MIC4684
Micrel, Inc.
MIC4684
2A High-Efficiency SuperSwitcher™ Buck Regulator
General Description
The MIC4684 is a high-efficiency 200kHz stepdown (buck)
switching regulator. Power conversion efficiency of above
85% is easily obtainable for a wide variety of applications.
The MIC4684 achieves 2A of continuous current in an 8-lead
SO (small outline) package at 60°C ambient temperature.
High efficiency is maintained over a wide output current range
by utilizing a boost capacitor to increase the voltage available
to saturate the internal power switch. As a result of this high
efficiency, no external heat sink is required. The MIC4684,
housed in an SO-8, can replace larger TO-220 and TO-263
packages in many applications.
The MIC4684 allows for a high degree of safety. It has a wide
input voltage range of 4V to 30V (34V transient), allowing
it to be used in applications where input voltage transients
may be present. Built-in safety features include over-current
protection, frequency-foldback short-circuit protection, and
thermal shutdown.
The MIC4684 is available in an 8-lead SO package with a
junction temperature range of –40°C to +125°C.
Features
•
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•
•
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SO-8 package with 2A continuous output current
Over 85% efficiency
Fixed 200kHz PWM operation
Wide 4V to 30V input voltage range
Output voltage adjustable to 1.235V
All surface mount solution
Internally compensated with fast transient response
Over-current protection
Frequency foldback short-circuit protection
Thermal shutdown
Simple high-efficiency step-down regulator
5V to 3.3V/1.7A converter (60°C ambient)
12V to 1.8V/2A converter (60°C ambient)
On-card switching regulator
Dual-output ±5V converter
Battery charger
Applications
Ordering Information
Part Number
Standard
Pb-Free
Adj
-40°C to +125°C
SOP-8
MIC4684BM
MIC4684YM
Voltage
Junction Temp. Range
Package
Typical Application
V
IN
6.5V to 25V
3
8
MIC4684BM
VIN
EN
GND
2, 6, 7
BS
SW
FB
4
1
5
C
BS
0.33µF/50V
68µH
3A
40V
R1
3.01k
R2
3.01k
V
OUT
2.5V/1.5A
330µF
6.3V
100
80
60
40
20
0
0
Efficiency
vs. Output Current
V
OUT
= 3.3V
EFFICIE
N
CY
(
%
)
C
IN
33µF
35V
V
OUT
= 1.8V
V
OUT
= 2.5V
Adjustable Buck Converter
V
IN
= 5.0V
0.5
1
1.5
OUTPUT CURRENT (A)
2
Efficiency vs. Output Current
SuperSwitcher is a trademark 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
January 2010
1
M9999-012610
Micrel, Inc.
MIC4684
Pin Configuration
SW
GND
VIN
BS
1
2
3
4
8
7
6
5
EN
GND
GND
FB
8-Pin SOP (M)
Pin Description
Pin Number
1
2, 6, 7
3
4
5
Pin Name
SW
GND
IN
BS
FB
Pin Function
Switch (Output): Emitter of NPN output switch. Connect to external storage
inductor and Shottky diode.
Ground
Supply (Input): Unregulated +4V to 30V supply voltage (34V transient)
Booststrap Voltage Node (External Component): Connect to external boost
capacitor.
Feedback (Input): Outback voltage feedback to regulator. Connect to output
of supply for fixed versions. Connect to 1.23V tap of resistive divider for
adjustable versions.
Enable (Input): Logic high = enable; logic low = shutdown
8
EN
Detailed Pin Description
Switch (SW, pin 1)
The switch pin is tied to the emitter of the main internal NPN
transistor. This pin is biased up to the input voltage minus the
V
SAT
of the main NPN pass element. The emitter is also driven
negative when the output inductor’s magnetic field collapses
at turn-off. During the OFF time the SW pin is clamped by
the output schottky diode to a –0.5V typically.
Ground (GND, pins 2,6,7)
There are two main areas of concern when it comes to the
ground pin, EMI and ground current. In a buck regulator
or any other non-isolated switching regulator the output
capacitor(s) and diode(s) ground is referenced back to the
switching regulator’s or controller’s ground pin. Any resistance
between these reference points causes an offset voltage/IR
drop proportional to load current and poor load regulation.
This is why its important to keep the output grounds placed
as close as possible to the switching regulator’s ground pin.
To keep radiated EMI to a minimum its necessary to place
the input capacitor ground lead as close as possible to the
switching regulators ground pin.
Input Voltage (V
IN
, pin 3)
The V
IN
pin is the collector of the main NPN pass element.
