SI-8005Q
Description
The SI-8005Q is a step-down switching regulator IC, designed as
an output voltage regulator at the secondary stage of switch mode
power supplies. The current-mode control system permits small
ceramic capacitors to be used as output capacitors. Together
with the compact HSOP8 package, this allows reduction of
regulator circuitry area on the PCB by approximately 50% in
comparison with conventional topologies.
Designed to save power, losses in the SI-8005Q are reduced
by controlling the maximum on-resistance of a built-in output
MOSFET to as low as 165 m. Furthermore, die miniaturization
has been accomplished through a proprietary BCD process.
The SI-8005Q supplies an output current of 3.5 A and an output
voltage that is variable from 0.5 to 24 V, which is easily set to
a voltage compatible with the diverse reduced power supply
voltages required by signal processing ICs. Accepting a wide
input voltage range, from 4.75 to 28 V, the SI-8005Q can be
driven directly by a 24 V power supply.
Applications include power supplies for signal processing ICs
for memories and microcomputers used in plasma display panel
(PDP) TVs, liquid crystal display (LCD) TVs, computer hard
drives, and DVD recorders.
Features and Benefits
Current-mode control system employed
Excellent line regulation (60 mV maximum)
165 m maximum on-resistance of built-in MOSFET
Output current 3.5 A
Wide range of input voltages (4.75 to 28 V), supports 24
V direct drive
Output voltage 0.5 to 24 V, compatible with various IC
power supply voltages, through low VREF of 0.5 V.
High efficiency, 94% maximum at VIN = 8 V, VO = 5 V,
and IO = 0.5 A
Operating frequency 500 kHz, supports downsizing of
smoothing choke coil
Soft start and output on/off functions built-in
Built-in protection:
Drooping overcurrent protection
Overtemperature protection
Undervoltage lockout (UVLO)
Step-Down Switching Regulator with Current-Mode Control
Functional Block Diagram
Not to scale
Package: HSOP8 surface mount with
exposed thermal pad
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Step-Down Switching Regulator with Current-Mode Control
SI-8005Q
2
All performance characteristics given are typical values for circuit or
system baseline design only and are at the nominal operating voltage and
an ambient temperature, TA, of 25°C, unless oth er wise stated.
Recommended Operating Conditions*
Characteristic Symbol Remarks Min. Typ. Max. Units
DC Input Voltage Range VIN
VIN(min) is the greater of either 4.75 V or VO+1 V; except
if VO + 0.5 VIN VO +1 V, then VIN(min) is set such that
IO 2 A
See
remarks –28V
DC Output Current Range IO
Using the circuit defined in the Typical Application
diagram and within PD limits 0 – 3.5 A
Operating Junction
Temperature Range TJOP –30 – 125 °C
Operating Temperature
Range TOP Operation within PD limits –30 – 85 °C
*Recommended operating range indicates conditions which are required for maintaining normal circuit functions shown in the Electrical Characteristics
table.
Selection Guide
Part Number Packing
SI8005Q-TL 1000 pieces per reel
Absolute Maximum Ratings
Characteristic Symbol Remarks Rating Unit
DC Input Voltage VIN 30 V
DC Input Voltage VEN 6V
Allowable Power Dissipation PD
Limited by internal thermal shutdown, mounted on a 30 mm × 30 mm
glass epoxy PCB with 25 mm × 25 mm exposed copper area,
TJ(max) = 125°C
1.35 W
Junction Temperature TJInternal thermal shutdown activates at approximately 140°C –30 to 150 °C
Storage Temperature Tstg –40 to 150 °C
Thermal Resistance (Junction to Ambient) RJA
Mounted on a 30 mm × 30 mm glass epoxy PCB with 25 mm ×
25 mm exposed copper area 74 °C/W
Thermal Resistance (Junction to Case) RJC 40 °C/W
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0–25 0 25 50
Ambient Temperature, TA (°C)
Power Dissipation, PD (W)
75 100 125
Results calculated as:
PDVO × IO100
Hx
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛–1
–VF × IOVO
VIN
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛1–
where:
VO is the output voltage,
VIN is the Input voltage (0.4 V for these results),
IO is the Output current (0.3 A for these results),
ηx is the efficiency (%), which varies with VIN and IO (derived from the
Efficiency curves in the Characteristic Performance section), and
VF is the diode forward voltage for D1, determination of the value for D1
should be made based on testing with the actual application (Sanken
diode SJPB-D4 was used for these results).
