ANPEC APW1172KAC-TU

APW1172
2.5A SWITCH STEP DOWN SWITCHING REGULATOR
Features
General Description
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The APW1172 is a step down monolithic power
switching regulator with a switching current limit of
3.8A so it is able to deliver more than 2.5A DC current
to the load depending on the application conditions.
The output voltage can be set from 1.235V to 22V.The
high current level is also achieved utilize an SO8
package with exposed pad frame. The type of package
allows to re-duce the Rth (j-amb) down to approximately
45°C/W.
An internal oscillator fixes the switching frequency at
250KHz.
Having a minimum input voltage of 4.8V only, it is
particularly suitable for 5V bus, available in all computer
related applications.
Pulse by pulse current limit with the internal frequency
modulation offers an effective constant current short
circuit protection.
2.5A Internal Switch
Operating Input Voltage from 4.8V to 22V
3.3V ±2% Reference Voltage
Output Voltage :
APW1172 - adjustable from 1.235V to 20V
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Low Dropout Operation: 100% Duty Cycle
250KHz Internally Fixed Frequency
Voltage Feed-Forward
Zero Load Current Operation
Internal Current Limit
Inhibit for Zero Current Consumption
Synchronization
Protection Against Feedback Disconnection
Thermal Protection
External Soft-Start
Pin Description
Over-Voltage Protection
Lead Free Available (RoHS Compliant)
Applications
•
Consumer: STB, DVD, TV, VCR, Car Radio,
LCD monitors
•
•
OUT
1
8
VCC
SYNC
2
7
GND
INH
3
6
VREF
COMP
4
5
FB
Networking: XDSL, Modems, DC-DC Modules
SOP-8-P (Top View)
Computer: Printers, Audio/Graphic Cards,
Optical Storage, Hard Disk Drive
•
= Thermal Pad
(connected to GND plane for better heat
dissipation)
Industrial: Chargers, Car Battery DC-DC
Converters
ANPEC reserves the right to make changes to improve reliability or manufacturability without notice, and advise
customers to obtain the latest version of relevant information to verify before placing orders.
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
1
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APW1172
Ordering and Marking Information
Package Code
KA : SOP-8-P
Operating Ambient Temp. Range
C : 0 to 70 ° C
I : -40 to 85 ° C
Handling Code
TU : Tube
TR : Tape & Reel
Lead Free Code
L : Lead Free Device
Blank : Orginal Device
APW1172
Lead Free Code
Handling Code
Temp. Range
Package Code
APW1172
XXXXX
APW1172 KA :
XXXXX - Date Code
Note: ANPEC lead-free products contain molding compounds/die attach materials and 100% matte tin plate
termination finish; which are fully compliant with RoHS and compatible with both SnPb and lead-free soldiering
operations. ANPEC lead-free products meet or exceed the lead-free requirements of IPC/JEDEC J STD-020C
for MSL classification at lead-free peak reflow temperature.
Block Diagram
VREF
VC C
VREF
Buffer
Voltages
Monitor
Thermal
Protection
COMP
Peak to Peak
Current Limit
FB
E/A
Driver
PWM
V REF =1.235V
D
OVP
Oscillator
1.25V REF
Q
Ck
Frequency
Shifter
SYNC
OUT
Inhibit
GND
INH
Absolute Maximum Ratings
Symbol
VCC
VOUT
Parameter
Input voltage (VCC to GND)
Output DC voltage
Value
Unit
25
-1 to 25
V
V
-0.7 ~ VCC
V
VIO
COMP and FB to GND
IOUT
Output current
0 to current limit
A
VREF
VREF to GND
3.3
V
PD
Average Power Dissipation, TA < 50°
2.2
W
TJ
Junction Temperature
150
°C
TSTG
Storage Temperature
-65 ~ 150
°C
TSDR
Soldering Temperature, 10 seconds
300
°C
VESD
Minimum ESD rating (Human body mode)
±3
KV
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
2
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APW1172
Pin Function Description
No.
PIN
Description
1
OUT
2
SYNC
3
INH
4
COMP
5
FB
6
VREF
3.3V reference voltage output, no Capacitor Is requested for stability.
7
GND
Ground.
8
VCC
Unregulated DC input voltage.
Regulator Output.
Master/Slave synchonization.
A logical signal (active high) disables the device. If INH not used the pin must be
connected to GND. When it is open an internal pull-up disable the device.
