Transcript MICREL DC to DC Converters

Designing Small, Simple and Efficient
DC to DC Converters
Andy Cowell
Applications Manager
Asia
Feb 2004
Page 1
MICREL’S DC to DC Converters
 SMALL
SIMPLE and EFFICIENENT
 Small
 Any DC to DC converter must be as small as possible for the given
application
 Simple
 The DC to DC converter must use as few external components as
possible, without sacrificing performance
 Efficient
 The DC to DC converter must be highest efficiency to minimize any
losses
Page 2
The Issues – making a DC-DC Small

The biggest component of a DC to DC converter are
the Inductor L, and the Capacitance C

Increasing the switching frequency decreases the size
of L and C, but decreases the Efficiency.

The DC to DC converter must have high speed loop
response to keep the output voltage stable under all
conditions with a small value of L and C
Page 3
The Issues – Making a DC-DC Simple
 To
make a DC to DC converter simple all the
stability components need to be inside the
Integrated Circuit
 The
DC to DC converter needs to have high
loop speeds without any external components
to keep the L and C small
Page 4
The Issues – Making a DC-DC Efficient
 The
DC to DC converter needs to have a high
switching frequency to keep the L and the C
small
 As
the switching Frequency increases the
switching losses increase, making it less
efficient
Note Switching Power Loss in a MOSFET device used in
most DC to DC converters , Is proportional to
Mosfet gate charge ,Q, x Gate Voltage, Vgs, x Frequency, f

 A new
drive scheme is needed to minimize
switching losses
Page 5
Introducing MIC2202
Page 6
2MHz PWM Synchronous Buck Regulator
2.2mH
2.3V to 5.5V
Input
2.2mF
Output down to
0.5V 600mA
1mF
MIC2202
Industry’s Smallest Output Components
 Ultra-fast transient response
Over 95% efficient
 Tiny MSOP-10 and 3mm x 3mm MLF-10L

Page 7
MIC2202 Benefits

Small
 Tiny 2.2mH inductor and 1mF capacitor
(…or visa-versa, 1mH inductor and 2.2mF capacitor!! )
 Few external components
 3mm x 3mm MLF package has same pcb area as SOT23
 4x better thermal performance than SOT23

Low Noise
 No variable frequency modes of operation
 MIC2202 always operates in fixed frequency PWM mode
 Ideal for noise sensitive applications
 RF and high speed communications systems
Page 8
MIC2202 Benefits

FAST!
 Up to 500KHz closed loop band width
 Fast transient response allows smaller COUT
 Ideal for applications that need fastest response
 DAC-controlled VOUT applications such as CDMA RF
Power

Efficient
 >95% efficient
 Proprietary gate drive minimizes shoot-through current
Page 9
How the MIC2202 can use small values
of L and C
The 2Mhz switching frequency keeps the L and C
Low.
 To Reduce the L and C to Only 2.2uH and 1uF output
Capacitor, a very high loop bandwidth was required.
 Traditionally a tantalum output capacitor is required to
add an extra zero into the loop to help stabilize.
 The MIC2202 uses a 1uF ceramic output capacitor to
reduce size

A new compensation scheme is needed to achieve high
stable bandwidths
Page 10
MIC2202 Ultra high Bandwidth loop
compensation
Internal Error Amplifier Pole
60dB
Gain (dB)
40dB
Internal Error Amplifier Zero
Internal Compensation Zero
Patent Pending Technique
20dB
External Double Pole from LC
Filter
0dB
0.01
0.1
1.0
10
Frequency (kHz)
100
1000
ULTRA HIGH BW
Page 11
MIC2202 Performance: L = 2.2mH , COUT =
1mF
Excellent Load Transient
Response
Switching Waveforms
Page 12
High Efficiency with MIC2204
VIN
SYNC_OUT
CIN
INTERNAL
SUPPLY
BIAS
+
OSCILLATOR
RAMP
GENERATOR
SYNC_IN
-
PWM
Comparator
L
VOUT
DRIVER
SW
COUT
+
Error
Amplifier
REF
GND
EN
FB
High Efficient drive scheme reduces switching losses
Page 13
MIC2202 Efficiency
Efficiency (1.8Vout)
95
90
Efficiency (%)
85
80
75
70
4.2Vin
L = 2.2mH
COUT = 1mF
65
3.6Vin
3Vin
60
0
0.1
0.2
0.3
0.4
0.5
0.6
Output Current (A)
Page 14
MIC2202 Inductor Selection versus
Efficiency
Efficiency vs Inductance
100
2.2mH is optimal inductor
value for small size and
high efficiency

