KIT34713EPEVBE, Using the 5.0A 1.0MHz Fully Integrated Single Switch-Mode Power Supply (34713) - User Guide

Freescale Semiconductor
User Guide
Document Number: KT34713UG
Rev. 4.0, 1/2009
Using the 5.0A 1.0MHz Fully Integrated Single
Switch-Mode Power Supply (KIT34713EPEVBE)
1
Introduction
This User’s Guide will help the designer become
better acquainted with the 34713 IC and Evaluation
board. It contains a procedure to configure each
block of the 34713 in a practical way, which is based
on a working Evaluation Board designed by
Freescale (KIT34713EPEVBE).
2
34713 Specification
The 34713 is a highly integrated, space-efficient, low
cost, single synchronous buck switching regulator
with integrated N-channel power MOSFETs. It is a
high performance point-of-load (PoL) power supply,
with the ability to track an external reference voltage
in different configurations. The 34713 has a high
efficient 5.0 A continuous output current capability
combined with its voltage tracking/sequencing ability
and tight output regulation.
© Freescale Semiconductor, Inc., 2007-2009. All rights reserved.
Contents
1
2
3
4
5
6
7
8
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
34713 Specification. . . . . . . . . . . . . . . . . . . . . 1
Application Diagram . . . . . . . . . . . . . . . . . . . . 2
Board’s Specifications . . . . . . . . . . . . . . . . . . 2
Component Selection for 34713 Eval Board. 3
Layout Design . . . . . . . . . . . . . . . . . . . . . . . . 13
Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . 17
References. . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Application Diagram
3
Application Diagram
3.0 to 6.0 V
VIN
PVIN
CIN
VMASTER
0.1μF
BOOT
SW
VIN
VOUT
R3
VREFIN
R4
RILH
RFQH
RFQL
0.1μF
RILL
INV
VDDI
FREQ
CBOOT
L
RS
VOUT
R1
CO
CS
RF
CX
R2
CF
COMP
34713
ILIM
GND
PGND
VIN
1kΩ
PG
SD
Microcontroller
Figure 1. Application diagram for 34713
4
Board’s Specifications
The Board was designed to have an operating range defined by:
PVIN_MIN = 3.0 V
Pvin_max = 6.0 V
VOUT_MIN = 0.7 V
VOUT_MAX = 3.6 V
IOUT_MIN = 0A
IOUT_MAX = 5A
Using the 34713, Rev. 4.0
2
Freescale Semiconductor
Component Selection for 34713 Eval Board
5
Component Selection for 34713 Eval Board
5.1
I/O Parameters:
Vin = Pvin = 3.3V (typical)
VREFIN = 1 V
Vo = 1.8 V
Io = 3 A
FSW = 1 MHz
5.2
Configuring the Output Voltage:
The channel SW of the 34713 is a general purpose DC-DC converter. The resistor divider to the
INV1 node is responsible for setting the output voltage. The equation is:
Where VREF could be the voltage in the VREFIN terminal or the internal reference VBG=0.7V,
VREF is chosen as follows: VREF = VREFIN when VREFIN < 0.7V.
For a regulated output at 1.8 V, we choose R1 = 20kΩ, and R2 is calculated as:
V R1
R 2 = REF
= 12.72 KΩ
Vo − V REF
Using the 34713, Rev. 4.0
Freescale Semiconductor
3
Component Selection for 34713 Eval Board
5.3
Switching Frequency Configuration
The switching frequency will have a default value of 1.0 MHz, by connecting the FREQ terminal
to the GND terminal. If the lowest frequency value of 200 KHz is desired, then connect the FREQ
terminal to VDDI. To program the switching frequency to another value, connect an external
resistor divider to the FREQ terminal to achieve the voltages given by the Frequency Selection
Table.
Frequency Khz
Voltage applied to pin FREQ [V]
200
2.341 – 2.500
253
2.185 - 2.340
307
2.029 - 2.184
360
1.873 - 2.028
413
1.717 – 1.872
466
1.561 – 1.716
520
1.405 - 1.560
573
1.249 - 1.404
627
1.093 - 1.248
680
0.936 - 1.092
733
0.781 - 0.936
787
0.625 - 0.780
840
0.469 - 0.624
893
0.313 - 0.468
947
0.157 - 0.312
1000
0.000 - 0.156
Table 1. Frequency Selection Table
The EVB frequency was set to 1 MHz by connecting the FREQ terminal directly to GND.