This pin is also connected to the internal regulator. The output
diode or clamping diode should have its cathode as close as
possible to this point to avoid voltage spikes adding to the
voltage across the collector.
Bootstrap (BS, pin 4)
The bootstrap pin in conjunction with the external bootstrap
capacitor provides a bias voltage higher than the input volt-
age to the MIC4684’s main NPN pass element. The bootstrap
capacitor sees the dv/dt of the switching action at the SW
pin as an AC voltage. The bootstrap capacitor then couples
the AC voltage back to the BS pin plus the dc offset of V
IN
where it is rectified and used to provide additional drive to
the main switch, in this case a NPN transistor.
This additional drive reduces the NPN’s saturation voltage and
increases efficiency, from a V
SAT
of 1.8V, and 75% efficiency
to a V
SAT
of 0.5V and 88% efficiency respectively.
Feedback (FB, pin 5)
The feedback pin is tied to the inverting side of a GM error
amplifier. The noninverting side is tied to a 1.235V bandgap
reference. Fixed voltage versions have an internal voltage
divider from the feedback pin. Adjustable versions require an
external resistor voltage divider from the output to ground,
with the center tied to the feedback pin.
Enable (EN, pin 8)
The enable (EN) input is used to turn on the regulator and is
TTL compatible. Note: connect the enable pin to the input if
unused. A logic-high enables the regulator. A logic-low shuts
down the regulator and reduces the stand-by quiescent
input current to typically 150µA. The enable pin has an up-
per threshold of 2.0V minimum and lower threshold of 0.8V
maximum. The hysterisis provided by the upper and lower
thresholds acts as an UVLO and prevents unwanted turn on
of the regulator due to noise.
2
M9999-012610
January 2010
MIC4684
Micrel, Inc.
Absolute Maximum Ratings
(Note 1)
Supply Voltage (V
IN
),
Note 3
....................................... +34V
Enable Voltage (V
EN
)......................................–0.3V to +V
IN
Steady-State Output Switch Voltage (V
SW
) .........–1V to V
IN
Feedback Voltage (V
FB
) .............................................. +12V
Storage Temperature (T
S
) ........................ –65°C to +150°C
ESD Rating ...............................................................
Note 3
Operating Ratings
(Note 2)
Supply Voltage (V
IN
)
Note 4
............................ +4V to +30V
Ambient Temperature (T
A
) .......................... –40°C to +85°C
Junction Temperature (T
J
) ........................ –40°C to +125°C
Package Thermal Resistance
θ
JA
,
Note 5
.......................................................... 75°C/W
θ
JC
,
Note 5
.......................................................... 25°C/W
Electrical Characteristics
V
IN
= V
EN
=
12V, V
OUT
= 5V; I
OUT
= 500mA; T
A
= 25°C, unless otherwise noted.
Bold
values indicate –40°C ≤ T
J
≤ +125°C.
Parameter
Condition
(±2%)
(±3%)
8V ≤ V
IN
≤ 30V, 0.1A ≤ I
LOAD
≤ 1A, V
OUT
= 5V
Feedback Bias Current
Maximum Duty Cycle
Output Leakage Current
Quiescent Current
Bootstrap Drive Current
Bootstrap Voltage
Frequency Fold Back
Oscillator Frequency
Saturation Voltage
Short Circuit Current Limit
Shutdown Current
Enable Input Logic Level
Enable Pin Input Current
Thermal Shutdown @ T
J
Note 1.
Note 2.
Note 3.
Note 4.
Note 5.
Min
Typ
Max
Units
V
V
V
V
nA
%
Feedback Voltage
1.210
1.198
1.186
1.173
1.235
1.235
50
1.260
1.272
1.284
1.297
V
FB
= 1.0V
94
5
1.4
6
250
5.5
30
180
2.2
150
2
0.8
16
–1
–0.83
160
50
380
6.2
50
200
0.59
120
225
500
20
12
V
FB
= 1.5V
V
IN
= 30V, V
EN
= 0V, V
SW
= –1V
V
FB
= 1.5V, V
SW
= 0V
V
IN
= 30V, V
EN
= 0V, V
SW
= 0V
µA
mA
mA
mA
V
kHz
kHz
V
A
µA
V
V
µA
mA
°C
I
BS
= 10mA, V
FB
= 1.5V, V
SW
= 0V
V
FB
= 0V
V
FB
= 0V, See
Test Circuit
V
EN
= 0V
regulator on
regulator off
V
EN
= 0V (regulator off)
V
EN
= 12V (regulator on)
I
OUT
= 1A
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.
