SP7655, Wide Input Voltage Range 8A, 300kHz, Buck Regulator
1
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
SP7655
FEATURES
2.5V to 28V Step Down Achieved Using Dual Input
Output Voltage down to 0.8V
8A Output Capability
Built in Low R
DSON
Power Switches (15 m typ)
Highly Integrated Design, Minimal Components
300 kHz Fixed Frequency Operation
UVLO Detects Both V
CC
and V
IN
Over Temperature Protection
Short Circuit Protection with Auto-Restart
Wide BW Amp Allows Type II or III Compensation
Programmable Soft Start
Fast Transient Response
High Efficiency: Greater than 95% Possible
Asynchronous Start-Up into a Pre-Charged Output
Small 7mm x 4mm DFN Package
U.S. Patent #6,922,041
Wide Input Voltage Range, 8Amp
300kHz, Buck Regulator
The SP7655 is a synchronous step-down switching regulator optimized for high efficiency. The part is designed to be
especially attractive for dual supply, 12V or 24V distributed power systems stepped down with 5V used to power the
controller. This lower V
CC
voltage minimizes power dissipation in the part and is used to drive the top switch. The
SP7655 is designed to provide a fully integrated buck regulator solution using a fixed 300kHz frequency, PWM voltage
mode architecture. Protection features include UVLO, thermal shutdown and output short circuit protection. The
SP7655 is available in the space saving DFN package
.
TYPICAL APPLICATION CIRCUIT
Now Available in Lead Free Packaging
DESCRIPTION
Power
Blox
Blox
TM
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
2 2
23
24
25
26
BOTTOM VIEW
Heatsink Pad 1
Connect to Lx
Heatsink pad 2
Connect to GND
Heatsink pad 3
Connect to V
IN
P
GND
P
GND
GND
V
FB
COMP
UVIN
GND
SS
V
IN
LX
LX
LX
LX
V
CC
GND
GND
GND
BST
NC
LX
LX
LX
DFN PACKAGE
7mm x 4mm
SP7655
P
GND
V
IN
V
IN
V
IN
16V
CBST
6,800pF
L1
2.2uH, Irate=8A
C1
22uF
CVCC
2.2uF
U1
SP7655
PGND
1
PGND
2
PGND
3
GND
4
VFB
5
COMP
6
UVIN
7
GND
8
SS
9
VIN
10
VIN
11
VIN
12
VIN
13
LX
14
LX
15
LX
16
NC
17
BST
18
GND
19
GND
20
GND
21
VCC
22
LX
23
LX
24
LX
25
LX
26
DBST
CSS
47nF
CP1
22pF
3.30V
0-8A
RSET
21.5k,1%
GND
C3
47uF
C4
22uF
Notes:
12V
VIN
SD101AWS
have three contacts isolated from
one another: Vin, SWNODE, and GND.
RZ3
7.15k
1%
VOUT
CZ3
150pF
CZ2
1,000pF
R1
68.1k,1%
RZ2
15k,1%
CF1
100pF
f
s=300Khz
ENABLE
+5V
VCC
2. RSET=54.48/(Vout-0.8V) KOhms
(note 2)
6.3V
1. U1 Bottom side layout should
16V
2
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
ELECTRICAL SPECIFICATIONS
Unless otherwise specified: -40C < T
AMB
< 85C, -40C < Tj< 125C, 4.5V < V
CC
< 5.5V, 3V< Vin< 28V, BST=LX
+ 5V,
LX = GND = 0.0V, UVIN = 3.0V, CV
CC
= 1F, C
COMP
= 0.1F, C
SS
= 50nF, Typical measured at V
CC
= 5V.
The denotes the specifications which apply over the full temperature range, unless otherwise specified.
V
CC
.................................................................................................. 7V
V
IN ...........................................................................................................................................
30V
I
LX ............................................................................................................................................