E/A output for frequency compensation.
Feedback input. Connecting directly to this pin results in an output voltage of
1.235V(APW1172). An external resistive divider is required for higher output
voltages.
Thermal Characteristics
Symbol
θJA
Parameter
Junction to ambient thermal resistance in free air
Value
Unit
45.7
°C/W
* The area of the thermal pad is 4.5mm X 2mm and the GND plane is 60mm X 60mm. Connect the thermal
pad and the GND plane by 8 vias. TA=25°C.
Electrical Characteristics
The * denotes the specifications that apply over TA = -40 ~ 85oC. Typical values are at TA = 25oC.
VCC = 12V unless otherwise specified.
Symbol
Parameter
APW1172
Test condition
Min
VCC
V UVLO
Operating input voltage range V O = 1.235V; I O = 2A
*
4.7
UVLO threshold voltage
*
3.8
V CC rising
Hysteresis
Dropout voltage
V CC = 4.8V; IO = 2A
*
ILIM
Maximum limiting current
V CC = 4.8V to 22V
*
Switching frequency
Main design
*
Duty cycle
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
4.2
Unit
Max
22
V
4.6
V
0.3
Vd
fs
Typ
1.0
1.2
V
3.3
3.8
4.3
A
200
250
300
205
250
295
0
3
V
100
KHz
%
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APW1172
Electrical Characteristics (Cont.)
The * denotes the specifications that apply over TA = -40 ~ 85oC. Typical values are at TA = 25oC.
VCC = 12V unless otherwise specified.
Symbol
Parameter
APW1172
Test condition
Unit
Min
Typ
Max
1.22
1.235
1.25
Dynamic Characteristics
VFB
η
Voltage feedback
APW1172
4.8V < VCC < 22V, 20Ma < IO < 2A
Efficiency
VO = 5V, VCC = 12V, IOUT = 1A
* 1.198 1.235 1.272
84
V
%
DC Characteristics
Iqop
Iq
Total Operating Quiescent Current
Quiescent Current
Iqst-by Total Stand-by Quiescent Current
*
Duty Cycle = 0; VFB = 1.5V
12
mA
10
mA
VINH > 2.2V
*
50
100
µA
VCC = 22V; VINH > 2.2V
*
80
150
µA
Inhibit
VINH
INH Threshold Voltage
Device ON
1.1
1.3
1.5
V
Device OFF
1.2
1.4
1.6
V
INH Pull-Up Current
VINH < 3V
1
µA
Maximum INH Voltage
IINH = 0A
4.3
V
3.8
V
Error Amplifier
VOH
High Level Output Voltage
VFB = 1V
VOL
Low Level Output Voltage
VFB = 1.5V
IO source Source Output Current
IO sink Sink Output Current
IFB
gm
3.5
0.4
VCOMP = 1.9V; VFB = 1V
VCOMP = 1.9V; VFB = 1.5V
V
200
300
µA
1
1.5
mA
4
µA
Source Bias Current
VFB = 1.5V
2.5
Maximum FB Voltage
IFB = 0µA
2.1
V
Trans-conductance
VFB = 1.255V to 1.215V, ICOMP =
-0.1mA to 0.1mA VCOMP = 1.9V
2.3
mA/V
SYNC Function
High Input Voltage
VCC = 4.8 to 22V
Low Input Voltage
VCC = 4.8V to 22V
2.5
VREF
V
0.74
V
VSYNC = 0.74V
0.11
0.25
VSYNC = 2.33V
0.21
0.45
Master Output Amplitude
ISOURCE = 3mA
2.75
3
V
Output Pulse Width
No load, VSYNC = 1.65V
0.2
0.35
µs
Slave Sink Current
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
4
mA
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APW1172
Electrical Characteristics (Cont.)
The * denotes the specifications that apply over TA = -40 ~ 85oC. Typical values are at TA = 25oC.
VCC = 12V unless otherwise specified.
