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APW1172
2.5A SWITCH STEP DOWN SWITCHING REGULATOR
Features
* * * * * * * * * * * * * * * *
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 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 Over-Voltage Protection Lead Free Available (RoHS Compliant)
General Description
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 45C/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.
Pin Description
OUT SYNC
1 2 3 4 8 7 6 5
Applications
* * * *
Consumer: STB, DVD, TV, VCR, Car Radio, LCD monitors Networking: XDSL, Modems, DC-DC Modules Computer: Printers, Audio/Graphic Cards, Optical Storage, Hard Disk Drive Industrial: Chargers, Car Battery DC-DC Converters
VCC GND VREF FB
INH COMP
SOP-8-P (Top View) = Thermal Pad (connected to GND plane for better heat dissipation)
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 (c) ANPEC Electronics Corp. Rev. A.4 - Aug., 2005 1 www.anpec.com.tw
APW1172
Ordering and Marking Information
APW1172 Lead Free Code Handling Code Temp. Range Package Code APW1172 KA :
APW1172 XXXXX
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 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 COMP FB
E/A PWM
V REF =1.235V
VCC VREF Buffer Voltages Monitor Thermal Protection Peak to Peak Current Limit Driver
D
Q Ck
OVP
Oscillator Frequency Shifter
1.25VREF
SYNC
Inhibit
OUT GND
Absolute Maximum Ratings
Symbol VCC VOUT VIO IOUT VREF PD TJ TSTG TSDR VESD Parameter Input voltage (VCC to GND) Output DC voltage COMP and FB to GND Output current VREF to GND Average Power Dissipation, TA < 50 Junction Temperature Storage Temperature Soldering Temperature, 10 seconds Minimum ESD rating (Human body mode)
2
INH
Value 25 -1 to 25 -0.7 ~ VCC 0 to current limit 3.3 2.2 150 -65 ~ 150 300 3
Unit V V V A V W C C C KV
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APW1172
Pin Function Description
No. 1 2 3 4 5 PIN OUT SYNC INH COMP FB 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. 3.3V reference voltage output, no Capacitor Is requested for stability. Ground. Unregulated DC input voltage. Description
6 7 8
VREF GND VCC
Thermal Characteristics
Symbol JA Parameter Junction to ambient thermal resistance in free air Value 45.7 Unit 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=25C.
Electrical Characteristics
The * denotes the specifications that apply over TA = -40 ~ 85oC. Typical values are at TA = 25oC. VCC = 12V unless otherwise specified.
Symbol VCC VUVLO Vd ILIM fs Parameter Test condition Min Operating input voltage range VO = 1.235V; IO = 2A UVLO threshold voltage Hysteresis Dropout voltage Maximum limiting current Switching frequency Duty cycle
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APW1172 Typ Max 22 4.2 0.3 4.6
Unit V V V 1.2 4.3 300 295 100 % V A KHz
* *
4.7 3.8
VCC rising
VCC = 4.8V; IO = 2A VCC = 4.8V to 22V Main design
* * * 3.3 200 205 0
1.0 3.8 250 250
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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.
APW1172 Min Dynamic Characteristics VFB Iqop Iq Voltage feedback APW1172 Efficiency 4.8V < VCC < 22V, 20Ma < IO < 2A VO = 5V, VCC = 12V, IOUT = 1A 1.22 1.235 1.25 V % Typ Max
Symbol
Parameter
Test condition
Unit
* 1.198 1.235 1.272 84
DC Characteristics Total Operating Quiescent Current Quiescent Current Duty Cycle = 0; VFB = 1.5V VINH > 2.2V VCC = 22V; VINH > 2.2V * * 50 80 * 12 10 100 150 mA mA A A
Iqst-by Total Stand-by Quiescent Current Inhibit VINH INH Threshold Voltage INH Pull-Up Current Maximum INH Voltage Error Amplifier VOH VOL High Level Output Voltage Low Level Output Voltage
Device ON Device OFF VINH < 3V IINH = 0A
1.1 1.2
1.3 1.4 1 4.3
1.5 1.6
V V A V
VFB = 1V VFB = 1.5V VCOMP = 1.9V; VFB = 1V VCOMP = 1.9V; VFB = 1.5V VFB = 1.5V IFB = 0A VFB = 1.255V to 1.215V, ICOMP = -0.1mA to 0.1mA VCOMP = 1.9V VCC = 4.8 to 22V VCC = 4.8V to 22V VSYNC = 0.74V VSYNC = 2.33V ISOURCE = 3mA No load, VSYNC = 1.65V
4
3.5
3.8 0.4
V V A mA 4 A V mA/V
IO source Source Output Current IO sink Sink Output Current IFB Source Bias Current Maximum FB Voltage gm Trans-conductance
200 1
300 1.5 2.5 2.1 2.3
SYNC Function High Input Voltage Low Input Voltage Slave Sink Current Master Output Amplitude Output Pulse Width
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2.5
VREF 0.74
V V mA V s
0.11 0.21 2.75 0.2 3 0.35
0.25 0.45
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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.