10A
BST ............................................................................................... 35V
LX-BST ............................................................................. -0.3V to 7V
LX ....................................................................................... -1V to 30V
All other pins .......................................................... -0.3V to V
CC
+0.3V
Storage Temperature .................................................. -65C to 150C
Power Dissipation ...................................... Internally Limited via OTP
ESD Rating .......................................................................... 2kV HBM
Thermal Resistance
JC ....................................................................................
5C/W
ABSOLUTE MAXIMUM RATINGS
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These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the
specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
3
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
ELECTRICAL SPECIFICATIONS
Unless otherwise specified: -40C < T
AMB
< 85C, -40C< Tj< 125C, 4.5V < V
CC
< 5.5V, 3V< Vin< 28V, BST=LX
+ 5V,
LX = GND = 0.0V, UVIN = 3.0V, CV
CC
= 1F, C
COMP
= 0.1F, C
SS
= 50nF, Typical measured at V
CC
= 5V.
The denotes the specifications which apply over the full temperature range, unless otherwise specified.
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4
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
General Overview
The SP7655 is a fixed frequency, voltage mode,
synchronous PWM regulator optimized for high
efficiency. The part has been designed to be
especially attractive for high voltage applica-
tions utilizing 5V to power the controller and
2.5V to 28V for step down conversion.
The heart of the SP7655 is a wide bandwidth
transconductance amplifier designed to accom-
modate Type II and Type III compensation
schemes. A precision 0.8V reference, present on
the positive terminal of the error amplifier,
permits the programming of the output voltage
down to 0.8V via the V
FB
pin. The output of the
error amplifier, COMP, compared to a 1.1V
peak-to-peak ramp is responsible for trailing
edge PWM control. This voltage ramp, and
PWM control logic are governed by the internal
oscillator that accurately sets the PWM fre-
quency to 300kHz.
THEORY OF OPERATION
The SP7655 contains two unique control fea-
tures that are very powerful in distributed appli-
cations. First, asynchronous driver control is
enabled during startup, to prohibit the low side
switch from pulling down the output until the
high side switch has attempted to turn on. Sec-
ond, a 100% duty cycle timeout ensures that the
low side switch is periodically enhanced during
extended periods at 100% duty cycle. This guar-
antees the synchronized refreshing of the BST
capacitor during very large duty cycle ratios.
The SP7655 also contains a number of valuable
protection features. Programmable V
IN
UVLO
allows the user to set the exact value at which the
conversion voltage can safely begin down con-
version, and an internal V
CC
UVLO which en-
sures that the controller itself has enough volt-
age to operate properly. Other protection fea-
PIN DESCRIPTION
Pin #
Pin Name
Description
1-3
P
GND
Ground connection for the synchronous rectifier
4,8,19-21
GND
Ground Pin. The control circuitry of the IC and lower power driver are
referenced to this pin. Return separately from other ground traces to the (-)
terminal of C
OUT
.
5
V
FB
Feedback Voltage and Short Circuit Detection pin. It is the inverting input of
the Error Amplifier and serves as the output voltage feedback point for the
Buck Converter. The output voltage is sensed and can be adjusted through
an external resistor divider. Whenever V
FB
drops 0.25V below the positive
reference, a short circuit fault is detected and the IC enters hiccup mode.
6
COMP
Output of the Error Amplifier. It is internally connected to the inverting input of
the PWM comparator. An optimal filter combination is chosen and connected
to this pin and either ground or V
FB
to stabilize the voltage mode loop.
7
UVIN
UVLO input for V
IN
voltage. Connect a resistor divider between V
IN
and UV
IN
to set minimum operating voltage.
9
SS
Soft Start. Connect an external capacitor between SS and GND to set the
soft start rate based on the 10A source current. The SS pin is held low via a
1mA (min) current during all fault conditions.
10-13
V
IN
Input connection to the high side N-channel MOSFET. Place a decoupling
capacitor between this pin and PGND.
