SI-8005Q
Step-Down Switching Regulator with Current-Mode Control
Features and Benefits
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Current-mode control system employed
Excellent line regulation (60 mV maximum)
165 mΩ 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 V
REF
of 0.5 V.
High efficiency, 94% maximum at V
IN
= 8 V, V
O
= 5 V,
and I
O
= 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)
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 mΩ. 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.
Package: HSOP8 surface mount with
exposed thermal pad
Not to scale
Functional Block Diagram
27469.058
SI-8005Q
Selection Guide
Part Number
SI8005Q-TL
Step-Down Switching Regulator with Current-Mode Control
Packing
1000 pieces per reel
Absolute Maximum Ratings
Characteristic
DC Input Voltage
DC Input Voltage
Allowable Power Dissipation
Junction Temperature
Storage Temperature
Thermal Resistance (Junction to Ambient)
Thermal Resistance (Junction to Case)
Symbol
V
IN
V
EN
P
D
T
J
T
stg
R
θJA
R
θJC
Remarks
Rating
30
6
Unit
V
V
W
°C
°C
°C/W
°C/W
Limited by internal thermal shutdown, mounted on a 30 mm × 30 mm
glass epoxy PCB with 25 mm × 25 mm exposed copper area,
T
J
(max) = 125°C
Internal thermal shutdown activates at approximately 140°C
Mounted on a 30 mm × 30 mm glass epoxy PCB with 25 mm ×
25 mm exposed copper area
1.35
–30 to 150
–40 to 150
74
40
Recommended Operating Conditions*
Characteristic
DC Input Voltage Range
DC Output Current Range
Operating Junction
Temperature Range
Operating Temperature
Range
Symbol
V
IN
I
O
T
JOP
T
OP
Operation within P
D
limits
Remarks
V
IN
(min) is the greater of either 4.75 V or V
O
+1 V; except
if V
O
+ 0.5
≤
V
IN
≤
V
O
+1 V, then V
IN
(min) is set such that
I
O
≤
2 A
Using the circuit defined in the Typical Application
diagram and within P
D
limits
Min.
See
remarks
0
–30
–30
Typ.
–
–
–
–
Max.
28
3.5
125
85
Units
V
A
°C
°C
*Recommended operating range indicates conditions which are required for maintaining normal circuit functions shown in the Electrical Characteristics
table.
Maximum Allowable Package Power Dissipation
1.6
1.4
Power Dissipation, P
D
(W)
1.2
1.0
0.8
0.6
0.4
0.2
0
–25
0
25
50
75
Ambient Temperature, T
A
(°C)
100
125
Results calculated as:
⎛
100
⎞
P
D
=
V
O
×
I
O
⎜
–
1
⎟
–
V
F
×
I
O
⎜
x
⎟
⎝
⎠
where:
V
O
is the output voltage,
⎛
V
O
⎞
⎜
1
–
⎟
⎜
V
IN
⎟
⎝
⎠
V
IN
is the Input voltage (0.4 V for these results),
I
O
is the Output current (0.3 A for these results),
ηx
is the efficiency (%), which varies with V
IN
and I
O
(derived from the
Efficiency curves in the Characteristic Performance section), and
V
F
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).
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, T
A
, of 25°C, unless otherwise stated.
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
2
SI-8005Q
Step-Down Switching Regulator with Current-Mode Control
ELECTRICAL CHARACTERISTICS
1
, valid at T
A
=25°C, unless otherwise noted
Characteristics
Reference Voltage
Output Voltage Temperature
Coefficient
Efficiency
2
Operating Frequency
Line Regulation
Load Regulation
Overcurrent Protection Threshold
Quiescent Current 1
Quiescent Current 2
SS Terminal Leakage Current
3
EN Terminal High Level Voltage
EN Terminal Low Level Voltage
EN Terminal Leakage Current
Error Amplifier Voltage Gain
Error Amplifier Transconductance
Current Sense To COMP
Transimpedance
Maximum Duty Cycle (On)
Minimum On-Time
1
Using
2
Efficiency
Symbol
V
REF
∆V
REF
/∆T
η
f
O
V
LINE
V
LOAD
I
S
I
IN
I
IN(off)
I
SSL
V
CEH
V
CEL
I
CEH
A
EA
G
EA
1/G
CS
DC
MAX
t
MIN
Conditions
V
IN
= 12 V, I
O
= 1.0 A
V
IN
= 12 V, I
O
= 1.0 A, T
A
= –40°C to 85°C
V
IN
= 12 V, V
O
= 5 V, I
O
= 1 A
V
IN
= 16 V, V
O
= 5 V, I
O
= 1 A
V
IN
= 8 to 28 V, V
O
= 5 V, I
O
= 1 A
V
IN
= 12 V, V
O
= 5 V, I
O
= 0.1 to 3.5 A
V
IN
= 12 V, V
O
= 5 V
V
IN
= 12 V, V
O
= 5 V, I
O
= 0 A, V
EN
= open
V
IN
= 12 V, V
O
= 5 V, I
O
= 0 A,V
EN
= 0 V
V
SSL
= 0 V, V
IN
= 16 V
V
IN
= 12 V
V
IN
= 12 V
V
EN
= 0 V
Min
0.485
–
–
450
–
–
3.6
–
–
–
2.8
–
–
–
–
–
–
–
Typ
0.500
±0.05
90
500
10
10
–
18
–
5
–
–
1
1000
800
0.35
92
100
Max
0.515
–
–
550
60
60
6.0
–
20
–
–
2.0
–
–
–
–
–
–
Units
V
mV/°C
%
kHz
mV
mV
A
mA
μA
μA
V
V
μA
V/ V
μA/V
V/A
%
ns
circuit shown in Measurement Circuit diagram.