Maximum Allowable Package Power Dissipation
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Step-Down Switching Regulator with Current-Mode Control
SI-8005Q
3
ELECTRICAL CHARACTERISTICS1, valid at TA=25°C, unless otherwise noted
Characteristics Symbol Conditions Min Typ Max Units
Reference Voltage VREF VIN = 12 V, IO = 1.0 A 0.485 0.500 0.515 V
Output Voltage Temperature
Coefficient VREF/TV
IN = 12 V, IO = 1.0 A, TA = –40°C to 85°C – ±0.05 – mV/°C
Efficiency2VIN = 12 V, VO = 5 V, IO = 1 A – 90 – %
Operating Frequency fOVIN = 16 V, VO = 5 V, IO = 1 A 450 500 550 kHz
Line Regulation VLINE VIN = 8 to 28 V, VO = 5 V, IO = 1 A – 10 60 mV
Load Regulation VLOAD VIN = 12 V, VO = 5 V, IO = 0.1 to 3.5 A – 10 60 mV
Overcurrent Protection Threshold ISVIN = 12 V, VO = 5 V 3.6 – 6.0 A
Quiescent Current 1 IIN VIN = 12 V, VO = 5 V, IO = 0 A, VEN = open – 18 – mA
Quiescent Current 2 IIN(off) VIN = 12 V, VO = 5 V, IO = 0 A,VEN = 0 V – – 20 A
SS Terminal Leakage Current3ISSL VSSL = 0 V, VIN = 16 V – 5 – A
EN Terminal High Level Voltage VCEH VIN = 12 V 2.8 – – V
EN Terminal Low Level Voltage VCEL VIN = 12 V – – 2.0 V
EN Terminal Leakage Current ICEH VEN = 0 V – 1 – A
Error Amplifier Voltage Gain AEA – 1000 – V/ V
Error Amplifier Transconductance GEA – 800 – A/V
Current Sense To COMP
Transimpedance 1/GCS – 0.35 – V/A
Maximum Duty Cycle (On) DCMAX –92– %
Minimum On-Time tMIN – 100 – ns
1Using circuit shown in Measurement Circuit diagram.
2Efficiency is calculated as: (%) = ([VO × IO] × [VIN × IIN]) × 100.
3SS terminal enables soft start when a an external capacitor is connected to it. Because a pull-up resistor is provided inside the IC, no external voltage
can be applied to this terminal.
SI-8005Q
II N BS SW
SS
GND COMP
FB
EN
C1
C3
Di
C4 L1
C2
R1
R2
IIIN
VIIN
VO
IO
VSS
VEN
VFB
IEN ISS
RL
1
23
4
5
6
7
8
R3
Component Rating
C1 22 F / 50 V
C2 47 F / 25 V
C3 220 pF / 10 V
C4 10 nF / 25 V
Di SPB-G56S
L1 10 H
R1 46 k
R2 5.1 k
R3 62 k
Measurement Circuit Diagram
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Step-Down Switching Regulator with Current-Mode Control
SI-8005Q
4
Performance Characteristics
at TA = 25°C
100
90
80
70
60
50
40
012345
η(%)
Efficiency versus
Output Current
V
O
= 1.2 V
4.75 V
6V
5 V
I
O
(A)
100
90
80
70
60
50
40
012345
η(%)
Efficiency versus
Output Current
V
O
= 3.3 V
I
O
(A)
8V
12 V
V
IN
V
IN
8V
16 V
12 V
24 V
28 V
100
90
80
70
60
50
40
012345
η(%)
Efficiency versus
Output Current
V
O
= 5 V
I
O
(A)
100
90
80
70
60
50
40
012345
η(%)
Efficiency versus
Output Current
V
O
= 12 V
I
O
(A)
V
IN
V
IN
16 V
20 V
28 V
8V
16 V
12 V
20 V
28 V
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Step-Down Switching Regulator with Current-Mode Control
SI-8005Q
5
Performance Characteristics
at TA = 25°C
6
5
4
3
2
1
0
0246810
V
O
(V)
V
O
(V)
Overcurrent
Protection
Load = CR
0 A
1 A
2 A
3 A
V
IN
(V)
6
5
4
3
2
1
0
01234 65
V
O
(V)
Overcurrent
Protection
I
O
(A)
IO
VIN
8V
15 V
12 V
20 V
24 V
28 V
5.05
5.04
5.03
5.02
5.01
5.00
4.99
4.98
4.97
4.96
4.95
012345
Load
Regulation
I
O
(A)
25
20
15
10
5
0
0 10203040
0 10203040
Quiescent
Current versus
Input Voltage
I
O
= 0 A
V
IN
(V)
V
IN
(V)
VIN
8V
15 V
12 V
20 V
28 V
I
O(Q)
(μA)
I
O(Q)
(mA)
10
9
8
7
6
5
4
3
2
1
0
Quiescent
Current versus
Input Voltage
V
EN
= 0 V
Overvoltage
Protection
V
IN
= 12 V
I
O
= 0 A
f
O
(kHz)
550
540
530
520
510
500
490
480
470
460
450
550
540
530
520
510
500
490
480
470
460
450
012345
Operating
Frequency versus
Output Current
I
O
(A)
0 10203040
f
O
(kHz)
Operating
Frequency versus
Input Voltage
V
IN
(V)
VIN
8V