14-16,23-26
LX
Connect an inductor between this pin and V
OUT
17
NC
No Connect
18
BST
High side driver supply pin. Connect BST to the external boost diode and
capacitor as shown in the Typical Application Circuit on page 1. High side
driver is connected between BST pin and SWN pin.
22
Vcc
Input for external 5V bias supply
5
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
tures include thermal shutdown and short-cir-
cuit detection. In the event that either a thermal,
short-circuit, or UVLO fault is detected, the
SP7655 is forced into an idle state where the
output drivers are held off for a finite period
before a restart is attempted.
Soft Start
"Soft Start" is achieved when a power converter
ramps up the output voltage while controlling
the magnitude of the input supply source cur-
rent. In a modern step down converter, ramping
up the positive terminal of the error amplifier
controls soft start. As a result, excess source
current can be defined as the current required to
charge the output capacitor.
IV
IN
= C
OUT
* (
V
OUT
/
T
SOFT-START
)
The SP7655 provides the user with the option to
program the soft start rate by tying a capacitor
from the SS pin to GND. The selection of this
capacitor is based on the 10
A pullup current
present at the SS pin and the 0.8V reference
voltage. Therefore, the excess source can be
redefined as:
IV
IN
= C
OUT
* (
V
OUT
*10
A / (C
SS
* 0.8V)
Under Voltage Lock Out (UVLO)
The SP7655 contains two separate UVLO com-
parators to monitor the bias (V
CC
) and conver-
sion (V
IN
) voltages independently. The V
CC
UVLO threshold is internally set to 4.25V,
whereas the V
IN
UVLO threshold is program-
mable through the UVIN pin. When the UVIN
pin is greater than 2.5V, the SP7655 is permitted
to start up pending the removal of all other
faults. Both the V
CC
and V
IN
UVLO compara-
tors have been designed with hysteresis to pre-
vent noise from resetting a fault.
Thermal and Short-Circuit
Protection
Because the SP7655 is designed to drive large
output current, there is a chance that the power
converter will become too hot. Therefore, an
internal thermal shutdown (145
C) has been
included to prevent the IC from malfunctioning
at extreme temperatures.
A short-circuit detection comparator has also
been included in the SP7655 to protect against
an accidental short at the output of the power
converter. This comparator constantly monitors
the positive and negative terminals of the error
amplifier, and if the V
FB
pin falls more than
250mV (typical) below the positive reference, a
short-circuit fault is set. Because the SS pin
overrides the internal 0.8V reference during soft
start, the SP7655 is capable of detecting short-
circuit faults throughout the duration of soft
start as well as in regular operation.
Handling of Faults:
Upon the detection of power (UVLO), thermal,
or short-circuit faults, the SP7655 is forced into
an idle state where the SS and COMP pins are
pulled low and both switches are held off. In the
event of UVLO fault, the SP7655 remains in this
idle state until the UVLO fault is removed.
Upon the detection of a thermal or short-circuit
fault, an internal 200ms timer is activated. In the
event of a short-circuit fault, a restart is at-
tempted immediately after the 200ms timeout
expires. Whereas, when a thermal fault is de-
tected, the 200ms delay continuously recycles
and a restart cannot be attempted until the ther-
mal fault is removed and the timer expires.
Error Amplifier and Voltage Loop
Since the heart of the SP7655 voltage error loop
is a high performance, wide bandwidth current-
limited (+/-150
A) transconductance ampli-
fier, there are many ways to compensate the
voltage loop or to control the COMP pin exter-
nally. If a simple, single pole, single zero
response is desired, then compensation can be
THEORY OF OPERATION
6
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
THEORY OF OPERATION
as simple as an RC circuit to Ground. If a more
complex compensation is required, then the
amplifier has enough bandwidth (45
at 4 MHz)
and enough gain (60dB) to run Type III compen-
sation schemes with adequate gain and phase
margins at crossover frequencies greater than
50kHz.
