slua267

Application Report
SLUA267 - April 2002
3.3-V to 12-V High-Efficiency Ceramic Only
Non-Synchronous Boost Converter
Sophie Chen
Systems Power
ABSTRACT
This reference design describes the functionality of the controller in more detail. This design
explains the procedures of a non-synchronous boost converter from 3.3 V to 12.0 V with
TPS43000 PWM controller.
Contents
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2
Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3
Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4
PCB Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5
List of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
List of Figures
1
Schematic of PMP145 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2
Power Stage Gain and Phase vs Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
Efficiency vs Load Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4
Typical Operation Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5
Output Ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6
Transient Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7
PCB Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
List of Tables
1
List of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Trademarks are the property of their respective owners.
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1
Introduction
The TPS43000 is a high-frequency, voltage-mode, synchronous PWM controller that can be
flexibly used in buck, boost, buck-boost, and SEPIC topologies. This full-featured controller is
designed to drive a pair of external MOSFETs (N/P) and can be used with a wide range of output
voltages and power level. It can be widely used in networking equipment, servers, PDAs, cellular
phones, and telecommunication applications.
A schematic of this board is shown in Figure 1. Recommended parts list is provided in Table 1.
The layout of the PCB board is shown in Figure 7.
The specification for this board is as follows:
•
VIN = 3.3 V ±10%
•
VOUT = 12 V
•
IOUT = 0.2 to 1.5 A, nominal current is 1 A and no PFM.
•
Ripple = 1.5%
•
Efficiency at nominal load > 90%
+
Figure 1. Schematic of PMP145
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3.3-V to 12-V High-Efficiency Ceramic Only Non-Synchronous Boost Converter
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2
Design Procedure
2.1
Frequency Setting
The TPS43000 can operate either in constant frequency, or in an automatic PFM mode. In the
automatic PFM mode, the controller goes to sleep when the inductor current goes
discontinuous, and wakes up when the output voltage has fallen by 2%. Please refer to the
slus489 datasheet for more detail. The PFM mode is not used in this application. The converter
operates at fixed 300 kHz.
A resistor R4, which is connected from RT pin to ground, programs the oscillator frequency. The
approximate operating frequency is calculated in equation (1).
f ( MHz ) +
38
R4( kW )
(1)
R4 = 127 kΩ is chosen for 300 kHz operation.
2.2
Inductance Value
The inductance value is calculated in equation (2).
L MIN +
f
(1 * D)
D
V OUT
2
2
(2)
I OUTǒminǓ
IRIPPLE is the ripple current flowing through the inductor, which affects the output voltage ripple
and core losses. Based on 20% current ripple and 300 kHz, the inductance value is calculated
as 5.5 µH and a 5.6-µH inductor is used.
2.3
Input and Output Capacitors
The output capacitance and the ESR needed is calculated in equations (3) and (4).
C OUTPUTǒminǓ +
ESR OUT +
I OUT(max)
f
D MAX
(3)
V RIPPLE
V RIPPLE
(4)
I
INǒ ripple Ǔ
OUTǒmaxǓ
)
2
1*D
MAX
I
With 1% output voltage ripple, the capacitance needed is at least 31 µF and the ESR should be
less than 17 mΩ. Four 10-µF/16-V ceramic capacitors are used.
The input capacitance is shown in equation (5). The calculated value is about 78-µF and a
180-µF low-ESR SP capacitor is used.
C INǒminǓ + I INǒ ripple Ǔ
D MAX
TS
V INǒ ripple Ǔ
3.3-V to 12-V High-Efficiency Ceramic Only Non-Synchronous Boost Converter
(5)
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2.4
Compensation Design
For the boost converter, there is a right-half-plane (RHP) zero, which moves with the operating
conditions. The phase starts to drop off a decade before this zero, limiting the system’s
bandwidth. In this circuit, the RHP zero is around 17.2 kHz. The L-C frequency of the power
stage, ƒC, is around 2.9 kHz and the ESR zero is around 1.6 MHz, as shown in Figure 2. The
overall crossover frequency, ƒ0db, is chosen at 5 kHz for reasonable transient response and
stability. R1 to R3 and C1 to C3 form a Type III compensator network. Both zeros (ƒZ1 and ƒZ2)
from the compensator are set at 0.5 ƒC and ƒC to compensate the phase delay caused by RHP
zero. Only one pole, (ƒp1) is set up at the RHP zero. C2, related to the second pole, is open
because the ESR zero is as high as 1.6 MHz. The frequency of poles and zeros are defined by
the following equations:
f Z1 +
2
p
1
R2
C1
f P1 +
2
p
1
R3
C3
;
f Z2 [
2
p
1
R1
C3
;
f P2 [
2
p
1
R2
C1
,
assuming R1 ơ R3
(6)
,
assuming C1 ơ C2
(7)
The compensator values are shown below:
C1 = 33 nF, C2: open, C3 = 1000 pF, R1 = 100 kΩ, R2 = 1.65 kΩ; R3 = 9.31 kΩ.
POWER STAGE GAIN AND PHASE
vs
FREQUENCY
200
100
160
70
120
40
10
GFIL(mag)
40
–20
0
–50
–40
–80
–80
–110
GFIL(ph)
–120
–140
–180
–170
–200
10
Phase – Degree
Gain – db
80
–200
100
1k
10 k
100 k
1M
f – Frequency – Hz
Figure 2.
