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參數(shù)資料
| 型號(hào)： | LTC3835IUFD |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3 A SWITCHING CONTROLLER, 580 kHz SWITCHING FREQ-MAX, PQCC20 |
| 封裝： | 4 X 5 MM, PLASTIC, MO-220, QFN-20 |
| 文件頁(yè)數(shù)： | 7/30頁(yè) |
| 文件大?。?/td> | 1775K |
| 代理商： | LTC3835IUFD |
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LTC3835
15
3835fd
APPLICATIONS INFORMATION
CIN and COUT Selection
Incontinuousmode,thesourcecurrentofthetopMOSFET
is a square wave of duty cycle (VOUT)/(VIN). To prevent
large voltage transients, a low ESR capacitor sized for the
maximumRMScurrentmustbeused.ThemaximumRMS
capacitor current is given by:
CIN RequiredIRMS ≈
IMAX
VIN
VOUT
( ) V
IN – VOUT
(
)
1/2
This formula has a maximum at VIN = 2VOUT, where IRMS
= IOUT/2. This simple worst-case condition is commonly
used for design because even significant deviations do not
offermuchrelief.Notethatcapacitormanufacturers’ripple
current ratings are often based on only 2000 hours of life.
This makes it advisable to further derate the capacitor, or
to choose a capacitor rated at a higher temperature than
required. Several capacitors may be paralleled to meet
size or height requirements in the design. Due to the high
operating frequency of the LTC3835, ceramic capacitors
can also be used for CIN. Always consult the manufacturer
if there is any question.
The selection of COUT is driven by the effective series
resistance (ESR). Typically, once the ESR requirement
is satisfied, the capacitance is adequate for filtering. The
output ripple (VOUT) is approximated by:
VOUT ≈ IRIPPLE ESR +
1
8fCOUT
where f is the operating frequency, COUT is the output
capacitance and IRIPPLE is the ripple current in the induc-
tor. The output ripple is highest at maximum input voltage
since IRIPPLE increases with input voltage.
Setting Output Voltage
The LTC3835 output voltage is set by an external feed-
back resistor divider carefully placed across the output,
as shown in Figure 1. The regulated output voltage is
determined by:
VOUT = 0.8V 1+
RB
RA
To improve the frequency response, a feed-forward ca-
pacitor, CFF, may be used. Great care should be taken to
route the VFB line away from noise sources, such as the
inductor and the SW line.
SENSE+ and SENSE– Pins
The common mode input range of the current comparator
is from 0V to 10V. Continuous linear operation is provided
throughout this range allowing output voltages from 0.8V
to 10V. The input stage of the current comparator requires
thatcurrenteitherbesourcedorsunkfromtheSENSEpins
depending on the output voltage, as shown in the curve in
Figure 2. If the output voltage is below 1.5V, current will
flow out of both SENSE pins to the main output. In these
cases, the output can be easily pre-loaded by the VOUT
resistordividertocompensateforthecurrentcomparator’s
negative input bias current. Since VFB is servoed to the
0.8V reference voltage, RA in Figure 1 should be chosen
to be less than 0.8V/ISENSE, with ISENSE determined from
Figure 2 at the specified output voltage.
Figure 1. Setting Output Voltage
LTC3835
VFB
VOUT
RB
CFF
RA
3835 F01
Figure 2. SENSE Pins Input Bias Current
vs Common Mode Voltage
VSENSE COMMON MODE VOLTAGE (V)
0
–700
INPUT
CURRENT
(A)
–600
–400
–300
–200
6
7
8
9
200
3835 F02
–500
1
2
3
4
5
10
–100
0
100
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| LTC3836EGN#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無(wú) 升壓:是 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
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