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PDF MIC2169A Data sheet ( Hoja de datos )
| Número de pieza | MIC2169A | |
| Descripción | 500kHz PWM Synchronous Buck Control IC | |
| Fabricantes | Micrel Semiconductor | |
| Logotipo |  |
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MIC2169A
MIC2169A
Micrel
500kHz PWM Synchronous Buck Control IC
General Description
The MIC2169A is a high-efficiency, simple to use 500kHz
PWM synchronous buck control IC housed in a small MSOP-
10 package. The MIC2169Aallows compact DC/DC solutions
with a minimal external component count and cost.
The MIC2169A operates from a 3V to 14.5V input, without
the need of any additional bias voltage. The output voltage
can be precisely regulated down to 0.8V. The adaptive all
N‑Channel MOSFET drive scheme allows efficiencies over
95% across a wide load range.
The MIC2169A senses current across the high-side N-
Channel MOSFET, eliminating the need for an expensive
and lossy current-sense resistor. Current limit accuracy is
maintained by a positive temperature coefficient that tracks
the increasing RDS(ON) of the external MOSFET. Further cost
and space are saved by the internal in-rush-current limiting
digital soft-start.
The MIC2169A is available in a 10-pin MSOP package, with
a wide junction operating range of –40°C to +125°C.
All support documentation can be found on Micrel’s web site
at www.micrel.com.
Features
• 3V to 14.5V input voltage range
• Adjustable output voltage down to 0.8V
• Up to 95% efficiency
• 500kHz PWM operation
• Adjustable current limit senses high-side N-Channel
MOSFET current
• No external current-sense resistor
• Adaptive gate drive increases efficiency
• Overvoltage protection protects the load in fault
conditions
• Dual mode current limit speeds up recovery time
• Hiccup mode short-circuit protection
• Internal soft-start
• Dual function COMP and EN pin allows low-power shut-
down
• Small size MSOP 10-lead package
Applications
• Point-of-load DC/DC conversion
• Set-top boxes
• Graphic cards
• LCD power supplies
• Telecom power supplies
• Networking power supplies
• Cable modems and routers
Typical Application
VIN = 5V
100F
5
150pF
100nF
4k
0.1µF
SD103BWS
4.7F
0.1F
0.1F
VDD
BST
CS
VIN HSD
MIC2169A
VSW
COMP/EN
LSD
GND FB
2
1k
IRF7821
2.5H
IRF7821
1.4
1000pF
3.3V
10k
3.24k
150F x 2
MIC2169A Adjustable Output 500kHz Converter
100
95
90
85
80
75
70
65
60
55
50 0
MIC2169A Efficiency
VIN = 5V
VOUT = 3.3V
2 4 6 8 10 12 14 16
ILOAD (A)
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 2009
1 M9999-040609
1 page  
MIC2169A
Typical Characteristics
VIN = 5V
PWM Mode Supply Current
2.9 vs. Temperature
2.7
2.5
2.3
2.1
1.9
1.7
1.5
1.3
1.1
0.9
0.7
0.5-40 -20 0 20 40 60 80 100120140
TEMPERATURE (C)
0.806
VFB vs. Temperature
0.804
0.802
0.800
0.798
0.796
0.794
0.792-60 -30 0 30 60 90 120 150
TEMPERATURE (C)
VDD Line Regulation
vs. Temperature
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0-60 -30 0 30 60 90 120 150
TEMPERATURE (C)
Current Limit Foldback
4
3
2
1 Top MOSFET = Si4800
RCS = 1k
00 2 4 6 8
ILOAD (A)
10
April 2009
PWM Mode Supply Current
vs. Supply Voltage
2.0
1.5
1.0
0.5 0
5 10 15
SUPPLY VOLTAGE (V)
VDD Line Regulation
6
5
4
3
2
1
00 5 10 15
VIN (V)
Oscillator Frequency
vs. Temperature
550
540
530
520
510
500
490
480
470
460
