BUCK无隔离电路设计分析
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– limits the load current
• Thermal shutdown
– turns the device off if the temperature exceeds a specified threshold
14
© 2003 National Semiconductor Corporation
3
© 2003 National Semiconductor Corporation
Linear voltage regulator as power supply
Series pass transistor
Q Iload + Vg + – C Vo – +
Load
-
Vref
Bandgap reference
13
© 2003 National Semiconductor Corporation
Device/Converter Specifications
• Overvoltage protection
– prevents the output voltage from rising above a specified limit
7
© 2003 National Semiconductor Corporation
Buck converter ideal static characteristic
vs(t)
Vg area = DTsVg
〈vs〉 = DVg
0 DTs
V Vg
0
t Conversion ratio:
Ts
0
Vo =D Vg
9
© 2003 National Semiconductor Corporation
Impact of efficiency: a system example
uP/DSP core mode % of time in this mode Load current Io [mA] Linear regulator Efficiency [%] Battery current Ig [mA] Average Ig in this mode [mA] 4.45 Efficiency [%] Battery current Ig [mA] Average Ig in this mode [mA] 2.12 29.1 0.14 0.13 78.4 0.53 0.02 93.7 4.45 0.13 93.0 44.82 1.12 87.7 142.60 0.71 Stand-by 90.0 0.1 34.7 0.12 0.11 Wait 4.0 1.0 40.9 1.02 0.04 Run1 3.0 10.0 41.6 10.02 0.30 Run2 2.5 100.0 41.7 100.02 2.50 FullRun 0.5 300.0 41.7 300.02 1.50
Magnetic Buck Converters for Portable Applications
Frank De Stasi Mathew Jacob
1
Outline
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Why use Switching Regulators? Common Device/Converter Specifications Buck Converter Analysis CCM/DCM modes Selection of L and C Synchronous Buck Converters Conduction and Switching Losses Efficiency improvement using PWM/PFM/LDO modes Control Approaches Current Mode Models and Compensation Guidelines Transient Measurement Techniques Layout Guidelines
11
© 2003 National Semiconductor Corporation
Buck regulators in the system
Power distribution : Vg = 2.8-5.5 V
PS 3.6 V PS 2.5 V PS 1.5 V
Battery
Charger
Buck SMPS regulators
Ig
1
Low-pass LC filter
+
2
L + C
Io
Vg
+ –
vs (t) –
v( t) –
Load
vs(t)
Vg DTs 0 DTs 1 2 D' Ts 0 Ts
fs = 1/Ts = switching frequency
t
1
Switch position:
D = switch duty cycle
Advantages of using SMPS over Linear regulators
• SMPS results in significantly lower average battery current • High efficiency over a wide range of loads and output voltages is achieved with a SMPS • SMPS with low quiescent current modes provide longer battery life for mobile systems that spend most of their time in “stand-by”
Linear regulator power model
Ig Rs Io + Vg + – IQ Vo –
Bias current
I g = Io + IQ
Efficiency:
Vo ?< Linear regulator efficiency cannot be greater Vg than the ratio of the output and the input voltage
• Simple, low noise, small footprint area • Output voltage lower than the battery voltage • High efficiency only if Vo is close to Vg
4
© 2003 National Semiconductor Corporation
0 1 D
8
© 2003 National Semiconductor Corporation
switch duty cycle
Switch-Mode Power Supplies
• Step-up, step-down and inverting configurations available • Switching converters are ideally 100% efficient • Real efficiency can be close to 100%; depends on operating conditions and implementation
– Losses and efficiency will be discussed
• Converters generate switching noise • Discrete filter components (L, C) are required • Higher switching frequency => smaller L, C
Total linear reg average Ig [mA] SMPS
Total SMPS average Ig [mA]
Example: • Vg = 3.6 V • Vo = 1.5 V • 0 < Io < 300 mA
10
© 2003 National Semiconductor Corporation
12
© 2003 National Semiconductor Corporation
Device/Converter Specifications
• Static voltage regulation
– DC output voltage precision, i.e., % variation with respect to the nominal value over: • input voltage range (“line regulation”) • output load range (“load regulation”) • temperature
Buck regulator
Example: • Vg = 3.6 V • Vo = 1.5 V • 0 < Io < 300 mA
Linear regulator
6
© 2003 National Semiconductor Corporation
Buck (step-down) switching power converter
• Undervoltage shutdown
– turns the device off if the input (battery) voltage drops below a specified threshold
• Current limiting (overload protection)
Device/Converter Specifications
• Frequency synchronization
– allows synchronization of the switching frequency to an external system clock
5
© 2003 National Semiconductor Corporation
Vo I o Vo I o ?= = Vg I g Vg ( I o + I Q )
SMPS efficiency as a function of load
100 90 80 70 Efficiency [%] 60 50 40 . 30 20 10 0 0.1 1 10 Io [mA] 100 1000
1-3.6 V
PS
Antenna
Display
PS 2.7-5.5 V
Audio Interface
µP/DSP core I/O
Baseband digital 2.5 V PS
wenku.baidu.com
D/A
LO
PA
LNA
A/D
Analog/RF 2.5 V PS
2.5 V PS
Buck regulators are often used as switch-mode power supplies for baseband digital core and the RF power amplifier (PA)
2
© 2003 National Semiconductor Corporation
Efficiency
Ig Io
Power supply
Vg + –
+ Vo _
µP/DSP core
output DC power Po Vo I o η= = = input DC power Pg Vg I g
• Dynamic voltage regulation
– “Load transient response,” including peak output voltage variation and settling time for a step load transient – “Line transient response,” including output voltage variation and settling time for a step input voltage transient
– Component selection will be discussed
• Duty cycle is the control variable • Closed-loop output voltage control is usually applied
