SI-8001FDE
DC-to-DC Step-Down Converter
Features and Benefits
▪
3.5 A output current supplied in a small, surface mount
power package
▪
High efficiency: 83% at V
IN
= 15 V, I
O
= 2.0 A,V
O
= 5 V
▪
Requires only six external components (optional soft
start requires an additional capacitor)
▪
Oscillation circuit built-in (frequency 300 kHz typical)
▪
Constant-current mode overcurrent protection circuit and
overtemperature protection circuit built-in
▪
Soft start function built-in (can be implemented as an
on/off function; output-off state at low level)
▪
Low current consumption during output-off state
Description
The SI-8001FDE DC voltage regulator is a DC-to-DC buck
convertor that attains an oscillation frequency of 300 kHz,
and has an integrated miniaturized choke coil, allowing it to
serve as a small, high efficiency power supply in a compact
TO263 package.
The internal switching regulator function provides high
efficiency switching regulation without any need for adjustment.
The device requires only six external support components. The
optional soft start function requires an additional capacitor.
Optional on/off control can be performed using a transistor.
The SI-8001FDE includes overcurrent and overtemperature
protection circuits.
Applications include:
▪
DVD recorder
▪
FPD TV
▪
Telecommunications equipment
▪
Office automation equipment, such as printers
▪
On-board local power supply
▪
Output voltage regulator for second stage of SMPS
(switched mode power supply)
Package: TO263-5
Not to scale
Functional Block Diagram
V
IN
1 IN
C1
PReg
Overcurrent
Protection
Latch and
Driver
SW
2
L1
Di
SPB-G56S
(Sanken)
V
OUT
C2
Reset
5 SS
On/Off
Soft Start
Osc
Comparator
R1
C3
Overtemperature
Protection
Error
Amplifier
ADJ
4
R2
Reference
Voltage
GND
3
27469.056
SI-8001FDE
DC-to-DC Step-Down Converter
Selection Guide
Part Number
SI-8001FDE-TL
Output Voltage
Adjustable Range
(V)
0.8 to 24
Efficiency,
Typ.
(%)
83
Input Voltage,
Max.
(V)
40
Output Current,
Max.
(A)
3.5
Packing
800 pieces per reel
Absolute Maximum Ratings
Characteristic
DC Input Voltage
Power Dissipation
Junction Temperature
Storage Temperature
Thermal Resistance (junction-to-case)
Thermal Resistance (junction-to-ambient air)
Symbol
V
IN
P
D
T
J
T
stg
R
θJC
R
θJA
Mounted on 40 mm × 40 mm exposed copper area on 40 mm ×
40 mm glass-epoxy PCB.
Mounted on 40 mm × 40 mm exposed copper area on 40 mm ×
40 mm glass-epoxy PCB.
Mounted on 40 mm × 40 mm exposed copper area on 40 mm
× 40 mm glass-epoxy PCB; limited by internal overtemperature
protection.
Internal overtemperature protection circuit may enable when T
J
≥
130°C. During product operation, recommended T
J
≤
125°C.
Remarks
Rating
43
3
–40 to 150
–40 to 150
3
33.3
Units
V
W
°C
°C
°C/W
°C/W
Recommended Operating Conditions*
Characteristic
DC Input Voltage Range
DC Output Voltage Range
DC Output Current Range
Operating Junction Temperature Range
Operating Temperature Range
Symbol
V
IN
V
O
I
O
T
JOP
T
OP
To be used within the allowable package power dissipation
characteristics (refer to Power Dissipation chart).
V
IN
≥
V
O
+ 3 V; to be used within the allowable package
power dissipation characteristics (refer to Power Dissipation
chart).
Remarks
V
IN
(min) is the greater of 4.5 V or V
O
+3 V.
Min.
See
remarks
0.8
0
–30
–30
Max.
40
24
3.5
100
85
Units
V
V
A
°C
°C
*Required for normal device functioning according to Electrical Characteristics table.
