Datasheet > LTC1174

LTC1174

更新时间： 2023-12-20 18:44:20

品牌	Logo	应用领域
亚德诺 - ADI		转换器
页数	文件大小	规格书
20页	256K
描述
高效率、降压型和负输出 DC/DC 转换器

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LTC1174 数据手册

LTC1174

LTC1174-3.3/LTC1174-5

W U U

APPLICATIO S I FOR ATIO

Catch Diode Selection

comparedwitha1.25Vreferencevoltage. Withthecurrent

going into Pin 3 being negligible, the following expression

is used for setting the trip limit:

Thecatchdiodecarriesloadcurrentduringtheoff-time.The

average diode current is therefore dependent on the

P-channel switch duty cycle. At high input voltages the

diode conducts most of the time. As V_INapproaches V_OUT

the diode conducts only a small fraction of the time. The

most stressful condition for the diode is when the output is

short-circuited. Under this condition the diode must safely

handleI_PEAKatcloseto100%dutycycle.Afastswitchingdiode

must also be used to optimize efficiency. Schottky diodes are

a good choice for low forward drop and fast switching times.

Most LTC1174 circuits will be well served by either a 1N5818,

a MBRS140T3 or a MBR0520L Schottky diode.

⎛

⎝

R4⎞

V_LBTRIP= 1.25 1+

⎜

⎟

⎠

When the LTC1174 is shut down, the low-battery detector

is inactive.

LTC1174

–

1.25V

REFERENCE

Short-Circuit Protection

1174 F03

The LTC1174 is protected from output short by its internal

current limit. Depending on the condition of I_PGMpin, the

limit is either set to 340mA or 600mA. In addition, the off-

time of the switch is increased to allow the inductor’s

current to decay far enough to prevent any current build-up

(see Figure 2).

Figure 3. Low-Battery Comparator

LTC1174 Adjustable/Low Noise Applications

The LTC1174 develops a 1.25V reference voltage between

thefeedback(Pin1)terminalandground(seeFigure4).By

selecting resistor R1, a constant current is caused to flow

through R1 and R2 to set the overall output voltage. The

regulated output voltage is determined by:

I_PGM= V_IN

⎛

⎝

R ⎞

V_OUT= 1.25 1+

⎜

⎟

⎠

I_PGM= 0

For most applications, a 30k resistor is suggested for R1.

To prevent stray pickup, a 100pF capacitor is suggested

across R1 located close to the LTC1174. Alternatively, a

capacitor across R2 can be used to increase the switching

frequency for low noise operation.

GND

1174 F02

L = 100µH

V_IN= 13.5V

20µs/DIV

Figure 2. Inductor's Current with Output Shorted

Inverting Applications

Low-Battery Detector

The LTC1174 can easily be set up for a negative output

voltage. If –5V is desired, the LTC1174-5 is ideal for this

application as it requires the least components. Figure 5

shows the schematic for this application. Note that the

Thelow-batteryindicatorsensestheinputvoltagethrough

anexternalresistivedivider. Thisdividedvoltageconnects

to the “–” input of a voltage comparator (Pin 3) which is

1174fe

1...6 7 8910 11 12...20

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