slua268

Application Report
SLUA268 - April 2001
2.5-V to 5.0-V, 600-kHz High-Efficiency Synchronous Boost
Converter With TPS43000 PWM Controller
Sopie Chen
System Power
ABSTRACT
The application report describes the functionalities of the cTPS43000 controller and explains
the design procedures of a step-up application from 2.5 V to 5.0 V.
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 PMP144 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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
Top Side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7
Bottom Side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
List of Tables
1
List of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Trademarks are the property of their respective owners.
1
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 = 2.5 V ±10%
•
VOUT = 5.0 V
•
IOUT = 0.2 A to 4 A, nominal current is 3 A and enters PFM at 1 A.
•
Ripple = 1%
•
Efficiency > 90%
+
+
+
Figure 1. Schematic of PMP144
2
2.5-V to 5.0-V, 600-kHz High-Efficiency Synchronous Boost Converter With TPS43000 PWM Controller
2
Design Procedure
2.1
Frequency Setting
The TPS43000 operates 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%. Refer to the TPS43000
datasheet (TI literature number SLUS489) for more detail. The PFM mode is used in this
application. The converter operates at fixed 600 kHz above 1 A and enters into PFM at 1 A.
A resistor R4, which is connected from the RT pin to ground, programs the oscillator frequency.
The approximate operating frequency is calculated in equation (1).
f ( MHz ) +
38
R4( kW )
(1)
R4 = 63.4 kΩ is chosen for 600 kHz operation.
2.2
Inductance Value
The inductance value is calculated in equation (2).
L MIN +
V OUT
f
(1 * D)
D
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 the requirement to enter PFM at 1 A and 600 kHz, the inductance
value is calculated as 0.52 µH and a 0.6-µH inductor is used.
2.3
Input and Output Capacitors
The output capacitance and its ESR needed is calculated in equations (3) and (4).
C OUTPUTǒminǓ +
ESR OUT +
I OUT(max)
f
D MAX
(3)
V RIPPLE
V RIPPLE
I
INǒ ripple Ǔ
OUTǒmaxǓ
)
2
1*D
MAX
I
(4)
With 1% output voltage ripple, the required capacitance is at least 73 µF and its ESR should be
less than 5 mΩ. In order to meet the 1% output ripple requirement, at least four Panasonic
6.3-V/150-µF capacitors, whose ESR is 18 mΩ, are needed. Instead of using four expensive
low-ESR capacitors, two capacitors (C8 and C9) are used and a second L-C filter (L2 and C10)
is used to filter output voltage. The secondary L-C filter parameters are L2: FB784729 from GCI
and C10 = 10 µF
2.5-V to 5.0-V, 600-kHz High-Efficiency Synchronous Boost Converter With TPS43000 PWM Controller
3
The input capacitance is calculated in equation (5). The calculated value is about 65 µF and a
150-µF low-ESR specialty polymer, (SP), capacitor is used.
C INǒminǓ + I INǒ ripple Ǔ
2.4
D MAX
TS
(5)
V INǒ ripple Ǔ
Compensation Design
For the boost converter, there is a right-half-plane (RHP) zero, which moves with operating
conditions. The system phase starts to drop off a decade before this zero, limiting the system’s
bandwidth. In this circuit, the RHP zero is around 88 kHz. The L-C frequency of the power stage,
ƒC, is around 6.0 kHz and the ESR zero is around 70.7 kHz, as shown in Figure 2. The overall
crossover frequency, ƒ0db, is chosen at 10 kHz for reasonable transient response and stability.
R1 to R3 and C1 to C3 combine to form a Type III compensator network. Both zeros, ƒZ1 and
ƒZ2, from the compensator are set at 0.5 ƒC to compensate the phase delay caused by RHP
zero. The two poles ƒP1 and ƒP2 and are set at ESR zero and half of switching frequency
separately. 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
C2
,
assuming R1 ơ R3
(6)
,
assuming C1 ơ C2
(7)
The compensator values are shown below:
C1 = 4700 F, C2 = 68 pF, C3 = 270 pF, R1 = 100 kΩ, R2 = 9.09 kΩ; R3 = 9.09 kΩ.
POWER STAGE GAIN AND PHASE
vs
FREQUENCY
100
100
70
70
40
40
10
10
−20
−20
−50
−50
−80
−80
Phase
−110
−110
−140
−140
−170
−170
−200
−200
10
Phase − Degree
Gain − db
Gain
100
1k
10 k
100 k
1M
f − Frequency − Hz
Figure 2.
4
2.5-V to 5.0-V, 600-kHz High-Efficiency Synchronous Boost Converter With TPS43000 PWM Controller
2.5
MOSFETS and Diode
For a 5-V output voltage, the lower the RDS(on) of the MOSFET, the higher the efficiency. Si4486
(RDS(on) = 10 mΩ) and Si4403DV (RDS(on) = 20 mΩ) are chosen. MBRS340T3 is used for a
parallel diode with Q2.
2.6
Voltage Sense Resistor
R1 and R6 operate as the output voltage divider. The internal reference voltage is 0.8 V. The
relationship between the output voltage and divider is described in equation (8).