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-8001FDE
DC-to-DC Step-Down Converter
ELECTRICAL CHARACTERISTICS
1
,
valid at T
A
= 25°C, V
O
= 5 V (adjusted), R1 = 4.2 kΩ, R1 = 0.8 kΩ
Characteristic
Reference Voltage
Reference Voltage Temperature Coefficient
Efficiency
2
Operating Frequency
Line Regulation
Load Regulation
Overcurrent Protection Threshold Current
SS Terminal On/Off Operation Threshold Voltage
SS Terminal On/Off Operation Outflow Current
Quiescent Current 1
Quiescent Current 2
1
Using
2
Efficiency
Symbol
V
ADJ
∆V
ADJ
/∆T
η
f
O
V
Line
V
Load
I
S
V
SSL
I
SSL
I
q
I
q(off)
V
SSL
= 0 V
Test Conditions
1
V
IN
= 15 V, I
O
= 0.2 A
V
IN
= 15 V, I
O
= 0.2 A, T
C
= 0 to 100 °C
V
IN
= 15 V, I
O
= 2 A
V
IN
= 15 V, I
O
= 2 A
V
IN
= 10 to 30 V, I
O
= 2 A
V
IN
= 15 V, I
O
= 0.2 to 3.5 A
V
IN
= 15 V
Min.
0.784
–
–
270
–
–
3.6
–
–
–
–
Typ.
0.800
±0.1
83
300
–
–
–
–
6
6
200
Max.
0.816
–
–
330
80
50
–
0.5
30
–
600
Units
V
mV/°C
%
kHz
mV
mV
A
V
μA
mA
μA
V
IN
= 15 V, I
O
= 0 A
V
IN
= 15 V, V
SS
= 0 V
circuit shown in Typical Application Circuit diagram.
is calculated as:
η(%)
= ([V
O
×
I
O
] × [V
IN
×
I
IN
]) × 100.
Pin-out Diagram
Terminal List Table
Name
IN
SW
GND
ADJ
Number
1
2
3
4
Supply voltage
Regulated supply output
Ground terminal
Terminal for resistor bridge feedback
The SS terminal is used to enable soft start and to control on/off operation of the IC output,
V
O
(see figure 2). If neither soft start nor on/off control is used, leave pin open.
To enable soft start, connect a capacitor between SS and ground. To control on/off
operation, connect an NPN bipolar transistor, in a TTL open collector output configuration,
between the SS terminal and GND. Turn off is done by decreasing V
SSL
below its rated
level.
When both soft start and V
O
on/off are used, a protection measure such as current limiting
is required because, if the capacitance of C3 large, the discharge current of C3 flows
across the transistor for on/off operation. Because a pull-up type resistor is provided inside
the IC, no external voltage can be applied.
Function
SS
5
1
2
3
4
5
SI-8000FDE
SS
5
SI-8000FDE
SS
5
SI-8000FDE
SS
5
System
TTL
C3
System
TTL
C3
(a)
V
O
on/off
control only
(b)
Soft start
only
(c)
V
O
on/off and
soft start control
Figure 2. Alternative configurations for SS pin. If neither soft start nor V
O
on/off is required, the SS pin is left open.
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
3
SI-8001FDE
DC-to-DC Step-Down Converter
Performance Characteristics
At T
A
= 25°C, V
O
= 5 V Adjusted, R1 = 4.2 kΩ, R2 = 0.8 kΩ
90
85
6.00
5.00
8V
15 V
20 V
30 V
V
IN
I
O
0A
0.5 A
80
4.00
V
O
(V)
Efficiency versus
Output Current
V
O
= 3.3 V
η
(%)
1A
2A
3.5 A
75
70
65
60
40 V
Low Voltage
Behavior:
Output Voltage
versus
Supply Voltage
3.00
2.00
1.00
0
0
0.5
1.0
1.5
2.0
I
O
(A)
2.5
3.0
3.5
0
1
2
3
4
5
V
IN
(V)
6
7
8
90
5.10
8V
15 V
5.08
V
IN
85
80
5.06
5.04
V
IN
40 V
30 V
15 V
10 V
8V
Efficiency versus
Output Current
V
O
= 5.0 V
75
70
20 V
30 V
40 V
Load Regulation:
5.02
Output Voltage
5.00
versus
Output Current
4.98
V
O
(V)
η
(%)
4.96
4.94
4.92
4.90
0
0.5
1.0
1.5
2.0
I
O
(A)
2.5
3.0
3.5
65
60
0
10
1
2
I
O
(A)
3
100
95
15V
90
20 V
V
IN
8
6
4
2
0
Efficiency versus
Output Current
V
O
= 12.0 V
85
30 V
80
Quiescent Current
versus
Supply Voltage
I
O
= 0 A
SS pin open
η
(%)
40 V
75
70
0
0.5
1.0
1.5
2.0
I
O
(A)
2.5
3.0
3.5
I
q
(mA)
0
10
20
V
IN
(V)
30
40
400
6
5
Behavior at
Turn-Off:
Quiescent Current
versus
Input Voltage
I
O
= 0 A
V
SS
= 0 V
300
8V
200
Overcurrent
Protection:
Output Voltage
versus
Output Current
4
V
O
(V)
V
IN
I
Q
(μA)
15 V
30 V
3
2
100
40 V
1
0
0
0.5
1.0
1.5
2.0
V
IN
(V)
2.5
3.0
3.5
0
0
1
2
I
O
(A)
3
4
5
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
4
SI-8001FDE
DC-to-DC Step-Down Converter
Thermal Performance Characteristics
The application must be designed to ensure that the T
J
(max)
of the device is not exceeded during operation. To do so, it is
necessary to determine values for maximum power dissipation,
P
D
(max), and ambient temperature, T
A
(max).
