MIC2174/MIC2174C
Synchronous Buck Controller
Featuring Adaptive On-Time Control
40V Input, 300kHz
Hyper Speed Control™ Family
General Description
The Micrel MIC2174/MIC2174C is a fixed-frequency,
synchronous buck controller featuring adaptive on-time
control. The MIC2174/MIC2174C operates over an input
supply range of 3V to 40V at a fixed switching frequency of
300kHz and is capable of driving 25A of output current.
The output voltage is adjustable down to 0.8V.
A unique Hyper Speed Control™ architecture allows for
ultra-fast transient response while reducing the output
capacitance. It also makes ultra-fast transient response
while reducing the output capacitance and also allows for
extremely low duty-cycle operation. The MIC2174 /
MIC2174C utilizes an adaptive T
ON
ripple controlled
architecture. A UVLO is provided to ensure proper
operation under power-sag conditions to prevent the
external power MOSFET from overheating. A soft-start is
provided to reduce inrush current. Foldback current limit
and “hiccup” mode short-circuit protection ensure FET and
load protection.
The MIC2174/MIC2174C is available in a 10-pin MSOP
(MAX1954A-compatible) package with an operating
junction temperature range from –40°C to +125°C.
All support documentation can be found on Micrel’s web
site at:
www.micrel.com.
Features
•
Hyper Speed Control™ architecture enables:
– High delta V operation (V
HSD
= 40V and V
OUT
= 0.8V)
– Smaller output capacitors than competitors
3V to 40V input voltage
Any Capacitor
TM
stable
-
Zero ESR to high ESR
300kHz switching frequency
Adjustable output from 0.8V to 5.5V (V
HSD
≤
28V)
Adjustable output from 0.8V to 3.6V (V
HSD
> 28V)
±1% FB accuracy (MIC2174)
±3% FB accuracy (MIC2174C)
Up to 94% efficiency
Foldback current limit and “hiccup” mode short-circuit
protection
Thermal shutdown
Safe start-up into pre-biased loads
–40°C to +125°C junction temperature range
•
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Applications
•
Telecom Networking
•
Industrial Equipment
•
Distributed DC power systems
____________________________________________________________________________________________________________
Typical Application
12V to 3.3V Efficiency
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
0
2
4
6
8
10
VIN=5V
Synchronous Buck Controller Featuring Adaptive On-Time Control
OUTPUT CURRENT (A)
Hyper Speed Control and Any Capacitor are trademarks of Micrel, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (
408
) 944-0800 • fax + 1 (408) 474-1000 •
http://www.micrel.com
September 2010
M9999-091310-C
Micrel, Inc.
MIC2174/MIC2174C
Ordering Information
Part Number
MIC2174-1YMM
MIC2174C-1YMM
Voltage
Adj.
Adj.
Accuracy
±1%
±3%
Switching Frequency
300kHz
270kHz
Junction Temperature
Range
–40° to +125°C
–40° to +125°C
Package
10-Pin MSOP
10-Pin MSOP
Lead Finish
Pb-Free
Pb-Free
Pin Configuration
10-Pin MSOP (MM)
Pin Description
Pin Number
1
Pin Name
HSD
Pin Function
High-Side N-MOSFET Drain Connection (input): Power to the drain of the external high-side N-
channel MOSFET. The HSD operating voltage range is from 3V to 40V. Input capacitors between
HSD and the power ground (PGND) are required.
Enable (input): A logic level control of the output. The EN pin is CMOS-compatible. Logic high or
floating = enable, logic low = shutdown. In the off state, supply current of the device is greatly reduced
(typically 0.8mA).
Feedback (input): Input to the transconductance amplifier of the control loop. The FB pin is regulated
to 0.8V. A resistor divider connecting the feedback to the output is used to adjust the desired output
voltage.
Signal ground. GND is the ground path for the device input voltage V
IN
and the control circuitry. The
loop for the signal ground should be separate from the power ground (PGND) loop.
Input Voltage (input): Power to the internal reference and control sections of the MIC2174/MIC2174C.
The IN operating voltage range is from 3V to 5.5V. A 2.2µF ceramic capacitors from IN to GND are
recommended for clean operation. V
IN
must be powered up no earlier than V
HSD
to make the soft-start
function behavior correctly.
Low-Side Drive (output): High-current driver output for external low-side MOSFET. The DL driving
voltage swings from ground to IN.
Power Ground. PGND is the ground path for the MIC2174/MIC2174C buck converter power stage.
The PGND pin connects to the sources of low-side N-Channel MOSFETs, the negative terminals of
input capacitors, and the negative terminals of output capacitors. The loop for the power ground
should be as small as possible and separate from the Signal ground (GND) loop.
High-Side Drive (output): High-current driver output for external high-side MOSFET. The DH driving
voltage is floating on the switch node voltage (LX). It swings from ground to V
IN
minus the diode drop.
Adding a small resistor between DH pin and the gate of the high-side N-channel MOSFETs can slow
down the turn-on and turn-off time of the MOSFETs.
2
EN
3
4
FB
GND
5
IN
6
DL
7
PGND
8
DH
September 2010
2
M9999-091310-C
Micrel, Inc.
MIC2174/MIC2174C
Pin Description (Continued)
Pin Number
Pin Name
Pin Function
Switch Node and Current Sense input: High current output driver return. The LX pin connects directly
to the switch node. Due to the high speed switching on this pin, the LX pin should be routed away
from sensitive nodes.
LX pin also senses the current by monitoring the voltage across the low-side MOSFET during OFF
time. In order to sense the current accurately, connect the low-side MOSFET drain to LX using a
Kelvin connection.
