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參數(shù)資料
| 型號： | LT3689IUD-5#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PQCC16 |
| 封裝： | 3 X 3 MM, LEAD FREE, PLASTIC, MO-220WEED-2, QFN-16 |
| 文件頁數(shù)： | 8/32頁 |
| 文件大?。?/td> | 2188K |
| 代理商： | LT3689IUD-5#PBF |
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LT3689/LT3689-5
16
3689fd
Choose an inductor using the previous inductor selection
equation to guarantee 700mA of output current. If using
a smaller inductor, check the DA current limit equation to
verify that the DA circuitry will not lower the switching
frequency.
When the switch is off, the potential across the inductor
is the output voltage plus the catch diode drop. This gives
the peak-to-peak ripple current in the inductor:
IL =
(1DC)(VOUT + VD)
L fSW
where fSW is the switching frequency of the LT3689 and L
is the value of the inductor. The peak inductor and switch
current is:
ISW(PK) =IL(PK) =IOUT +
IL
2
To maintain output regulation, this peak current must be
less than the LT3689’s switch current limit ILIM. ILIM is at
least 1.5A for at low duty cycles and decreases linearly
to 0.87A at DC = 85%. The maximum output current is a
function of the chosen inductor value.
IOUT(MAX) = ILIM
IL
2
= 1.15A (1 0.28 DC)
IL
2
Choosing an inductor value so that the ripple current is
small will allow a maximum output current near the switch
current limit.
One approach to choosing the inductor is to start with the
preceding simple rule, determine the available inductors,
and choose one to meet cost or space goals. Next, use
these equations to check that the LT3689 will be able to
deliver the required output current. Note again that these
equations assume that the inductor current is continu-
ous. Discontinuous operation occurs when IOUT is less
than IL/2.
Of course, such a simple design guide will not always
result in the optimum inductor for the application. A larger
value inductor provides a slightly higher maximum load
current and will reduce the output voltage ripple. If the
load is lower than 0.7A, decrease the value of the inductor
and operate with a higher ripple current. This allows the
use of a physically smaller inductor, or one with a lower
DCR resulting in higher efficiency. There are graphs in
the Typical Performance Characteristics section of this
data sheet that show the maximum load current as a
function of input voltage for several popular output volt-
ages. Low inductance may result in discontinuous mode
operation, which is okay but further reduces maximum
load current. For details of maximum output current and
discontinuous mode operation, see Linear Technology
Application Note 44. Finally, for duty cycles greater than
50% (VOUT/VIN > 0.5), a minimum inductance is required
to avoid subharmonic oscillations:
LMIN =
1.4 VOUT + VD
(
)
fSW
where LMIN is in H, VOUT and VD are in volts, and fSW
is in MHz.
Input Capacitor
Bypass the input of the LT3689 circuit with a ceramic
capacitor of an X7R or X5R type. Y5V types have poor
performance over temperature and applied voltage, and
should not be used. The minimum value of input capaci-
tance depends on the switching frequency. Use an input
capacitor of 1F or more for switching frequencies be-
tween 1MHz to 2.2MHz, and 2.2F or more for frequen-
cies lower than 1MHz. If the input power source has high
impedance, or there is significant inductance due to long
wires or cables, additional bulk capacitance may be nec-
essary. This can be provided with a lower performance
electrolytic capacitor. Step-down regulators draw current
from the input supply in pulses with very fast rise and
fall times. The input capacitor is required to reduce the
resulting voltage ripple at the LT3689 input and to force
this very high frequency switching current into a tight local
loop, minimizing EMI. A ceramic capacitor is capable of
this task, but only if it is placed close to the LT3689 and
the catch diode (see the PCB Layout section). A second
precautionregardingtheceramicinputcapacitorconcerns
themaximuminputvoltageratingoftheLT3689.Aceramic
input capacitor combined with trace or cable inductance
forms a high quality (under damped) tank circuit. If the
APPLICATIONS INFORMATION
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LT3689EMSE-5#TRPBF | 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PDSO16 |
| LT3689EUD-5#TRPBF | 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PQCC16 |
| LT3689EMSE-5#PBF | 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PDSO16 |
| LT3689IUD-5#TRPBF | 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PQCC16 |
| LT3689IMSE-5#TRPBF | 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PDSO16 |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LT3689IUD-5-TRPBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:700mA Step-Down Regulator with Power-On Reset and Watchdog Timer |
| LT3689IUD-PBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:700mA Step-Down Regulator with Power-On Reset and Watchdog Timer |
| LT3689IUD-TRPBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:700mA Step-Down Regulator with Power-On Reset and Watchdog Timer |
| LT3690 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:36V, 4A, 1.5MHz Synchronous Step-Down Switching Regulator |
| LT3690EUFE#PBF | 功能描述:IC REG BUCK SYNC ADJ 4A 26QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:250 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V 輸入電壓:2.05 V ~ 6 V PWM 型:電壓模式 頻率 - 開關(guān):2MHz 電流 - 輸出:500mA 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:6-UFDFN 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:6-SON（1.45x1） 產(chǎn)品目錄頁面:1032 (CN2011-ZH PDF) 其它名稱:296-25628-2 |
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