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PWM IC Step down 2A_图文

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PWM IC
Buck and Synchronous conversion
Jasper Hou http://www.gmt.com.tw

GMT Products
USB SW DCDC-FAN Control LDO OP

Reset

PCMCIA Switch Thermal

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致新科技股份有限公司 Global Mixed-mode Technology Inc.

2011/9/27

2

Step down conversions
Non-Synchronous conversion Buck conversion Synchronous conversion

Vin
HS DH SW DH HS

Vin IDH IL
SW LS DL

ILOAD Vout

Vout

IDL+ID

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2011/9/27

3

Synchronous buck conversion theory
DH t DL t IHS t ILS
+ _ _

t ILOAD IL VOUT IC t t t
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+

VOUT Ripple voltage = IC × ESR
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2011/9/27

4

Formulas deduction Volt-Second balance
Vin
HS DH SW LS DL

IHS IL ILOAD

ILS+ID

vL

1 = Tsw



Tsw

0

vL (t )dt = 0

f sw =

1 Tsw

DH

DTsw

Tsw 1 ? DTsw (Vin ? Vout )dt + ∫DT (? Vout )dt ? = 0 ? ? sw ? Tsw ? ∫0

DTsw

Tsw (1-D)Tsw

DL

t

1 (Vin ? Vout ) × t Tsw

(

DTsw 0

+ (? Vout ) × t Tswsw = 0 DT
VL
1/4

)

Tsw 15V (1-D)Tsw

t

(Vin ? Vout )× D + (? Vout )× (1 ? D ) = 0
Vout = D × Vin

3/4

1 3 15V × + (? 5V ) × = 0 4 4

-5V DTsw Tsw

t
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2011/9/27

5

Formulas deduction- △I
vL = L di dt
sw

(Vin ? Vout ) = L
Vout = D × Vin
f sw =
Vin
HS DH SW LS DL

?I DTsw

(Vin ? Vout ) DT ?I =
L
L Vin

(V ? V ) V ?I = in out out T
V × (Vin ? Vout ) ?I L = out Vin × f sw × L

sw

1 Tsw

IHS IL ILOAD

?I I P = I LOAD + L 2 ?I I V = I LOAD ? L 2

ILS+ID
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2011/9/27

6

Power consumptions distribution
Vin
HS DH SW
Power loss of parasitic resistance on copper Power loss of HS MOSFET Power loss of DCR Power loss of DCR

L

DCR

Rsense Power loss of ESR

DL LS

ESR Cout

L O A D

Vout

Power loss of LS MOSFET and schottky diode
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2011/9/27

7

Root square of a saw-toothed pulse
I HS ( rms ) =
I HS ( rms ) =
DTsw I p ? I V 1 ( × t + IV ) 2 dt T sw ∫0 DTsw

1 3 D 2Tsw



DTsw

0

( I p t + IV ( DTsw ? t )) 2 dt

I HS ( rms) =
I HS ( rms ) =
I HS ( rms ) =

1 3 D 2Tsw



DTsw

0

[ I P t 2 + 2 I P IV t ( DTsw ? t ) + IV ( DTsw ? t ) 2 ]dt
2 2

1 2 2 ( I P ( DTsw )3 + I P IV ( DTsw )3 + IV ( DTsw )3 ) 3 3D 2Tsw
D 2 2 ( I P + I P IV + IV ) 3
I LS ( rms ) = (1 ? D ) 2 2 ( I P + I P IV + IV ) 3
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2011/9/27

8

Root square of a saw-toothed pulse
IHS

I HS ( rms ) =
I LS ( rms ) =

D 2 2 ( I P + I P IV + IV ) 3
(1 ? D ) 2 2 ( I P + I P IV + IV ) 3
2 2

Ip

?IL= IP - IV
DTsw DTsw

Iv
Tsw

t

ILS & ID

Ip

?IL= IP - IV
Iv
(1-D)Tsw

DTsw

Tsw

I L ( rms ) = I HS ( rms ) + I LS ( rms )
I L ( rms ) =

1 2 2 ( I P + I P IV + IV ) 3
2 2

I C ( rms) = I L ( rms) ? I LOAD

I C ( rms) =

?I 2

1 3
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致新科技股份有限公司 Global Mixed-mode Technology Inc.

2011/9/27

9

Brief and Summarized formulas
Assuming Then
I HS ( rms ) = I LOAD D I LS ( rms ) = I LOAD (1 ? D )
Tf =

I LOAD = I V = I P

Assuming Then
Tr = Qgd I g _ souce =

I g = I g _ souce = I g _ sin k
C gd × Vin Ig Crss × Vin Ig

=

Qgd I g _ sin k

=

C gd × Vin Ig

=

Crss × Vin Ig

The conduction loss

Pcon? HS = I LOAD × D × RDSon? HS
2

Trf = Tr = T f
The switching loss

Pcon? LS = I LOAD × (1 ? D) × RDSon? LS
2

Psw = Vin × I LOAD × Trf × f sw
Psw = Vin × I LOAD × C rss × Vin × f sw Ig
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2011/9/27