V REF
R6
+
V OUT
(8)
R1 ) R6
Setting resistor R1 to 100 kΩ using a value of 5.0-V output regulation, R6 is calculated as
19.1 kΩ.
3
Test Results
3.1
Efficiency Curves
Efficiency tested at different loads and input voltages are shown in Figure 3. The maximum
efficiency is as high as 91.8% at light load. This comes from the PFM function and the losses
from driving the gate are reduced significantly.
EFFICIENCY
vs
LOAD CURRENT
92
VIN = 2.75 V
Efficiency − %
90
88
VIN = 2.5 V
86
VIN = 2.25 V
84
0.0
0.5
1.0
1.5
2
2.5
3.0
3.5
4.0
ILOAD −Load Current − A
Figure 3.
2.5-V to 5.0-V, 600-kHz High-Efficiency Synchronous Boost Converter With TPS43000 PWM Controller
5
3.2
Typical Operation Waveform
Typical operation waveform is shown in Figure 4 with VIN = 2.5 and IOUT = 3.0 A.
TYPICAL OPERATION
VDS(Q1) (5.0 V/div)
VGS(Q2) (5.0 V/div)
VGS(Q1) (5.0 V/div)
t − Time − 500 ns/div
Figure 4.
3.3
Transient Response and Output Ripple Voltage
The output ripple is approximately 18.6 mV peak-to-peak with a 3.0-A output.
When the load changes from 2.4 A to 3.0 A, the overshooting voltage is approximately 76 mV.
OUTPUT RIPPLE
TRANSIENT RESPONSE
VOUT (100 mV/div)
VOUT(ac) (10 mV/div)
IOUT (1 A/div)
t − Time − 500 ns/div
Figure 5.
6
t − Time − 1 ms/div
Figure 6.
2.5-V to 5.0-V, 600-kHz High-Efficiency Synchronous Boost Converter With TPS43000 PWM Controller
4
PCB layout
Figures 7 and 8 show the PCB layout and the photo of a built-up board. All 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.
Figure 7. Top Side
Figure 8. Bottom Side
2.5-V to 5.0-V, 600-kHz High-Efficiency Synchronous Boost Converter With TPS43000 PWM Controller
7
5
List of Materials
Table 1 lists board components and their values, which can be modified to meet the application
requirements.
Table 1. List of Materials
Reference
Capacitor
Qty
Description
Manufacturer
Part Number
C1
1
Ceramic, 4.7 nF, 16 V, X7R, 10%, 603
Murata
GRM219R71C472K
C2
1
Ceramic, 68 pF, 50 V, COG, 5%, 603
Murata
GRM1885C1H680J
C3
1
Ceramic, 270 pF, 50 V, COG, 5%, 603
Murata
GRM1885C1H271J
C4, C5, C6
3
Ceramic, 0.47 µF, 16 V, X7R, 10%, 805
Murata
GRM219R71C474K
C9
2
Ceramic, 10 µF, 6.3 V, 20%, 1210
Taiyo−yuden
JMK325BJ106MM
C7, C8, C10
3
150 µF, 6.3 V, 18 mΩ, 20%, 7343 (D)
Panasonic
EEFUE0J151R
Diode, Schottky
D1
1
3 A, 40 V, SMC
On Semiconductor
MBRS340
Terminal Block
J1, J2
2
2-pin, 6 A, 3.5 mm, 0.27 x 0.25””
OST
ED1514
Inductor
L1
1
SMT, 0.6 µH, 24 A, 6 mΩ, 13.5 mm x 6 mm
Sumida
CEP12D38−0R6
Ferrite
L2
1
Bead, 0.9 mΩ DCR, 48 Ω at 25 Mhz,
12.25 mm x 5 mm
GCI Technologies
FB784729
Resistor
R1
1
Chip, 100 kΩ, 1/16 W, 1%, 603
Std
Std
R2, R3
2
Chip, 9.09 kΩ, 1/16 W, 1%, 603
Std
Std
R4
1
Chip, 63.4 kΩ, 1/16 W, 1%, 603
Std
Std
R5
1
Chip, 1.00 kΩ, 1/16 W, 1%, 603
Std
Std
R6
1
Chip, 19.1 kΩ, 1/16 W, 1%, 603
Std
Std
R7
1
Chip, 49.9 Ω, 1/16 W, 1%, 603
Std
Std
Q2
1
P-channel, 1.8 Vgs, 9 A, 17 mΩ, SO−8
Siliconix
Si4403DY
Q1
1
N-channel, 2.5 Vgs, 17 A, 10 mΩ, SO−8
Siliconix
Si4866DY
IC
U1
1
Multi-topology high-frequency, PWM controller,
TSSOP−16
Texas Instruments
TPS43000PW
Test Point
TP1, TP2, TP3,
TP4, TP5, TP6
6
Black, 1mm, 0.038”
Farnell
240−333
N/A
1
FR4, 0.032, SMOBC
any
PMP144
MOSFET
PCB
8
2.5-V to 5.0-V, 600-kHz High-Efficiency Synchronous Boost Converter With TPS43000 PWM Controller
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