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參數(shù)資料
| 型號(hào)： | MAX1878EGC |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Analog IC |
| 中文描述： | 0.8 A SWITCHING REGULATOR, 500 kHz SWITCHING FREQ-MAX, CQCC12 |
| 封裝： | 4 X 4 MM, 0.90 MM HEIGHT, QFN-12 |
| 文件頁(yè)數(shù)： | 4/8頁(yè) |
| 文件大?。?/td> | 313K |
| 代理商： | MAX1878EGC |
E
Customizing the
MAX1800 EV Kit
Setting the Main Output Voltage
MAIN is set by a voltage divider, which drops the out-
put voltage to the 1.25V feedback threshold voltage. To
change the 3.3V setting of MAIN, change the resistor
divider ratio by changing R21. Use:
R21 = 80k
/ V
( V
MAIN
- 1.25V )
The MAIN output voltage may be set to any voltage
between 2.7V and 5.5V. For additional information, see
the MAX1800 data sheet.
Setting the LDO Output Voltage
The LDO output voltage is set by a voltage divider,
which drops the output voltage to the 1.25V feedback
threshold voltage. To change the 1.8V setting of LDO,
change the resistor divider ratio by changing R18. Use:
R18 = 80k
/ V
( V
LDO
- 1.25V )
The LDO output voltage may be set to any voltage
between 1.25V and 5.5V but must remain less than the
voltage at MAIN when powered from MAIN. The
MAX1800 EV kit is configured so that MAIN powers the
LDO input; however, opening up the short across R33
and shorting R34 will allow LDO to be powered from IN.
Setting the Flyback Circuit Voltages
(OUT1_ and OUT2_)
A flyback circuit generates OUT1_ and OUT2_. This
allows multiple, positive, or negative voltages to be
generated by a single converter and allows the volt-
ages to drop to 0V when the converter is disabled. The
transformer must be designed for a given set of output
voltages.
On the flyback circuits, only a single output voltage is
used to regulate all the voltages. All other voltages are
controlled by the turns-ratio of the transformer. If anoth-
er set of output voltages is required, a transformer with
a different secondary turns-ratio must be used. Consult
the transformer manufacturer for details. Typically the
highest power, positive voltage output of the flyback
transformer is fed back to the controller. To change the
regulated output voltage, use a different resistor in the
voltage divider. Table 2 lists the resistors used for each
output. Leave the resistors off (open) for unregulated
outputs.
For a given output voltage, the resistor value (Table 2) is:
R = 80k
/ V
( V
OUT
- 1.25V )
Setting the Step-Up Output Voltage (OUT3
and OUT4)
The output voltage of the step-up circuit voltages
(OUT3 and OUT4) may be set to any voltage above
1.25V. Note that if the battery voltage is greater than
the step-up regulation voltage, the output voltage will
rise above the regulation voltage. To set the output volt-
age, choose the voltage divider resistors. For OUT3,
choose:
R4 = 80k
/ V
( V
OUT3
- 1.25V )
For OUT4, choose:
R24 = 80k
/ V
( V
OUT4
- 1.25V )
Setting the Maximum Duty Cycle
DCON1, DCON2, and DCON3 set the maximum duty
cycle for controllers 1, 2, and 3, respectively. A resistor
divider from REF to DCON_ sets the corresponding
maximum duty cycle up to 90%. The EV kit has DCON_
shorted to REF, producing a default duty cycle of 84%.
See the MAX1800 data sheet for additional information.
Setting the Switching Frequency
All of the switching regulators are synchronized to a
single oscillator frequency. The oscillator capacitor
(C2) is charged through R1 and discharged internally
by the MAX1800. The EV kit is designed to operate at
440kHz with MAIN set to 3.3V. If a different MAIN volt-
age is used, or if a different oscillator frequency is
desired, change resistor R1 or capacitor C2. Consult
the MAX1800 data sheet for the correct values to use
for R1 and C2.
Logic Control of the Output Voltages
Each controller may be independently turned off or on
using jumpers (JU1
–
JU6) or with logic voltages. To
control an output using an external logic signal, remove
the ON/OFF jumper for that output, and place the con-
trol signal on the corresponding ON_ pad. To enable
the output, make sure that the voltage of the control
signal at the corresponding ON_ pad is >1.6V. To dis-
able it, make sure the voltage at the corresponding
ON_ pad is <0.3V.
MAX1800 Evaluation Kit
4
_______________________________________________________________________________________
OUTPUT
OUT_A
OUT_B
OUT_C
OUT1_
R13
R11
R12
OUT2_
R14
R16
R15
Table 2. Flyback Converter Feedback
Resistors
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| MAX1878EGC-T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1878EPD | 制造商:Maxim Integrated Products 功能描述: |
| MAX1878ETC+ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Dual-Output Step-Down RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1878ETC+T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Dual-Output Step-Down RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1878EVKIT | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Evaluation Kit for the MAX1878 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
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