The common mode output of the error amplifier
is 0.9V to 2.2V. Therefore, the PWM voltage
ramp has been set between 1.1V and 2.2V to
ensure proper 0% to 100% duty cycle capability.
The voltage loop also includes two other very
important features. One is an asynchronous
startup mode. Basically, the synchronous recti-
fier cannot turn on unless the high side switch
has attempted to turn on or the SS pin has
exceeded 1.7V. This feature prevents the con-
troller from "dragging down" the output voltage
during startup or in fault modes. The second
feature is a 100% duty cycle timeout that en-
sures synchronized refreshing of the BST ca-
pacitor at very high duty ratios. In the event that
the high side NFET is on for 20 continuous
clock cycles, a reset is given to the PWM flip-
flop half way through the 21
st
cycle. This forces
GL to rise for the cycle, in turn refreshing the
BST capacitor. The boost capacitor is used to
generate a high voltage drive supply for the high
side switch, which is 5V above V
IN
.
Power MOSFETs
The SP7655 contains a pair of integrated low
resistance N-channel switches designed to drive
up to 10 Amps of output current. Care should be
taken to de-rate the output current based on the
thermal conditions in the system such as ambi-
ent temperature, airflow and heat sinking. Maxi-
mum output current could be limited by thermal
limitations of a particular application by taking
advantage of the integrated-over-temperature
protective scheme employed in the SP7655.
The SP7655 incorporates a built-in over-tem-
perature protection to prevent internal overheat-
ing.
GH
Voltage
GL
Voltage
V(VIN)
0V
-0V
-V(Diode) V
V(VIN)+V(VCC)
BST
Voltage
V(VCC)
TIME
SWN
Voltage
VBST
VSWN
V(VCC)
The SP7655 can be set to different output volt-
ages. The relationship in the following formula
is based on a voltage divider from the output to
the feedback pin VFB, which is set to an internal
reference voltage of 0.80V. Standard 1% metal
film resistors of surface mount size 0603 are
recommended.
Vout = 0.80V ( R1 / R2 + 1 ) =>
R2 =
R1
.
[
( Vout / 0.80V ) 1
]
Where R1 = 68.1K
and for V
OUT
= 0.80V
setting, simply remove R2 from the board. Fur-
thermore, one could select the value of the R1
and R2 combination to meet the exact output
voltage setting by restricting R1 resistance range
such that 50K
< R1 < 100K for overall
system loop stability.
Setting Output Voltages
7
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
APPLICATIONS INFORMATION
Inductor Selection
There are many factors to consider in selecting
the inductor including core material, inductance
vs. frequency, current handling capability, effi-
ciency, size and EMI. In a typical SP7655 cir-
cuit, the inductor is chosen primarily for value,
saturation current and DC resistance. Increasing
the inductor value will decrease output voltage
ripple, but degrade transient response. Low in-
ductor values provide the smallest size, but
cause large ripple currents, poor efficiency and
require more output capacitance to smooth out
the larger ripple current. The inductor must be
able to handle the peak current at the switching
frequency without saturating, and the copper
resistance in the winding should be kept as low
as possible to minimize resistive power loss. A
good compromise between size, loss and cost is
to set the inductor ripple current to be within
20% to 40% of the maximum output current.
The switching frequency and the inductor oper-
ating point determine the inductor value as fol-
lows:
( max)
(max )
(max)
)
(
OUT
r
S
IN
OUT
IN
OUT
I
K
F
V
V
V
V
L
-
=
where:
F
S
= switching frequency
K
r
= ratio of the AC inductor ripple current to
the maximum output current
The peak-to-peak inductor ripple current is:
L
F
V
V
V
V
I
S
I N
OUT
IN
OUT
PP
(max)
(max)
)
(
-
=
Once the required inductor value is selected, the
proper selection of core material is based on
peak inductor current and efficiency require-
ments. The core must be large enough not to
saturate at the peak inductor current...
