參數(shù)資料
型號(hào): TL2575-33I
廠商: Texas Instruments, Inc.
元件分類: 基準(zhǔn)電壓源/電流源
英文描述: 1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATORS
中文描述: 1,一個(gè)簡單的步驟式開關(guān)穩(wěn)壓器
文件頁數(shù): 18/31頁
文件大?。?/td> 923K
代理商: TL2575-33I
www.ti.com
V
= V
OUT
REF
1 +
(
where V
= 1.23 V
REF
(
R2
R1
(
(
R2 = R1
– 1
V
OUT
V
REF
C
7758
OUT
3
(μF)
V
IN(Max)
V
L1(μH)
OUT
·
TL2575, TL2575HV
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATORS
SLVS638B–MAY 2006–REVISED JANUARY 2007
PROCEDURE (Adjustable Output)
EXAMPLE (Adjustable Output)
Known:
V
OUT(Nom)
V
IN(Max)
= Maximum input voltage
I
LOAD(Max)
= Maximum load current
Known:
V
OUT
= 10 V
V
IN(Max)
= 25 V
I
LOAD(Max)
= 1 A
1. Programming Output Voltage (Selecting R1 and R2)
Referring to Fig. 2, V
OUT
is defined by:
1. Programming Output Voltage (Selecting R1 and R2)
Select R1 = 1 k
R2 = 1 (10/1.23 – 1) = 7.13 k
Select R2 = 7.15 k
(closest 1% value)
Choose a value for R1 between 1 k
and 5 k
(use 1% metal-film
resistors for best temperature coefficient and stability over time).
2. Inductor Selection (L1)
2. Inductor Selection (L1)
A.
Calculate the "set" volts-second (E
T) across L1:
E
T = (V
IN
– V
OUT
)
×
t
on
E
T = (V
IN
– V
OUT
)
×
(V
OUT
/V
IN
)
×
{1000/f
osc
(in kHz)} [V
μ
s]
NOTE:
Along with I
, the "set" volts-second (E
T) constant
establishes the minimum energy storage requirement for the
inductor.
A.
Calculate the "set" volts-second (E
T) across L1:
E
T = (25 – 10)
×
(10/25)
×
(1000/52) [V
μ
s]
E
T = 115 V
μ
s
B.
Using
Figure 19
, select the appropriate inductor code based on
the intersection of E
T value and I
LOAD(Max)
.
B.
Using
Figure 19
, the intersection of 115 V
μ
s and 1 A
corresponds to an inductor code of H470.
C.
From
Table 2
, choose the appropriate inductor based on the
inductor code. Parts from three well-known inductor manufacturers
are given. The inductor chosen should be rated for operation at
52-kHz and have a current rating of at least 1.15 x I
to
allow for the ripple current. The actual peak current in L1 (in normal
operation) can be calculated as follows:
I
L1(pk)
= I
LOAD(Max)
+ (V
IN
– V
OUT
)
×
t
on
/2L1
Where t
on
= V
OUT
/V
IN
×
(1/f
osc
)
C.
H470
L1 = 470
μ
F
Choose from:
34048 (Schott)
PE-53118 (Pulse Engineering)
RL1961 (Renco)
3. Output Capacitor Selection (C
OUT
)
3. Output Capacitor Selection (C
OUT
)
A.
The TL2575 control loop has a two-pole two-zero frequency
response. The dominant pole-zero pair is established by C
and
L1. To meet stability requirements, C
OUT
must meet the following
requirement:
A.
C
OUT
7785
×
25/(10
×
470) [
μ
F]
C
OUT
41.4
μ
F
To obtain an acceptable output voltage ripple
C
OUT
= 220
μ
F electrolytic
However, C
may need to be several times larger than the
calculated value above in order to achieve an acceptable output
ripple voltage of ~0.01
×
V
OUT
.
B.
C
should have a voltage rating of at least 1.5
×
V
. But if a
low output ripple voltage is desired, choose capacitors with a higher
voltage ratings than the minimum required due to their typically
lower ESRs.
4. Catch Diode Selection (D1) (see
Table 1
)
4. Catch Diode Selection (D1) (see
Table 1
)
A.
In normal operation, the catch diode requires a current rating of
at least 1.2
×
I
. For the most robust design, D1 should be
rated for a current equal to the TL2575 maximum switch peak
current; this represents the worst-case scenario of a continuous
short at V
OUT
.
A.
Pick a diode with a 3-A rating.
B.
The diode requires a reverse voltage rating of at least
1.25
×
V
IN(Max)
.
B.
Pick a 40-V rated Schottky diode (1N5822, MBR340, 31QD04, or
SR304) or 100-V rated Fast Recovery diode (31DF1, MURD310, or
HER302)
5. Input Capacitor (C
IN
)
An aluminum electrolytic or tantalum capacitor is needed for input
bypassing. Locate C
IN
as close to V
IN
and GND pins as possible.
5. Input Capacitor (C
IN
)
C
IN
= 100
μ
F, 35 V, aluminum electrolytic
18
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