APW1172 Min Reference Section IREF = 0mA VREF VREF Output Voltage Line Regulation Load Regulation Short Circuit Current Other Thermal Limiting Protection Hysteresis Over-Voltage Protection Threshold Voltage VCOMP = 0.8V * 120 160 30 125 130 C C % IREF = 0mA to 5mA, VCC = 4.4A to * 22V IREF = 0mA, VCC = 4.4A to 22V IREF = 0mA to 5mA 10 3.234 3.2 3.3 3.3 5 8 18 3.366 3.399 10 15 30 V V mV mV mA Typ Max
Symbol
Parameter
Test condition
Unit
Typical Application Circuit
VOUT = 3.3V L 22uH
1 2 3 4 OUT SYNC INH COMP VCC GND VREF FB 8 7 6 5
VREF = 3.3V
COUT 100uF
D1 1N5819
RC1 4.3K CC1 2.2nF
D2 1N4148
APW1172 CIN 22uF VIN 4.8V to 22V
R1 C1 137K 1uF CC2 220pF
RF2 3.3K
RF1 5.6K
Soft Start Circuit
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APW1172
Other Application Circuits
Dual output voltage application
VOUT2 = 5V
VOUT1 = 3.3V
N1/N2=2
1N4148
VREF = 3.3V
1
OUT SYNC INH COMP
VCC GND VREF FB
8 7 6 5
RF1 5.6K
L 22uH
2 3 4
COUT2 47uF
RF2 3.3K
COUT1 100uF
D1 1N5819
RC1 4.3K CC1 2.2nF CC2 220pF
APW1172 CIN 22uF VIN=5V
BuckBoost regulator
VOUT = -12V
VREF = 3.3V L 15uH
1 2 8 7 6 5
OUT SYNC INH COMP
VCC GND VREF FB
D1 1N5819 RC1 4.3K CC1 2.2nF
3 4
APW1172 CIN2 CIN1 22uF25V 22uF CC2 220pF VIN=5V
RF2 24K
RF1 2.7K
COUT 100uF
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APW1172
Typical Operating Characteristics
Line regulation of VREF
12
0 -2
Load regulation of VREF
10
Line regulation (mV)
8
Load regulation (mV)
-50 -25 0 25 50 75 100 125
-4 -6 -8 -10 -12 -14
6
4
2
0
-16 -50 -25 0 25 50 75 100 125
Junction Temperature (o C)
Junction Temperature (o C)
Short circuit current of VREF
0 -2
3.40 3.38 3.36
VREF
Short circuit current (mA)
-4
3.34
-6
3.32
VREF (V)
-50 -25 0 25 50 75 100 125
-8 -10 -12
3.30 3.28 3.26 3.24
-14 -16
3.22 3.20 -50 -25 0 25 50 75 100 125
Junction Temperature (o C)
Junction Temperature (o C)
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APW1172
Typical Operating Characteristics (Cont.)
Source ability of EA
300
0.0
Sink ability of EA
250
-0.5
Source current (uA)
200
Sink current (mA)
-1.0
150
-1.5
100
-2.0
50
0 -50 -25 0 25 50 75 100 125
-2.5 -50 -25 0 25 50 75 100 125
Junction Temperature (o C)
Junction Temperature (o C)
Quiescent current
12 90
Quiescent standby current
VCC=12V
10
80 70
VCC=12V
8
60
6
Iqst-by (V)
IQ (mA)
VCC=5V
50 40 30 20
4
VCC=5V
2 10 0 -50 -25 0 25 50 75
o
0 100 125 -50 -25 0 25 50 75
o
100
125
Junction Temperature ( C)
Junction Temperature ( C)
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APW1172
Typical Operating Characteristics (Cont.)