2
(max)
P P
OUT
PEAK
I
I
I
+
=
...and provide low core loss at the high switch-
ing frequency. Low cost powdered-iron cores
have a gradual saturation characteristic but can
introduce considerable AC core loss, especially
when the inductor value is relatively low and the
ripple current is high. Ferrite materials, although
more expensive, have an abrupt saturation char-
acteristic with the inductance dropping sharply
when the peak design current is exceeded. Nev-
ertheless, they are preferred at high switching
frequencies because they present very low core
loss while the designer is only required to
prevent saturation. In general, ferrite or
molypermalloy materials are a better choice for
all but the most cost sensitive applications.
Optimizing Efficiency
The power dissipated in the inductor is equal to
the sum of the core and copper losses. To mini-
mize copper losses, the winding resistance needs
to be minimized, but this usually comes at the
expense of a larger inductor. Core losses have a
more significant contribution at low output cur-
rent where the copper losses are at a minimum,
and can typically be neglected at higher output
currents where the copper losses dominate. Core
loss information is usually available from the
magnetics vendor. Proper inductor selection can
affect the resulting power supply efficiency by
more than 15%!
The copper loss in the inductor can be calculated
using the following equation:
WINDING
RMS
L
Cu
L
R
I
P
2
)
(
)
(
=
where I
L(RMS)
is the RMS inductor current that
can be calculated as follows:
I
L(RMS)
= I
OUT(max)
1 + 1
(
I
PP
)
2
3 I
OUT(max)
8
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
Output Capacitor Selection
The required ESR (Equivalent Series Resis-
tance) and capacitance drive the selection of the
type and quantity of the output capacitors. The
ESR must be small enough that both the resis-
tive voltage deviation due to a step change in the
load current and the output ripple voltage do not
exceed the tolerance limits expected on the
output voltage. During an output load transient,
the output capacitor must supply all the addi-
tional current demanded by the load until the
SP7655 adjusts the inductor current to the new
value.
In order to maintain V
OUT
,the capacitance must
be large enough so that the output voltage is held
up while the inductor current ramps to the value
corresponding to the new load current. Addi-
tionally, the ESR in the output capacitor causes
a step in the output voltage equal to the current.
Because of the fast transient response and inher-
ent 0% to100% duty cycle capability provided
by the SP7655 when exposed to an output load
transient, the output capacitor is typically cho-
sen for ESR, not for capacitance value.
The ESR of the output capacitor, combined with
the inductor ripple current, is typically the main
contributor to output voltage ripple. The maxi-
mum allowable ESR required to maintain a
specified output voltage ripple can be calculated
by:
R
ESR
V
OUT
I
PK-PK
where:
V
OUT
= Peak-to-Peak Output Voltage Ripple
I
PK-PK
= Peak-to-Peak Inductor Ripple Current
The total output ripple is a combination of the
ESR and the output capacitance value and can
be calculated as follows:
V
OUT
=
(
I
PP
(1 D)
)
2
+ (I
PP
R
ESR
)
2
C
OUT
F
S
F
S
= Switching Frequency
D = Duty Cycle
C
OUT
= Output Capacitance Value
Input Capacitor Selection
The input capacitor should be selected for ripple
current rating, capacitance and voltage rating.
The input capacitor must meet the ripple current
requirement imposed by the switching current.
In continuous conduction mode, the source cur-
rent of the high-side MOSFET is approximately
a square wave of duty cycle V
OUT
/V
IN
. More
accurately the current wave form is trapezoidal,
given a finite turn-on and turn-off, switch tran-
sition slope. Most of this current is supplied by
the input bypass capacitors. The RMS current
handling capability of the input capacitors is
determined at maximum output current and
under the assumption that the peak-to-peak in-
ductor ripple current is low, it is given by:
I
CIN(RMS)
= I
OUT(max)
D(1 - D)
The worst case occurs when the duty cycle D is
50% and gives an RMS current value equal to
I
OUT
/2.