Symbol
Parameter
APW1172
Test condition
Unit
Min
Typ
Max
3.234
3.3
3.366
V
3.2
3.3
3.399
V
Reference Section
IREF = 0mA
VREF
VREF Output Voltage
IREF = 0mA to 5mA, VCC = 4.4A to
*
22V
Line Regulation
IREF = 0mA, VCC = 4.4A to 22V
5
10
mV
Load Regulation
IREF = 0mA to 5mA
8
15
mV
18
30
mA
Short Circuit Current
10
Other
Thermal Limiting Protection
160
°C
Hysteresis
30
°C
Over-Voltage Protection
Threshold Voltage
VCOMP = 0.8V
*
120
125
130
%
Typical Application Circuit
VREF = 3.3V
VOUT = 3.3V
L
22uH
1
2
3
4
COUT
100uF
D1
1N5819
RC1
4.3K
D2
1N4148
CC2
220pF
Rev. A.4 - Aug., 2005
VCC
SYNC
GND
INH
VREF
COMP
FB
8
7
6
5
APW1172
C1
1uF
CC1
2.2nF
Copyright  ANPEC Electronics Corp.
OUT
R1
137K
RF2
3.3K
RF1
5.6K
CIN
22uF
VIN
4.8V to 22V
Soft Start
Circuit
5
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APW1172
Other Application Circuits
Dual output voltage application
VOUT2 = 5V
N1/N2=2
VOUT1 = 3.3V
1N4148
VREF = 3.3V
1
2
L
22uH
RF1
5.6K
3
RF2
3.3K
GND
VREF
COMP
RC1
4.3K
D1
1N5819
COUT1
100uF
VCC
SYNC
INH
4
COUT2
47uF
OUT
FB
8
7
6
5
APW1172
CIN
22uF
CC1
2.2nF
VIN =5V
CC2
220pF
BuckBoost regulator
VREF = 3.3V
VOUT = -12V
L
15uH
1
2
D1
1N5819
RF2
24K
RF1
2.7K
COUT
100uF
3
4
RC1
4.3K
CC1
2.2nF
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
OUT
SYNC
INH
COMP
VCC
GND
VREF
FB
8
7
6
5
APW1172
CIN2
CIN1
22uF25V 22uF
VIN=5V
CC2
220pF
6
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APW1172
Typical Operating Characteristics
Line regulation of VREF
Load regulation of VREF
12
0
-2
Load regulation (mV)
Line regulation (mV)
10
8
6
4
-4
-6
-8
-10
-12
2
-14
0
-16
-50
-25
0
25
50
75
100
125
-50
Junction Temperature (o C)
-25
0
25
50
75
100
125
100
125
Junction Temperature (o C)
Short circuit current of VREF
VREF
3.40
0
3.38
-2
3.34
-6
3.32
VREF (V)
Short circuit current (mA)
3.36
-4
-8
-10
3.30
3.28
3.26
-12
3.24
-14
3.22
-16
3.20
-50
-25
0
25
50
75
100
125
-50
Junction Temperature (o C)
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
-25
0
25
50
75
Junction Temperature (o C)
7
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APW1172
Typical Operating Characteristics (Cont.)
Source ability of EA
Sink ability of EA
0.0
300
-0.5
Sink current (mA)
Source current (uA)
250
200
150
100
-1.0
-1.5
-2.0
50
-2.5
0
-50
-25
0
25
50
75
100
-50
125
-25
0
25
50
75
100
Junction Temperature (o C)
Junction Temperature (o C)
Quiescent current
Quiescent standby current
12
125
90
VCC=12V
80
10
VCC=12V
70
60
VCC=5V
Iqst-by (V)
IQ (mA)
8
6
4
50
40
30
VCC=5V
20
2
10
0
0
-50
-25
0
25
50
75
100
125
-50
o
Junction Temperature ( C)
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
-25
0
25
50
75
100
125
o
Junction Temperature ( C)
8
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APW1172
Typical Operating Characteristics (Cont.)
Efficiency vs. Output Current at VIN=5V
Efficiency vs. Output Current at VIN=12V
80%
86%
84%
78%
82%
76%
80%
74%
Efficiency (%)
78%
Efficiency (%)
72%
70%
68%
66%
76%
74%
72%
70%
VO=2.5V
68%
VO=3.3V
VO=5V
66%
64%
VO=1.8V
VO=2.5V
VO=3.3V
64%
62%
62%
60%
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6
60%
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6
Output Current (A)
Output Current (A)
VCE vs. ICE
VFB vs. Temperature
1.5
1.241
1.240
1.4
1.239
1.3
VIN=5V
1.238
1.237
VFB (V)
VCE (V)
1.2
1.1
1.0
VIN=12V
1.236
1.235
1.234
0.9
1.233
0.8
1.232
0.7
1.231
0.0
0.5
1.0
1.5
2.0
2.5
3.0
-50
Rev. A.4 - Aug., 2005
0
25
50
75
100
125
o
ICE (A)
Copyright  ANPEC Electronics Corp.
