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參數(shù)資料
| 型號(hào)： | CM3702-50MS |
| 元件分類(lèi)： | 穩(wěn)壓器 |
| 英文描述： | SWITCHED CAPACITOR REGULATOR, DSO10 |
| 封裝： | MO-229WEED, TDFN-10 |
| 文件頁(yè)數(shù)： | 3/12頁(yè) |
| 文件大小： | 298K |
| 代理商： | CM3702-50MS |
2006 California Micro Devices Corp. All rights reserved.
03/20/06
490 N. McCarthy Blvd., Milpitas, CA 95035-5112
●
Tel: 408.263.3214
●
Fax: 408.263.7846
●
www.cmd.com
11
CM3702
Efficiency
The power efficiency in % of the combined charge
pump and LDO is approximately:
100 x (VOUT) / (VIN x 2)
Power Dissipation
The dissipation of the part is approximately:
((VIN x 2) - VOUT) x IOUT
The MSOP-10 package heats at a rate of about 200°C/
W (
θJA). Note that this value is approximate because it
depends upon the copper tracks and ground planes on
the pcb. If VIN = 5V and IOUT = 100mA then the power
dissipation will be approximately 500mW. Multiplying
this by the
θJA of 200, the part's internal temperature
will be about 100°C higher than the ambient tempera-
ture. If the ambient temperature is 70°C then the inter-
nal temperature will be approximately 170°C which will
typically trigger the overtemperature circuit and
depower the part.
Internal temperature = Ambient temperature
+ (
θJA x Power dissipation )
(Must be less than 170°C)
How to Reduce the Power Dissipation of the Part
and How to Get More Than 100mA
If VIN = 5V typ., then the charge pump / LDO combina-
tion is capable of providing more than 100mA. The only
problem is power dissipation.
If the input voltage is lowered using an external diode
then the output current can be increased without caus-
ing the part to overheat. The circuit below illustrates an
example of how to increase the output current.
Using this circuit, IOUT can be 200mA if VIN = 4.75V,
and yet the part will not overheat even if VIN = 5.25V,
IOUT=200mA and the ambient temperature is 85°C.
Warnings
The charge pump output CS (pin 3) must not be
shorted to GND or held below its internally-set voltage
while the part is powered. This usually results in the
destruction of the part.
With VIN = 5V, the maximum current that can be con-
tinuously drawn from CS is approximately 100mA dc.
Never short CP+ (pin 9) to CP- (pin 10). This will cause
large currents to flow from VIN to DGND through the
part, usually causing its destruction. This will happen
even if EN_CHIP and EN_LDO are off.
Troubleshooting Guide
1) Is the output voltage is drooping under heavy loads?
Perhaps the charge pump cannot provide the neces-
sary current. Try increasing the value of CP. If that
does not work then is VIN too low? Is VIN dropping dur-
ing the CP charging cycle? If VIN is not suitably decou-
pled and drops below 3.0V then the available current
will be very low.
2) Is the output voltage oscillating between 5V and 0V?
The part may be reaching its overtemperature limit.
Reduce current consumption, reduce
θJA or add an
external diode on the input to reduce VIN.
3. Is the part too noisy? Try increasing value (or reduc-
ing ESR) of CS, Ci, CO, CBYP. At minimum current the
charge pump ripple frequency will be low. If VOUT noise
is at the charge pump ripple frequency then change
values of CP and CS. Reducing the input voltage VIN
will reduce the charge pump ripple frequency noise on
VOUT.
4. Will the part power up? Pin 6 must be HIGH to
power up. Even if pin 7 is HIGH, pin 6 must also be
high to power up.
5. Can the cold start power-up time be reduced? Yes,
by reducing the value of the BYP capacitor.
CM3702
4
3
2
1
6
7
8
9
MSOP-10
5
10
5V
Ci
10
μF
CS
3
μF
+
CBYP
0.1
μF
+
VOUT
CO
0.1
μF
+
CP
+
Enable
1
μF
PACDN042
±10%
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