Using the 34713, Rev. 4.0
4
Freescale Semiconductor
Component Selection for 34713 Eval Board
5.4
Selecting Inductor
Inductor calculation is straightforward. The equation is the following:
L = D'MAX ∗T ∗
(Vo + I 0 * ( Rds(on) _ ls + r _ w))
ΔI o
Maximum Off time percentage
T = 1μs
Rds (on) _ ls = 45mΩ
Switching period
Drain – to – source resistance of FET
Winding resistance of Inductor
Output current ripple
L = 1.15uH
Freescale has selected L = 1 .5 μ H to allow some operating margin.
5.5
Input Capacitors
The input capacitor selection should be based on the current ripple allowed on the input line. The
input capacitor should provide the ripple current generated during the inductor charge time. This
ripple is dependent on the output current sourced by 34713 so that:
I RMS = Io d (1 − d )
Where:
IRMS is the RMS value of the input capacitor current,
I0 is the output current, and
d= VO/VIN is the duty cycle.
For a buck converter, IRMS has its maximum at Vin = 2VO
Since:
I RMS_MAX =
PMAX
ESR
Where PMAX is the maximum power dissipation of the capacitor, and is a constant, based on its
physical size (generally given in the datasheets under the heading AC power dissipation).
Freescale derives that the lower the ESR, the higher the ripple current capability. In other words,
Using the 34713, Rev. 4.0
Freescale Semiconductor
5
Component Selection for 34713 Eval Board
a low ESR capacitor (i.e., with high ripple current capability) can withstand high ripple current
levels without overheating.
Therefore, for greater efficiency and because the overall voltage ripple on the input line also
depends on the input capacitor ESR, we recommend using low ESR capacitors.
Cin MIN =
0.5 * L * ( I RMS ) 2
ΔVo * Vin
For a ΔVO = 0.5*VIN, Then CinMIN = 35μF
The EVB input capacitor of 300μF was selected to assure less input voltage ripple and have
better regulation.
5.6
Selecting the Output Filter Capacitor
The following output capacitor considerations are the most important and not the actual Farad
value: the physical size, the ESR of the capacitor, and the voltage rating.
Calculate the minimum output capacitor using the following formula
ΔI 0
C 0 = ------------------------------8 ⋅ F SW ⋅ ΔV 0
However, a more significative calculation must include the transient response, in order to
calculate the real minimum capacitor value, and to assure a good performance.
Transient Response percentage: TR_% = 3%
Maximum Transient Voltage: TR_V_dip = Vo*TR_% = 0.75*.03=0.054V
Maximum current step: ΔIo _ step =
(Vin _ min − Vo ) * D _ max
=0.72A
Fsw * L
T * Io
Inductor Current rise time: dt _ I _ rise = ΔIo _ step = 4.7μs
Co =
Io * dt _ I _ rise
= 296.3μF
TR _ V _ dip
To find the Maximum allowed ESR, the following formula was used:
ESR max =
ΔVo * Fsw * L
= 8mΩ
Vo (1 − D min)
An array of capacitors in parallel were used, with 3 Low ESR Ceramic capacitors of 100 μF.
Using the 34713, Rev. 4.0
6
Freescale Semiconductor
Component Selection for 34713 Eval Board
5.7
Bootstrap Capacitor
Freescale recommends a 0.1μF capacitor.
5.8
Soft Start
Table 2 shows the voltage that should be applied to the terminal ILIM to get the desired
configuration of the soft start timing.
SoftStart [ms]
Voltage applied to ILIM
3.2
1.25 - 1.49V
1.6
1.50 - 1.81V
0.8
1.82 - 2.13V
0.4
2.14 - 2.50V
Table 2. Soft Start Configuration
The ILIM pin remains connected to VDDI to achieve the minimum soft start timing (0.4ms).