Efficiency vs. Output Current at VIN=5V
80% 78% 76%
Efficiency vs. Output Current at VIN=12V
86% 84% 82% 80%
74%
78%
Efficiency (%)
72%
76% 74% 72% 70% 68% 66%
Efficiency (%)
70% 68% 66% 64% 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
VO=2.5V
VO=3.3V
VO=5V
VO=1.8V
VO=2.5V
VO=3.3V
64% 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
Output Current (A)
Output Current (A)
VCE vs. ICE
1.5 1.4 1.3 1.2
VFB vs. Temperature
1.241 1.240 1.239
VIN=5V
1.238 1.237
VCE (V)
1.1 1.0 0.9
VFB (V)
3.0
1.236 1.235 1.234 1.233
VIN=12V
0.8 0.7 0.0 0.5 1.0 1.5 2.0 2.5
1.232 1.231 -50 -25 0 25 50 75
o
100
125
ICE (A)
Junction Temperature ( C)
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APW1172
Typical Operating Characteristics (Cont.)
Switching Frequency
258
Switching Frequenct (KHz)
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 = 22F, COUT = 220F, L = 15 H 2. Power ON (external SS) : - VIN = 12V,VOUT = 3.3V - CIN = 22F, COUT = 220F, L = 15 H
IL
IL
VOUT
VIN
VOUT
VIN
COMP
Ch1 : VOUT,1V/div Ch2 : COMP,2V/div Ch3 : VIN,5V/div Ch4 : IL,2A/div Time : 400us/div Ch1 : VOUT,1V/div Ch2 : COMP,2V/div Ch3 : VIN,5V/div Ch4 : IL,2A/div Time : 1ms/div
COMP
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APW1172
Operating waveforms (Cont.)
3. Current Limit : - VIN = 12V,VOUT = 3.3V - CIN = 22F, COUT = 220F, L = 15 H 4. Load Transient : - VIN = 12V,VOUT = 3.3V - CIN = 22F, COUT = 220F, L = 15 H
IOUT
IOUT
V OUT
VOUT
COMP
Ch1 : VOUT,2V/div Ch2 : COMP,2V/div Ch3 : IOUT,2A/div Time : 2ms/div
Ch1 : VOUT,200mV/div,offset 3.3V Ch2 : IOUT,1A/div,100mA-3A Ch2 rising time : 4us 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' limit after the supply voltage exceed firstly it' s s threshold voltage after powering on. Output Voltage Regulation 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' output called error signal. The s error signal feeds into the input terminal of PWM 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. Current Limit 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. Over-Voltage Protection (OVP) The over voltage protection is realized by using an
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APW1172
Functional Description (Cont.)
Over-Voltage Protection (OVP) (Cont.) 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 160C. A hysteresis of the thermal protection function is approximately 30C, in order to avoid pass element turns on and off immediately. 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 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' limitation. In this time, the actual duty was very s 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. 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.
Application Description
Input Capacitor 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(>100F, ESR<300m) is recommended as the input capacitor. It is not necessary t o use low-ESR capacitors. More capacitance reduce the variations of the input voltage of VCC pin. 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
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APW1172
Application Description (Cont.)
Inductor (Cont.) 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) 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 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. Consider the output ripple voltage that absorbed in the application.Output ripple voltage consist of two parts.It show as (4)
L=
VIN - VCE - VO Ton I
(1)
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
(2)
Where VD is the forward voltage of the wheeling diode.
Ton = DTS
(3)
Vripple = V1 + V2
(4)
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)
by (2)
V1 = ESR x I
(5)
Ton = DTS = 34.78% x 4s = 1.3912s by (3)
For the worst case ripple current equal 0.6A ~ 1.2A
The second part of output ripple voltage,V2,can calculated by (6)
12V - 1.2V - 3.3V L1 = 1.3912s = 17.39H 0.6 A
for ripple current is 0.6A... ...
V2 =
I TS 8C
(6)
by (1)
L2 =
12V - 1.2V - 3.3V 1.3912s = 8.695H 1. 2 A
for ripple current is 1.2A... ...
by (1)
Use the worst case to approximate the minimum value of inductor. In worst ripple current condition, smaller
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
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APW1172
Application Description (Cont.)
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. 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. Thermal Consideration 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)
PD = VD x I D x (1 - D )
(8)
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. 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.
48
Thermal Resistance of Junction
46
to Ambient ( o C/W)
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 x I L x D) + (VIN x I L x 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. The wheeling diode is another thermal source. It' s power dissipation approximated by (8)
f natural =
1 2 LC
(9)
Where L is the inductance of the LPF and C is the capacitance of the output capacitor. These double poles
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APW1172
Application Description (Cont.)
L
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.
