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参数资料
| 型号： | MAX1742-MAX1842 |
| 厂商： | Maxim Integrated Products, Inc. |
| 元件分类： | 数字信号处理 |
| 英文描述： | Replaced by TMS320C6410 : Digital Signal Processor 40-PDIP 0 to 0 |
| 中文描述： | 1A/2.7A的1MHz，降压型同步整流和内部开关稳压器 |
| 文件页数： | 12/16页 |
| 文件大小： | 597K |
| 代理商： | MAX1742-MAX1842 |
M
1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches
12
______________________________________________________________________________________
2) Select the constant off-time as a function of input
voltage, output voltage, and switching frequency.
3) Select R
TOFF
as a function of off-time.
4) Select the inductor as a function of output voltage,
off-time, and peak-to-peak inductor current.
Setting the Output Voltage
The output of the MAX1742/MAX1842 is selectable
between one of three preset output voltages: 2.5V,
1.8V, and 1.5V. For a preset output voltage, connect FB
to the output voltage and connect FBSEL as indicated
in Table 3. For an adjustable output voltage, connect
FBSEL to GND and connect FB to a resistive divider
between the output voltage and ground (Figure 4).
Regulation is maintained for adjustable output voltages
when V
FB
= V
REF
. Use 50k
for R1. R2 is given by the
equation:
where V
REF
is typically 1.1V.
Programming the Switching Frequency
and Off-Time
The MAX1742/MAX1842 features a programmable
PWM mode switching frequency, which is set by the
input and output voltage and the value of R
TOFF
, con-
nected from TOFF to GND. R
TOFF
sets the PMOS
power switch off-time in PWM mode. Use the following
equation to select the off-time according to your
desired switching frequency in PWM mode:
where:
t
OFF
= the programmed off-time
V
IN
= the input voltage
V
OUT
= the output voltage
V
PMOS
= the voltage drop across the internal
PMOS power switch
V
NMOS
= the voltage drop across the internal
NMOS synchronous-rectifier switch
f
PWM
= switching frequency in PWM mode
Select R
TOFF
according to the formula:
R
TOFF
= (t
OFF
- 0.07μs) (110k
/ 1.00μs)
Recommended values for R
TOFF
range from 36k
to
430k
for off-times of 0.4μs to 4μs.
Inductor Selection
The key inductor parameters must be specified: inductor
value (L) and peak current (I
PEAK
). The following equa-
tion includes a constant, denoted as LIR, which is the
ratio of peak-to-peak inductor AC current (ripple current)
to maximum DC load current. A higher value of LIR allows
smaller inductance but results in higher losses and ripple.
A good compromise between size and losses is found at
approximately a 25% ripple-current to load-current ratio
(LIR = 0.25), which corresponds to a peak inductor cur-
rent 1.125 times the DC load current:
where: I
OUT
= maximum DC load current
LIR = ratio of peak-to-peak AC inductor current
to DC load current, typically 0.25
L
V
t
I
LIR
OUT
OFF
OUT
×
=
×
t
V
V
V
+
f
V
V
V
OFF
IN
(
OUT
PMOS
PWM
IN
PMOS
NMOS
–
=
(
)
)
R2
R1
V
V
1
OUT
REF
=
Figure 4. Adjustable Output Voltage
PIN
2.5
V
CC
Output voltage
1.5
1.8
REF
Output voltage
Adjustable
GND
Resistive
divider
FB
OUTPUT
VOLTAGE
(V)
FBSEL
Unconnected
Output voltage
Table 3. Output Voltage Programming
LX
R2
R1
R1 = 50k
R2 = R1(V
OUT
/ V
REF
- 1)
V
REF
= 1.1V
FB
V
OUT
MAX1742
MAX1842
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| MAX17435ETG+T | 功能描述:电池管理 High f SMBus Battery Charger RoHS:否 制造商:Texas Instruments 电池类型:Li-Ion 输出电压:5 V 输出电流:4.5 A 工作电源电压:3.9 V to 17 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:VQFN-24 封装:Reel |
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| MAX1744AUB | 功能描述:DC/DC 开关控制器 Step-Down DC/DC Controller RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
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