10

Control methods – Hysteretic Mode
Output ripple voltage is set by hysteresis voltage Advances
No compensation network required Simple application circuit Fast load transient response

Disadvantages
Switching frequency is varied by Vin, Choke, Vout, and ESR Minimum ripple voltage is required Can not use MLCC Large ripple voltage

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2011/9/27

11

Control methods – Voltage Mode
Output voltage is feedback signal Advances
Single feedback loop Switching frequency is fixed Good load regulation

Disadvantages
Poor load transient response Output capacitance and ESR effect compensation network MLCC unstable

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2011/9/27

12

Control methods – Current Mode
Output voltage and (Choke, high side FET, or Low side FET) current are feedback signals Peak current, average current, or valley current Advances
Switching frequency is fixed Good load regulation Cycle-by-cycle current limit MLCC stable

Disadvantage
Acceptable load regulation Limitation of choke (Inductance)

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2011/9/27

13

Control methods – Constant on-time
Constant On-time is pre-calculated by the ratio of Vin and Vout High sigh FET has a minimum on-time Advances
Fast load transient response Fast line transient response No current sense resistor required Switching frequency is similar fixed Simple for application Stable with low ESR capacitor

GMT Confidential 致新科技股份有限公司 Global Mixed-mode Technology Inc. jasper@gmt.com.tw jasperhou@yahoo.com.tw

2011/9/27

14

PWM IC G5625/G5628
Features
High Efficiency: Up to 93% Internal Soft Start Function 2.5V to 5.5V Input Voltage Range No Schottky Diode Required Less than1uA Shutdown Current Current Mode for Excellent

Line Transient Response Load Transient Response
Over Temperature Protected 1MHz Switching Frequency 100% Duty Cycle 800mA for G5625 1000mA for G5628 0.6V VREF

GMT Confidential 致新科技股份有限公司 Global Mixed-mode Technology Inc. jasper@gmt.com.tw jasperhou@yahoo.com.tw

2011/9/27

15

Block diagram of G5625/G5628

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2011/9/27

16

Efficiency of G5625 and G5628
G5625 G5628

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2011/9/27

17

PWM IC G5626/G5627
Features
10uF MLCC Cin and Cout 2uH Inductor for 1.5A Output Efficiency Up to 94% Operate from 2.5V to 5.5V supply 1MHz Switching Frequency 2A Output Current for G5626 3A Output Current for G5627 Internal Soft-Start SCP and OTP 0.8 VREF

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2011/9/27

18

PWM IC G5640/G5642
Features
Fixed 500kHz Fsw Output Current G5640 for 2.5A G5642 for 3A 1.2V Internal Reference 4.75V to 20V Operating Range
Current-Mode Buck PWM Converter

Shutdown Control Internal Soft Start UVLP, OTP, OCP SOP-8 Package

Synchronous Switches
Internal Soft Start SCP and OTP SOP-8 Package
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2011/9/27

19

System Power PWM IC G5610

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2011/9/27

20

System Power PWM IC G5611

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2011/9/27

21

PWM IC G5614
Features
Ultra-High Efficiency 100ns Load-Step Response 1% VOUT Line and Load Regulation Output

1.8V/2.5V Fixed 1V to 5.5V Adjustable Output Range
4.5V to 24V Battery Input Range Fsw of 200/300/600kHz OVP & UVP 1.7ms Digital Soft-Start Drives Large Synchronous-Rectifier FETs Power-Good Indicator

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2011/9/27

22

Application circuit G5614

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23

Efficiency
Conditions
HS Si4800BDY*1 LS Si4810DY*1 Choke of 2.2uH Cout of 220uF/15mohm Without Rooststrap resistor Without Snubber Vout of 1.8V TON is Float
96 94 V+=8V 92 V+=12V E ff ic ie n c y (% ) 90 88 86 84 82 0.01 V+=16V

V+=19V

Fsw of 300KHz
SKIP is Low

pulse-skipping operation

0.1 Load(A)

1

10

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2011/9/27

24

Dual PWM IC G5615

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2011/9/27

25

Dual PWM IC G5615

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2011/9/27

26

Single PWM IC G5617
Features
Ultra-High Efficiency No Current-Sense Resistor (Lossless ILIMIT) Quasi-PWM with 100ns Load-Step Response 1.2% VOUT Accuracy Over Line and Load Drives Large Synchronous-Rectifier FETs 4.5V to 24V Battery Input Range Output

1.8V/2.5V Fixed 1V to 5.5V Adjustable Output Range
Fsw of 200/300/600kHz OVP & UVP 1.7ms Digital Soft-Start Power-Good Indicator

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2011/9/27

27

Efficiency
Conditions
Choke of 2.2uH Cout of 220uF/15mohm Vout of 1.8V TON is Float
1 Efficiency of 1V8

0.95

Fsw of 300KHz
SKIP is Low

0.9

Vin=8V 0.85 Vin=12V Vin=16V Vin=20V Efficiency 0.8

pulse-skipping operation

0.75

0.7 0.01 0.10 1.00 10.00

Load(A)

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2011/9/27

28