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Micrel Semiconductor

MIC2155 Datasheet Preview

MIC2155 Datasheet

PWM Synchronous Buck Control IC

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MIC2155/2156
Two-Phase, Single-Output, PWM
Synchronous Buck Control IC
General Description
The MIC2155 and MIC2156 are a family of two-phase,
single-output synchronous buck control ICs featuring small
size, high efficiency, and a high level of flexibility. The ICs
implement a 500kHz (MIC2155) and 300kHz (MIC2156)
voltage mode PWM control, with the outputs switching
180° out of phase. The result of the out-of-phase operation
is 1MHz (or 600kHz) input ripple with ripple current
cancellation, minimizing the required input filter
capacitance. A 1% output voltage tolerance allows the
maximum level of system performance. Internal drivers
with adaptive gate drive allow the highest efficiency with
the minimum external components.
Two independent enable pins and a power good output
are provided, allowing a high level of control and
sequencing capability.
The MIC215x family has a junction operating range from
-40°C to +125°C.
Data sheets and support documentation can be found on
Micrel’s web site at www.micrel.com.
Features
Synchronous buck control ICs with outputs switching
180° out-of-phase
Remote sensing with internal differential amplifier
4.5V to 14.5V input voltage range
Adjustable output voltages down to 0.7V
1% output voltage accuracy
Starts up into a pre-biased output
500kHz PWM operation (MIC2155)
300kHz PWM operation (MIC2156)
Adaptive gate drive allows efficiencies over 95%
Adjustable current limit with no sense resistor
Senses low-side MOSFET current
Internal drivers allow 25A per phase
Power Good output allow simple sequencing
Dual enables with micro-power shutdown and UVLO
Programmable soft-start pin
Output over-voltage protection
Works with ceramic output capacitors
Multi-input supply capability
Single-output high-current capability with master/slave
current sharing
External synchronization
Small footprint 32-pin 5mm × 5mm MLF®
Junction temperature range of -40°C to +125°C
Applications
Multi-output power supplies with sequencing
DSP, FPGA, CPU and ASIC power supplies
DSL modems
Telecom and networking equipment
Servers
MLF and MicroLead Frame are registered trademarks of Amkor Technologies
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
November 2009
M9999-111209-B




Micrel Semiconductor

MIC2155 Datasheet Preview

MIC2155 Datasheet

PWM Synchronous Buck Control IC

No Preview Available !

Micrel, Inc.
www.DMataISChe2e1t45U5.c/o2m156
Contents
Ordering Information ............................................................................................................................................................... 3
Typical Application .................................................................................................................................................................. 3
Pin Configuration..................................................................................................................................................................... 4
Pin Description ........................................................................................................................................................................ 4
Absolute Maximum Ratings .................................................................................................................................................... 6
Operating Ratings ................................................................................................................................................................... 6
Electrical Characteristics......................................................................................................................................................... 6
Typical Characteristics ............................................................................................................................................................ 9
Functional Diagram ............................................................................................................................................................... 11
Functional Description........................................................................................................................................................... 12
Startup .............................................................................................................................................................................. 12
Soft Start ........................................................................................................................................................................... 12
Enable............................................................................................................................................................................... 13
Supply Voltages and Internal References ........................................................................................................................ 13
UVLO ................................................................................................................................................................................ 14
Power Good ...................................................................................................................................................................... 14
Oscillator and Frequency Synchronization ....................................................................................................................... 15
MOSFET Gate Drive Circuitry .......................................................................................................................................... 15
dv/dt Induced Turn On of the Low-Side MOSFET............................................................................................................ 16
Remote Sense .................................................................................................................................................................. 16
Setting the Output Voltage................................................................................................................................................ 17
Current Limit and Overcurrent Protection ......................................................................................................................... 17
Current Limit Setting ......................................................................................................................................................... 18
The simple method ....................................................................................................................................................... 18
Accurate method .......................................................................................................................................................... 18
Example: ........................................................................................................................................................................... 18
Inductor Current Sensing.................................................................................................................................................. 19
Current Sharing................................................................................................................................................................. 19
Startup into a Pre-Biased Output...................................................................................................................................... 20
Separate Input Supplies ................................................................................................................................................... 20
Component Selection, Guidelines and Design Example .................................................................................................. 21
Output Filter Selection ...................................................................................................................................................... 21
Output Capacitor Selection............................................................................................................................................... 23
Inductor Current Sense Components ............................................................................................................................... 24
Input Capacitor Selection.................................................................................................................................................. 24
MOSFET Selection ........................................................................................................................................................... 24
RMS Current and MOSFET Power Dissipation Calculation............................................................................................. 25
External Schottky Diode ................................................................................................................................................... 26
Snubber Design ................................................................................................................................................................ 26
Compensation of the Output Voltage Loop ...................................................................................................................... 28
Error Amplifier Design Procedure ......................................................................................................................................... 30
Step 1: Decide on the crossover frequency...................................................................................................................... 30
Step 2: Determine the gain required at the crossover frequency ..................................................................................... 30
Step 3: Determine the gain boost needed at the crossover frequency (fc) ...................................................................... 30
Step 4: Determine the frequencies fz2 and fp1 ................................................................................................................ 30
Step 5: Determine the frequency for fz1........................................................................................................................... 30
Step 6: Determine the frequency for fp2........................................................................................................................... 31
Calculating Error Amplifier Component Values ................................................................................................................ 31
Compensation of the Current Sharing Loop ..................................................................................................................... 31
General Layout and Component Placement .................................................................................................................... 33
Design and Layout Checklist ............................................................................................................................................ 34
Package Information ............................................................................................................................................................. 35
November 2009 2 M9999-111209-B


Part Number MIC2155
Description PWM Synchronous Buck Control IC
Maker Micrel Semiconductor
Total Page 30 Pages
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