MIC2178
Micrel, Inc.
MIC2178
2.5A Synchronous Buck Regulator
General Description
The Micrel MIC2178 is a 200kHz synchronous buck (step-
down) switching regulator designed for high-efficiency, bat-
tery-powered applications.
The MIC2178 operates from a 4.5V to 16.5V input and
features internal power MOSFETs that can supply up to 2.5A
output current. It can operate with a maximum duty cycle of
100% for use in low-dropout conditions. It also features a
shutdown mode that reduces quiescent current to less than
5µA.
The MIC2178 achieves high efficiency over a wide output
current range by operating in either PWM or skip mode. The
operating mode is externally selected, typically by an intelli-
gent system, which chooses the appropriate mode according
to operating conditions, efficiency, and noise requirements.
The switching frequency is preset to 200kHz and can be
synchronized to an external clock signal of up to 300kHz.
The MIC2178 uses current-mode control with internal current
sensing. Current-mode control provides superior line regula-
tion and makes the regulator control loop easy to compen-
sate. The output is protected with pulse-by-pulse current
limiting and thermal shutdown. Undervoltage lockout turns
the output off when the input voltage is less than 4.5V.
The MIC2178 and is packaged in a 20-lead wide power SOIC
package with an operating temperature range of –40°C to
+85°C.
See the MIC2177 for automatic selection of PWM or skip-
mode operation.
Features
• 4.5V to 16.5V input voltage range
• Dual-mode operation for high efficiency (up to 96%)
PWM mode for > 200mA load current
Skip mode for < 200mA load current
• 100mΩ internal power MOSFETs at 12V input
• 200kHz preset switching frequency
• Low quiescent current
1.0mA in PWM mode
600µA in skip mode
< 5µA in shutdown mode
• Current-mode control
Simplified loop compensation
Superior line regulation
• 100% duty cycle for low dropout operation
• Current limit
• Thermal shutdown
• Undervoltage lockout
Applications
•
•
•
•
•
•
•
High-efficiency, battery-powered supplies
Buck (step-down) dc-to-dc converters
Palmtop computers
Laptop computers
Cellular telephones
Hand-held instruments
Battery Chargers
Typical Application
V
IN
5.4V to 18V
C1
22µF
35V
C2
22µF
35V
R1
20k
ON
OFF
20
11
Skip Mode
PWM Mode
10
18
ENABLE
U1
1,2,9
10
3,8
4–7
12
100
5V Output
Efficiency
Ouput Good
Output Low
L1, 33µH
D1
MBRS140
C5
220µF
10V
EFFICIENCY (%)
VIN
EN
MIC2178-5.0
OUT
PWRGD
PWM
SYNC
COMP SGND
13
14–17
V
OUT
5V/2.5A
C6
220µF
10V
95
90
85
80
75
SKIP
PWM
100
1000 2500
OUTPUT CURRENT (mA)
V
IN
= 6V
SW
PGND
FB
BIAS
19
R1
10k
C3
6.8nF
C4
0.01µF
R2
10k
70
10
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
March 2005
1
M9999-031805
MIC2178
Micrel, Inc.
Ordering Information
Part Number
Standard*
MIC2178BWM
MIC2178-3.3BWM
MIC2178-5.0BWM
Pb-Free
MIC2178YWM
MIC2178-3.3YWM
MIC2178-5.0YWM
Voltage
ADJ
3.3V
5.0V
Junction Temp.
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Package
20-lead WSOIC
20-lead WSOIC
20-lead WSOIC
* Standard product will be supported as Pb-Free IAW PPCN #040004 effective 1-1-2005.
Pin Configuration
VIN 1
VIN 2
SW 3
PGND 4
PGND 5
PGND 6
PGND 7
SW 8
VIN 9
PWM 10
20 EN
19 BIAS
18 SYNC
17 SGND
16 SGND
15 SGND
14 SGND
13 COMP
12 FB
11 PWRGD
20-Lead Wide Power SOIC
Pin Description
Pin Number
1, 2, 9
3, 8
4, 5, 6, 7
10
Pin Name
VIN
SW
PGND
PWM
Pin Function
Supply Voltage (Input): Requires bypass capacitor to PGND. All three pins
must be connected to V
IN
.