-25
Junction Temperature ( C)
9
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APW1172
Typical Operating Characteristics (Cont.)
Switching Frequency
Switching Frequenct (KHz)
258
256
254
252
250
248
246
244
-50
-25
0
25
50
75
100
125
Junction Temperature (o C)
Operating waveforms
1. Power ON (no SS) :
- VIN = 12V,VOUT = 3.3V
- CIN = 22µF, COUT = 220µF, L = 15 µH
2. Power ON (external SS) :
- VIN = 12V,VOUT = 3.3V
- CIN = 22µF, COUT = 220µF, L = 15 µH
IL
IL
V OUT
V IN
V OUT
COMP
COMP
Ch1 : VOUT,1V/div
Ch1 : VOUT,1V/div
Ch2 : COMP,2V/div
Ch2 : COMP,2V/div
Ch3 : VIN,5V/div
Ch3 : VIN,5V/div
Ch4 : IL,2A/div
Ch4 : IL,2A/div
Time : 400us/div
Time : 1ms/div
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
V IN
10
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APW1172
Operating waveforms (Cont.)
3. Current Limit :
- VIN = 12V,VOUT = 3.3V
- CIN = 22µF, COUT = 220µF, L = 15 µH
4. Load Transient :
- VIN = 12V,VOUT = 3.3V
- CIN = 22µF, COUT = 220µF, L = 15 µH
IOUT
IOUT
V OUT
V OUT
COMP
Ch1 : VOUT,2V/div
Ch1 : VOUT,200mV/div,offset 3.3V
Ch2 : COMP,2V/div
Ch2 : IOUT,1A/div,100mA-3A
Ch3 : IOUT,2A/div
Ch2 rising time : 4us
Time : 2ms/div
Ch2 falling time : 4us
Time : 10us/div
Functional Description
Power-On-Reset
A Power-On-Reset circuit monitors input voltages at
VCC pin to prevent wrong logic controls. The POR
function initiates immediately by the inductor current
with it’s limit after the supply voltage exceed firstly it’s
threshold voltage after powering on.
comparator and compared with internal saw tooth wave.
It generates a PWM control signal by the PWM
comparator. The PWM signal feeds into the logic circuit
and turns on or off the pass element. The Buck type
output stage regulates the correct output voltage
depends on the previous mechanism.
Output Voltage Regulation
Current Limit
An error amplifier working with a temperature-compensated 1.235V reference. The error amplifier designed
with high bandwidth and DC gain provides very fast
transient response and less load regulation. It compares
the reference with the feedback voltage and amplifies
the difference in it’s output called error signal. The
error signal feeds into the input terminal of PWM
The APW1172 monitors the current flow through the
pass element and limits the maximum output current
to prevent damages during overload or short-circuit
conditions.
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
Over-Voltage Protection (OVP)
The over voltage protection is realized by using an
11
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APW1172
Functional Description (Cont.)
Over-Voltage Protection (OVP) (Cont.)
current limit function acting and VOUT dropping. This
results the switching frequency decreased. In the practical application, when the load current increase big
enough such that current limit occurring. In this
situation,more load current cause the output voltage
get away the regulatory point and begin dropping until
it’s limitation. In this time, the actual duty was very
small in general. But the on time period limited by the
minimum on time limitation of the control circuit. This
on time limitation induce the load current runs away
the limiting boundary. To prevent this drawback, the
frequency fold back is used to ensure that load current was limited by the setup value.
internal comparator. The input of the OVP comparator
connects to the feedback, that turns off the pass
element when the OVP threshold is reached. This
threshold is typically 25% higher than the feedback
voltage.
Thermal protection
The thermal protection function generates a control
signal to shut off the APW 1172. It prevents the
damages caused by over heat situation. The thermal
function was acted when the temperature of chip
reaching 160°C. A hysteresis of the thermal protection
function is approximately 30°C, in order to avoid pass
element turns on and off immediately.