Select input capacitors with adequate ripple
current rating to ensure reliable operation.
The power dissipated in the input capacitor is:
)
(
2
)
(
CIN
ESR
rms
CIN
CIN
R
I
P
=
This can become a significant part of power
losses in a converter and hurt the overall energy
transfer efficiency. The input voltage ripple
primarily depends on the input capacitor ESR
and capacitance. Ignoring the inductor ripple
current, the input voltage ripple can be deter-
mined by:
APPLICATIONS INFORMATION
2
)
(
)
(
(max)
)
(
IN
IN
S
OUT
I N
OUT
MAX
OUT
CIN
E SR
out
IN
V
C
F
V
V
V
I
R
I
V
-
+
=
9
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
APPLICATIONS INFORMATION
The capacitor type suitable for the output capac-
itors can also be used for the input capacitors.
However, exercise additional caution when tanta-
lum capacitors are used. Tantalum capacitors are
known for catastrophic failure when exposed to
surge current, and input capacitors are prone to
such surge current when power supplies are con-
nected "live" to low impedance power sources.
Although tantalum capacitors have been success-
fully employed at the input, it is generally not
recommended.
Loop Compensation Design
The open loop gain of the whole system can be
divided into the gain of the error amplifier,
PWM modulator, buck converter output stage,
and feedback resistor divider. In order to cross
over at the desired frequency cut-off (FCO), the
gain of the error amplifier compensates for the
attenuation caused by the rest of the loop at this
frequency. The goal of loop compensation is to
manipulate loop frequency response such that
its cross-over gain at 0db, results in a slope of -
20db/dec.
The first step of compensation design is to pick
the loop crossover frequency. High crossover
frequency is desirable for fast transient response,
but often jeopardizes the power supply stability.
Crossover frequency should be higher than the
ESR zero but less than 1/5 of the switching
frequency or 60kHz. The ESR zero is contrib-
uted by the ESR associated with the output
capacitors and can be determined by:
Z(ESR)
=
1
2
C
OUT
R
ESR
The next step is to calculate the complex conju-
gate poles contributed by the LC output filter,
P(LC)
=
1
2
L C
OUT
When the output capacitors are of a Ceramic
Type, the SP7655 Evaluation Board requires a
Type III compensation circuit to give a phase
boost of 180
in order to counteract the effects of
an underdamped resonance of the output filter at
the double pole frequency.
SP7655 Voltage Mode Control Loop with Loop Dynamic
(SRz2Cz2+1)(SR1Cz3+1)
(SR
ESR
C
OUT
+ 1)
[S^2LC
OUT
+S(R
ESR
+R
DC
) C
OUT
+1]
V
IN
SR1Cz2(SRz3Cz3+1)(SRz2Cp1+1)
V
RAMP_PP
V
OUT
(Volts)
+
_
V
REF
(Volts)
Notes: R
ESR
= Output Capacitor Equivalent Series Resistance.
R
DC
= Output Inductor DC Resistance.
V
RAMP_PP
= SP6132 Internal RAMP Amplitude Peak to Peak Voltage.
Condition: Cz2 >> Cp1 & R1 >> Rz3
Output Load Resistance >> R
ESR
& R
DC
R
2
V
REF
(R
1
+ R
2
)
or
V
OUT
V
FBK
(Volts)
Type III Voltage Loop
Compensation
G
AMP
(s) Gain Block
PWM Stage
G
PWM
Gain
Block
Output Stage
G
OUT
(s) Gain
Block
Voltage Feedback
G
FBK
Gain Block
Definitions:
R
ESR
= Output Capacitor Equivalent Series Resistance
R
DC
= Output Inductor DC Resistance
R
RAMP_PP
= SP7655 internal RAMP Amplitude Peak to Peak Voltage
Conditions:
C
Z
2 >> Cp1 and R1 >> Rz3
Output Load Resistance >>
R
ESR
and
R
DC
10
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
SP765X Thermal Resistance
The SP765X family has been tested with a
variety of footprint layouts along with different
copper area and thermal resistance has been
measured. The layouts were done on 4 layer
FR4 PCB with the top and bottom layers using
3 ounces of copper and the power and ground
layers using 1 ounce of copper.
