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| 型号： | MAX1742EEE+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 12/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC 1A 16QSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 两者兼有 |
| 输出数： | 1 |
| 输出电压： | 1.5V，1.8V，2.5V，可调 |
| 输入电压： | 3 V ~ 5.5 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 1MHz |
| 电流 - 输出： | 1A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 16-QSOP |
1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches
Table 3. Output Voltage Programming
Programming the Switching Frequency
and Off-Time
PIN
OUTPUT
The MAX1742/MAX1842 features a programmable
FBSEL
V CC
Unconnected
FB
Output voltage
Output voltage
VOLTAGE
(V)
2.5
1.5
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:
REF
GND
Output voltage
Resistive
divider
1.8
Adjustable
t OFF =
( V IN – V OUT ? V PMOS )
f PWM ( V IN ? V PMOS + V NMOS )
where:
t OFF = the programmed off-time
MAX1742
MAX1842
R1 = 50k Ω
R2 = R1(V OUT / V REF - 1)
V REF = 1.1V
LX
FB
R2
R1
V OUT
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 Ω / 1.00μs)
Figure 4. Adjustable Output Voltage
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
Recommended values for R TOFF range from 36k Ω to
430k Ω 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:
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).
L =
V OUT × t OFF
I OUT × LIR
R2 = R1 ? OUT ? 1 ?
Regulation is maintained for adjustable output voltages
when V FB = V REF . Use 50k Ω for R1. R2 is given by the
equation:
? V ?
? V REF ?
where V REF is typically 1.1V.
where: I OUT = maximum DC load current
LIR = ratio of peak-to-peak AC inductor current
to DC load current, typically 0.25
12
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