is calculated as:
η(%)
= ([V
O
×
I
O
] × [V
IN
×
I
IN
]) × 100.
3
SS 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.
Measurement Circuit Diagram
2
7
EN
C1
I
IN
I
EN
1
IN
BS
S I- 8005Q
5
FB
GND
4
COM P
6
C3
3
SW
C4
L1
Component
R1
C2
Rating
22
μF
/ 50 V
47
μF
/ 25 V
220 pF / 10 V
10 nF / 25 V
SPB-G56S
10
μH
46 kΩ
5.1 kΩ
62 kΩ
8
SS
Di
I
O
I
SS
V
FB
R2
V
O
RL
V
IN
V
EN
V
SS
R3
C1
C2
C3
C4
Di
L1
R1
R2
R3
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
3
SI-8005Q
Step-Down Switching Regulator with Current-Mode Control
Performance Characteristics
at T
A
= 25°C
100
90
80
100
8V
V
IN
4.75 V
5V
90
80
12 V
Efficiency versus
Output Current
V
O
= 1.2 V
70
60
50
40
8V
12 V
6V
Efficiency versus
Output Current
V
O
= 3.3 V
70
60
50
40
16 V
24 V
28 V
V
IN
η
(%)
0
1
2
3
4
5
η
(%)
0
1
2
3
4
5
I
O
(A)
100
90
I
O
(A)
100
8V
12 V
90
16 V
20 V
16 V
80
20 V
V
IN
η
(%)
80
Efficiency versus
Output Current
V
O
= 5 V
η
(%)
28 V
70
60
50
40
Efficiency versus
Output Current
V
O
= 12 V
28 V
70
60
50
40
V
IN
0
1
2
3
4
5
0
1
2
3
4
5
I
O
(A)
I
O
(A)
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
4
SI-8005Q
Step-Down Switching Regulator with Current-Mode Control
Performance Characteristics
at T
A
= 25°C
6
5
4
V
O
(V)
6
0A
1A
2A
5
4
20 V
24 V
28 V
8V
12 V
15 V
Overcurrent
Protection
Load = CR
3
2
1
0
Overcurrent
Protection
I
O
V
O
(V)
3A
3
2
1
0
V
IN
0
2
4
6
8
10
0
1
2
3
4
5
6
V
IN
(V)
5.05
5.04
5.03
5.02
V
O
(V)
25
I
O
(A)
V
IN
I
O(Q)
(mA)
20
Load
Regulation
5.01
5.00
4.99
4.98
4.97
4.96
4.95
0
1
28 V
20 V
15 V
8V
12 V
Quiescent
Current versus
Input Voltage
I
O
= 0 A
15
10
5
2
3
4
5
0
0
10
20
30
40
I
O
(A)
10
9
8
7
I
O(Q)
(μA)
5
4
6
V
IN
(V)
OTP On
Quiescent
Current versus
Input Voltage
V
EN
= 0 V
V
O
(V)
6
5
4
3
2
1
0
0
10
20
30
40
Overvoltage
Protection
V
IN
= 12 V
I
O
= 0 A
3
2
1
OTP Off
0
120
550
130
140
T
J
(°C)
150
160
V
IN
(V)
550
540
530
520
540
8V
12 V
15 V
V
IN
530
520
f
O
(kHz)
490
480
470
460
450
0
1
f
O
(kHz)
Operating
Frequency versus
Output Current
510
500
Operating
Frequency versus
Input Voltage
20 V
24 V
28 V
510
500
490
480
470
460
2
3
4
5
450
0
10
20
30
40
I
O
(A)
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
V
IN
(V)
5
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