Thick Film Hybrid IC
Ordering number : EN4533B
61096HA (OT)/82793YO (OT)No. 4533-1/6
SANYO Electric Co.,Ltd. Semiconductor Bussiness Headquarters
TOKYO OFFICE Tokyo Bldg., 1-10, 1 Chome, Ueno, Taito-ku, TOKYO, 110 JAPAN
15 V Single Output MOS Chopper Regulator
STK732C
Overview
The STK732C is a chopper type step-down dedicated
15 V single output regulator that uses a power MOSFET
as its switching element. The STK732C covers the 2 A
and higher current regions, regions that are difficult to
handle with three terminal step-down regulators. As
compared with earlier chopper regulator products that
used bipolar transistors, the efficiency of the STK732C
has been further improved by the adoption of MOSFET
technology, and use of the STK732C enables further
miniaturization and increased performance in the end
product since it corresponds to the adoption of a
dedicated switching controller IC. Furthermore, due to
the development of a unique MOS drive circuit, the
STK732C can be used with a single power supply input.
The STK732C can prove useful when standardizing and
rationalizing power supply circuit design, since it can
handle a wide range of power supply circuits in a
number of applications, either as the secondary side
regulator in a switching power supply or as the output
regulator following AC transformer rectification.
Applications
Power supplies in printers and other office equipment
Power supplies in robots and other factory automation
related equipment
Power supplies in VCRs and other consumer products
Secondary side regulators in switching power supplies
Features
IMST substrate (insulated metal substrate technology)
High efficiency realized by the adoption of MOSFET
technology.
An auxiliary drive power supply is no longer required
due to the development of a unique NMOS FET drive
circuit. This means that the STK732C can be used
with a single power supply, thus allowing
simplification of the input system.
Built-in reverse going linear overload characteristic
curve overcurrent protection circuit
Ground line handling is eased even in multi-output
power supply structures due to placement of the
overcurrent detection resistor on the plus line.
The STK732C's separate excitation oscillator
structure provides high stability in the switching
frequency.
A built-in cutoff function allows an external signal to
switch the output on and off.
The STK732C's switching operating frequency is set
at 85 kHz, which minimizes beating when used in a
multiple output structure with STK730 type (5 V
output, 125 kHz) products.
Package Dimensions
unit: mm
4137
[STK732C]
STK732C
Specifications
Maximum Ratings
at Ta = 25C
Parameter
Symbol
Condition
Rating
Unit
Maximum DC input voltage
V
IN
(DC) max
60
V
Maximum output current
I
O
max
5/10 pk
A
Thermal resistance
j-c
3.5
C/W
Junction temperature
Tj max
150
C
Operating substrate temperature
Tc max
105
C
Storage temperature
T
stg
30 to +105
C
Electrical Characteristics
at Ta = 25C, for the specified test circuit
Rating
Parameter
Symbol
Condition
min
typ
max
Unit
Output voltage setting
V
O
V
IN
(DC) = 35 V, I
O
= 1 A
14.7
15.0
15.3
V
Ripple voltage
Vrp
V
IN
(DC) = 35 V, I
O
= 1 A
25
mVrms
Input regulation
Reg-IN
V
IN
(DC) = 20 to 45 V, I
O
= 1 A
20
mV/V
Load regulation
Reg-L
V
IN
(DC) = 35 V, I
O
= 0.5 to 5 A
40
mV/A
Overcurrent protection start current
I
OCP
V
IN
(DC) = 35 V
10
A
Efficiency
V
IN
(DC) = 35 V, I
O
= 2.5 A
90
%
Operating frequency
f
V
IN
(DC) = 35 V, I
O
= 1 A
85
kHz
Output voltage temperature coefficient
T
CVO
V
IN
(DC) = 35 V, I
O
= 1 A
0.01
%/C
Cutoff voltage
Voff
Output on
3
20
V
(Pin 12 input voltage)
Output off
0
0.8
V
Peak Current
Block Diagram
No. 4533-2/6
Test Circuit
STK732C
No. 4533-3/6
C1
220 F/63 V
L1
200 H (HP-054/TOKIN)
C2
1000 F/25 V
Rs1
0.05
C3
0.1 F/50 V
R1
10
C4
1 F/50 V
C5
1000 pF
Note: Since pin 5 is grounded to the substrate, the noise level and other characteristics may be adversely affected if the heat sink is connected to the FG or
GND lines. If this is a problem either make the heat sink floating or use an insulating sheet.
P, V
O
,
V
IN
Output voltage, V
O
V, Efficiency,
%
Input voltage, V
IN
V
V
O
, f Tc
Output voltage, V
O
V, Operating frequency, f kHz
Substrate temperature, Tc C
P, V
O
,
I
O
Output voltage, V
O
V, Efficiency,
%
Output current, I
O
A
STK732C
Thermal Design
The power dissipating sections of a power supply block consist of the power transistor (PTR), the flywheel diode
(FWD), the choke coil, and the current detection resistor. Of these, the components that are incorporated in the hybrid IC
itself are the PTR and the FWD.
Taking PT to be the power dissipated in the PTR and PF to be the power dissipated in the FWD, the power dissipation
Pd for the whole hybrid IC and the heat sink thermal resistance
c-a can be expressed as follows.