5.9
Compensation Network
1. Choose a value for R1 = 20kΩ
2. Using a Crossover frequency of 50 kHz, set the Zero pole frequency to Fcross/10
1
1
= 5.0kHz
FP 0 =
Fcross =
10
2π * R1C F
3. Knowing the LC frequency, the Frequency of Zero 1 and Zero 2 in the compensation network
are equal to FLC:
1
1
FZ 1 =
FZ 2 =
2π * RF C F
2π * R1C S
RF =
1
1
= 14.66 KΩ C S =
= 1.06 nF
2π * C F FZ 1
2π * R1 FZ 2
4. Calculate RS by placing the first pole at the ESR zero frequency:
1
FP1 =
2π * RS C S
RS =
1
= 570Ω
2π * FP1C S
Using the 34713, Rev. 4.0
Freescale Semiconductor
7
Component Selection for 34713 Eval Board
5. Set the second pole at ten times the Crossover Frequency to achieve a faster response and
a proper phase margin.
1
= 500 kHz
FP 2 =
Cmargin.
Cx
a proper
phase
F
2π * R F
CF + Cx
CX =
CF
= 24 pF
2π * R F C F FP 2 − 1
The Actual values used on the EVB might change due to the precision of L and C components.
Thus, on EVB where selected as follows.
CF = 1.9 nF RF = 15 kΩ Cs = 1 nF Rs = 300 Ω Cx = 20 pF
1
10
100
1000
Hz
10000
100000
1000000
10000000
100000000
120
100
80
60
40
20
dB/Deg
0
-20
-40
-60
-80
-100
-120
-140
-160
-180
-200
Open Loop Gain and phase
User Values
Gain (dB)
Phase (Degrees)
Figure 2. Compensated Open Loop Bode Plot
Using the 34713, Rev. 4.0
8
Freescale Semiconductor
Component Selection for 34713 Eval Board
5.10
Tracking Configurations
This device allows two tracking configurations: Ratiometric and Co-incidental Tracking.
Figure 3. Ratiometric Tracking
Figure 4. Co-incidental Tracking
Circuit Configuration:
The master voltage (VM) feedback resistor divider network will be used in place of R3 and R4, as
shown below. The slave output (VS) is connected through its own feedback resistor divider
network to the INV- terminal, resistors R1 and R2 below. All four resistors will affect the accuracy
of the system, and they need to be 1% accurate resistors.
To achieve this tracking configuration, the master voltage must be connected as in Figure 5, on
page 10 and cannot be directly connected to the VREFIN terminal.
Using the 34713, Rev. 4.0
Freescale Semiconductor
9
Component Selection for 34713 Eval Board
V MASTER
VBG
VRE FIN
R3
R4
To INV - of
Vmas ter
Reference
selector
V SLAVE
Rs
+
EA
-
I NV
R1
Cs
CX
RF
CF
CO
R2
COMP
Figure 5. Ratiometric Tracking Circuit Connections
Equations:
• VM = VBG_M(1+R3/R4)
• VREFIN = VM * R4/(R3+R4)
• VREFOUT = VREFIN
• VS = VREFOUT(1+R1/R2) = VM* R4/(R3+R4)*(R2+R1)/R2, if VREFOUT < VBG_S
• VS = VBG_S(1+R1/R2), if VREFOUT ≥ VBG_S
Figure 6. Ratiometric Tracking Plot
Circuit Configuration:
Connect a three resistor divider to the master voltage (VM) and route the upper tap point of the
divider to the VREFIN terminal, resistors R3, R4, and R5, as shown in Figure 7, on page 11. This
resistor divider must be the same ratio as the slave output’s (VS) feedback resistor divider, which
in turn connects to the INV- terminal, and resistors R1 and R2 in Figure 7
(Condition: R1 = R3 and R2 = R4 + R5). The master’s feedback resistor divider would be
Using the 34713, Rev. 4.0
10
Freescale Semiconductor
Component Selection for 34713 Eval Board
(R3+R4) and R5. All five resistors will affect the accuracy of the system and they need to be 1%
accurate resistors.
To achieve this tracking configuration, the master voltage must be connected in the way shown
and cannot be directly connected to the VREFIN terminal.