450-60 -30 0 30 60 90 120 150
TEMPERATURE (C)
Overcurrent Trip Point
vs. Temperature
260
240
220
200
180
160
140
120
100-60 -30 0 30 60 90 120 150
TEMPERATURE (C)
5
Micrel
0.8010
VFB Line Regulation
0.8005
0.8000
0.7995
0.7990
0.7985
0.7980 0
5 10
VIN (V)
15
5.02 VDD Load Regulation
5.00
4.98
4.96
4.94
4.92
4.90 0
5 10 15 20 25 30
LOAD CURRENT (mA)
Oscillator Frequency
vs. Supply Voltage
1.5
1.0
0.5
0
-0.5
-1.0
-1.5 0
5 10
VIN (V)
15
M9999-040609
5 Page 
MIC2169A
00
50
100
150
180
100
100
1.103
1 .104
f
1 .105
1 .106
1000000
Figure 5. Phase Curve for G(s)
It can be seen from the transfer function G(s) and the gain
curve that the output inductor and capacitor create a two pole
system with a break frequency at:
fLC 2
1
L COUT
Therefore, fLC = 3.6kHz
By looking at the phase curve, it can be seen that the output
capacitor ESR (0.050Ω) cancels one of the two poles (LCOUT)
system by introducing a zero at:
fZERO
2
1
ESR
COUT
Therefore, FZERO = 6.36kHz.
From the point of view of compensating the voltage loop, it is
recommended to use higher ESR output capacitors since they
provide a 90° phase gain in the power path. For comparison
purposes, Figure 6, shows the same phase curve with an
ESR value of 0.002Ω.
00
Micrel
stabilize the MIC2169A voltage control loop by using high
ESR value output capacitors.
gm Error Amplifier
It is undesirable to have high error amplifier gain at high
frequencies because high frequency noise spikes would be
picked up and transmitted at large amplitude to the output,
thus, gain should be permitted to fall off at high frequencies.
At low frequency, it is desired to have high open-loop gain to
attenuate the power line ripple. Thus, the error amplifier gain
should be allowed to increase rapidly at low frequencies.
The transfer function with R1, C1, and C2 for the internal
gm error amplifier can be approximated by the following
equation:
Error Amplifier(z)
gm
s
C1
1 R1 S
C2 1 R1
C1
C1 C2
C1 C2
S
The above equation can be simplified by assuming
C2<<C1,
Error Amplifier(z)
gm
s
1 R1 S
C11 R1
C1
C2
S
From the above transfer function, one can see that R1 and
C1 introduce a zero and R1 and C2 a pole at the following
frequencies:
Fzero= 1/2 π × R1 × C1
Fpole = 1/2 π × C2 × R1
Fpole@origin = 1/2 π × C1
Figures 7 and 8 show the gain and phase curves for the above
transfer function with R1 = 9.3k, C1 = 1000pF, C2 = 100pF,
and gm = .005Ω–1. It can be seen that at 50kHz, the error
amplifier exhibits approximately 45° of phase margin.
60 60
50 40
100
150
180
100
100
1.103
1 .104
f
1 .105
1 .106
1000000
Figure 6. The Phase Curve with ESR = 0.002Ω
It can be seen from Figure 5 that at 50kHz, the phase is
approximately –90° versus Figure 6 where the number is
–150°. This means that the transconductance error ampli-
fier has to provide a phase boost of about 45° to achieve a
closed loop phase margin of 45° at a crossover frequency
of 50kHz for Figure 4, versus 105° for Figure 6. The simple
RC and C2 compensation scheme allows a maximum error
amplifier phase boost of about 90°. Therefore, it is easier to
April 2009
11
20
.001
1 .103
1000
1 .104
1 .105
f
1 .106
1 .107
10000000
Figure 7. Error Amplifier Gain Curve
M9999-040609
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet MIC2169A.PDF ] | |
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