For the Minimum footprint, only about 0.1 square
inch (of 3 ounces of) copper was used on the top
or footprint layer, and this layer had no vias to
connect to the 3 other layers. For the Medium
footprint, about 0.7 square inches (of 3 ounces
of) copper was used on the top layer, but vias
were used to connect to the other 3 layers. For
the Maximum footprint, about 1.0 square inch
(of 3 ounces of) copper was used on the top layer
and many vias were used to connect to the 3
other layers.
The results show that only about 0.7 square
inches (of 3 ounces of) copper on the top layer
and vias connecting to the 3 other layers are
needed to get the best thermal resistance of
36
C/W. Adding area on the top beyond the 0.7
square inches did not reduce thermal resistance.
SP765X Thermal Resistance
4 Layer Board:
Top Layer 3ounces Copper
GND Layer 1ounce Copper
Power Layer 1ounce Copper
Bottom Layer 3ounces Copper
Minimum Footprint: 44C/W
Top Layer: 0.1 square inch
No Vias to other 3 Layers
Medium Footprint: 36C/W
Top Layer: 0.7 square inch
Vias to other 3 Layers
Maximum Footprint: 36C/W
Top Layer: 1.0 square inch
Vias to other 3 Layers
APPLICATIONS INFORMATION
Using a minimum of 0.1 square inches of (3
ounces of) copper on the top layer with no vias
connecting to the 3 other layers produced a
thermal resistance of 44
C/W. This thermal
impedance is only 22% higher than the medium
and large footprint layouts, indicating that space
constrained designs can still benefit thermally
from the Powerblox family of ICs. This indi-
cates that a minimum footprint of 0.1 square
inch, if used on a 4 layer board, can produce
44
C/W thermal resistance. This approach is
still very worthwhile if used in a space con-
strained design.
The following page shows the footprint layouts
from an ORCAD file. The thermal data was
taken for still air, not with forced air. If forced
air is used, some improvement in thermal resis-
tance would be seen.
11
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
12
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
Bode Plot of Type III Error Amplifier Compensation.
CP1
RZ2
CZ2
-
+
6
5
VFB
COMP
+
- 0.8V
CF1
V
OUT
R1
68.1k, 1%
R
SET
CZ3
RZ3
R
SET
=54.48/ (VOUT -0.8) (k)
Type III Error Amplifier Compensation Circuit
APPLICATIONS INFORMATION
Frequency
(Hz)
Error Amplifier Gain
Bandwidth Product
Condition:
C22 >> CP1, R1 >> RZ3
20 Log (RZ2/R1)
Gain
(dB)
1/6.28(R22) (CZ2)
1/6.28 (R1) (CZ3)
1/6.28 (R1) (CZ2)
1/6.28 (RZ2) (CP1)
1/6.28 (RZ3) (CZ3)
13
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load at 3.3Vin
60
70
80
90
100
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Output Load (A)
Vout=2.5V
Vout=1.8V
Vout=1.2V
Efficiency vs Load at 5.0Vin
60
70
80
90
100
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Output Load (A)
Vout=3.3V
Vout=2.5V
Vout=1.8V
Vout=1.2V
Efficiency vs Load at 12Vin
60
70
80
90
100
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Output Load (A)
Vout=5.0V
Vout=3.3V
