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參數(shù)資料
| 型號(hào)： | CM3702-50MS |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHED CAPACITOR REGULATOR, DSO10 |
| 封裝： | MO-229WEED, TDFN-10 |
| 文件頁(yè)數(shù)： | 2/12頁(yè) |
| 文件大?。?/td> | 298K |
| 代理商： | CM3702-50MS |
2006 California Micro Devices Corp. All rights reserved.
10
490 N. McCarthy Blvd., Milpitas, CA 95035-5112
●
Tel: 408.263.3214
●
Fax: 408.263.7846
●
www.cmd.com 03/20/06
CM3702
Application Information
Ripple Frequency
The charge pump internal oscillation frequency is
about 250kHz. However, this is the continuous, free-
running frequency, which is usually only seen while the
charge pump is powering up. After the charge pump
output voltage (CS) reaches approximately 5.8V, the
charge pump pauses until the CS voltage drops to
approximately 5.7V. Then the charge pump restarts
and runs until the CS voltage is greater than approxi-
mately 5.8V, when it pauses again, and this process
repeats. This gives rise to a sawtooth 'ripple' waveform
on CS which can have a much lower frequency than
250kHz. This mode of operation is necessary to con-
serve power - if it were not done this way then a much
larger package with heatsink would be required.
The frequency of this 'ripple' is affected by VIN, IOUT,
CS capacitor value and CP capacitor value.
Guidelines for Choosing Values for External
Capacitors
(1) To find CP: specify value of VIN, and highest value
of IOUT:
If VIN= 3.3V +/- 5%, then minimum value
of CP (F) = IOUT (mA) / 85.
If VIN= 5.0V +/- 10%, then minimum value
of CP (F) = IOUT (mA) / 700
(2) Ci, the VIN decoupling capacitor, should typically be
much greater than CP to prevent voltage droop during
CP charging.
Excessive glitches on VIN will affect the output voltage
VOUT.
Typically Ci is 10X greater than CP. But usually there
are already some capacitors on this supply, so adding
extra capacitors is not necessary - simply move an
already-present low-ESR capacitor close to the
CM3702.
This is especially important for VIN = 5V.
(3) Choose value of CS. CS should be small to ensure
that the ripple frequency is high, but CS should be at
least 2x greater than CP otherwise the ripple amplitude
will be very high. Reducing the value of CS will
increase the ripple frequency.
Examples of CS ripple frequencies (CS=10μF,
TA=25°C) are shown in following tables:
(4) CO, the optional VOUT decoupling capacitor, helps
minimize noise and improve load regulation. 0.1F -
100F is recommended.
(5) CBYP, the optional bypass capacitor helps reduce
noise in the LDO. 0.1F is recommended.
After choosing external component values, check in-
system performance (at min/max VIN, max tempera-
ture, and min/max IOUT). See the troubleshooting guide
on next page for tips if there are problems.
Charge Pump Noise
The charge pump is 'digital' in operation and can pro-
duce digital noise at both the free-running frequency
and at the ripple frequency.
To minimize noise, PCB grounding is important! This
part requires short, low-impedance ground connec-
tions for DGND (pin 1), GND (pin 4), the VIN decou-
pling capacitor (pin 2), the CS capacitor (pin 3), the
Bypass decoupling capacitor (pin 5) and the VOUT
decoupling capacitor (pin 8). All decoupling capacitors
and the CS capacitor should be low-ESR ceramics.
The CP capacitor does NOT need to be low-ESR.
CP = 0.47μF
VIN
IOUT
CS Frequency
3.14
15mA
46kHz
3.60
15mA
35kHz
4.50
70mA
76kHz
5.50
70mA
56kHz
CP = 1.0μF
VIN
IOUT
CS Frequency
3.14
100mA
250kHz
3.60
100mA
110kHz
4.50
100mA
67kHz
5.50
100mA
49kHz
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