15 V
12 V
20 V
28 V
24 V
6
5
4
3
2
1
0
120 130 140 160150
T
J
(°C)
V
O
(V)
OTP On
OTP Off
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Step-Down Switching Regulator with Current-Mode Control
SI-8005Q
6
Component Selection
SI-8005Q
IIN BSSW
SS GND
COMP FB
R3
R2
R1
C4
C1
C2
5 V
C5 C3
C6
OPEN
L1
EN
Di
V
IIN
V
O
12
3
4
5
6
7
8
GND GND
V
FB
I
ADJ
Component Rating Manufacturer
C1 (2 ea) 10 F / 50 V Murata, P/N GRM55DB31H106KA87
C2 (2 ea) 22 F / 16 V Murata, P/N GRM32ER71A226KE20
C3 220 pF Murata, P/N GRM18 series
C4, C5 10 nF Murata, P/N GRM18 series
Di Sanken, P/N SPB-G56S or SJPB-L4
L1 10 H
R1 46 k
R2 5.1 k
R3 62 k
All external components should be mounted as closely as possible to the
SI-8005Q. The ground of all components should be connected at one point.
The exposed copper area on the PCB that is connected to the heat sink
on the reverse side of package is ground. Enlarging the PCB copper area
enhances thermal dissipation from the package.
Recommended PCB Layout Recommended Solder Pad Layout
Typical Application Diagram
Diode Di A Schottky-barrier diode must be used for Di. If other
diode types, such as like fast recovery diodes, are used, the IC
may be destroyed because of reverse voltages applied by the
recovery voltage or turn-on voltage.
Choke Coil L1 If the winding resistance of the choke coil is too
high, IC efficiency may go down to the extent that the resistance
is beyond the rating. Because the overcurrent protection threshold
current is approximately 4 A, attention must be paid to the heat-
ing of the choke coil by magnetic saturation due to overload or
short-circulated load.
Capacitors C1, C2, and C5 Because large ripple currents for
SMPS flow across C1 and C2, capacitors with high frequency
and low impedance must be used. Especially when the impedance
of C2 is high, the switching waveform may not be normal at low
temperatures.
C5 is used to enable soft start. If the soft start function is not
used, leave the SS terminal open.
Resistors R1 and R2 R1 and R2 set the output voltage, VO.
Select the resistor values to set IADJ to 0.1 mA. R1 and R2 are
calculated by the following expression:
( ) ()()()
Ω
×
==Ω
×
−
=
−
=−− k
IV
R
V
IVV
RADJ
FB
O
ADJ
FB
O5
101.0
5.0
2
101.0
5.0
133 ≒，
For optimum performance, minimize the distance between com-
ponents.
Phase Compensation Components C3, C6, and R3 The
stability and response of the loop is controlled through the COMP
pin. The COMP pin is the output of the internal transconductance
4.30 1.35
0.54
1.27
2.80
3.00
Unit:mm
C2
R1
R2
L1
FB
GND
Vout
Vsw D1
Vin C4
C1
C6
C5
U1
COMP
C3
R3
EN SS
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Step-Down Switching Regulator with Current-Mode Control
SI-8005Q
7
amplifier. The combination of a series-connected capacitor and
resistor sets the combination of a pole and zero frequency point
that decide the characteristics of the control system. The DC gain
of the voltage feedback loop is calculated by the following equa-
tion:
Vout
V
AGcs
FB
EA
×××= RlAdc
,
(1)
where
VFB is the feedback voltage (0.5 V),
AEA is the error amplifier voltage gain,
GCS is the current sense transconductance, and
Rl is the load resistor value.
The system has two important poles. One is set by the phase
compensation capacitor (C3) and the output resistor of the error
amplifier. The other is set by the output capacitor and load resis-
tor. These poles are calculated by the following equations:
EA
EA
AC
G
fp ××
=32
1
π
,
(2)
RlC
fp ××
=22
1
2
π
,
(3)
where GEA is the error amplifier transconductance.
