.20
3.25
3.30
3.35
3.40
2.5 4.0 5.5 7.0 8.5 10.0
V
IN (V)
V OUT (V)
I
OUT
=
0.1 mA 100 mA
400 mA
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
24 Seiko Instruments Inc.
2. Transient Response Characteristics
2. 1 Power-on (IOUT: no Load)
(1) S-8540A33FN (VIN: 0 → 4.95 V) (2) S-8540A33FN (VIN: 0 → 10 V)
10 V
0 V
3 V
0 V
VIN
(
2.5 V/di v
)
VOUT
(
1 V/div
)
t
(
2 ms/div
)
10 V
0 V
3 V
0 V
VIN
(
2.5 V/div
)
VOUT
(
1 V/div
)
t
(
1 ms/div
)
(3) S-8540C33FN (VIN: 0 → 4.95 V) (4) S-8540C33FN (VIN: 0 → 10 V)
10 V
0 V
3 V
0 V
VIN
(
2.5 V/div
)
VOUT
(
1 V/div
)
t (2 ms/div)
10 V
0 V
3 V
0 V
VIN
(2.5 V/div)
VOUT
(
1 V/div
)
t
(
1 ms/di v
)
(5) S-8540A18FN (VIN: 0 → 2.7 V) (6) S-8540A18FN (VIN: 0 → 10 V)
10 V
0 V
2 V
0 V
VIN
(
2.5 V/div
)
VOUT
(0.5 V /div)
t (4 ms/div)
10 V
0 V
2 V
0 V
VIN
(
2.5 V/div
)
VOUT
(
0.5 V/div
)
t
(
1 ms/div
)
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 25
2. 2 Shutdown pin response (VON/OFF : 0 → 2.5 V IOUT: no Load)
(1) S-8540A33FN (VIN: 4.95V) (2) S-8540A33FN (VIN: 10V)
4 V
0 V
3 V
0 V
VON/OFF
(
1 V/div
)
VOUT
(
1 V/div
)
t
(
4 ms/div
)
4 V
0 V
3 V
0 V
VON/OFF
(
1 V/div
)
VOUT
(
1 V/div
)
t (4 ms/div)
(3) S-8540C33FN (VIN: 4.95 V) (4) S-8540C33FN (VIN: 10 V)
4 V
0 V
3 V
0 V
VON/OFF
(
1 V/div
)
VOUT
(
1 V/div
)
t (4 ms/div)
4 V
0 V
3 V
0 V
VON/OFF
(
1 V/div
)
VOUT
(
1 V/div
)
t
(
4 ms/di v
)
(5) S-8540A18FN (VIN: 4.95 V) (6) S-8540A18FN (VIN: 10 V)
4 V
0 V
1.5 V
0 V
VON /OFF
(
1 V/div
)
VOUT
(
0.5 V/div
)
t
(
4 ms/div
)
4 V
0 V
1.5 V
0 V
VON/OFF
(
1 V/div
)
VOUT
(
0.5 V/div
)
t
(
4 ms/div
)