90
80
Efficiency (%)
70
60
MIC2202 works with as
low as 1mH inductor for the
smallest size

50
VIN = 3.6V
VOUT = 1.8V
40
30
Up to 4.7mH inductor for
reduced ripple current and
higher light load efficiency.
4.7uH Inductor
20

2.2uH Inductor
10
1uH Inductor
0
1
10
100
Output Current (mA)
Page 15
MIC2202 Eval Boards

2 evaluation boards are available:
 MIC2202BMM EV (MSOP-10 package)
 MIC2202BML EV (3x3 MLF package)
VIN
VOU
T
1cm x 1.3cm
pcb area
Page 16
MIC2202 Applications
802.11 WLAN power supply
 Camera / video chip power
 Cellular phones
 PDAs
 Digital cameras
 CDMA Dynamic VOUT RF Power Amp power supply
 Wireless and DSL modems
 Storage drives
 CD/DVD ROM power
 PHY core and I/O power supply
 ASIC / FPGA / DSP / CPU power supply
 Portable applications

Page 17
A High Power Guide to the World
of Low Power
DC to DC Converters
Andy Cowell
Applications Manager
Asia
Email [email protected]
Tel +64 6 378 9799
WWW.MICREL.COM
Page 18
Technical Sheet – Buck Converter
Buck - Technical Sheet
ISW
SW
IL
+
Vin
+
ID
ON
OFF
ON
OFF
ON
OFF
Vin
VSW
Vout
t
IL
IL
Vout(DC) = .Vin
where the duty cycle  
t
ton
T
ISW
Slope ,
di
Vin  Vout

dton
L
Slope ,
di
VD  Vout

dtoff
L
ton
t
T
ID
t
Page 19
Selector Guides
Micrel
Part number.
Feature
Synchrous
Buck?
External
Switch(es)
required
Switching
Frequency
Input
Voltage
(Volts DC)
Output
Current
Min
Output
voltage
MIC2202/4
**
Ultra small L and C
for up to 600mA out
YES
No
2 MHz
2.7 to 5.5V
50mA600mA
0.5V
MIC2168/9
**
Small size Buck
controller
YES
YES
1Mhz/500k
Hz
3 to 14V
500mA-20A
0.8V
MIC4680/4
**
Small Simple
NO
NO
200kHz
4.5-34V
1-1.5A
1.25V
MIC4685
Small Simple
NO
NO
200kHz
4.5V-32V
3A
1.25V
MIC2193/4
Low voltage SO-8
controller
YES
YES
400Khz
2.9V-14V
500mA-10A
1.25V
MIC2183/4
Flexable SO-16
Controller Ics
YES
YES
200/400KHz
2.9V-14V
500mA-10A
1.25V
MIC2198/9
Utra small High
voltage Buck
YES
YES
200/400Khz
4.5-32V
500mA-20A
1V
MIC2182
Controller with light
load mode
YES
YES
200Khz
4.5V to 32V
500mA to
20A
1.25V
** Most popular
Page 20
MIC2168/9 Small, Simple DC/DC Controllers
Page 21
MIC2168/9 Simple Synchronous Buck
Controllers




3VIN to 14.5VIN
VOUT down to 0.8V
500KHz fixed frequency PWM
(MIC2169)
1MHz fixed frequency PWM (MIC2168)
VIN