Switch (Output): Internal power MOSFET output switches. Both pins must
be externally connected together.
Power Ground: Connect all pins to central ground point.
PWM/Skip-Mode Control (Input): Logic-level input. Controls regulator
operating mode. Logic low enables PWM mode. Logic high enables skip
mode. Do not allow pin to float.
Error Flag (Output): Open-drain output. Active low when FB input is 10%
below the reference voltage (V
REF
).
Feedback (Input): Connect to output voltage divider resistors.
Compensation: Output of internal error amplifier. Connect capacitor or
series RC network to compensate the regulator control loop.
Signal Ground: Connect all pins to ground, PGND*.
Frequency Synchronization (Input): Optional. Connect an external clock
signal to synchronize the oscillator. Leading edge of signal above 1.7V
terminates switching cycle. Connect to SGND if not used.
Internal 3.3V Bias Supply: Decouple with 0.01µF bypass capacitor to
SGND. Do not apply any external load.
Enable (Input): Logic high enables operation. Logic low shuts down
regulator. Do not allow pin to float.
11
12
13
14, 15, 16, 17
18
PWRGD
FB
COMP
SGND
SYNC
19
20
BIAS
EN
M9999-031805
2
March 2005
MIC2178
Micrel, Inc.
Absolute Maximum Ratings
Supply Voltage [100ms transient] (V
IN
) ......................... 18V
Output Switch Voltage (V
SW
) ........................................ 18V
Output Switch Current (I
SW
) ......................................... 6.0A
Enable, PWM Control Voltage (V
EN
, V
PWM
) ................. 18V
Sync Voltage (V
SYNC
) ..................................................... 6V
Operating Ratings
Supply Voltage (V
IN
) ..................................... 4.5V to 16.5V
Junction Temperature Range (T
J
) ........... –40°C to +125°C
Electrical Characteristics
V
IN
= 7.0V; T
A
= 25°C,
bold
indicates –40°C
≤
T
A
≤
85°C; unless noted.
Symbol
I
SS
Parameter
Input Supply Current
Condition
PWM mode, output not switching,
4.5V
≤
V
IN
≤
16.5V
skip mode, output not switching,
4.5V
≤
V
IN
≤
16.5V
V
EN
= 0V, 4.5V
≤
V
IN
≤
16.5V
V
BIAS
V
FB
V
OUT
Bias Regulator Output Voltage
Feedback Voltage
Output Voltage
V
IN
= 16.5V
MIC2178 [adj.]: V
OUT
= 3.3V, I
LOAD
= 0
MIC2178 [adj.]: V
OUT
= 3.3V,
5V
≤
V
IN
≤
16V, 10mA
≤
I
LOAD
≤
2A
MIC2178-5.0: I
LOAD
= 0
MIC2178-5.0:
6V
≤
V
IN
≤
16V, 10mA
≤
I
LOAD
≤
2A
MIC2178-3.3: I
LOAD
= 0
MIC2178-3.3:
5V
≤
V
IN
≤
16V, 10mA
≤
I
LOAD
≤
2A
V
TH
V
TL
I
FB
A
VOL
Feedback Bias Current
Undervoltage Lockout
upper threshold
lower threshold
MIC2178 [adj.]