V MASTER
VBG
VRE FIN
R3
R4
Referenc e
selec tor
To INV- of
V mas ter
R5
V SLAVE
Rs
I NV
+
EA
-
R1
Cs
CX
RF
CF
CO
R2
COMP
Figure 7. Co-incidental Tracking Circuit Connections
Equations:
VM = VBG_M[1+(R3+R4)/R5]
VREFIN = VM*(R4+R5)/(R3+R4+R5)
VREFOUT = VREFIN
VS = VREFOUT(1+R1/R2) = VM*(R4+R5)/(R3+R4+R5)*(R2+R1)/R2 = VM if VREFOUT < VBG_S
VS = VBG_S(1+R1/R2), if VREFOUT ≥ VBG_S
Figure 8. Co-incidental Tracking Plot
When no tracking is needed, VREFIN should be attached to a DC voltage higher than 0.7 V. For
instance, it can be attached to the VDDI pin.
Using the 34713, Rev. 4.0
Freescale Semiconductor
11
Component Selection for 34713 Eval Board
5.11
EVB Schematic Design
VIN
BOOT
VIN
BOOT
VDDI
C15
I/O SIGNALS
SW
VDDI
0.1uF
PVIN
4.7_nopop
PVIN
R10
10k
J3
ILIM
GND
VMASTER
VOUT
R11
10k
3
2
1
R13
10k_nopop
FREQ
ILIM
19
PVIN
20
PVIN
BOOT
22
VIN
24
R12
10k_nopop FREQ
VDDI
VIN
GND
PVIN 3
2
1
VIN
R16
U1
23
C14
0.1uF
21
J2
1
SGND
PVIN
18
2
FREQ
SW
17
3
ILIM
SW
16
SW
SW
MC34713
PG
PG
SW
15
5
N/C
GND
14
6
SD
GND
13
R7
1k
R8
10k
GND
12
GND
VOUT
N/C
INV
11
10
9
VIN
8
SD
COMP
SD
7
VMASTER
4
VREFIN
VMASTER PGOOD LED
PG
VREFIN
VREFIN
C11
VREFIN
D1
LED
C13
0.1uF
0.1uF
R9
10k
VOUT
LED
INV
INV
COMP
C12
0.1uF
COMP
JUMPERS
BUCK CONVERTER
VOUT1
VOUT
VOUT2
J1
L1
SW
1
VOUT
2
1.5uH
D2
PVIN
VMASTER
STBY_nopop
LED
R3
4.7_nopop
C6
100uF
C7
100uF
1
2
1
2
C8
100uF
1
3
5
7
9
2
4
6
8
10
VREFIN
PG
SD
PMEG2010EA_nopop
C9
1nF_nopop
CON10A
SD
COMPENSATION NETWORK
PVIN CAPACITORS
OPTIONAL nopop
VOUT
VDDI
PVIN
ILIM
C20
1nF
15k
C3
100uF
C4
100uF
C5
100uF
C19
FREQ
R6
POT_50K_nopop
R5
POT_50K_nopop
R14
300
0.02nF
R15
C2
1uF
R1
20k
INV
C18
COMP
C1
0.1uF
VIN CAPACITORS
R2
12.7k
VIN
12.7k
1.9nF
C17
10uF
C16
0.1uF
Figure 9. EVB Schematic Design
Using the 34713, Rev. 4.0
12
Freescale Semiconductor
Layout Design
6
Layout Design
Figure 10. PCB Layout Top View
Figure 11. PCB Layout Inner Layer
Using the 34713, Rev. 4.0
Freescale Semiconductor
13
Layout Design
Figure 12. PCB Layout Bottom Layer
6.1
•
•
•
•
•
•
•
•
•
•
•
PCB Layout Recommendations
Place decoupling capacitors as close as possible to their corresponding pad(s).
Try to place all components on just one Layer.
Do not place a Ground Plane on component and routing side.
Create a Ground plane layer and tie it to ground signals with vias.
To effectively transfer heat from the center thermal pad on the top layer to the ground plane, vias
need to be used in the center pad. Use 5 to 9 vias spaced evenly with a finished diameter of
0.3mm.
Place Test vias as close as possible to the IC to ensure a good measurement value.
PVIN, VIN, VOUT signals have to be tracked with a wide and straight copper area.
Never trace the Feedback signal in parallel to the SW signal.
Ensure the SW Inductor is placed as close as possible to its pads.
SW track has to be as thin and short as possible.
Make sure the I/O connectors are capable of managing the Load current.
Note: Freescale does not recommend connecting the PGND pins to the thermal pad. The thermal pad is
connected to the signal ground and should not be used to make the connection from the PGND pins to
the ground plane. Doing so can cause ground bounce on the signal ground from the high di/dt switch
current and parasitic trace inductance.