2.5V of headroom is required between V
IN
and V
OUT
. The headroom can be reduced by implementing a feed-forward diode a seen on the 5V
to 3.3V circuit on page 1.
Measured on 1” square of 1 oz. copper FR4 printed circuit board connected to the device ground leads.
January 2010
3
M9999-012610
Micrel, Inc.
MIC4684
+12V
Device Under
Test
3
Test Circuit
8
VIN
EN
GND
SW
BS
FB
5
2,6,7
1
68µH
4
I
SOP-8
Current Limit Test Circuit
Shutdown Input Behavior
OFF
GUARANTEED
OFF
TYPICAL
OFF
GUARANTEED
ON
TYPICAL
ON
ON
0.8V
1.25V
1.4V
2V
0V
V
IN(max)
Enable Hysteresis
January 2010
4
M9999-012610
MIC4684
Micrel, Inc.
Typical Characteristics
(T
A
= 25°C unless otherwise noted)
100
5V
OUT
Efficiency without Feed
Forward Diode
3.3V
OUT
Efficiency without
100
Feed Forward Diode
100
5V
IN
Efficiency with Feed
Forward Diode
95
V
IN
=
8V
90
EFFICIECNY (%)
EFFICIECNY (%)
85
80
75
70
65
60
V
IN
= 12V
EFFICIENCY (%)
95
90
V
=
8V
IN
85
80
75
70
65
60
V
IN
= 12V
V
IN
= 24V
95
V
=
3.3V
90
OUT
85
80
75
70
65
60
55
50
0
V
OUT
=
2.5V
V
IN
= 24V
V
OUT
=
1.8V
V
IN
=
5.0V
0.5
1
1.5
OUTPUT CURRENT (A)
2
55
V
OUT
=
5V
50
0
0.2 0.4 0.6 0.8
1
1.2 1.4 1.6
OUTPUT CURRENT (A)
55
V
OUT
=
3.3V
50
0
0.2 0.4 0.6 0.8
1
1.2 1.4 1.6
OUTPUT CURRENT (A)
100
90
80
70
60
50
40
30
20
10
0
0
Efficiency vs. Output Current
with Feed Forward Diode
BOOTSTRAP VOLTAGE (V)
5V
OUT
7
6
5
4
3
2
1
0
0
Bootstrap Voltage
vs. Input Voltage
BOOTSTRAP CURRENT (mA)
350
300
250
200
150
100
50
Bootstrap Drive Current
vs. Input Voltage
EFFICIENCY (%)
3.3V
OUT
2.5V
OUT
1.8V
OUT
V
IN
=
12V
0.5
1
1.5
2
2.5
OUTPUT CURRENT (A)
3
V
IN
=
12V
V
FB
=
1.5V
5
10 15 20 25
INPUT VOLTAGE (V)
30
0
0 2 4 6 8 10 12 14 16 18 20
INPUT VOLTAGE (V)
V
IN
=
12V
V
FB
=
1.5V
10.9
Minimum Duty Cycle
vs. Input Voltage
REFERENCE VOLTAGE (V)
1.245
1.240
1.235
1.230
1.225
0
5
V
IN
=
12V
V
OUT
=
V
REF
I
OUT
= 500mA
10 15 20 25
30 35
40
INPUT VOLTAGE (V)
10.6
10.5
10.4
10.3
0
5
10 15 20 25
30 35
40
INPUT VOLTAGE (V)
INPUT CURRENT (mA)
DUTY CYCLE (%)
V
IN
=
12V
10.8 V
OUT
=
5V
V
FB
=
1.3V
10.7
1.255
1.250
Reference Voltage
vs. Input Voltage
6.3
6.2
6.1
6
Quiescent Current
vs. Input Voltage
5.9
5.8
5.7
0
V
EN
=
5V
5 10 15 20 25
30 35
40
INPUT VOLTAGE (V)
200
180
160
140
120
100
80
60
40
20
0
0
Shutdown Current
vs. Input Voltage
SATURATION VOLTAGE (mV)
605
600
595
590
585
580
575
570
0
5
Saturation Voltage
vs. Input Voltage
51.5
FREQUENCY (kHz)
51
50.5
50
49.5
49
48.5
0
Foldback Frequency
vs. Input Voltage
INPUT CURRENT (µA)
V
EN
=
0V
5 10 15 20 25
30 35
40
INPUT VOLTAGE (V)
I
OUT
=
1A
V
OUT
=
5V
10 15 20 25
30 35
40
INPUT VOLTAGE (V)
V
FB
=
0V
5
10 15 20 25
30 35
40
INPUT VOLTAGE (V)
January 2010
5
M9999-012610
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