MIC2178-5.0, MIC2178-3.3
Error Amplifier Gain
Error Amplifier Output Swing
0.6V
≤
V
COMP
≤
0.8V
upper limit
lower limit
Error Amplifier Output Current
f
O
D
MAX
t
ON min
Oscillator Frequency
Maximum Duty Cycle
Minimum On-Time
SYNC Frequency Range
SYNC Threshold
SYNC Minimum Pulse Width
I
SYNC
I
LIM
R
ON
I
SW
SYNC Leakage
Current Limit
V
SYNC
= 0V to 5.5V
PWM mode, V
IN
= 12V
skip mode
Switch On-Resistance
high-side switch, V
IN
= 12V
low-side switch, V
IN
= 12V
Output Switch Leakage
V
SW
= 16.5V
V
FB
= 1.0V
V
FB
= 1.5V
220
0.8
500
–1
3.8
0.01
4.7
600
90
110
1
250
250
10
1
5.7
1.6
source and sink
15
160
100
300
400
300
2.2
15
0.9
3.90
3.10
1.22
3.20
3.14
4.85
4.85
4.75
3.20
3.20
3.14
Min
Typ
1.0
600
1
3.30
1.245
3.3
5.0
5.0
3.3
3.3
4.25
4.15
60
20
18
1.5
0.05
25
200
0.1
35
240
150
40
20
V
V
µA
kHz
%
ns
kHz
V
ns
µA
A
mA
mΩ
mΩ
µA
Max
1.5
750
25
3.4
1.27
3.40
3.46
5.15
5.15
5.25
3.40
3.40
3.46
4.35
Units
mA
µA
µA
V
V
V
V
V
V
V
V
V
V
V
nA
µA
March 2005
3
M9999-031805
MIC2178
Symbol
Parameter
Enable Threshold
I
EN
I
PWM
Enable Leakage
PWM Threshold
PWM Leakage
PWRGD Threshold
V
PWM
= 0V to 5.5V
MIC2178 [adj.]: measured at FB pin
MIC2178-5.0: measured at FB pin
MIC2178-3.3: measured at FB pin
PWRGD Output Low
PWRGD Off Leakage
I
SINK
= 1.0mA
V
PWRGD
= 5.5V
V
EN
= 0V to 5.5V
Condition
Min
0.8
–1
0.6
–1
1.09
4.33
2.87
Typ
1.6
0.01
1.1
0.01
1.13
4.54
3.00
0.25
0.01
Micrel, Inc.
Max
2.2
1
1.4
1
1.17
4.75
3.13
0.4
1
Units
V
µA
V
µA
V
V
V
V
µA
General Note:
Devices are ESD sensitive. Handling precautions recommended.
M9999-031805
4
March 2005
MIC2178
Micrel, Inc.
Typical Characteristics
Oscillator Frequency
vs. Temperature
REFERENCE VOLTAGE (V)
205
200
FREQUENCY (kHz)
195
190
185
180
1.252
1.250
1.248
1.246
1.244
1.242
1.240
Reference Voltage
vs. Temperature
REFERENCE VOLTAGE (V)
3.320
3.315
3.310
3.305
3.300
3.295
3.290
3.285
Reference Voltage
vs. Temperature
MIC2178-3.3
MIC2178 [adj.]
175
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
1.238
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
3.280
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
5.030
REFERENCE VOLTAGE (V)
5.020
5.010
5.000
4.990
4.980
Reference Voltage
vs. Temperature
AMPLIFIER VOLTAGE GAIN
19.0
18.5
18.0
17.5
17.0
16.5
Error-Amplifier Gain
vs. Temperature
120
BIAS CURRENT (nA)
Feedback Input Bias Current
vs. Temperature
MIC2178-5.0
100
80
60
40
20
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
4.970
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
16.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
5.0
4.9
Current Limit
vs. Temperature
ON-RESISTANCE (mΩ)
250
200
150
100
50
0
High-Side Switch
On-Resistance
ON-RESISTANCE (mΩ)
125°C
85°C
25°C
0°C
350
300
250
200
150
100
50
0
2
4
Low-Side Switch
On-Resistance
125°C
85°C
25°C
0°C
CURRENT LIMIT (A)
4.8
4.7
4.6
4.5
4.4
4.3
4.2
4.1
4.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
2
4
6 8 10 12 14 16 18
INPUT VOLTAGE (V)
6 8 10 12 14 16 18
INPUT VOLTAGE (V)
12
PWM-Mode
Supply Current
OUTPUT
SWITCHING
EFFICIENCY (%)
100
95
3.3V Output
Efficiency
100
95
EFFICIENCY (%)
5V Output
Efficiency
V
IN
= 6V
SUPPLY CURRENT (mA)
10
8
6
4
2
0
2
90
85
80
75
70
65
V
IN
= 5V
8V
12V
90
8V
85
12V
80
75
70
10
SKIP
PWM
100
1000 2500
OUTPUT CURRENT (mA)
4
6 8 10 12 14 16 18
INPUT VOLTAGE (V)
60
10
SKIP
PWM
100
1000 2500
OUTPUT CURRENT (mA)
March 2005
5
M9999-031805
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