參數(shù)資料
型號(hào)： LTC1778
廠商： Linear Technology Corporation
英文描述： Wide Operating Range, No RSENSE Step-Down Controller
中文描述： 寬工作，無檢測(cè)電阻范圍步降控制器
文件頁(yè)數(shù)： 17/24頁(yè)
文件大?。?/td> 303K
代理商： LTC1778
17
LTC1778/LTC1778-1
1778fa
APPLICATIOU
Other losses, including C
OUT
ESR loss, Schottky diode D1
conduction loss during dead time and inductor core loss
generally account for less than 2% additional loss.
When making adjustments to improve efficiency, the
input current is the best indicator of changes in efficiency.
If you make a change and the input current decreases, then
the efficiency has increased. If there is no change in input
current, then there is no change in efficiency.
W
U
U
Checking Transient Response
The regulator loop response can be checked by looking at
the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, V
OUT
immediately shifts by an amount
equal to
I
LOAD
(ESR), where ESR is the effective series
resistance of C
OUT
.
I
LOAD
also begins to charge or
discharge C
OUT
generating a feedback error signal used by
the regulator to return V
OUT
to its steady-state value.
During this recovery time, V
OUT
can be monitored for
overshoot or ringing that would indicate a stability prob-
lem. The I
TH
pin external components shown in Figure 9
will provide adequate compensation for most applica-
tions. For a detailed explanation of switching control loop
theory see Application Note 76.
Design Example
As a design example, take a supply with the following
specifications: V
IN
= 7V to 28V (15V nominal), V
OUT
= 2.5V
±
5%, I
OUT(MAX)
= 10A, f = 250kHz. First, calculate the
timing resistor with V
ON
= V
OUT
:
V
V
kHz
)(
0 7
250
10
.
and choose the inductor for about 40% ripple current at
the maximum V
IN
:
R
pF
M
ON
=
(
)(
)
=
2 5
.
1 42
.
L
V
0 4 10
.
kHz
A
V
V
H
=
(
)(
)(
)
=
μ
2 5
.
250
1
2 5
28
2 3
.
.
Selecting a standard value of 1.8
μ
H results in a maximum
ripple current of:
=
(
)
μ
(
)
=
I
V
1 8
kHz
H
V
V
A
L
2.
250
1
2 5
28
5 1
.
.
–
.
Next, choose the synchronous MOSFET switch. Choosing
a Si4874 (R
DS(ON)
= 0.0083
(NOM) 0.010
(MAX),
θ
JA
= 40
°
C/W) yields a nominal sense voltage of:
V
SNS(NOM)
= (10A)(1.3)(0.0083
) = 108mV
Tying V
RNG
to 1.1V will set the current sense voltage range
for a nominal value of 110mV with current limit occurring
at 146mV. To check if the current limit is acceptable,
assume a junction temperature of about 80
°
C above a
70
°
C ambient with
ρ
150
°
C
= 1.5:
I
mV
.
A
A
LIMIT
≥
( )
and double check the assumed T
J
in the MOSFET:
(
28
T
J
= 70
°
C + (1.97W)(40
°
C/W) = 149
°
C
Because the top MOSFET is on for such a short time, an
Si4884 R
DS(ON)(MAX)
= 0.0165
, C
RSS
= 100pF,
θ
JA
=
40
°
C/W will be sufficient. Checking its power dissipation
at current limit with
ρ
100
°
C
= 1.4:
(
( )(
=
+
=
0 30
0 40
.
.
(
)
+
(
2
)
=
146
1 5 0 010
.
1
5 1
.
12
P
V
V
V
A
W
BOT
=
) ( )
(
)
=
28
–2 5
12
15 0 010
.
197
.
2
.
P
V
V
A
V
A
pF
kHz
W
W
W
TOP
=
) ( )
) (
(
)
+
)(
)(
)
2 5
28
12
1 4 0 0165
.
1 7 28
.
12
100
250
0 7
.
2
2
.
.
T
J
= 70
°
C + (0.7W)(40
°
C/W) = 98
°
C
The junction temperatures will be significantly less at
nominal current, but this analysis shows that careful
attention to heat sinking will be necessary in this circuit.
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參數(shù)描述
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LTC1778EGN#TR 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 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 升壓:是 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:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
LTC1778EGN#TRPBF 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 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 升壓:是 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:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
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