參數(shù)資料
型號： LTC1266ACS
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： Synchronous Regulator Controller for N- or P-Channel MOSFETs
中文描述： SWITCHING CONTROLLER, 400 kHz SWITCHING FREQ-MAX, PDSO16
封裝： 0.150 INCH, PLASTIC, SO-16
文件頁數(shù)： 15/20頁
文件大?。?/td> 361K
代理商： LTC1266ACS
15
LTC1266
LTC1266-3.3/LTC1266-5
APPLICATIU
unacceptable levels (see Figure 7). With Burst Mode
operation, the DC supply current represents the lone (and
unavoidable) loss component which continues to become
a higher percentage as output current is reduced. As
expected the I
2
R losses dominate at high load currents.
Other losses including C
IN
and C
OUT
ESR dissipative
losses, MOSFET switching losses, Schottky conduction
losses during deadtime and inductor core losses, gener-
ally account for less than 2% total additional loss.
W
U
U
Design Example
As a design example, assume V
IN
= 5V (nominal),
V
OUT
= 3.3V, I
MAX
= 5A and f = 200kHz; R
SENSE
, C
T
and L
can immediately be calculated:
R
SENSE
= 100mV/5 = 0.02
t
OFF
= (1/200kHz)
×
[1 – (3.3/5)] = 1.7
μ
s
C
T
= 1.7
μ
s/(1.3
×
10
4
) = 130pF
L
MIN
= 5.1
×
10
5
×
0.02
×
130pF
×
3.3V = 5
μ
H
Assume that the MOSFET dissipations are to be limited to
P
T
= P
B
= 2W.
If T
A
= 40
°
C and the thermal resistance of each MOSFET
is 50
°
C/W, then the junction temperatures will be 140
°
C
and
δ
T
=
δ
B
= 0.60. The required R
DS(ON)
for each MOSFET
can now be calculated:
TS R
DS(ON)
=
5(2)
3.3(5)
2
(1.60)= 0.076
BS R
DS(ON)
=
5(2)
1.7(5)
2
(1.60)= 0.147
The topside FET requirement can be met by an N-channel
Si9410DY which has an R
DS(ON)
of about 0.04
at
V
GS
= 5V. The bottom-side FET requirement is exceeded
by an Si9410DY. Note that the most stringent requirement
for the bottom-side MOSFET is with V
OUT
= 0 (i.e., short
circuit). During a continuous short circuit, the worst-case
dissipation rises to:
P
B
= I
SC(AVG)2
×
R
DS(ON)
×
(1 +
δ
B
)
With the 0.02
sense resistor, I
SC(AVG)
≈
6A will result,
increasing the 0.04
bottom-side FET dissipation to 2.3W.
C
IN
will require an RMS current rating of at least 2.5A at
temperature and C
OUT
will require an ESR of 0.02
for
optimum efficiency.
Now allow V
IN
to drop to its minimum value. The minimum
V
IN
can be calculated from the maximum duty cycle and
voltage drop across the topside FET,
V
MIN
=
D
MAX
V
OUT
+ I
LOAD
×
(R
DS(ON)
+ R
L
+ R
SENSE
) = 4.0V
At this lower input voltage, the operating frequency de-
creases and the topside FET will be conducting most of the
time, causing the power dissipation to increase.
At dropout,
1
t
ON (MAX)
+ t
OFF
P
T
= I
2LOAD
×
R
DS(ON)
×
(1 +
δ
T
)
×
D
MAX
This last step is necessary to assure that the power
dissipation and junction temperature of the topside FET
are not exceeded.
These last calculations assume that Power V
IN
is high
enough to keep the topside FET fully turned on at dropout,
as would be the case with the Figure 11circuit. If this isn’t
true (as with the Figure 1 circuit) the R
DS(ON)
will increase
which in turn increases V
MIN
and P
T
.
f
MIN
=
= 16kHz
Adjustable Applications
When an output voltage other than 3.3V or 5V is required,
the LTC1266 adjustable version is used with an external
resistive divider from V
OUT
to V
FB
, Pin 10. The regulated
voltage is determined by:
)
R1
V
OUT
= 1.25
)
1 +R2
To prevent stray pickup a 100pF capacitor is suggested
across R1 located close to the LTC1266.
For Figure 1 applications with V
OUT
below 2V, or when
R
SENSE
is moved to ground, the current sense comparator
inputs operate near ground. When the current comparator
is operated at less than 2V common mode, the off-time
increases approximately 40%, requiring the use of a
smaller timing capacitor C
T
.
相關(guān)PDF資料
PDF描述
LTC1266CS Synchronous Regulator Controller for N- or P-Channel MOSFETs
LTC1266CS-3.3 Synchronous Regulator Controller for N- or P-Channel MOSFETs
LTC1266CS-5 Synchronous Regulator Controller for N- or P-Channel MOSFETs
LTC1267- ADJ 500kHz and 1MHz High Efficiency 1.5A Switching Regulators; Package: SO; No of Pins: 8; Temperature Range: -40?°C to 85?°C
LTC1267- ADJ5 500kHz and 1MHz High Efficiency 1.5A Switching Regulators; Package: SO; No of Pins: 8; Temperature Range: -40?°C to 85?°C
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LTC1266ACS#PBF 功能描述:IC REG CTRLR BST PWM CM 16-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝: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 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 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
LTC1266ACS#TR 功能描述:IC REG CTRLR BST PWM CM 16-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝: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 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 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
LTC1266ACS#TRPBF 功能描述:IC REG CTRLR BST PWM CM 16-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝: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 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 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
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