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参数资料
| 型号： | LTC3891HFE#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 900 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封装： | 4.40 MM, LEAD FREE, PLASTIC, TSSOP-20 |
| 文件页数： | 18/32页 |
| 文件大小： | 1931K |
| 代理商： | LTC3891HFE#TRPBF |
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LTC3891
25
3891f
APPLICATIONS INFORMATION
assumption. The highest value of ripple current occurs
at the maximum input voltage. Tie the FREQ pin to GND,
generating 350kHz operation. The minimum inductance
for 30% ripple current is:
Δ
IL =
VOUT
f
( ) L
( )
1–
VOUT
VIN(NOM)
A 4.7μH inductor will produce 29% ripple current. The
peak inductor current will be the maximum DC value plus
one half the ripple current, or 5.73A. Increasing the ripple
current will also help ensure that the minimum on-time
of 95ns is not violated. The minimum on-time occurs at
maximum VIN:
tON(MIN) =
VOUT
VIN(MAX) f
( )
=
3.3V
22V 350kHz
(
)
= 429ns
The equivalent RSENSE resistor value can be calculated by
using the minimum value for the maximum current sense
threshold (64mV):
RSENSE ≤
64mV
5.73A
≈ 0.01
Choosing 1% resistors: RA = 25k and RB = 78.7k yields
an output voltage of 3.32V.
ThepowerdissipationonthetopsideMOSFETcanbeeasily
estimated. Choosing a Fairchild FDS6982S dual MOSFET
results in: RDS(ON) = 0.035Ω/0.022Ω, CMILLER = 215pF. At
maximum input voltage with T(estimated) = 50°C:
PMAIN =
3.3V
22V
5A
( )2 1+ 0.005
(
) 50°C– 25°C
(
)
0.035
(
)+ 22V
( )2 5A
2
2.5
( ) 215pF
(
)
1
5V – 2.3V
+ 1
2.3V
350kHz
(
) =331mW
A short-circuit to ground will result in a folded back cur-
rent of:
ISC =
34mV
0.01
– 1
2
95ns 22V
( )
4.7H
= 3.18A
with a typical value of RDS(ON) and δ = (0.005/°C)(25°C)
= 0.125. The resulting power dissipated in the bottom
MOSFET is:
PSYNC = 3.28A
(
)2 1.125
(
) 0.022
(
)
= 250mW
which is less than under full-load conditions. CINischosen
for an RMS current rating of at least 3A at temperature
assuming only this channel is on. COUT is chosen with an
ESR of 0.02Ω for low output ripple. The output ripple in
continuous mode will be highest at the maximum input
voltage. The output voltage ripple due to ESR is approxi-
mately:
VORIPPLE = RESR(DIL) = 0.02Ω(1.45A) = 29mVP-P
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the IC.
Check the following in your layout:
1. Are the signal and power grounds kept separate? The
combined IC signal ground pin and the ground return
of CINTVCC must return to the combined COUT (–) ter-
minals. The path formed by the top N-channel MOSFET,
Schottky diode and the CIN capacitor should have short
leads and PC trace lengths. The output capacitor (–)
terminals should be connected as close as possible
to the (–) terminals of the input capacitor by placing
the capacitors next to each other and away from the
Schottky loop described above.
2. Does the LTC3891 VFB pin’s resistive divider connect to
the (+) terminal of COUT? The resistive divider must be
connected between the (+) terminal of COUT and signal
ground. The feedback resistor connections should not
be along the high current input feeds from the input
capacitor(s).
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相关代理商/技术参数 |
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| LTC3891HUDC#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 20-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC3891HUDC#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 20-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
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