Vout=2.5V
Vout=1.8V
Vout=1.2V
Efficiency vs Load at 24Vin
60
70
80
90
100
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
Output Load (A)
Vout=12V
Vout=5.0V
Vout=3.3V
Vout=2.5V
14
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
TYPICAL PERFORMANCE CHARACTERISTICS
SP7655 Effi. v.s Iout Plots @
Vin=12V, and Vout=3.3V
83.0
84.0
85.0
86.0
87.0
88.0
89.0
90.0
91.0
92.0
1
2
3
4
5
6
7
8
Load Current (A)
Efficiency (%)
SP7655 Vout v.s Iout Plots @
Vin=12V, and Vout=3.3V
3.3
3.31
3.32
3.33
3.34
0
1
2
3
4
5
6
7
8
Load Current (A)
Output Voltage (V)
SP7655 Effi. v.s Iout Plots @
Vin=12V, and Vout=5.0V
82.0
84.0
86.0
88.0
90.0
92.0
94.0
96.0
1
2
3
4
5
6
7
8
Load Current (A)
Efficiency (%)
SP7655 Vout v.s Iout Plots @
Vin=12V, and Vout=5.0V
4.9600
4.9700
4.9800
4.9900
5.0000
0
1
2
3
4
5
6
7
8
Load Current (A)
Output Voltage (V)
15
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
PACKAGE: 26 PIN DFN
TOP VIEW
D
E
(7 x 4 mm)
Pin #1
Identification
Note: Fused Pin Area for pins 1-3 and
pins 14-16 = (2e+b)xL - 2x(e-b) x L/2
= 0.376mm
2
or 0.0148 in
2
BOTTOM VIEW
A
SIDE VIEW
A3
A1
(K)
b
e
L
E2
D3
D2
D2
J
J1
J1
5 4 3 2 1
1 4 1 5 1 6 1 7 1 8
1 3
2 6
L/2
L
SYMBOL
MIN
NOM
MAX
MIN
NOM
MAX
A
0.800
0.900
1.000
0.0315
0.0354
0.0394
A1
0.000
-
0.050
0.0000
-
0.0020
A3
0.178
0.203
0.228
0.0070
0.0080
0.0090
b
0.170
0.220
0.270
0.0067
0.0087
0.0106
D
6.950
7.000
7.050
0.2736
0.2756
0.2776
D2
2.000
2.050
2.100
0.0787
0.0807
0.0827
D3
1.780
1.830
1.880
0.0701
0.0720
0.0740
e
E
3.950
4.000
4.050
0.1555
0.1575
0.1594
E2
2.730
2.780
2.830
0.1075
0.1094
0.1114
J
0.200
0.250
0.300
0.0079
0.0098
0.0118
J1
0.250
0.300
0.350
0.0098
0.0118
0.0138
K
0.340
0.390
0.440
0.0134
0.0154
0.0173
L
0.350
0.400
0.450
0.0138
0.0157
0.0177
26 Pin DFN
Dimensions in Millimeters:
Controlling Dimension
Dimensions in Inches
Conversion Factor:
1 Inch = 25.40 mm
SIPEX Pkg Signoff Date/Rev: JL Feb16-06 / RevB
0.500 BSC
0.0197 BSC
16
Date: 2/17/06
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator Copyright 2006 Sipex Corporation
ORDERING INFORMATION
Part Number
Temperature
Package
SP7655ER .............................................. -40C to +85C ................................. 26 Pin 7 X 4 DFN
SP7655ER-L ........................................... -40C to +85C ............. (Lead Free) 26 Pin 7 X 4 DFN
SP7655ER/TR ........................................ -40C to +85C ................................. 26 Pin 7 X 4 DFN
SP7655ER-L/TR ..................................... -40C to +85C ............. (Lead Free) 26 Pin 7 X 4 DFN
Bulk Pack minimum quantity is 500.
/TR = Tape and Reel. Pack quantity is 3,000 DFN.
Sipex Corporation
Headquarters and
Sales Office
233 South Hillview Drive
Milpitas, CA 95035
TEL: (408) 934-7500
FAX: (408) 935-7600
Solved By Sipex
TM
Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the
application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others.
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