The system has one important zero point. This is set by the phase
compensation capacitor (C3) and phase compensation resistor
(R3). The zero point is shown by the following equation:
332
1
1RC
fz ××
=
π
.
(4)
If the value of the output capacitor is the large or if it has a high
ESR, the system may have another important zero point. This
zero point would be set by the ESR and capacitance of the output
capacitor. The zero point is shown by the following equation:
RESRC
fESR ××
=22
1
π
.
(5)
In this case a third pole, which is set by the phase compensation
capacitor (C6) and phase compensation resistor (R3), is used to
compensate the effect of the ESR zero point on the loop gain.
The pole is shown by the following equation:
362
1
3RC
fp ××
=
π
.
(6)
The goal of phase compensation design is to shape the con-
verter transfer function to get the required loop gain. The system
crossover frequency, where the feedback loop has unity gain, is
important. Lower crossover frequencies result in slower line and
load transient responses. On the other hand, higher crossover fre-
quencies cause system instability. A good standard is to adjust the
crossover frequency to approximately one-tenth of the switching
frequency.
The optimal selection of phase compensation components can be
determined using the following procedure:
1. Choose the phase compensation resistor (R3) to adjust the
required crossover frequency. R3 value is calculated by the fol-
lowing equation:
FB
V
Vout
GCSGEA fsC
VFB
Vout
GCSGEA fcC
R×
×
×××
<×
×
××
=1.02222
3ππ
,
(7)
where fc is the required crossover frequency. This is usually
adjusted to less than one-tenth of the switching frequency.
2. Choose the phase compensation capacitor (C3) to get the
required phase margin. For applications that have typical inductor
values, adjusting the compensation zero point to less than one-
quarter of crossover frequency provides sufficient phase margin.
The value of C3 is calculated by the following equation:
fcR
C××
>32
4
3
π
,
(8)
where R3 is the phase compensation resistor.
3. It is necessary to determine whether a second compensation
capacitor (C6) is required. It is required if the ESR zero point of
the output capacitor is less than half of the switching frequency,
expressed as follows:
222
1fs
RESRC<
××π
.
(9)
If this is the case, add the second compensation capacitor (C6)
and adjust ESR zero frequency (fp3). C6 value is calculated by
the following equation:
3
2
6R
RESRC
C×
=
.
(10)
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Step-Down Switching Regulator with Current-Mode Control
SI-8005Q
8
Package Outline Drawing
Leadframe plating Pb-free. Device composition
complies with the RoHS directive.
5.20
0.15
1.50
0.08 ±0.08
0.05 ±0.05
0.40
0.695 TYP
Tracking number
in dimple
4.40
6.20
2.90
2.70
1.27
0.40
21
8
Dimensions in millimeters
Branding codes (exact appearance at manufacturer discretion):
1st line, type: 8005Q
2nd line, lot: SK YMDD
Where: Y is the last digit of the year of manufacture
M is the month (1 to 9, O, N, D)
DD is the date
3rd line, control : NNNN
Branding area
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Step-Down Switching Regulator with Current-Mode Control
SI-8005Q
9
Packing Specification
Empty tape
Trailer IC occupied tape Leade
r
Cover Tape
Empty Tape
160mm 1,000pcs
(1,000 pockets)
More than 160mm
More than 400mm
4 2 8 Direction of reel
1.55
5.6
7
2
5.5
(
4.75
)
12
180
60
13 0.3
15.4 0.1
13 0.2
B
3
R22
Voi
d
10
Voi
d
Voi
d
Voi
d
60 60
13
3
R
22
5
5
2
30
3
60 60
10
10.5
Center extension
4
11.9
Voi
d
Voi
d
Voi
d
Voi
d
Units mm
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Step-Down Switching Regulator with Current-Mode Control
SI-8005Q
10
In general, the junction temperature level of surface mount pack-
age ICs is dependent upon the area and material of the PC board
and its copper area. Therefore, please design the PCB to allow
sufficient margin for heat dissipation.
Parallel Operation Parallel operation of multiple products to
increase the current is not allowed.
Thermal Shutdown The SI-8000Q series has a thermal protec-
tion circuit. This circuit keeps the IC from the damage by over-
load. But this circuit cannot guarantee the long-term reliability
against the continuous overload conditions.
ESD Susceptibility Take precautions against damage by static
electricity.
Cautions
The products described herein are manufactured in Ja pan by Sanken Electric Co., Ltd. for sale by Allegro MicroSystems, Inc.