Inhibit Function
The Inhibit function disables when the Inhibit voltage
lower than 1.3V. APW1172 entered the standby mode
with Inhibit voltage higher than 1.4V. The quiescent
current in the standby mode is less than 100uA to
saving power. If the Inhibit pin left floating, the Inhibit
voltage will be pull up by internal current source.
Voltage Feed Forward
The Voltage Feed Forward is acting when VCC goes
higher than 10V. This will increases the upper bond of
the internal sawtooth wave and results duty keeping
constant. The change of the upper bond is linear and
proportion with VCC.
Frequency Fold Back
The Frequency Fold Back function acts when both the
Application Description
Input Capacitor
necessary t o use low-ESR capacitors. More
capacitance reduce the variations of the input voltage
of VCC pin.
The APW1172 requires proper input capacitors to supply current surge during stepping load transients to
prevent the input rail from dropping.Due to the wide
range of input voltage, the input capacitor must be
able to support the input operating voltage. Ultra-lowESR capacitors, such as ceramic chip capacitors,
are very good for the input capacitors. An aluminum
electrolytic capacitor(>100µF, ESR<300mΩ) is
recommended as the input capacitor. It is not
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
Inductor
Inductor is an important component in the application.
In the switching regulator, energy stored in the
inductor by magnetic field when the pass element
conducting. This behavior cause the ripple current
cycle by cycle, the ripple current flowing through the
12
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APW1172
Application Description (Cont.)
Inductor (Cont.)
dimension of inductor to save the board space. In
other way, devote the performance by higher ripple
current. If select a greater inductor, the ripple current
will be smaller and a better performance is got. This
tradeoff is an useful method to decide a better
performance or a smaller inductor size.
output capacitor induce the output ripple voltage. In
general, the ripple current is usually fixed at 20%~40%
of maximum output current,that is 0.6A~1.2A with
maximum output current equal 3A. The value of
inductor can approximate by (1)
L=
VIN − VCE − VO
Ton
∆I
Output Capacitor
(1)
The APW1172 requires a proper output capacitor to
maintain stability and improve transient response over
temperature and current. The output capacitor
selection is dependent upon ESR (equivalent series
resistance) and capacitance of the output capacitor
over the operating temperature.
Where VIN is the input voltage, VCE is the voltage
across the pass element when it conduct, VO is the
output voltage, ∆I is the ripple current flowing through
the inductor and Ton is the on period that determined
by VO and VIN. The exact Ton can obtained by (2) and(3)
D=
VO + VD
VIN − VCE + VD
Consider the output ripple voltage that absorbed in
the application.Output ripple voltage consist of two
parts.It show as (4)
(2)
Where VD is the forward voltage of the wheeling diode.
Ton = DTS
(3)
Vripple = V1 + V2
Where TS is the period of whole cycle. It equal 1/FS
where FS is the switching frequency of APW1172. For
example, VIN = 12V, VO = 3.3V, VD = 0.7V, IO = 3A,
ripple current is IO (20%~40%) = 0.6A ~ 1.2A, VCE
=1.2V, FS = 250KHz
D=
3.3V + 0.7V
= 34.78%
12V − 1.2V + 0.7V
In previously,use the parameter ∆I to decide the value of
the inductor. As the same manner,use the parameter ∆I
to approximate the value of output capacitor.
The first part of output ripple voltage,V1,is related to
the ESR of output capacitor.It show as (5)
V1 = ESR × ∆I
by (2)
For the worst case ripple current equal 0.6A ~ 1.2A
V2 =
12V − 1.2V − 3.3V
L1 =
1.3912µs = 17.39µH
0.6 A
L2 =
by (1)
Use the worst case to approximate the minimum value
of inductor. In worst ripple current condition, smaller
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
∆I
TS
8C
(6)
These two parameters determine the value of output
ripple voltage and the efficiency. More output ripple
voltage cause the efficiency decreased.The output
ripple voltage means the energy loss in the ESR and
the energy loss in the transition path while the energy
stored and removed in the output capacitor.In other
aspect,the ESR and the value of output capacitor
by (1)
12V − 1.2V − 3.3V
1.3912µs = 8.695µH
1. 2 A
for ripple current is 1.2A… …
(5)
The second part of output ripple voltage,V2,can
calculated by (6)
Ton = DTS = 34.78% × 4µs = 1.3912µs by (3)
for ripple current is 0.6A… …
(4)
13
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APW1172
Application Description (Cont.)
