1. Designing Small, Simple and Efficient DC to DC Converters
Andy Cowell
Applications Manager
Asia
Feb 2004

2. 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

3. 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

4. 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

5. 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

6. Introducing MIC2202

7. 2MHz PWM Synchronous Buck Regulator
Output down to
0.5V 600mA
2.3V to 5.5V Input
1mF
2.2mF
PWM Regulator with World’s
Smallest LC
Industry’s Smallest Output Components
Ultra-fast transient response
Over 95% efficient
Tiny MSOP-10 and 3mm x 3mm MLF-10L

8. 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

9. 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

10. 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

11. MIC2202 Ultra high Bandwidth loop compensation
ULTRA HIGH BW

12. MIC2202 Performance: L = 2.2mH , COUT = 1mF
Excellent Load Transient Response
Switching Waveforms

13. High Efficiency with MIC2204
High Efficient drive scheme reduces switching losses

14. MIC2202 Efficiency

15. MIC2202 Inductor Selection versus Efficiency
2.2mH is optimal inductor value for small size and high efficiency
MIC2202 works with as low as 1mH inductor for the smallest size
Up to 4.7mH inductor for reduced ripple current and higher light load efficiency.

16. MIC2202 Eval Boards 2 evaluation boards are available:
MIC2202BMM EV (MSOP-10 package)
MIC2202BML EV (3x3 MLF package)
VIN
VOUT
1cm x 1.3cm pcb area

17. 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

18. A High Power Guide to the World of Low Power
DC to DC Converters
Andy Cowell
Applications Manager
Asia
Tel

19. Technical Sheet – Buck Converter
Buck - Technical Sheet

20. Selector Guides MIC2202/4 ** MIC2168/9 MIC4680/4 MIC4685 MIC2193/4
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
50mA-600mA
0.5V
MIC2168/9
Small size Buck controller
1Mhz/500kHz
3 to 14V
500mA-20A
0.8V
MIC4680/4
Small Simple NO
200kHz
4.5-34V
1-1.5A
1.25V
MIC4685
4.5V-32V 3A
MIC2193/4
Low voltage SO-8 controller
400Khz
2.9V-14V
500mA-10A
MIC2183/4
Flexable SO-16 Controller Ics
200/400KHz
MIC2198/9
Utra small High voltage Buck
200/400Khz
4.5-32V 1V
MIC2182
Controller with light load mode
200Khz
4.5V to 32V
500mA to 20A
** Most popular

21. MIC2168/9 Small, Simple DC/DC Controllers

22. 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)
Up to 97% efficiency
No sense resistor
Output over-voltage protection
Adaptive gate drive
VIN
RSET
VOUT

23. 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 12V; IOUT up to 20A
Powers the latest ICs
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

24. MIC2168/9 Features
Dual mode current limit allows fastest recovery time
Hard current limit until VOUT drops ~16%
Hiccup current limit after VOUT drops below 16% (output short-circuit protection)
Output over-voltage protection
Protects system downstream in fault conditions
Hysteretic transient recovery mode
Allows ultra-fast transient response
Internal soft-start
Reduces in-rush current
Dual function COMP / EN pin
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

25. 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

26. MIC2168 versus MIC2169 MIC2168 (1MHz) MIC2169 (500KHz)
Use for smallest size applications
1MHz operation allows smaller external inductor
The trade off with higher frequency is slightly less efficiency (up to ~3-5%) and lower output current
MIC2168 is optimal for < ~5A applications
MIC2169 (500KHz)
Use for highest current applications that require the most efficiency

27. 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
VOUT No
Shoot-Through!

28. MIC2169 Internal Soft Start
Turn on characteristic, VOUT rise time:
2ms rise time
Reduces in-rush current

29. 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
Inductor Current sinking 1A
OVP Test Circuit: Switch High Voltage to MIC2169 Output

30. MIC2169 All Ceramic Capacitor Circuit
VIN 5V
VOUT
3.3V 4A

31. MIC2169 All Ceramic Circuit Performance

32. MIC2169 Ceramic Circuit Bode Plot
STABLE! 54 Phase Margin
29kHz cross-over frequency

33. MIC2169 7A Eval Board Available on on-line sample order system TOP
1.75”
4.5cm
VIN
MIC2169
CIN
VOUT selector jumpers
N-Channel MOSFETs 2”
5cm
Inductor
COUT
VOUT
TOP
BOTTOM

34. MIC2169 7A General Purpose Eval Board
VIN
5V to 12V
VOUT
(Jumper Adjustable)
Shut Down
(optional) *
(optional) *
* 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.

35. MIC2169 Eval Board Performance
Eval Board Efficiency
Eval Board supports 10A with airflow, 7A without. Current is limited by the PCB thermals

36. MIC2169 Eval Board Bode Plot (12VIN to 3.3VOUT )
STABLE! 64 Phase Margin
26kHz cross-over frequency

37. Technical Sheet – Boost Converter
Boost - Technical Sheet

38. Selector guide- Boost MIC2288 ** MIC2290 MIC2196 MIC2171 MIC2185/6
Micrel
Part number.
Feature
Synchronous Boost?
External
Switch(es)
required
Switching
Frequency
Input
Voltage
(Volts DC)
Output Current
Max Output voltage
MIC2288 **
Small SOT23 Package, high output power NO
1.2 MHz V
Up to 500mA
34V
MIC2290
2288 with internal schottky diode
YES
1.2MHz
2.5V- 10V
Up to 300mA
MIC2196
Small Simple in SO-8
400kHz
2.9V-14V
5A+
>50V
MIC2171
High power Boost with internal switch
100Khz
3.0V-40V 3A
60V
MIC2185/6
Flexable SO-16 Controller Ics
200/400KHz
MIC2145
High Power MSOP-8
450Khz
2.2V-14V
Up to 700mA
18V
MIC3171/2
High voltage simple SO-8
3V - 40V
500mA
MIC2141/2
Small SOT23
330kHz
2.7-16V
to 100mA
** Most popular

39. MIC2288 Boost Regulator OEL Driver 2.5V to 10VIN
1.2MHz fixed frequency PWM
>1A switch current
Up to 34VOUT
Tiny 2x2mm MLF-8L and Thin SOT23-5L package options
OEL Driver

40. MIC2288 Boost Regulator
L = 10mH
COUT = 10mF

41. MIC2288 Boost Regulator
VOUT <0.35%!!!

42. MIC2288 Load Transient Performance
12VOUT
150mA
50mA
L = 10mH
COUT = 10mF
VOUT <0.25%!!!

43. MICREL DC to DC Converters
For Small Simple Efficient DC to DC Converters
Think MICREL