MIC2177
2.5A Synchronous Buck Regulator
General Description
The Micrel MIC2177 is a 200kHz synchronous buck (step-
down) switching regulator designed for high-efficiency,
battery-powered applications.
The MIC2177 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 MIC2177 achieves high efficiency over a wide output
current range by switching between PWM and skip mode.
Operating mode is automatically selected according to output
conditions. Switching frequency is preset to 200kHz and can
be synchronized to an external clock signal of up to 300kHz.
The MIC2177 uses current-mode control with internal current
sensing. Current-mode control provides superior line
regulation and makes the regulator control loop easy to
compensate. 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 MIC2177 is packaged in a 20-pin wide power SO
package with an operating temperature range of –40°C to
+85°C.
See the MIC2178 for externally selected PWM or skip-mode
operation.
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
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
– 500µA in skip mode
– < 5µA in shutdown mode
•
100% duty cycle for low dropout operation
•
Current-mode control
– Simplified loop compensation
– Superior line regulation
•
Current limit
•
Thermal shutdown
•
Undervoltage lockout
Applications
•
High-efficiency, battery-powered supplies
•
Buck (step-down) dc-to-dc converters
•
Cellular telephones
•
Laptop computers
•
Hand-held instruments
•
Battery Charger
_________________________________________________________________________________________________________
Typical Application
V
IN
5.4V to 18V
C1
22µF
35V
ENABLE
SHUTDOWN
20
18
11
100
U1
EN
1,2,9
5V Output
Efficiency
VIN
OUT
SW
MIC
SYNC
2177-5.0
PGND
AUTO
FB
COMP SGND BIAS
13
14–17
19
95
3,8
4–7
12
L1, 50µH
D1
MBRS130L
EFFICIENCY (%)
10
V
OUT
5V/1A
C2
100µF
10V
90
85
80
75
V
IN
= 6V
2.2
nF
R1
10k
C
C
6.8nF
C3
0.01µF
R1
10k
70
10
SKIP
PWM
100
1000 2500
OUTPUT CURRENT (mA)
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (
408
) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
April 2008
M9999-042108
Micrel, Inc.
MIC2177
Ordering Information
Part Number
MIC2177-3.3BWM
MIC2177-5.0BWM
MIC2177BWM
MIC2177-3.3YWM
Output
Voltage
3.3V
5.0V
Adj.
3.3V
Switching
Frequency
200kHz
200kHz
200kHz
200kHz
Temperature Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Package
20-Pin Wide SOIC
20-Pin Wide SOIC
20-Pin Wide SOIC
20-Pin Wide SOIC
Lead Finish
Standard
Standard
Standard
Pb-Free
Pin Configuration
VIN 1
VIN 2
SW 3
P GND 4
P GND 5
P GND 6
P GND 7
SW 8
VIN 9
OUT 10
20 E N
19 B I A S
18 S Y N
C
17 S G N D
16 S G N D
15 S G N D
14 S G N D
13 C O M P
12 F B
O
11 AUT
20-Pin Wide SOIC (WM)
April 2008
2
M9999-042108
Micrel, Inc.
MIC2177
Pin Description
Pin Number
1, 2, 9
Pin Name
VIN
Pin Function
Supply Input: Controller and switch supply. Unregulated supply input to internal
regulator, output switches, and control circuitry. Requires bypass capacitor to PGND.
All three pins must be connected to VIN.
Switch (Output): Internal power MOSFET switch output. Both pins must be
externally connected together.
Power Ground: Output stage ground connections. Connect all pins to a common
ground plane.
Output Voltage Sense (Input): Senses output voltage to determine minimum switch
current for PWM operation. Connect directly to VOUT.
Automatic Mode: Connect 2.2nF timing capacitor for automatic PWM-/skip-mode
switching. Regulator operates exclusively in PWM mode when pin is pulled low.
Feedback (Input): Error amplifier inverting input. For adjustable output version,
connect FB to external resistive divider to set output voltage. For 3.3V and 5V fixed
output versions, connect FB directly to output.
