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PDF MIC4742 Data sheet ( Hoja de datos )
| Número de pieza | MIC4742 | |
| Descripción | 2 MHz Dual 2A Integrated Switch Buck Regulator | |
| Fabricantes | Micrel Semiconductor | |
| Logotipo |  |
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MIC4742
2 MHz Dual 2A Integrated Switch
Buck Regulator
www.datasheet4u.com
General Description
The Micrel MIC4742 is a high efficiency dual PWM buck
(step-down) regulator that provides dual 2A current output.
The MIC4742 operates at 2MHz. A proprietary internal
compensation technique allows a closed loop bandwidth of
over 200kHz.
The low on-resistance internal P-Channel MOSFET of the
MIC4742 allows efficiencies over 92%, reduces external
components count and eliminates the need for an
expensive current sense resistor.
The MIC4742 operates from 2.9V to 5.5V input and the
output can be adjusted down to 0.6V. The device can
operate with a maximum duty cycle of 100% for use in low-
dropout conditions.
The MIC4742 is available in the exposed pad 16-pin
3mm x 3mm MLF® and EPAD TSSOP-16 packages with a
junction operating range from –40°C to +125°C.
All support documentation can be found on Micrel’s web
site at: www.micrel.com.
Features
• 2.9 to 5.5V supply voltage
• 2MHz PWM mode
• 2A Dual output
• Greater than 92% efficiency
• 100% maximum duty cycle
• Adjustable output voltage option down to 0.6V
• Ultra-fast transient response
• Ultra-small external components
Stable with a 1µH inductor and a 4.7µF output
capacitor
• Fully integrated 2A MOSFET switches
• Micro-power shutdown
• Thermal shutdown and current limit protection
• Available in a 3mm x 3mm 16-pin MLF® and 16-pin
TSSOP
• –40°C to +125°C junction temperature range
Applications
• Broadband: xDSL modems
• Automotive satellite radios
• HD STB, DVD/TV recorder
• Computer peripherals: printers and graphic cards
• FPGA/ASIC
• General point of load
Typical Application
5.0Vin 3.3Vout Efficiency
100
98
96
94
92
90
88
86
84
82
80
0
0.4 0.8 1.2 1.6
OUTPUT CURRENT (A)
2
2A 2MHz Dual Buck Regulator
MLF and MicroLeadFrame are registered trademarks of Amkor Technology, 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
March 2009
1 M9999-030209-D
1 page  
Micrel, Inc.
Typical Characteristics
3.3Vin 1.0Vout Efficiency
80
78
76
www.datas74heet4u.com
72
70
68
66
64 3.0Vin
3.3Vin
62
3.6Vin
60
0 0.4 0.8 1.2 1.6 2
OUTPUT CURRENT (A)
5.0Vin 1.2Vout Efficiency
84
82
80
78
76
74
72
70
68 4.5Vin
66 5.0Vin
5.5Vin
64
0 0.4 0.8 1.2 1.6 2
OUTPUT CURRENT (A)
3.3Vin 1.8Vout Efficiency
92
90
88
86
84
82
80
78
76 3.0Vin
3.3Vin
74
3.6Vin
72
0 0.4 0.8 1.2 1.6 2
OUTPUT CURRENT (A)
5.0Vin 2.5Vout Efficiency
96
94
92
90
88
86
84
82
80 4.5Vin
5.0Vin
78
5.5Vin
76
0 0.4 0.8 1.2 1.6 2
OUTPUT CURRENT (A)
March 2009
5.0Vin 1.0Vout Efficiency
80
78
76
74
72
70
68
66
64 4.5Vin
5.0Vin
62
5.5Vin
60
0 0.4 0.8 1.2 1.6 2
OUTPUT CURRENT (A)
3.3Vin 1.5Vout Efficiency
88
86
84
82
80
78
76
74
72
70
68
0
3.0Vin
3.3Vin
3.6Vin
0.4 0.8 1.2 1.6
OUTPUT CURRENT (A)
2
5.0Vin 1.8Vout Efficiency
92
90
88
86
84
82
80
78
76
74
72
0
4.5Vin
5.0Vin
5.5Vin
0.4 0.8 1.2 1.6
OUTPUT CURRENT (A)
2
5.0Vin 3.3Vout Efficiency
100
98
96
94
92
90
88
86
84 4.5Vin
5.0Vin
82
5.5Vin
80
0 0.4 0.8 1.2 1.6 2
OUTPUT CURRENT (A)
5
MIC4742
3.3Vin 1.2Vout Efficiency
84
82
80
78
76
74
72
70
68
66
64
0
3.0Vin
3.3Vin
3.6Vin
0.4 0.8 1.2 1.6
OUTPUT CURRENT (A)
2
5.0Vin 1.5Vout Efficiency
88
86
84
82
80
78
76
74
72
70
68
0
4.5Vin
5.0Vin
5.5Vin
0.4 0.8 1.2 1.6
OUTPUT CURRENT (A)
2
3.3Vin 2.5Vout Efficiency
96
94
92
90
88
86
84
82
80 3.0Vin
3.3Vin
78
3.6Vin
76
0 0.4 0.8 1.2 1.6 2
OUTPUT CURRENT (A)
Load Regulation
1.005
1.000
0.995
0.990
0.985
0
Vin=3.3V
0.4 0.8 1.2 1.6
OUTPUT CURRENT (A)
2
M9999-030209-D
5 Page 
Micrel, Inc.
MIC4742
Ipk
=
IOUT
+
(VIN
−
VOUT
)×
VOUT
VIN
2 × fsw × L
Figure 4 demonstrates the off-time. During the off-time,
the high-side internal P-channel MOSFET turns off.
wwSwin.dcaetasthheeet4cuu.rcroemnt in the inductor has to discharge, the
current flows through the free-wheeling Schottky diode
to the output. In this case, the inductor discharge rate is
(where VD is the diode forward voltage);
− (VOUT + VD )
L
The total off time can be calculated as;
TOFF
=
1− D
fsw
Figure 4. Off-Time
Discontinuous Operation
Discontinuous operation is when the inductor current
discharges to zero during the off cycle. Figure 5
demonstrates the switch voltage and inductor currents
during discontinuous operation.
Figure 5. Discontinuous Operation
When the inductor current (IL) has completely
discharged, the voltage on the switch node rings at the
frequency determined by the parasitic capacitance and
the inductor value. In Figure 5, it is drawn as a DC
voltage, but to see actual operation (with ringing) refer to
the functional characteristics.
Discontinuous mode of operation has the advantage
over full PWM in that at light loads, the MIC4742 will skip
pulses as necessary, reducing gate drive losses,
drastically improving light load efficiency.
Efficiency Considerations
Calculating the efficiency is as simple as measuring
power out and dividing it by the power in;
Efficiency = POUT × 100
PIN
Where input power (PIN) is;
PIN = VIN × IIN
and output power (POUT) is calculated as;
POUT = VOUT × IOUT
The Efficiency of the MIC4742 is determined by several
factors.
• Rdson (Internal P-channel Resistance)
• Diode conduction losses
• Inductor Conduction losses
• Switching losses
Rdson losses are caused by the current flowing through
the high side P-channel MOSFET. The amount of power
loss can be approximated by;
PSW = RDSON × IOUT 2 × D
March 2009
11 M9999-030209-D
11 Page | ||
| Páginas | Total 23 Páginas | |
| PDF Descargar | [ Datasheet MIC4742.PDF ] | |
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