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
26 Seiko Instruments Inc.
2. 3 Supply Voltage Variation (VIN: 3.6 →9.0→3.6 V)
(1) S-8540A33FN (IOUT: 10 mA) (2) S-8540A33FN (IOUT: 500 mA)
10 V
0 V
VIN
(
2.5 V/di v
)
VOUT
(
0.1 V/div
)
t
(
0.4 ms/div
)
10 V
0 V
VIN
(2.5 V/div)
VOUT
(
0.1 V/div
)
t (0.4 ms/div)
(3) S-8540C33FN (IOUT: 10 mA) (4) S-8540C33FN (IOUT: 500 mA)
10 V
0 V
VIN
(
2.5 V/div
)
VOUT
(0.1 V/div)
t
(
0.4 ms/div
)
10 V
0 V
VIN
(
2.5 V/div
)
VOUT
(0.1 V/div)
t
(
0.4 ms/div
)
(5) S-8540A18FN (IOUT: 10 mA) (6) S-8540A18FN (IOUT: 500 mA)
10 V
0 V
VIN
(2.5 V/div)
VOUT
(
0.1 V/div
)
t
(
0.4 ms/div
)
10 V
0 V
VIN
(2.5 V /div)
VOUT
(
0.1 V/div
)
t
(
0.4 ms/div
)
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 27
2. 4 Load Variation (VIN: 2.7 V or 5.0 V or 7.5 V, IOUT: 0.1→500 mA, 500→0.1 mA)
(1) S-8540A33FN (VIN: 4.95 V) (2) S-8540A33FN (VIN: 4.95 V)
0.1 m
A
IOUT
VOUT
(
0.1 V/div
)
t
(
0.2 ms/div
)
500 mA
0.1 mA
IOUT
VOUT
(0.1 V /div)
t (4 m s/div)
500 m
A
(3) S-8540C33FN(VIN: 4.95 V) (4) S-8540C33FN(VIN: 4.95 V)
0.1 m
A
IOUT
VOUT
(
0.1 V/div
)
t
(
0.2 ms/div
)
500 m
A
0.1 m
A
IOUT
VOUT
(
0.1 V/div
)
t
(
8 ms /div
)
500 m
A
(5) S-8540A18FN (VIN: 2.7 V) (6) S-8540A18FN (VIN: 2.7 V)
0.1 m
A
IOUT
VOUT
(
0.1 V/div
)
t
(
0.2 ms/div
)
500 mA
0.1 m
A
IOUT
VOUT
(
0.1 V/di v
)
t
(
4 ms/div
)
500 m
A
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
28 Seiko Instruments Inc.
Reference Data
This reference data is intended to help you select peripheral components to be externally connected to the
IC. Therefore, this information provides recommendations on external components selected with a view to
accommodating a wide variety of IC applications. Characteristic data is duly indicated in the table below.
Table 9. External components list for efficiency
(Small and thin application using 1.3 mm or less tall components, maximum load current : IOUT = 0.9 A)
No. Product Name Output
Voltage Modulation fOSC Inductor Transistor Diode Output Capacitor
1.1 S-8540A33FN PWM
1.2 S-8541A33FN 3.3 V PWM/PFM
1.3 S-8540A25FN PWM
1.4 S-8541A25FN 2.5 V PWM/PFM
1.5 S-8540A18FN PWM
1.6 S-8541A18FN 1.8 V PWM/PFM
600kHz LDR655312T-4R7 CPH6301 RB491D F920J476MB × 2
Table 10 External components list for efficiency
(High efficiency application using 3.0mm or less tall components, maximum load current : IOUT = 1.0 A)
No. Product Name
Output
Voltage Modulation fOSC Inductor Transistor Diode Output Capacitor
1.7 S-8540C33FN PWM
1.8 S-8541C33FN 3.3 V PWM/PFM
1.9 S-8540C25FN PWM
1.10
S-8541C25FN 2.5 V PWM/PFM
1.11
S-8540C18FN PWM
1.12
S-8541C18FN 1.8 V PWM/PFM
300kHz CDRH6D28-220 CPH6301 RB491D
F931A476MC × 1
Table 11 External components list for ripple voltage
No. Product
Name Output
Voltage Modulation fOSC Inductor Transistor Diode Output
Capacitor
2.1
S-8540A33FN PWM
2.2
S-8541A33FN 3.3 V PWM/PFM
2.3
S-8540A18FN PWM
2.4
S-8541A18FN 1.8 V PWM/PFM
600kHz LDR655312T-4R7 CPH6301 RB491D F920J476MB × 2
2.5
S-8540C33FN PWM
2.6
S-8541C33FN 3.3 V PWM/PFM
2.7
S-8540C18FN PWM
2.8
S-8541C18FN 1.8 V PWM/PFM
300kHz CDRH6D28-220 CPH6301 RB491D
F931A476MC × 1
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 29
Table 12 External parts function
Component Product Name Manufacturer L-Value DC
Resistance Maximum
Current Size (L × W × H)
[mm]