Sanken and Allegro reserve the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be re quired to per mit im-
prove ments in the per for mance, reliability, or manufacturability of its prod ucts. Therefore, the user is cau tioned to verify that the in for ma tion in this
publication is current before placing any order.
When using the products described herein, the ap pli ca bil i ty and suit abil i ty of such products for the intended purpose shall be reviewed at the users
responsibility.
Although Sanken undertakes to enhance the quality and reliability of its prod ucts, the occurrence of failure and defect of semi con duc tor products
at a certain rate is in ev i ta ble.
Users of Sanken products are requested to take, at their own risk, preventative measures including safety design of the equipment or systems
against any possible injury, death, fires or damages to society due to device failure or malfunction.
Sanken products listed in this publication are designed and intended for use as components in general-purpose electronic equip ment or apparatus
(home ap pli anc es, office equipment, tele com mu ni ca tion equipment, measuring equipment, etc.). Their use in any application requiring radiation
hardness assurance (e.g., aero space equipment) is not supported.
When considering the use of Sanken products in ap pli ca tions where higher reliability is re quired (transportation equipment and its control systems
or equip ment, fire- or burglar-alarm systems, various safety devices, etc.), contact a company sales representative to discuss and obtain written
confirmation of your spec i fi ca tions.
The use of Sanken products without the written consent of Sanken in applications where ex treme ly high reliability is required (aerospace equip-
ment, nuclear power-control stations, life-support systems, etc.) is strictly prohibited.
The information in clud ed herein is believed to be accurate and reliable. Ap pli ca tion and operation examples described in this pub li ca tion are
given for reference only and Sanken and Allegro assume no re spon si bil i ty for any in fringe ment of in dus tri al property rights, intellectual property
rights, or any other rights of Sanken or Allegro or any third party that may result from its use.
Copyright © 2007 Allegro MicroSystems, Inc.
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Step-Down Switching Regulator with Current-Mode Control
SI-8005Q January, 2008
Sanken Electric Co., Ltd.
I02-010EA-080130
<Worldwide Contacts>
Asia Pacific
China
Sanken Electric Hong Kong Co., Ltd.
Suite 1026 Ocean Centre, Canton Road, Tsimshatsui, Kowloon, Hong Kong
Tel: 852-2735-5262
Fax: 852-2735-5494
Sanken Elect ric (Shanghai) Co., Ltd.
Room3202, Maxdo Centre, Xingyi Road 8, Changning district, Shanghai, China
Tel: 86-21-5208-1177
Fax: 86-21-5208-1757
Taiwan Sanken Electric Co., Ltd.
Room 1801, 18th Floor, 88 Jung Shiau East Road, Sec. 2, Taipei 100, Taiwan R.O.C.
Tel: 886-2-2356-8161
Fax: 886-2-2356-8261
India
Saket Devices Pvt. Ltd.
Office No.13, First Floor, Bandal - Dhankude Plaza, Near PMT Depot, Paud Road, Kothrud, Pune - 411 038, India
Tel: 91-20-5621-2340
91-20-2528-5449
Fax: 91-20-2528-5459
Japan
Sanken Electric Co., Ltd. Overseas Sales Headquaters
Metropolitan Plaza Bldg. 1-11-1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-0021, Japan
Tel: 81-3-3986-6164
Fax: 81-3-39 8 6- 8 637
Korea
Sanken Electric Korea Co., Ltd.
Mirae Asset Life Bldg. 6F, 168 Kongduk-dong, Mapo-ku, Seoul, 121-705, Korea
Tel: 82-2-714-3700
Fax: 82-2-32 7 2- 2 145
Singapore
Sanken Electric Singapore Pte. Ltd.
150 Beach Road, #14-03 The Gateway West, Singapore 189720
Tel: 65-6291-4755
Fax: 65-6297-1744
Step-Down Switching Regulator with Current-Mode Control
SI-8005Q January, 2008
Sanken Electric Co., Ltd.
I02-010EA-080130
Europe
United Kingdom
Sanken Power Systems (UK) Limited
Pencoed Technology Park Pencoe d, Bridgend CF35 5HY. UK
Tel: 44-1656-869-100
Fax: 44-1656-869-162
North America
United States
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Worcester, Massachusetts 01606, U.S.A.
Tel: 1-508-853-5000
Fax: 1-508-8 5 3- 3 353
Allegro MicroSystems, Inc. (Southern C ali forni a)
14 Hughes Street, Suite B105, Irvine, CA 92618
Tel: 1-949-460-2003
Fax: 1-949-4 6 0- 7 837
