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参数资料
| 型号： | DS1670S |
| 厂商： | DALLAS SEMICONDUCTOR |
| 元件分类： | Timer or RTC |
| 英文描述： | 0 TIMER(S), REAL TIME CLOCK, PDSO20 |
| 封装： | SOIC-20 |
| 文件页数： | 5/16页 |
| 文件大小： | 312K |
| 代理商： | DS1670S |
To choose the proper current-sense resistor, simply fol-
low the two-step procedure outlined below:
1) Determine:
Input voltage range, V+
Maximum (absolute) output voltage, VOUT
Maximum output current, ILOAD
For example, let V+ range from 4V to 6V, and
choose VOUT = -24V and IOUT = 150mA.
2) Next, referring to Figure 9, find the curve with the
lowest current limit whose output current (with the
lowest input voltage) meets your requirements.
In our example, a curve where IOUT is >150mA with a
4V input and a -24V output is optimal.
The RSENSE = 80m
(Figure 9) shows only approxi-
mately 125mA of output current with a 4V input, so we
look next at the RSENSE = 70m
line. It shows IOUT
>150mA for V+ = 4V and VOUT = -24V. The current limit
will be 0.210V / 0.070
= 3A. These curves take into
account worst-case inductor (±10%) and current-
sense trip levels, but not sense-resistor tolerance. The
switch on resistance is 70m
.
Standard wire-wound and metal-film resistors have
an inductance high enough to degrade performance.
Metal-film resistors are usually deposited on a ceramic
rod in a spiral, making their inductances relatively high.
Surface-mount (or chip) resistors have very little induc-
tance and are well suited for use as current-sense
resistors. To use through-hole resistors, IRC has a wire
resistor that is simply a band of metal shaped as a “U”
so that inductance is less than 10nH (an order of mag-
nitude less than metal-film resistors). These are avail-
able in resistance values between 5m
and 0.1.
External Switching Transistor
The MAX774/MAX775/MAX776 are capable of driving
P-channel enhancement-mode MOSFET transistors only.
The choice of power transistor is dictated by input and
output voltage, peak current rating, on-resistance, gate-
source threshold, and gate capacitance. The drain-to-
source rating must be greater than the V+ - VOUT
input-to-output voltage differential. The gate-to-source
rating must be greater than V+ (the source voltage) plus
the absolute value of the most negative swing of EXT.
For bootstrapped operation, the most negative swing of
EXT is VOUT. In nonbootstrapped operation, this may be
ground or some other negative voltage. Gate capaci-
tance is not normally a limiting factor, but values should
be less than 1nF for best efficiency. For maximum effi-
ciency, the MOSFET should have a very-low on-resis-
tance at the peak current and be capable of handling
that current. The transistor chosen for the typical operat-
ing circuit has a 30V drain-source voltage limit and a
0.07
drain-source on-resistance at VGS = -10V.
Table 1 lists suppliers of switching transistors suitable
for use with the MAX774/MAX775/MAX776.
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
______________________________________________________________________________________
13
Figure 8. MAX776 Maximum Output Current vs. Input Voltage
(VOUT = -15V)
Figure 9. MAX774/MAX775/MAX776 Maximum Output Current
vs. Input Voltage (VOUT = -24V)
MAXIMUM
OUTPUT
CURRENT
(mA)
100
INPUT VOLTAGE (V)
MAX776-FIG08
200
300
400
500
600
700
34
5
6
7
RSENSE = 0.05
RSENSE = 0.06
RSENSE = 0.07
RSENSE = 0.08
RSENSE = 0.09
VOUT = -15V
MAXIMUM
OUTPUT
CURRENT
(mA)
INPUT VOLTAGE (V)
0
3 4
5
678
9 10 11 12 13 14 15
MAX776-FIG09
200
400
600
800
RSENSE = 0.05
RSENSE = 0.06
RSENSE = 0.07
RSENSE = 0.08
RSENSE = 0.09
VOUT = -24V
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相关代理商/技术参数 |
参数描述 |
|---|---|
| DS1670S+ | 功能描述:实时时钟 Portable System Controller RoHS:否 制造商:Microchip Technology 功能:Clock, Calendar. Alarm RTC 总线接口:I2C 日期格式:DW:DM:M:Y 时间格式:HH:MM:SS RTC 存储容量:64 B 电源电压-最大:5.5 V 电源电压-最小:1.8 V 最大工作温度:+ 85 C 最小工作温度: 安装风格:Through Hole 封装 / 箱体:PDIP-8 封装:Tube |
| DS1671H | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Dual Clock Driver |
| DS1671J-8 | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Dual Clock Driver |
| DS-1671ZJ | 制造商:Hikvision USA 功能描述:4" Indoor Ceiling Embedded Mount |
| DS1672 | 制造商:DALLAS 制造商全称:Dallas Semiconductor 功能描述:Low Voltage Serial Timekeeping Chip |
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