– Dynamic models and control will be discussed
• Thermal shutdown
– turns the device off if the temperature exceeds a specified threshold
14
© 2003 National Semiconductor Corporation
3
© 2003 National Semiconductor Corporation
Linear voltage regulator as power supply
Series pass transistor
Q Iload + Vg + – C Vo – +
Load
-
Vref
Bandgap reference
13
© 2003 National Semiconductor Corporation
Device/Converter Specifications
• Overvoltage protection
– prevents the output voltage from rising above a specified limit
7
© 2003 National Semiconductor Corporation
Buck converter ideal static characteristic
vs(t)
Vg area = DTsVg
〈vs〉 = DVg
0 DTs
V Vg
0
t Conversion ratio:
Ts
0
Vo =D Vg
9
© 2003 National Semiconductor Corporation
Impact of efficiency: a system example
uP/DSP core mode % of time in this mode Load current Io [mA] Linear regulator Efficiency [%] Battery current Ig [mA] Average Ig in this mode [mA] 4.45 Efficiency [%] Battery current Ig [mA] Average Ig in this mode [mA] 2.12 29.1 0.14 0.13 78.4 0.53 0.02 93.7 4.45 0.13 93.0 44.82 1.12 87.7 142.60 0.71 Stand-by 90.0 0.1 34.7 0.12 0.11 Wait 4.0 1.0 40.9 1.02 0.04 Run1 3.0 10.0 41.6 10.02 0.30 Run2 2.5 100.0 41.7 100.02 2.50 FullRun 0.5 300.0 41.7 300.02 1.50
Magnetic Buck Converters for Portable Applications
Frank De Stasi Mathew Jacob
1
Outline
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Why use Switching Regulators? Common Device/Converter Specifications Buck Converter Analysis CCM/DCM modes Selection of L and C Synchronous Buck Converters Conduction and Switching Losses Efficiency improvement using PWM/PFM/LDO modes Control Approaches Current Mode Models and Compensation Guidelines Transient Measurement Techniques Layout Guidelines
11
© 2003 National Semiconductor Corporation
Buck regulators in the system
Power distribution : Vg = 2.8-5.5 V
PS 3.6 V PS 2.5 V PS 1.5 V
Battery
Charger
Buck SMPS regulators
Ig
1
Low-pass LC filter
+
2
L + C
Io
Vg
+ –
vs (t) –
v( t) –
Load
vs(t)
Vg DTs 0 DTs 1 2 D' Ts 0 Ts
fs = 1/Ts = switching frequency
t
1
Switch position:
D = switch duty cycle
Advantages of using SMPS over Linear regulators
• SMPS results in significantly lower average battery current • High efficiency over a wide range of loads and output voltages is achieved with a SMPS • SMPS with low quiescent current modes provide longer battery life for mobile systems that spend most of their time in “stand-by”
Linear regulator power model
Ig Rs Io + Vg + – IQ Vo –
Bias current
I g = Io + IQ
Efficiency:
Vo ?< Linear regulator efficiency cannot be greater Vg than the ratio of the output and the input voltage
• Simple, low noise, small footprint area • Output voltage lower than the battery voltage • High efficiency only if Vo is close to Vg
4
© 2003 National Semiconductor Corporation
0 1 D
8
© 2003 National Semiconductor Corporation
switch duty cycle
Switch-Mode Power Supplies
• Step-up, step-down and inverting configurations available • Switching converters are ideally 100% efficient • Real efficiency can be close to 100%; depends on operating conditions and implementation
– Losses and efficiency will be discussed
• Converters generate switching noise • Discrete filter components (L, C) are required • Higher switching frequency => smaller L, C
Total linear reg average Ig [mA] SMPS
Total SMPS average Ig [mA]
Example: • Vg = 3.6 V • Vo = 1.5 V • 0 < Io < 300 mA
10
© 2003 National Semiconductor Corporation
12
© 2003 National Semiconductor Corporation
Device/Converter Specifications
• Static voltage regulation
– DC output voltage precision, i.e., % variation with respect to the nominal value over: • input voltage range (“line regulation”) • output load range (“load regulation”) • temperature
Buck regulator
Example: • Vg = 3.6 V • Vo = 1.5 V • 0 < Io < 300 mA
Linear regulator
6
© 2003 National Semiconductor Corporation
Buck (step-down) switching power converter
• Undervoltage shutdown
– turns the device off if the input (battery) voltage drops below a specified threshold
• Current limiting (overload protection)
Device/Converter Specifications
• Frequency synchronization
– allows synchronization of the switching frequency to an external system clock
5
© 2003 National Semiconductor Corporation
Vo I o Vo I o ?= = Vg I g Vg ( I o + I Q )
SMPS efficiency as a function of load
100 90 80 70 Efficiency [%] 60 50 40 . 30 20 10 0 0.1 1 10 Io [mA] 100 1000
1-3.6 V
PS
Antenna
Display
PS 2.7-5.5 V
Audio Interface
µP/DSP core I/O
Baseband digital 2.5 V PS
wenku.baidu.com
D/A
LO
PA
LNA
A/D
Analog/RF 2.5 V PS
2.5 V PS
Buck regulators are often used as switch-mode power supplies for baseband digital core and the RF power amplifier (PA)
2
© 2003 National Semiconductor Corporation
Efficiency
Ig Io
Power supply
Vg + –
+ Vo _
µP/DSP core
output DC power Po Vo I o η= = = input DC power Pg Vg I g
• Dynamic voltage regulation
– “Load transient response,” including peak output voltage variation and settling time for a step load transient – “Line transient response,” including output voltage variation and settling time for a step input voltage transient
– Component selection will be discussed
• Duty cycle is the control variable • Closed-loop output voltage control is usually applied
– Dynamic models and control will be discussed