Pd = (PT + PF)
[W]
c-a =
Tc Ta
[C/W]
Pd
Tc: Substrate temperature (105C, maximum)
Ta: IC ambient temperature
The junction temperature, Tj, of each element can be expressed as follows.
Tj = PD
j-c + Tc
[C]
PD: Power loss for each element (PT, PF)
j-c: The junction/case thermal resistance of each element
Thermal design consists of deriving the heat sink thermal resistance
c-a that satisfies the two thermal conditions, i.e.,
the maximum IC substrate temperature Tc max (105C) and the maximum junction temperature Tj max for each
semiconductor device, and then implementing that thermal resistance. Since thermal dissipation is greatly influenced by
the ambient temperature, the structure of the equipment itself, and other factors, ample margins must be included in the
thermal design to take them into account.
The figure below left shows the relationship between area and thermal resistance when an aluminum plate is used in the
thermal design. The radiation characteristics of an aluminum plate can be improved by painting the surface in black. This
can reduce the thermal resistance by 20% for a given surface area.
j-c and Tj max for the STK732C
Parameter
j-c
Tj max
PTR (FET)
3.5C/W
150C
FWD (FRD)
6.9C/W
150C
No. 4533-4/6
c-a S
Heat sink thermal resistance,
c-a
C/W
Heat sink area, S cm
2
Pd I
O
Power dissipation, Pd W
Output current, I
O
A
Notes on PC Board Production
Capacitor C1 should be placed as close as possible to the pin 10 input in the layout. (This is to prevent voltage drops in
the input lines and pattern. Also, a separate smoothing capacitor is required if the input is a direct current input using
rectified and smoothed AC.)
Capacitor C2 should be placed as close as possible to the load in the layout. (This is to compensate for voltage drops
due to load fluctuations.)
Pins 2 and 5 are voltage sensing lines, and should be connected close to the load, i.e., close to C2. (This is to
compensate for voltage drops in the pattern.)
Pins 3 and 4 should be directly connected to the two terminals of the current detection resistor Rs1. (This is to prevent
detection based on pattern resistances.)
Pin 6 should be connected to the capacitor C1 ground using a thick, short line to reduce the related loop area. (This is
to reduce switching spikes.)
Power lines, i.e., lines that carry current, should be made as wide as possible in the pattern.
When a ripple suppression LC filter is added, connect it at the location indicated by dotted lines in the figure. The
sensing line from pin 2 should be connected to the same position (the C2 location) as it is when no filter is used.
C5 and R1, which are used to reduce switching spikes, should be connected as close as possible to the IC pins.
Locations where multiple pins are used (pins 7 and 8, and pins 9 and 10) must be connected in the printed circuit
pattern.
Output On/Off Control (cutoff)
The on/off control function uses pin 12. When pin 12 is at the low level, the output will be cut off.
STK732C
No. 4533-5/6
Connection diagram for circuits that do not
use the cutoff function.
STK732C
Choke Coil L1
1. The inductance value shown in the test circuit diagram is for times when the current is zero, and therefore is a
reference value. Circuit operation should be checked in the actual mounted configuration of the final product.
2. The inductor L1 should be a product that can handle the high frequencies used in a switching power supply.
3. Be sure to use an inductor with appropriate rated current and magnetic saturation specifications.
Current Detection Resistor Rs1
1. Since this resistor carries large currents, its power dissipation must be taken into consideration.
2. Manufacturing variations in the resistor value can change the overcurrent protection circuit's operating point.
Two Output Power Supply Structural Example (connecting to an STK730)
Note: It is possible for STK730 input ripple currents to cause L1 to vibrate audibly and adversely influence the 15 V system. If such problems occur, an
inductor can be inserted at the point marked with dotted lines in the figure to form an LC filter.
Caution: Step down chopper power supplies can generate an overvoltage on the output side equivalent to the input
voltage if there is an assembly error on the PC board or if the IC fails. Therefore we strongly recommend the
use of a crowbar or other overvoltage protection circuit in power supply designs.
No. 4533-6/6
x
This catalog provides information as of November, 1997. Specifications and information herein are subject to
change without notice.
s
No products described or contained herein are intended for use in surgical implants, life-support systems, aerospace
equipment, nuclear power control systems, vehicles, disaster/crime-prevention equipment and the like, the failure of
which may directly or indirectly cause injury, death or property loss.
s
Anyone purchasing any products described or contained herein for an above-mentioned use shall:
Accept full responsibility and indemnify and defend SANYO ELECTRIC CO., LTD., its affiliates, subsidiaries and
distributors and all their officers and employees, jointly and severally, against any and all claims and litigation and all
damages, cost and expenses associated with such use:
Not impose any responsibility for any fault or negligence which may be cited in any such claim or litigation on
SANYO ELECTRIC CO., LTD., its affiliates, subsidiaries and distributors or any of their officers and employees
jointly or severally.
s
Information (including circuit diagrams and circuit parameters) herein is for example only; it is not guaranteed for
volume production. SANYO believes information herein is accurate and reliable, but no guarantees are made or implied
regarding its use or any infringements of intellectual property rights or other rights of third parties.
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