Compensation: Internal error amplifier output. Connect to capacitor or series RC
network to compensate the regulator control loop.
Signal Ground: Ground connection of control section. Connect all pins to common
ground plane.
Frequency Synchronization (Input): Optional clock input. Connect to external clock
signal to synchronize oscillator. Leading edge of signal above 1.7V terminates
switching cycle. Connect to SGND if not used.
Bias Supply: Internal 3.3V bias supply output. Decouple with 0.01µF bypass
capacitor and 10kΩ 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.
3, 8
4, 5, 6, 7
10
11
12
SW
PGND
OUT
AUTO
FB
13
14, 15, 16, 17
18
COMP
SGND
SYNC
19
20
BIAS
EN
April 2008
3
M9999-042108
Micrel, Inc.
MIC2177
Absolute Maximum Ratings
Supply Voltage [100ms transient] (V
IN
) ..........................18V
Output Switch Voltage (V
SW
). .........................................18V
Output Switch Current (I
SW
)...........................................6.0A
Enable, Output-Sense Voltage (V
EN
, V
OUT
). ...................18V
Sync Voltage (V
SYNC
)........................................................6V
Operating Ratings
Supply Voltage (V
IN
)....................................... 4.5V to 16.5V
Junction Temperature (T
J
) ........................ –40°C to +125°C
Electrical Characteristics
V
IN
= 7.0V; T
A
= 25°C,
bold
values indicate –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
MIC2177 [adj.]: V
OUT
= 3.3V, I
LOAD
= 0
MIC2177 [adj.]: V
OUT
= 3.3V,
5V
≤
V
IN
≤
16V, 10mA
≤
I
LOAD
≤
2A
MIC2177-5.0: I
LOAD
= 0
MIC2177-5.0:
6V
≤
V
IN
≤
16V, 10mA
≤
I
LOAD
≤
2A
MIC2177-3.3: I
LOAD
= 0
MIC2177-3.3:
5V
≤
V
IN
≤
16V, 10mA
≤
I
LOAD
≤
2A
V
TH
V
TL
I
FB
A
VOL
Feedback Bias Current
Error Amplifier Gain
Error Amplifier Output Swing
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
SYNC Leakage
Current Limit
Switch On-Resistance
V
SYNC
= 0V to 5.5V
PWM mode, V
IN
= 12V
skip mode
high-side switch, V
IN
= 12V
low-side switch, V
IN
= 12V
V
FB
= 1.0V
V
FB
= 1.5V
220
0.8
500
–1
3.8
0.01
4.7
600
90
110
250
250
1
5.7
1.6
Undervoltage Lockout
upper threshold
lower threshold
MIC2177 [adj.]
MIC2177-5.0, MIC2177-3.3
0.6V
≤
V
COMP
≤
0.8V
upper limit
Lower limit
source and sink
15
160
100
300
400
300
2.2
15
0.9
3.9
3.10
1.22
3.20
3.14
4.85
4.85
4.75
3.20
3.20
3.14
Min
Typ
1.0
500
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
Max
1.5
650
25
3.40
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
V
nA
µA
V
V
V
µA
kHz
%
ns
kHz
V
ns
µA
A
mA
mΩ
mΩ
April 2008
4
M9999-042108
Micrel, Inc.
Symbol
I
SW
I
EN
Parameter
Output Switch Leakage
Enable Threshold
Enable Leakage
AUTO Threshold
AUTO Source Current
Minimum Switch Current for
PWM Operation
V
FB
= 1.5V, VAUTO < 0.8V
V
IN
– V
OUT
= 0V
V
IN
– V
OUT
= 3V
V
EN
= 0V to 5.5V
Condition
V
SW
= 16.5V
0.8
–1
0.8
7
Min
Typ
1
1.6
0.01
1.6
11
220
420
15
Max
10
2.2
1
MIC2177
Units
µA
V
µA
V
µA
mA
mA
General Note:
Devices are ESD sensitive. Handling precautions recommended.
April 2008
5
M9999-042108
嵌入式系统
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