Using the 34713, Rev. 4.0
14
Freescale Semiconductor
Layout Design
6.2
Item
Bill of Materials
Quantity
Reference
Value
Description
Footprint
1
16
VREFOUT, VREFIN, VOUT,
VIN, VDDI, SW, STBY, SD,
PVIN, PG, INV, ILIM, GND,
FREQ, COMP, BOOT
not populated
PC test point miniature
SMT
TP1
2
1
C2
1μF
Cap Cer 1.0μF 6.3V
10% X5R 0603
SM/C_0603
3
6
C3, C4, C5, C6, C7, C8
100μF
Cap Cer 100μF 10%
X5R 1210
SM/C_1210
4
1
C9
not populated
5
7
C1, C11, C12, C13 , C14
C15, C16
0.1μF
Cap Cer 0.1μF 50V
10% X7R 0603
SM/C_0603
6
1
C17
10μF
Cap Cer 10μF 6.3V
20% X5R 0603
SM/C_0603
7
1
C18
20pF
Cap Cer 20pF50V 5%
C0G 0603
SM/C_0603
8
1
C19
1.8nF
Cap Cer 1800pF 50V
5% C0G 0603
SM/C_0603
9
1
C20
1nF
Cap Cer 1000pF 25V
5% C0G CC0603
SM/C_0603
10
1
D1
LED
LED Green 0603
SM/C_0603
11
1
D2
not populated
12
1
J1
Pin Header
(2X5)
13
2
100mils jumpers
Jumpers
14
1
J2
not populated
15
1
J3
not populated
16
1
L1
1.5μH
Inductor Power 1.5μH
7.0A SMD
B82464G
17
1
R1
20k
Res MPF 20k ohm
1/10W 5% 0603
SM/C_0603
18
1
R2
12.7k
Res 12.7k ohm 1/10W
1% 0603 SMD
SM/C_0603
19
2
R3,R16
not populated
SM/C_0603
20
2
R5,R6
not populated
TRIMPOT
21
1
R7
1k
SMC
HDR 2X5 TH 100MIL
CTR 330H AU
0.1” (2.54mm)
100 mils
Res MF 1.0k 1/10W
1%0603
SM/C_0603
Using the 34713, Rev. 4.0
Freescale Semiconductor
15
Layout Design
22
2
R12,R13
not populated
SM/C_0603
23
3
R8, R9, R10
10k
Res MF 10.0k 1/10W
1% 0603
SM/C_0603
24
1
R11
10k
Res MF 10.0k 1/10W
1% 0603
SM/C_0603
25
1
R14
300
Res MF 300 Ohm
1/10W 5% 0603
SM/C_0603
26
1
R15
15k
Res MF 15.0k 1/10W
1% 0603
SM/C_0603
27
1
SD
Push_button
Switch tact mini 200GF
SLV GWING
28
1
U1
MC34713
29
1
STBY
not populated
QFN_24
Switch tact mini 200GF
SLV GWING
Notes: Freescale does not assume liability, endorse, or warrant components from external manufacturers that are referenced in circuit
drawings or tables. While Freescale offers component recommendations in this configuration, it is the customer’s responsibility to validate
their application.
Using the 34713, Rev. 4.0
16
Freescale Semiconductor
Conclusion
7
Conclusion
With this User’s Guide, the designer is capable of configuring the 34713 as a general purpose
switching power supply for devices that can make use of the capabilities the 34713 offers. The
board is fully configured to work at any desirable reference voltage within 0 and 2.5 V. However,
it is highly recommended to calculate all components for the specific application situation, in
order to assure a better efficiency and stability of the IC.
8
References
•
•
•
34713 Datasheet, “5A, 1MHz Fully Integrated Single Switch-Mode Power Supply”;
Freescale semiconductor, Inc.
Similar network compensation calculations are available in Application Note “AN1989
MC34701 and MC34702 Component Selection Guide”; Freescale Semiconductor, Inc.
Sanjaya Maniktala, “Switching Power Supplies A to Z”, Newnes, 2006.
Using the 34713, Rev. 4.0
Freescale Semiconductor
17
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Document Number: KT34713UG
Rev. 4.0
1/2009
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