LDR655312T-4R7 TDK
Corporation 4.7 μH 0.19 Ω 0.9 A 6.5 × 5. 3 × 1.25
Inductor CDRH6D28-220 Sumida
Corporation 22.0 μH 0.128 Ω 1.2 A 7.0 × 7.0 × 3.0
Diode RB491D Rohm
Corporation Forward current 1.0 A at VF = 0.45 V,
Vrm = 25V 3.0 × 3.1 × 1.3
Output
Capacity F920J476MB Nichicon
Corporation 47 μF, 6.3 V 3.6 × 3.0 × 1.2
(tantalum
electrolytic) F931A476MC Nichicon
Corporation 47 μF, 10.0 V 6.2 × 3.4 × 2.7
Transistor
(MOS FET) CPH6301 Sanyo Electric
Co., Ltd. Vdss =20 V max., Vgss =10 V max.,
ID =3.0 A max., Ciss =360 pF, Ron =110 mΩ 2.9 × 2.8 × 0.9
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
30 Seiko Instruments Inc.
1. Efficiency Characteristics : Efficiency (η) − Output current (IOUT)
1. 1 S-8540A33FN 1. 2 S-8541A33FN
50
60
70
80
90
100
1 10 100 1000
IOUT (mA)
Efficienc
y
η
(
%
)
VIN=4.0 V
(3.3 V, 600 kHz, PWM control)
5.0 V 7.2 V
5
0
6
0
7
0
8
0
9
0
100
5.0 V 7.2 V
(3.3 V, 600 kHz, PWM/PFM c ontrol)
1 10 100 1000
IOUT (mA)
Efficienc
y
η
(
%
)
VIN
=
4.0 V
1. 3 S-8540A25FN 1. 4 S-8541A25FN
50
60
70
80
90
100
1 10 100 1000
Efficienc
y
η
(
%
)
(2.5 V, 600 kHz, PWM control)
3.6 V 5.0 V
IOUT (mA)
VIN=3.0 V
50
60
70
80
90
100
1 10 100 1000
Efficienc
y
η
(
%
)
3.6 V 5.0 V
(2.5 V, 600 kHz, PWM/PF Mcontrol)
IOUT (mA)
VIN
=
3.0 V
1. 5 S-8540A18FN 1. 6 S-8541A18FN
50
60
70
80
90
100
1 10 100 1000
Efficienc
y
η
(
%
)
(
1.8 V, 600 kHz, PWM c ontrol)
3.6 V 5.0 V
IOUT (mA)
VIN=2.5 V
50
60
70
80
90
100
1 10 100 1000
Efficienc
y
η
(
%
)
3.6 V 5.0 V
(1.8 V, 600 kHz, PWM/PFM control)
IOUT (mA)
VIN=2.5 V
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.3.2_00 S-8540/8541 Series
Seiko Instruments Inc. 31
1. 7 S-8540C33FN 1. 8 S-8541C33FN
50
60
70
80
90
100
1 10 100 1000
Efficienc
y
η
(
%
)
(3.3 V , 300 kHz, PWM control)
5.0 V 7.2 V
IOUT (mA)
VIN=4.0 V
50
60
70
80
90
100
1 10 100 1000
Efficiency η (%)
5.0 V 7.2 V
(3.3 V, 300 kHz, PWM/PFM control)
IOUT (mA)
VIN
=
4.0 V
1. 9 S-8540C25FN 1. 10 S-8541C25FN
50
60
70
80
90
100
1 10 100 1000
Efficienc
y
η
(
%
)
(2.5 V, 300 kHz, PWM control)
3.6 V 5.0 V
IOUT (mA)
VIN=3.0 V
50
60
70
80
90
100
1 10 100 1000
Efficiency η (%)
3.6 V 5.0 V
(2.5 V, 300 kHz, PWM/PFM control)
IOUT (mA)
VIN
=
3.0 V
1. 11 S-8540C18FN 1. 12 S-8541C18FN
50
60
70
80
90
100
1 10 100 1000
Efficienc
y
η
(
%
)
(1.8 V, 300 k Hz, PWM control)
3
.6 V
5.0 V
IOUT (mA)
VIN=2.5 V
50
60
70
80
90
100
1 10 100 1000
Efficienc
y
η
(
%
)
3
.6 V 5.0 V
(1.8 V,300 kHz, PWM/PFM control)
IOUT (mA)