PD = VD × I D × (1 − D )
Output Capacitor (Cont.)
generate a zero to provide a positive phase for control
loop.This zero improved the stability without extra PID
compensator, if the zero is lower enough.
Where VD is the forward voltage of the wheeling diode,
ID is current flowing through the wheeling diode when
it conducting. In the PCB layout,usually place the
wheeling diode near the APW1172, the power
dissipation of wheeling diode will increase the ambient
temperature and limit the maximum power dissipation
of APW1172.These power dissipations are the major
energy loss in the voltage conversion.
Switch diode
APW1172 is an non-synchronous type buck regulator
and needs a Shottky diode as the wheeling diode.
This diode will conduct when the pass element turned
off.Current flows through the diode in the conducted
period, the order of the maximum peak current
reaches few Amperes. The diode requires the ability
to flow the great forward current. The peak forward
current of the diode denote in the specification must
great than 15A, and the conducting time in this
situation must great than 8ms. 1N5818 is a suitable
component.
To improve the thermal resistance by increasing
copper area is a suitable method. Design a copper
area according to the following curve to improve the
thermal resistance.
APW1172 is a switching regulator whose pass element
inside, it have the ability to provide 3 Amperes.As the
show in the block diagram, the structure of the pass
element consist of a NPN and a PNP transistors. The
voltage across the pass element, VCE, is about 0.8V
to 1.3V in the light load to heavy load. The product of
VCE and IL, where IL is current flowing through the
inductor, generate thermal cause the junction
temperature increased. The thermal stream conduct
via the thermal pad of SOP-8-P to the printed circuit
board.The power dissipation of APW1172 can be
approximated by (7)
44
42
40
38
36
34
32
30
0
2
4
6
8
10
12
Top Copper Area (cm^2)
Frequency Compensation
In the Buck converter,there is a LPF (Low Pass Filter)
in the output stage to filtering the switching noise.
The LPF consist of an inductor and a capacitor. These
two components generate the double poles in the
frequency domain.
P = (VCE × I L × D) + (VIN × I L × FS )(TR + TF ) (7)
Where VCE is the voltage across the pass element, IL
is the current flowing through the inductor, D is the
duty. TR and TF are the transition time.
f natural =
The wheeling diode is another thermal source. It’s
power dissipation approximated by (8)
Rev. A.4 - Aug., 2005
46
to Ambient ( o C/W)
Thermal Resistance of Junction
48
Thermal Consideration
Copyright  ANPEC Electronics Corp.
(8)
1
2π LC
(9)
Where L is the inductance of the LPF and C is the
capacitance of the output capacitor. These double poles
14
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APW1172
Application Description (Cont.)
L
VOUT
Frequency Compensation (Cont.)
cause the phase decrease rapidly at the natural
frequency and lead the phase margin not enough to
maintain the stable status. The stable issue improved
by apply a zero in the frequency domain to increase
the phase margin.
ESR
Loading
COUT
C e r a m ic
type
FB PIN
EA
Consider the Figure-2, find the transfer function H (s)
as:
COMP PIN
H (s) =
1.235V
RC1
pole1, 2 =
CC2
CC1
zero1 =
Adding a resistor and a capacitor at the COMP pin is
the simplest way to generate a zero. The placement
of the components is the show of Figure-1. The
frequency of the zero is
f zero =
1
2πRC1CC1
Q=
(10)
CC 2
0db
(12)
In the other applications, use the ceramic capacitor
as the output capacitor is very popular. Because the
small dimension of the ceramic capacitor save the PCB
(Printed Circuit Board) area, the low ESR (Equivalent
Series Resistance) of the ceramic one decrease the
power dissipation of the output capacitor. But the
serious drawbacks of the ceramic one is the stable
issue.
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
2π LCOUT
1
2π( ESR)COUT
L
1
( ESR) COUT
The frequency response of the output stage show as
Figure-3.
(11)
Locate the zero before the natural frequency to
compensate the phase. The another capacitor CC2 used
to bypass the noise. In general
1
= CC1
10
1
The pole1 and pole2 are the conjugate roots of the
denominator and the zero1 is the root of the numerator.
Find the Q factor from the quadratic function and the
description of Q factor as above.