Up to 97% efficiency
No sense resistor
Output over-voltage
protection
Adaptive gate drive
CIN
RSET
VIN VDD
BST CS
MIC2169
MSOP-10
HS
VSW
COMP/EN
GND
0.5 to 1.5K
1mH
VOU
T
FB
LS
COUT
Page 22
MIC2168/9 Features
 Wide 3V to 14.5 operating range
 Works from 3.3V, 5V, and 12V power busses
 Internal bootstrap allows single supply operation
 Other solutions require split supply operation
 VOUT range 0.8V to
 Powers the latest ICs
12V; IOUT up to 20A
 Adaptive gate drive
 Allows up to 97% efficiency
 Prevents shoot-through current
 High-side n-channel MOSFET current sensing
 No current-sense resistor saves cost and efficiency
Page 23
MIC2168/9 Features

Dual mode current limit allows fastest recovery time



Output over-voltage protection


Reduces in-rush current
Dual function COMP / EN pin


Allows ultra-fast transient response
Internal soft-start


Protects system downstream in fault conditions
Hysteretic transient recovery mode


Hard current limit until VOUT drops ~16%
Hiccup current limit after VOUT drops below 16% (output short-circuit protection)
Pull this pin to ground for low power shutdown mode
Flexible architecture



Tantalum capacitor capable for most applications
All-ceramic capacitor capable for smallest size
Electrolytic capacitor capable for lowest cost
Page 24
MIC2168/9 Applications
 Point-of-Load
DC/DC Conversion
 Telecom/Networking/Datacom systems
 DSP / CPU / FPGA / ASIC power supplies
 Set top boxes
 Graphics Cards
 LCD Power Supplies
 Cable modems
 HDD and tape drives
 DC/DC SIP modules
Page 25
MIC2168 versus MIC2169
 MIC2168 (1MHz)
 Use for smallest size applications
 1MHz operation allows smaller external inductor
 The trade off with higher frequency is slightly less efficiency (up to ~35%) and lower output current
 MIC2168 is optimal for < ~5A applications
 MIC2169 (500KHz)
 Use for highest current applications that require the most efficiency
Page 26
MIC2169 Proprietary Adaptive Gate
Drive
 Typical dc/dc controllers sacrifice efficiency by having a long fixed
dead time between the high- and low-side MOSFET drivers to prevent
shoot-through current. The dead time needs to account for maximum
MOSFET gate capacitance. Though it prevents shoot-through,
efficiency is lost during the low-side MOSFET parasitic diode or
external Schottky diode conduction time.

The MIC2168/9 self-adjusts the dead-time from 30ns to 100ns to
maximize efficiency and prevent shoot-through
VIN
HS
VSW
MIC2169
LS
VOUT
COUT
No
Shoot-Through!
Page 27
MIC2169 Internal Soft Start
 Turn
on characteristic, VOUT rise time:
2ms rise time
Reduces inrush current
Page 28
MIC2169 Output Over-Voltage Protection
 Output OVP protects load in fault conditions
 eg: solder-bridge in assembly, or if high-side NFET fails short
 Low-side
NFET turns on during output OVP
conditions