VIN
=
2.5 V
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8540/8541 Series Rev.3.2_00
32 Seiko Instruments Inc.
2. Ripple Voltage (Vrip) − Output Current (IOUT) Characteristics
2. 1 S-8540A33FN 2. 2 S-8541A33FN
0
20
40
60
80
100
1 10 100 1000
Ri
pp
le
(
mV
)
(
3.3 V, 600 kHz, PWM control
)
5.0 V
7.2 V
IOUT (mA)
VIN=4.0 V
0
20
40
60
80
100
1 10 100 1000
Ripple (mV)
5.0 V
7
.2 V
(3.3 V, 600 kHz, PWM/PFM control)
IOUT (mA)
VIN
=
4.0 V
2. 3 S-8540A18FN 2. 4 S-8541A18FN
0
20
40
60
80
100
1 10 100 1000
Ripple (mV)
(1.8 V, 600 kHz, PWM control)
3.6 V 5.0 V
IOUT (mA)
VIN=2.5 V
0
20
40
60
80
100
1 10 100 1000
Ripple (mV)
3.6 V 5.0 V
(1 .8 V, 600 kHz, PWM/PFM control)
IOUT (mA)
VIN
=
2.5 V
2. 5 S-8540C33FN 2. 6 S-8541C33FN
0
20
40
60
80
100
1 10 100 1000
Ripple (mV)
(3.3 V, 600 kHz, PW M control)
3.6 V
5.0 V
IOUT (mA)
VIN
=
2.5 V
0
20
40
60
80
100
1 10 100 1000
Ripple (mV)
3.6 V5.0 V
(3.3 V, 600 kHz, PWM/PFM control)
IOUT (mA)
VIN=2.5 V
2. 7 S-8540C18FN 2. 8 S-8541C18FN
0
20
40
60
80
100
1 10 100 1000
Ri
pp
le
(
mV
)
(
1.8 V, 300 kHz, PWM control
)
3.6 V
5.0 V
IOUT (mA)
VIN=2.5 V
0
20
40
60
80
100
1 10 100 1000
Ripple (mV)
3.6 V 5.0 V
(1.8 V , 300 kHz, PWM/PFM control)
IOUT (mA)
VIN=2.5 V
No.
TITLE
SCALE
UNIT mm
Seiko Instruments Inc.
2.95±0.2
85
0.2±0.1
0.65±0.1
0.13±0.1
14
MSOP8-A-PKG Dimensions
No. FN008-A-P-SD-1.1
FN008-A-P-SD-1.1
No.
TITLE
SCALE
UNIT mm
Seiko Instruments Inc.
0.3±0.05
1.35±0.15
1.05±0.05
1.55±0.05
2.0±0.05
4.0±0.1
3.1±0.15
4.0±0.1
1
4
58
MSOP8-A-Carrier Tape
Feed direction
No. FN008-A-C-SD-1.1
FN008-A-C-SD-1.1
No.
TITLE
SCALE
UNIT mm
Seiko Instruments Inc.
16.5max.
13.0±0.3
QTY. 3,000
(60°)
(60°)
13±0.2
Enlarged drawing in the central part
MSOP8-A-Reel
No. FN008-A-R-SD-1.1
FN008-A-R-SD-1.1
•
The information described herein is subject to change without notice.
• Seiko Instruments Inc. is not responsible for any problems caused by circuits or diagrams described herein
whose related industrial properties, patents, or other rights belong to third parties. The application circuit
examples explain typical applications of the products, and do not guarantee the success of any specific
mass-production design.
• When the products described herein are regulated products subject to the Wassenaar Arrangement or other
agreements, they may not be exported without authorization from the appropriate governmental authority.
• Use of the information described herein for other purposes and/or reproduction or copying without the
express permission of Seiko Instruments Inc. is strictly prohibited.
• The products described herein cannot be used as part of any device or equipment affecting the human
body, such as exercise equipment, medical equipment, security systems, gas equipment, or any apparatus
installed in airplanes and other vehicles, without prior written permission of Seiko Instruments Inc.
• Although Seiko Instruments Inc. exerts the greatest possible effort to ensure high quality and reliability, the
failure or malfunction of semiconductor products may occur. The user of these products should therefore
give thorough consideration to safety design, including redundancy, fire-prevention measures, and
malfunction prevention, to prevent any accidents, fires, or community damage that may ensue.