The relation of the zero and the natural frequency is
f zero = 0.8 ⋅ f natural
SCOUT ( ESR) + 1
S LCOUT + SCOUT ( ESR) + 1
2
slope=-40db/
decade
0d
phase
-90d
-135d
-180d
f
Pole1,2
Zero1
Figure-3
15
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APW1172
Application Description (Cont.)
Frequency Compensation (Cont.)
sented as Figure-5:
The problem is the phase nearly –180 degrees at the
natural frequency especially in the high Q situation. If
the Q factor is high, the phase decrease vary sharp at
the location of the double poles. This problem leads
the regulator oscillating when use ceramic one as the
output capacitor without compensation. The purpose
of the compensation is saving the phase. The manner
is added additional zeros to achieve the goal. A zero
have the ability that contribute the maximum phase of
90 degrees. According this characteristic, needs two
zeros to compensate the phase loss. The PID compensator is good for this.It shows as Figure-4.
0db
slope=-20db/
decade
270d
phase
180d
90d
45d
0d
f
C3
Zero2
Zero3 Pole3 Pole4
Figure-5
C2
R2
The assumption is 10(zero2)<zero3,10(zero3)<pole3,
10(pole3)<pole4.In order to compensate the phase,
place the two zeros closely and located before the
natural frequency. In general
R3
C1
FB
R1
zero 2 ≅ zero3 = k ⋅ pole1, 2
EA
(11)
COMP
Where k is a constant, the value of k is almost 0.7 to
0.8.
The useful rules are:
(1) Determine the value of C2,the value must smaller
than 5nF to get fast response time.
(2) Find R3 by the equation
Vref
Figure-4
The transfer function H(s) is
H ( s) =
(SC2 R3 + 1)[SC1 (R1 + R2 ) + 1]
S (SC1R2 + 1)[SC2C3 R3 + (C2 + C3 )]
zero2 =
R3 = (2π ⋅ C2 ⋅ k ⋅ pole1, 2 ) −1
1
2π ⋅ C2 R3
(3) Determine the value of C1 from 470pF to 1uF. This
range of C1 is for reference.
(4) The range of pole3 is from 150KHz to 300KHz.
Use this range to find the value of R2.
(5) Find R1 by the equation
1
zero3 =
2π ⋅ C1 ( R1 + R2 )
1
2π ⋅ C1R2
C2 + C3
pole4 =
2π ⋅ C2C3 R3
pole3 =
R1 = (2π ⋅ C1 ⋅ k ⋅ pole1,2 ) −1 − R2
(6) The location of pole4 is 5 times pole3. Use this
result to find the value of R3.
The frequency response of the PID compensator pre-
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
16
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APW1172
Layout Consideration
1. Please solder the Exposed Pad on the PCB.The heat generated by the power consumption will conduct by
the thermal pad.
2. Please place the input capacitors for VCC pin nearly as close as possible.
3. Connect the switching inductor and the Schottky diode and OUT pin by a wide track.
4. Place the output capacitor close to the inductor as possible and with a wide and short track.
5.The thermal pad is needed to improve the power dissipation.
V R E F = 3.3V
V OUT = 3.3V
1
L
22uH
2
3
4
COUT
100uF
D1
1N5819
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
V CC
SYNC
GND
INH
COMP
VREF
FB
8
7
6
5
APW1172
R C1
4.3K
CC1
2.2nF
OUT
R F1
5.6K
R F2
3.3K
C IN
22uF
V IN
4.8V to 22V
C C2
220pF
17
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APW1172
Packaging Information
E1
E
0.015X45
SOP-8-P pin ( Reference JEDEC Registration MS-012)
H
D1
e1
e2
D
A1
A
L
0.004max.
Dim
1
Millimeters
Inches
Min.
Max.
Min.
Max.
A
A1
1.35
0
1.75
0.15
0.053
0
0.069
0.006
D
D1
4.80
5.00
0.189
0.197
E
E1
3.80
4.00
0.150
H
L
5.80
0.40
6.20
1.27
0.228
0.016
0.244
0.050
e1
e2
0.33
0.51
0.013
0.020
3.00REF
2.60REF
φ1
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
0.118REF
0.157
0.102REF
1.27BSC
0.50BSC
8°
8°
18
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APW1172
Physical Specifications
Terminal Material
Lead Solderability
Solder-Plated Copper (Solder Material : 90/10 or 63/37 SnPb), 100%Sn
Meets EIA Specification RSI86-91, ANSI/J-STD-002 Category 3.
