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参数资料
| 型号： | MAX1515ETG |
| 厂商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | Low-Voltage, Internal Switch, Step-Down/DDR Regulator |
| 中文描述： | 4.7 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, QCC24 |
| 封装： | 4 X 4 MM, 0.8 MM HEIGHT, MO-220-WGGD, TQFN-8 |
| 文件页数： | 18/24页 |
| 文件大小： | 504K |
| 代理商： | MAX1515ETG |
M
Low-Voltage, Internal Switch,
Step-Down/DDR Regulator
18
______________________________________________________________________________________
where:
C = 5nF
f
SW
= switching frequency
The combined conduction losses (PCL) in the two
power switches are approximated by:
PCL = I
OUT
2
x R
NMOS
where:
I
OUT
= load current
R
NMOS
= NMOS switch on-resistance
Design Procedure
For typical DDR applications, use the recommended
component values in Table 1. For other applications,
use the recommended component values in Table 5, or
take the following steps:
1) Select the desired PWM-mode switching frequency.
See Figure 6 for maximum operating frequency.
2) Select the constant off-time as a function of input
voltage, output voltage, and switching frequency.
3) Select R
TOFF
as a function of off-time.
4) Select the inductor as a function of output voltage,
off-time, and peak-to-peak inductor current.
Programming the No-Load Switching
Frequency and Off-Time
The MAX1515 features a programmable PWM mode
switching frequency, which is set by the input and out-
put voltage and the value of R
TOFF
. R
TOFF
sets the
high-side NMOS power switch off-time in PWM mode.
Use the following equation to select the off-time
according to the desired no-load switching frequency
in PWM mode:
where:
t
OFF
= the programmed off-time
V
IN
= the input voltage
V
OUT
= the output voltage
f
PWM
= no-load switching frequency, PWM mode
Select R
TOFF
according to the formula:
V
RTOFF
is typically 1.1V and the recommended values
for R
TOFF
range from 33.2k
Ω
to 499k
Ω
for off-times of
0.35μs to 4.5μs.
Frequency Variation with Output Current
The operating frequency of the MAX1515 in PWM mode
is determined primarily by t
OFF
(set by R
TOFF
), V
IN
, and
V
OUT
as shown in the following formula:
where:
V
CHG
= the voltage drop in the inductor charge path
due to high-side FET R
NMOS
and inductor DCR
V
DISCHG
= the voltage drop in the inductor discharge
path due to low-side FET R
NMOS
and inductor DCR
f
V
V
(
V
V
V
t
V
PWM
IN
OUT
CHG
OFF
IN
CHG
DISCHG
+
=
)
R
t
s
k
μ
s
TOFF
OFF
=
(
)
.
.
0 035
110
1 00
μ
Ω
t
V
f
PWM
V
×
V
OFF
IN
OUT
IN
=
0
200
600
400
800
1000
F
MAXIMUM RECOMMENDED OPERATING
FREQUENCY vs. INPUT VOLTAGE
V
IN
(V)
1.5
2.5
2.0
3.0
3.5
NO LOAD
V
OUT
= 1.25V
V
OUT
= 0.9V
V
OUT
= 2.5V
V
OUT
= 1.8V
V
OUT
= 1.5V
Figure 6. Maximum Operating Frequency vs. Input Voltage
Table 5. Recommended Component
Values (I
OUT
= 3A)
V
IN
(V)
V
OUT
(V)
f
PWM
(kHz)
L
(μH)
C
OUT
(μF)
R
TOFF
(k
Ω
)
3.3
3.3
3.3
3.3
2.5
2.5
2.5
2.5
1.8
1.5
1.2
1.8
1.5
1.2
400
400
480
420
430
320
440
1.5
2.2
2.2
2.2
1.2
1.8
1.5
100
150
180
220
100
150
180
49.9
110
110
150
49.9
110
110
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