VOUT
ESR Loading
COUT C e r a m ic type
FB PIN
EA
1.235V
COMP PIN
Consider the Figure-2, find the transfer function H (s) as:
H (s) =
RC1 CC2 CC1
SCOUT ( ESR) + 1 S LCOUT + SCOUT ( ESR) + 1
2
pole1, 2 = zero1 =
1 2 LCOUT
1 2( ESR)COUT
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
Q=
L 1 ( ESR) COUT
f zero =
1 2RC1CC1
(10)
The relation of the zero and the natural frequency is
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 frequency response of the output stage show as Figure-3.
f zero = 0.8 f natural
(11)
Locate the zero before the natural frequency to compensate the phase. The another capacitor CC2 used to bypass the noise. In general
0db
CC 2
1 = CC1 10
(12)
slope=-40db/ decade
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.
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0d -90d -135d -180d Pole1,2 Zero1 phase
f
Figure-3
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APW1172
Application Description (Cont.)
Frequency Compensation (Cont.) 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.
C3
sented as Figure-5:
slope=-20db/ decade
0db
270d phase 180d 90d 45d 0d
f
Zero2 Zero3 Pole3 Pole4
Figure-5
C2 R2 C1
R3
FB R1 EA COMP Vref
The assumption is 10(zero2)zero 2 zero3 = k pole1, 2
(11)
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 = 1 2 C2 R3
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
R3 = (2 C2 k pole1, 2 ) -1
(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 = 2 C1 ( R1 + R2 ) 1 2 C1R2 C2 + C3 pole4 = 2 C2C3 R3 pole3 =
The frequency response of the PID compensator pre-
R1 = (2 C1 k pole1,2 ) -1 - R2
(6) The location of pole4 is 5 times pole3. Use this result to find the value of R3.
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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.
VOUT = 3.3V
1 8 7 6 5
VREF = 3.3V
OUT SYNC INH COMP
V CC GND VREF FB
L 22uH
2 3 4
COUT 100uF
D1 1N5819
R C1 4.3K CC1 2.2nF C C2 220pF
APW1172 R F1 5.6K RF2 3.3K C IN 22uF V IN 4.8V to 22V
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APW1172
Packaging Information
SOP-8-P pin ( Reference JEDEC Registration MS-012)
E1 D1
E
H
e1 D
e2
A1
A
1 L
0.004max.
Dim A A1 D D1 E E1 H L e1 e2 1
Millimeters Min. 1.35 0 4.80 3.00REF 3.80 2.60REF 5.80 0.40 0.33 1.27BSC 8 6.20 1.27 0.51 0.228 0.016 0.013 4.00 0.150 Max. 1.75 0.15 5.00 Min. 0.053 0 0.189
0.015X45
Inches Max. 0.069 0.006 0.197 0.118REF 0.157 0.102REF 0.244 0.050 0.020 0.50BSC 8
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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
TP
(IR/Convection or VPR Reflow)
tp Critical Zone T L to T P
Ramp-up
Temperature
TL Tsmax
tL
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 5C of actual Peak Temperature (tp) Ramp-down Rate Sn-Pb Eutectic Assembly 3C/second max. 100C 150C 60-120 seconds 183C 60-150 seconds See table 1 10-30 seconds Pb-Free Assembly 3C/second max. 150C 200C 60-180 seconds 217C 60-150 seconds See table 2 20-40 seconds
6C/second max. 6C/second max. 6 minutes max. 8 minutes max. Time 25C to Peak Temperature Note: All temperatures refer to topside of the package .Measured on the body surface.
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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/-5C 225 +0/-5C 2.5 mm 225 +0/-5C 225 +0/-5C
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 +0C* 260 +0C* 260 +0C* 1.6 mm - 2.5 mm 260 +0C* 250 +0C* 245 +0C* 2.5 mm 250 +0C* 245 +0C* 245 +0C* *Tolerance: The device manufacturer/supplier shall assure process compatibility up to and including the stated classification temperature (this means Peak reflow temperature +0C. For example 260C+0C) 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 245C , 5 SEC 1000 Hrs Bias @ 125 C 168 Hrs, 100 % RH , 121C -65C ~ 150C, 200 Cycles VHBM > 2KV, VMM > 200V 10ms , Itr > 100mA
Carrier Tape
t P P1 D Po E
F W
Bo
Ao
Ko D1
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APW1172
Carrier Tape(Cont.)
T2
J C A B
T1
Application
SOP-8-P Application SOP-8-P
A 3301 F 5.5 0.1
B 62 1.5
C 12.75 + 0.1 5
J 2 + 0.5
T1 12.4 +0.2
T2 2 0.2
W 12 + 0.3 - 0.1 Bo 5.2 0.1
P 8 0.1
E 1.75 0.1
D D1 Po 1.550.1 1.55+ 0.25 4.0 0.1
P1 Ao 2.0 0.1 6.4 0.1
Ko t 2.1 0.1 0.30.013
(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
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