參數(shù)資料
型號(hào)： LTC3856EFE#TRPBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： SWITCHING CONTROLLER, PDSO38
封裝： 4.4 MM, LEAD FREE, PLASTIC, TSSOP-38
文件頁(yè)數(shù)： 27/40頁(yè)
文件大?。?/td> 2222K
代理商： LTC3856EFE#TRPBF
LTC3856
3856f
applicaTions inForMaTion
A second, more severe transient is caused by switching
in loads with large (>1F) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with COUT, causing a rapid drop in VOUT. No regulator can
alter its delivery of current quickly enough to prevent this
sudden step change in output voltage if the load switch
resistance is low and it is driven quickly. If the ratio of
CLOAD to COUT is greater than 1:50, the switch rise time
should be controlled so that the load rise time is limited
to approximately 25 CLOAD. Thus a 10F capacitor would
require a 250s rise time, limiting the charging current
to about 200mA.
Design Example (Using Two Phases)
As a design example, assume:
VIN = 5V (nominal)
VIN = 5.5V (max),
VOUT = 1.8V,
IMAX = 20A
TA = 70°C
f = 300kHz
The inductance value is chosen first based on a 30% ripple
current assumption. The highest value of ripple current
occurs at the maximum input voltage. Use a 71.5k resistor
from FREQ to ground to set the switching frequency at
about 300kHz. The minimum inductance for 30% ripple
current is:
L
V
f I
V
kHz
OUT
IN
≥
( )
≥ (
)(
1
1 8
300
30
.
%
))( )
≥
10
1
1 8
5 5
1 35
A
V
H
.
A 2H inductor will produce 20% ripple current. The peak
inductor current will be the maximum DC value plus one
half the ripple current, or 11A. The minimum on-time oc-
curs at maximum VIN:
t
V
V f
V
kHz
s
ON MIN
OUT
IN
( ) =
= ( )(
)
=
1 8
5 5
300
1 1
.
With the ILIM pin tied to ground, the RSENSE resistors
value can be calculated by using the minimum current
sense voltage specification with some accommodation
for tolerances:
R
mV
A
SENSE =
≈
25
11
0 002
.
Choosing 1% resistors: R1 = 10k and R2 = 20k yields an
output voltage of 1.80V.
The power dissipation on the topside MOSFET can be
easily estimated. Using a Siliconix Si4420DY for example;
RDS(ON) = 0.013Ω, CRSS = 300pF. At maximum input
voltage with TJ(estimated)=110°Catanelevatedambient
temperature:
P
V
C
MAIN =
( ) +(
) ° °
(
)
1 8
5 5
10
1 0 005 110
25
2
.
+
( )
(
)(
)
.
.
0 013
5 5
10
2
300
1
5
2
V
A
pF
V
..
.
.
6
1
2 6
300
0 606 0 022 0 628
V
kHz
+
(
)
=
+
=
W
The worst-case power dissipated by the synchronous
MOSFET under normal operating conditions at elevated
ambient temperature and estimated 50°C junction
temperature rise is:
P
V
A
SYNC =
( ) ( )
(
)
=
5 5
1 8
5 5
10
1 25 0 013
1 0
2
.
. 99W
相關(guān)PDF資料
PDF描述
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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LTC3856EUH#TRPBF 功能描述:IC REG CTRLR BUCK PWM CM 38-QFN 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)
LTC3856IFE#PBF 功能描述:IC REG CTRLR BUCK PWM CM 38TFSOP 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:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無(wú) 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:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
LTC3856IFE#TRPBF 功能描述:IC REG CTRLR BUCK PWM CM 38TSSOP 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:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無(wú) 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:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
LTC3856IUH#PBF 功能描述:IC REG CTRLR BUCK PWM CM 32WFQFN 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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