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参数资料
| 型号： | LTC1574CS#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 6/8页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK INV ADJ 16SOIC |
| 标准包装： | 50 |
| 类型： | 降压（降压），反相 |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调 |
| 输入电压： | 4 V ~ 18.5 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 最高 200kHz |
| 电流 - 输出： | 340mA，600mA |
| 同步整流器： | 无 |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 供应商设备封装： | 16-SOIC |
| 产品目录页面： | 1333 (CN2011-ZH PDF) |
LTC1574
LTC1574-3.3/LTC1574-5
APPLICATIO S I FOR ATIO
inductor L1 is chosen for its excellent self-shielding prop-
For C OUT , the RMS current rating should be at least:
I RMS ≈
erties. Open magnetic structures such as drum and rod
cores are to be avoided since they inject high flux levels
into their surroundings. This can become a major source
of noise in any converter circuit.
I PEAK
2
= 300mA
( A RMS )
Design Example
As a design example, assume V IN = 9V (nominal),
V OUT = 5V and I OUT = 350mA maximum. The LTC1574-5
is used for this application with I PGM (Pin 6) connected to
V IN . The minimum value of L is determined by assuming
the LTC1574-5 is operating in continuous mode.
I PEAK
Absolute Maximum Ratings and Latchup Prevention
The absolute maximum ratings specify that SW
(Pins 3, 14) can never exceed V IN (Pin 5) by more than
0.3V. Normally this situation should never occur. It could,
however, if the output is held up while the supply is pulled
down. A condition where this could potentially occur is
when a battery is supplying power to an LTC1574 regula-
tor and also to one or more loads in parallel with the the
= PEAK
AVG CURRENT = I OUT
I
I V 2
+ I V
regulator’s V IN . If the battery is disconnected while the
LTC1574 regulator is supplying a light load and one of the
parallel circuits is a heavy load, the input capacitor of the
= 350mA
LTC1574 regulator could be pulled down faster than the
output capacitor, causing the absolute maximum ratings
TIME
1574 ? F06
to be exceeded. The result is often a latchup which can be
( A P-P )
I RIPPLE = 4 ? 10 ? 6 ? OUT D ?
f ≈ 2 . 5 ? 10 ? 1 ? OUT ?
? V ?
Figure 6. Continuous Inductor Current
With I OUT = 350mA and I PEAK = 0.6A (I PGM = V IN ), I V = 0.1A.
The peak-to-peak ripple inductor current, I RIPPLE , is 0.5A
and is also equal to:
? V + V ?
? L ?
Solving for L in the above equation and with V D = 0.5V,
L = 44 μ H. The next higher standard value of L is 50 μ H
(example: Coiltronics CTX50-4). The operating frequency,
ignoring voltage across diode V D is:
5
? V IN ?
= 111 kHz
With the value of L determined, the requirements for C IN
destructive if V IN is reapplied. Battery disconnect is pos-
sible as a result of mechanical stress, bad battery contacts
or use of a lithium-ion battery with a built-in internal
disconnect. The user needs to assess his/her application
to determine whether this situation could occur. If so,
additional protection is necessary.
Prevention against latchup can be accomplished by
simply connecting a Schottky diode across the SW and
V IN pins as shown in Figure 7. The diode will normally be
reverse biased unless V IN is pulled below V OUT at which
time the diode will clamp the (V OUT – V IN ) potential to less
than the 0.6V required for latchup. Note that a low
leakage Schottky should be used to minimize the effect
LATCHUP
PROTECTION
SCHOTTKY
and C OUT are calculated. For C IN , its RMS current rating
should be at least:
V IN SW
LTC1574
+
V OUT
[ (
) ]
I OUT V OUT V IN ? V OUT
I RMS =
V IN
= 174 mA
1 / 2
( A RMS )
1574 F07
Figure 7. Preventing Absolute Maximum
Ratings from Being Exceeded
6
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