Blows input fuse to protect the expensive downstream load
(1A current limited
for benign test)
OVP Test Circuit: Switch High
Voltage to MIC2169 Output
OVP Test
Inductor Current sinking 1A
Page 29
MIC2169 All Ceramic Capacitor Circuit
VIN
5V
SD103B
CIN
10mF
100mF
0.1mF
VIN VDD
BST CS
MIC2169
MSOP-10
470
IRF7821
HS
2.5mH
VSW
0.1mF
8.2K
COMP/EN
GND
10K
110
IRF7821
FB
LS
470pF
VOUT
3.3V
COUT
4A
100mF
3.16K
Page 30
MIC2169 All Ceramic Circuit
Performance
5VIN to 3.3VOUT Efficiency
Efficiency (%)
100
96
92
88
84
80
0
1
2
3
4
5
ILOAD (A)
Page 31
MIC2169 Ceramic Circuit Bode Plot
STABLE!
54 Phase Margin
29kHz cross-over
frequency
Page 32
MIC2169 7A Eval Board
 Available
on on-line sample order system
1.75”
4.5c
m
VIN
MIC2169
CIN
VOUT
selector
jumpers
N-Channel
MOSFETs
2”
5cm
Inductor
COUT
TOP
VOUT
BOTTOM
Page 33
VIN
5V to68mF
(x2)
12V
MIC2169 7A General Purpose Eval
Board
SD103B
10mF
10
10mF
0.1mF
0.1mF
1mF
VIN VDD
MIC2169
MSOP-10
0.1mF
(optional)
100K
4.02K
COMP/EN
GND
VOUT
HS
1.2mH
LS
)
4.02
*
FB
(Jumper
Adjustable
IRF7821
VSW
Shut
2N7002
Down
470
BST CS
IRF7821
10K
47
330mF
(x2)
0.1mF
(optional)
1N5819
*
100pF
Jumper
* Light snubbing is required for super low duty cycle
applications to maintain accurate current limiting
(ex: 12VIN to 1VOUT applications) . These components
can be removed for applications with higher duty cycle.
Page 34
MIC2169 Eval Board Performance
 Eval
Board Efficiency
Efficiency(%)
100
95
VIN=5V,
VOUT=3.3V
90
VIN=12V,
VOUT=3.3V
85
80
0
2
4
6
8
10
ILOAD(A)
Eval Board supports 10A with
airflow, 7A without. Current is
limited by the PCB thermals
Page 35
MIC2169 Eval Board Bode Plot (12VIN to
3.3VOUT )
STABLE!
64 Phase Margin
26kHz cross-over
frequency
Page 36
Technical Sheet – Boost Converter
Boost - Technical Sheet
IL
SW
OFF
ON
OFF
ON
OFF
ID
ID
+
ON
Slope ,
di
V in  V out  V D

dtoff
L
Iout
+
t
ISW
Slope ,
ISW
di V in

dton L
ton
t
Vout(DC) =
Vin
1- 
where the duty cycle  
ton
T
IL
IL
T
t
Vout
VSW
t
Page 37
Selector guide- Boost
Micrel
Part number.
Feature
Synchrono
us Boost?
External
Switch(es)
required
Switching
Frequency
Input
Voltage
(Volts DC)
Output
Current
Max
Output
voltage
MIC2288
**
Small SOT23
Package, high
output power
NO
NO
1.2 MHz
2.5- 10V
Up to
500mA
34V
MIC2290
**
2288 with internal
schottky diode
YES
NO
1.2MHz
2.5V- 10V
Up to
300mA
34V
MIC2196
**
Small Simple in
SO-8
NO
YES
400kHz
2.9V-14V
5A+
>50V
MIC2171
High power Boost
with internal switch
NO
NO
100Khz
3.0V-40V
3A
60V
MIC2185/6
Flexable SO-16
Controller Ics
YES
YES
200/400K
Hz
2.9V-14V
5A+
>50V
MIC2145
High Power MSOP8
NO
NO
450Khz
2.2V-14V
Up to
700mA
18V
MIC3171/2
High voltage simple
SO-8
NO
NO
100Khz
3V - 40V
500mA
60V
MIC2141/2
Small SOT23
NO
NO
330kHz
2.7-16V
to 100mA
18V
** Most popular
Page 38
MIC2288 Boost Regulator




2.5V to 10VIN
1.2MHz fixed frequency PWM
>1A switch current
Up to 34VOUT

15V / 100mA
10mH
2.2mF
1-Cell
Li Ion
SW
VIN
EN
MIC2288
Tiny 2x2mm MLF-8L and Thin
SOT23-5L package options
4.7mF
FB
GND
Page 39
MIC2288 Boost Regulator
15VOUT Efficiency
90
Efficiency (%)
85
80
75
70
VIN = 4.2V
VIN = 3.6V
65
L = 10mH
COUT = 10mF
VIN = 3.2V
60
0
0.05
0.1
0.15
0.2
Load (A)
Page 40
MIC2288 Boost Regulator
Total Regulation
15.2
VOUT (V)
15.15
15.1
VIN = 4.2V
15.05
VIN = 3.6V
VIN = 3.2V
15
0
0.05
0.1
0.15
0.2
Load (A)
Page 41
MIC2288 Load Transient Performance
12VOUT
150mA
50mA
L = 10mH
COUT = 10mF
Page 42
MICREL DC to DC Converters
For Small Simple Efficient DC to DC
Converters
Think MICREL
Page 43