The relationships of T
J
, P
D
, T
A
, and case temperature, T
C
, are as
shown in the following formulas:
T –T
P
D
=
J C
R
θJC
Power Dissipation versus Ambient Temperature
T
J
(max) = 125°C; Mounted on glass-epoxy PCB (40 mm × 40 mm),
with varying exposed copper areas
3.5
Cu Area: 1600 mm
2
R
θJA
= 33.3°C/W
3.0
Cu Area: 800 mm
2
R
θJA
= 37°C/W
and
T –T
P
D
=
J A
R
θJA
.
2.5
P
D
can be calculated from input values:
⎛
100
⎞
⎛
V
−
1
⎟ −
V
F
⋅
I
O
⎜
1
−
O
P
D
=
V
O
⋅
I
O
⎜
⎜
⎟
⎜
V
IN
⎝
x
⎠
⎝
where:
V
O
is output voltage in V,
V
IN
is input supply voltage in V,
I
O
is output current in A,
⎞
⎟
⎟
⎠
2.0
P
D
(W)
Cu Area: 400 mm
2
R
θJA
= 44°C/W
1.5
Cu Area: 100 mm
2
R
θJA
= 53°C/W
1.0
η
x
is IC efficiency in percent (varies with V
IN
and I
O
; refer to
efficiency performance curves for value), and
V
F
is forward voltage for the input diode, Di. In these tests, the
Sanken SPB-G56S was used, at 0.4 V. For application design,
obtain thermal data from the datasheet for the diode.
P
D
is substantially affected by the heat conductance properties of
the application, in particular any exposed copper area on the PCB
where the device is mounted. The relationships of P
D
, T
A
, and
copper area is represented in the Power Dissipation chart.
R
θJA
for a given copper area can be determined form the Device
Thermal Resistance chart. This can be substituted into the formula
above to determine the T
J
(max) allowable in the application.
Generally, more than 10% to 20% derating is required.
Because the heat dissipation capacity of the copper area depends
substantively on how it is used in the actual application, thermal
characteristics of the application must be confirmed by testing.
T
C
is determined by connecting a thermocouple to the device as
shown here:
0.5
0
–25
0
25
50
T
A
(°C)
75
100
125
Device Thermal Resistance versus Exposed Copper Area on PCB
55
R
θJA
(°C/W)
Glass-epoxy PCB, 40 mm × 40 mm
50
45
40
35
30
0
200
400
600
800
1000
2
1200
1400
1600
1800
Copper Area (mm )
6
OTP On
5
Overtemperature
Protection:
Output Voltage versus
Junction Temperature
V
IN
= 15 V, I
O
= 10 mA
4
V
O
(V)
3
2
1
Thermocouple mount
at tab center
And analyzing the results using the following formula:
T
J
=
P
D
×
R
θJC
+
T
C
,
for this device, R
θJC
is 3 °C/W.
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
OTP Off
0
0
20
40
60
80 100
T
J
(°C)
120
140
160
180
5
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