Boost (output): Bootstrapped voltage to the high-side N-channel MOSFET driver. A Schottky diode is
connected between the IN pin and the BST pin. A boost capacitor of 0.1μF is connected between the
BST pin and the LX pin. Adding a small resistor in series with the boost capacitor can slow down the
turn-on time of high-side N-Channel MOSFETs.
9
LX
10
BST
September 2010
3
M9999-091310-C
Micrel, Inc.
MIC2174/MIC2174C
Absolute Maximum Ratings
(1)
IN, FB, EN to GND ..........................................
−0.3V
to +6V
BST to LX ........................................................
−0.3V
to +6V
BST to GND ..................................................
−0.3V
to +46V
DH to LX............................................−0.3V to (V
BST
+ 0.3V)
DL, COMP to GND..............................
−0.3V
to (V
IN
+ 0.3V)
HSD to GND....................................................
−0.3V
to 42V
PGND to GND ..............................................
−0.3V
to +0.3V
Junction Temperature .............................................. +150°C
Storage Temperature (T
S
).........................−65°C to +150°C
Lead Temperature (soldering, 10sec)........................ 260°C
Operating Ratings
(2)
Input Voltage (V
IN
)............................................ 3.0V to 5.5V
Supply Voltage (V
HSD
) ....................................... 3.0V to 40V
Junction Temperature (T
J
) ........................
−40°C
to +125°C
Junction Thermal Resistance
MSOP (θ
JA
) ..................................................130.5°C/W
Continuous Power Dissipation (T
A
= 70°C) .......421mW
(derate 5.6mW/°C above 70°C)
.
Electrical Characteristics
(4)
V
BST
−
V
LX
= 5V; T
A
= 25°C, unless noted.
Bold
values indicate
−40°C
≤
T
J
≤
+125°C.
Parameter
General
Operating Input Voltage (V
IN
)
(5)
HSD Voltage Range (V
HSD
)
Quiescent Supply Current
Standby Supply Current
Undervoltage Lockout Trip Level
UVLO Hysteresis
DC-DC Controller
Output-Voltage Adjust Range (V
OUT
)
Error Amplifier
FB Regulation Voltage
0°C
≤
T
J
≤
85°C (MIC2174)
−40°C
≤
T
J
≤
125°C (MIC2174)
T
J
= 25°C (MIC2174C)
FB Input Leakage Current
V
FB
= 0.8V (MIC2174)
Current-Limit Threshold
V
FB
= 0V (MIC2174)
V
FB
= 0.8V(MIC2174C)
V
FB
= 0V (MIC2174C)
Notes:
1.
2.
3.
4.
5.
6.
Exceeding the absolute maximum rating may damage the device.
The device is not guaranteed to function outside its operating rating.
Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
Specification for packaged product only.
The application is fully functional at low IN (supply of the control section) if the external MOSFETs have enough low voltage V
TH
.
The current will come only from the internal 100kΩ pull-up resistor sitting on the EN Input and tied to IN.
Condition
Min.
Typ.
Max.
Units
3.0
3.0
(V
FB
= 1.5V, output switching but excluding external
MOSFET gate current)
V
IN
= V
BST
= 5.5V, V
HSD
= 40V, LX = unconnected, EN =
GND
(6)
2.4
1.4
0.8
2.7
50
3.0V
≤
V
HSD
≤
28V
28V < V
HSD
≤
40V
5.5
40
3.0
2
3
V
V
mA
mA
V
mV
0.8
0.8
5.5
3.6
V
-1
-2
-3
5
103
19
95
15
130
48
130
48
1
2
3
500
162
77
170
80
mV
nA
%
September 2010
4
M9999-091310-C
Micrel, Inc.
MIC2174/MIC2174C
Electrical Characteristics
(4)
V
BST
−
V
LX
= 5V; T
A
= 25°C, unless noted.
Bold
values indicate
−40°C
≤
T
J
≤
+125°C.
Parameter
Condition
Min.
Typ.
6
MIC2174
MIC2174C
Measured at DH
(7)
MIC2174C
Measured at DH, V
FB
= 1V
I
SINK
= 10mA
I
SOURCE
= 10mA
V
IN
-0.1V
or
V
BST
-0.1V
2.1
1.8
1.8
1.2
V
LX
= 40V, V
IN
= 5.5V,V
BST
= 45.5V
V
LX
= 40V, V
IN
= 5.5V,V
BST
= 45.5V
155
10
3.3
3.3
3.3
2.3
55
21
0.225
0.202
0.3
0.27
87
87
0
0.1
0.375
0.338
Max.
Units
ms
Soft-Start
Soft-Start Period
Oscillator
Switching Frequency
Maximum Duty Cycle
Minimum Duty Cycle
FET Drives
DH, DL Output Low Voltage
DH, DL Output High Voltage
DH On-Resistance, High State
DH On-Resistance, Low State
DL On-Resistance, High State
DL On-Resistance, Low State
LX Leakage Current
HSD Leakage Current
Thermal Protection
Over-Temperature Shutdown
Over-Temperature Shutdown
Hysteresis
Shutdown Control
EN Logic Level Low
EN Logic Level High
EN Pull-Up Current
Note:
7.
The maximum duty cycle is limited by the fixed mandatory off time T
OFF
of typical 363ns.
MHz
%
%
V
V
Ω
Ω
Ω
Ω
µA
µA
°C
°C
3V < V
IN
<5.5V
3V < V
IN
<5.5V
0.4
0.8
0.9
50
1.2
V
V
µA
September 2010
5
M9999-091310-C
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