Reflow Condition
(IR/Convection or VPR Reflow)
tp
TP
Critical Zone
T L to T P
Temperature
Ramp-up
TL
tL
Tsmax
Tsmin
Ramp-down
ts
Preheat
25
t 25 °C to Peak
Time
Classification Reflow Profiles
Profile Feature
Average ramp-up rate
(TL to TP)
Preheat
- Temperature Min (Tsmin)
- Temperature Max (Tsmax)
- Time (min to max) (ts)
Time maintained above:
- Temperature (T L)
- Time (tL)
Peak/Classificatioon Temperature (Tp)
Time within 5°C of actual
Peak Temperature (tp)
Ramp-down Rate
Sn-Pb Eutectic Assembly
Pb-Free Assembly
3°C/second max.
3°C/second max.
100°C
150°C
60-120 seconds
150°C
200°C
60-180 seconds
183°C
60-150 seconds
217°C
60-150 seconds
See table 1
See table 2
10-30 seconds
20-40 seconds
6°C/second max.
6°C/second max.
6 minutes max.
8 minutes max.
Time 25°C to Peak Temperature
Note: All temperatures refer to topside of the package .Measured on the body surface.
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
19
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APW1172
Classification Reflow Profiles(Cont.)
Table 1. SnPb Entectic Process – Package Peak Reflow Temperature s
Package Thickness
Volume mm 3
Volume mm 3
<350
≥350
<2.5 mm
240 +0/-5°C
225 +0/-5°C
≥2.5 mm
225 +0/-5°C
225 +0/-5°C
Table 2. Pb-free Process – Package Classification Reflow Temperatures
3
3
3
Package Thickness
Volume mm
Volume mm
Volume mm
<350
350-2000
>2000
<1.6 mm
260 +0°C*
260 +0°C*
260 +0°C*
1.6 mm – 2.5 mm
260 +0°C*
250 +0°C*
245 +0°C*
≥2.5 mm
250 +0°C*
245 +0°C*
245 +0°C*
*Tolerance: The device manufacturer/supplier shall assure process compatibility up to and
including the stated classification temperature (this means Peak reflow temperature +0°C.
For example 260°C+0°C) at the rated MSL level.
Reliability test program
Test item
SOLDERABILITY
HOLT
PCT
TST
ESD
Latch-Up
Method
MIL-STD-883D-2003
MIL-STD-883D-1005.7
JESD-22-B, A102
MIL-STD-883D-1011.9
MIL-STD-883D-3015.7
JESD 78
Description
245°C , 5 SEC
1000 Hrs Bias @ 125 °C
168 Hrs, 100 % RH , 121°C
-65°C ~ 150°C, 200 Cycles
VHBM > 2KV, VMM > 200V
10ms , Itr > 100mA
Carrier Tape
t
D
P
Po
E
P1
Bo
F
W
Ko
Ao
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
D1
20
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APW1172
Carrier Tape(Cont.)
T2
J
C
A
B
T1
Application
SOP-8-P
A
330±1
Application
SOP-8-P
F
5.5 ± 0.1
B
62 ± 1.5
C
12.75 +
0.1 5
J
2 + 0.5
D
D1
Po
1.55±0.1 1.55+ 0.25 4.0 ± 0.1
T1
12.4 +0.2
T2
2± 0.2
P1
Ao
2.0 ± 0.1 6.4 ± 0.1
W
12 + 0.3
- 0.1
Bo
5.2± 0.1
P
8± 0.1
E
1.75± 0.1
Ko
t
2.1± 0.1 0.3±0.013
(mm)
Cover Tape Dimensions
Application
SOP- 8-P
Carrier Width
12
Cover Tape Width
9.3
Devices Per Reel
2500
Customer Service
Anpec Electronics Corp.
Head Office :
5F, No. 2 Li-Hsin Road, SBIP,
Hsin-Chu, Taiwan, R.O.C.
Tel : 886-3-5642000
Fax : 886-3-5642050
Taipei Branch :
7F, No. 137, Lane 235, Pac Chiao Rd.,
Hsin Tien City, Taipei Hsien, Taiwan, R. O. C.
Tel : 886-2-89191368
Fax : 886-2-89191369
Copyright  ANPEC Electronics Corp.
Rev. A.4 - Aug., 2005
21
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