2.5
MOSFETs and Diode
Si4442DY (RDS(on) = 7.5 mΩ) is chosen. MBRD835L is used for the rectify diode.
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3.3-V to 12-V High-Efficiency Ceramic Only Non-Synchronous Boost Converter
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2.6
Voltage Sense Resistor
R1 and R6 operate as output voltage divider. The internal reference voltage is 0.8 V. The
relationship between the output voltage and divider is shown in equation (8).
V REF
R6
+
V OUT
(8)
R1 ) R6
With 100-kΩ R1 and 12.0-V output regulation, R6 is calculated as 7.15 kΩ.
3
Test Results
3.1
Efficiency Curves
The tested efficiency at different loads and input voltages are shown in Figure 3. The maximum
efficiency is as high as 93.3% at 0.5-A output.
EFFICIENCY
vs
LOAD CURRENT
94
VIN = 3.63 V
Efficiency – %
92
VIN = 3.3 V
90
88
VIN = 3.0 V
86
0.0
0.5
1.0
1.5
ILOAD –Load Current – A
Figure 3.
3.3-V to 12-V High-Efficiency Ceramic Only Non-Synchronous Boost Converter
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3.2
Typical Operation Waveform
Typical operation waveform is shown in Figure 4 with VIN = 3.3 V, IOUT = 1.0 A.
TYPICAL OPERATION
Vgs(Q1) (2.0 V/div)
Vds(Q1) (10.0 V/div)
t – Time – 1 µs/div
Figure 4.
Ch1: gate-source voltage of Q1; Ch2: drain-source voltage waveform of Q1.
3.3
Transient Response and Output Ripple Voltage
The output ripple is about 140 mV peak-to-peak at 1.5-A output.
When the load changes from 1.0 A to 1.2 A, the overshooting voltage is about 200 mV.
OUTPUT RIPPLE
TRANSIENT RESPONSE
IOUT (0.2 A/div)
VOUT(ac) (50 mV/div)
VOUT (100 mV/div)
t – Time – 1 µs/div
t – Time – 200 µs/div
Figure 5.
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3.3-V to 12-V High-Efficiency Ceramic Only Non-Synchronous Boost Converter
Figure 6.
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4
PCB Layout
Figure 7 shows the PCB layout. All the components are on the top side of the board. The bottom
side of the board is the ground plane. The PWB is made large to dissipate the losses.
Top View
Bottom View
Figure 7. PCB Layout
3.3-V to 12-V High-Efficiency Ceramic Only Non-Synchronous Boost Converter
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List of Material
Table 1 lists the board components and their values, which can be modified to meet the
application requirements.
Table 1. List of Materials
Size
Reference
Capacitor
C1
C2
Description
Manufacturer
Part Number
1
Ceramic, 33 nF, 25 V, X7R, 10%, 603
Murata
GRM188R71E333K
1
Ceramic, open, 50 V, COG, 5%, 603
Murata
GRM1885C1HxxxJ
C3
1
Ceramic, 1000 pF, 50 V, X7R, 10%, 603
Murata
GRM188R71H102K
C4,C5,C6
3
Ceramic, 0.47 µF, 25 V, X7R, 10%, 805
Murata
GRM21BR71E474K
C7
1
180 µF, 4.0 V, 18 mΩ, 20%, 7343 (D)
Panasonic
EEFUE0G181R
C8,C9,C10,C11
4
Ceramic, 10 µF, 16 V, 10%, 1210
Murata
GRM32ER61C106K
D1
1
Schottky, 8 A, 35 V, DPAK
ON Semiconductor
MBRD835L
Terminal Block J1,J2
2
2-pin, 6 A, 3.5 mm, 0.27 x 0.25””
OST
ED1514
Inductor
L1
1
SMT, 5.6 µH, 8.8 A, 11.4 mΩ, 12.9 mm sq
Sumida
CEP125–5R6
Resistor
R1
1
Chip, 100 kΩ, 1/16 W, 1%, 603
Std
Std
R2
1
Chip, 1.65 kΩ, 1/16 W, 1%, 603
Std
Std
R3
1
Chip, 9.31 kΩ, 1/16 W, 1%, 603
Std
Std
R4
1
Chip, 127 kΩ, 1/16 W, 1%, 603
Std
Std
R5
1
Chip, 1 kΩ, 1/16 W, 1%, 603
Std
Std
R6
1
Chip, 7.15 kΩ, 1/16 W, 1%, 603
Std
Std
R7
1
Chip, 49.9 Ω, 1/16 W, 1%, 603
Std
Std
MOSFET
Q1
1
N-channel, 30 V, 17 A, 7.5 mΩ, SO–8
Siliconix
Si4442DY
IC
U1
1
Multi-topology high-frequency, PWM controller,
TSSOP–16
Texas Instruments
TPS43000PW
Test Point
TP1,TP2,TP3,
TP4,TP5,TP6
6
Black, 1 mm, 0.038”
Farnell
240–333
N/A
1
Printed circuit board, FR4, 0.032, SMOBC
any
PMP145
Diode
8
Qty
3.3-V to 12-V High-Efficiency Ceramic Only Non-Synchronous Boost Converter
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