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, Inc.
MIC2155/2156
Contents
Ordering Information ............................................................................................................................................................... 3
Absolute Maximum Ratings .................................................................................................................................................... 6
Power Good ...................................................................................................................................................................... 14
Oscillator and Frequency Synchronization ....................................................................................................................... 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
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
Inductor Current Sense Components ............................................................................................................................... 24
Compensation of the Output Voltage Loop ...................................................................................................................... 28
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
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
Micrel, Inc.
MIC2155/2156
Ordering Information
Part Number
MIC2155YML
MIC2156YML
Frequency
500kHz
300kHz
Voltage
Adj.
Adj.
Junction Temp.
(1)
Range
-40°C to +125°C
-40°C to +125°C
Package
32-Pin 5mm × 5mm MLF
32-Pin 5mm × 5mm MLF
Lead Finish
Pb-Free
Pb-Free
Typical Application
VIN
500µF
30
29
28
1
21
5
13
10µF
FDMS7672
VOUT
1.8V
40A
1.5µH
0.1µF
2
3
4
25
24
23
27
18
FDMS7672
0.22µF
FDMS7660
×2
31
10
FDMS7660 ×2
250µF
11
32
17
15
26
20
9
8
6
16
7
12
19
40A Two-Phase Converter
November 2009
3
M9999-111209-B
Micrel, Inc.
MIC2155/2156
Pin Configuration
PGND1
LSD1
VIN1
EN1
VDD
LSD2
PGND2
BST2
HSD2
SW2
N/C
VIN2
VOUT
COMP2
EP
FB2
EA2+
PGOOD
BST1
HSD1
SW1
CS1
EN2
SS
COMP1
FB1
DIFFOUT
RMVOUT
RMGND
®
32-Pin MLF (ML)
Pin Description
Pin Number
Pin Name
Pin Function
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
BST1
HSD1
SW1
CS1
EN2
SS
COMP1
FB1
DIFFOUT
RMVOUT
RMGND
AGND
AVDD
N/C
SYNC
Boost 1 (Input): Provides voltage for high-side MOSFET driver 1. The gate drive
voltage is higher than the source voltage by V
DD
minus a diode drop.
High-Side Drive 1 (Output): High-current output-driver for external high-side
MOSFET.
Switch Node 1 (Output): Return for HSD1
Current Sense 1 (Input). Current-limit comparator non-inverting input. Current is
sensed across the side 1 low-side FET during the off-time. Current limit is set by
the resistor in series with the CS1 pin.
Enable 2 (Input): Channel 2 enable. Pull high to enable. Pull low to disable.
Soft Start (Input): Controls the turn-on time of the output voltage. Active at
Power-up, Enable, and Current Limit recovery.
Compensation 1 (Input): Output of the internal error amplifier for Channel 1.
Feedback 1 (Input): Negative input to the error amplifier of Channel 1.
Output of remote sense differential amplifier.
Remote V
OUT
: Connect to V
OUT
at the remote sense point. Input to precision
differential amplifier.
Remote Ground: Connect to Ground at the remote sense point. Input to
precision differential amplifier.
Analog Ground
Analog supply voltage (input). Connect to V
DD
through an RC filter network
No Connect
Sync (Input): Synchronizes switching to an external source. Leave floating when
not used.
November 2009
AGND
AVDD
N/C
SYNC
4
M9999-111209-B
Micrel, Inc.
MIC2155/2156
Pin Description cont.
Pin Number
Pin Name
Pin Function
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
EPAD
PGOOD
EA2+
FB2
COMP2
VOUT
VIN2
N/C
SW2
HSD2
BST2
PGND2
LSD2
VDD
EN1
VIN1
LSD1
PGND1
EP
Power Good (Output): Asserts high when voltage on the FB pin rises above
Power Good threshold.
(input) Positive input to Channel 2 (current sharing) Error Amplifier. Connect to
Channel 1 current sense.
Negative Input to Channel 2 (current sharing) Error Amplifier (Input). Connect to
Channel 2 current sense.
Compensation 2 (Input): Pin for external compensation of Channel 2.
Output Sense (input): Connect to output side of inductors. Used for current
sharing.
Supply Voltage for Channel 2 (Input). Used for Channel 2 UVLO circuit.
No Connect
Switch node 2 (Output): Return for HSD2.
High-Side Drive 2 (Output): High-current output-driver for the high-side
MOSFET.
Boost 2 (Input): Provides voltage for high-side MOSFET driver in Channel 2. The
gate drive voltage is higher than the source voltage by V
DD
minus a diode drop.
Power Ground 2. High current return for low-side driver 2.
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