參數(shù)資料
型號(hào)： MAX1809
廠商： Maxim Integrated Products, Inc.
英文描述： 3A, 1MHz, DDR Memory Termination Supply
中文描述： 3A、1MHz、DDR存儲(chǔ)器端接電源
文件頁(yè)數(shù)： 7/17頁(yè)
文件大小： 803K
代理商： MAX1809
M
3A, 1MHz, DDR Memory Termination Supply
_______________________________________________________________________________________
7
feedback voltage exceeds the external reference voltage
(V
EXTREF
) or the positive current limit is reached. When
the PMOS switch turns off, it remains off for the pro-
grammed off-time (t
OFF
). To control the current under
short-circuit conditions, the PMOS switch remains off for
approximately 4
t
OFF
when V
FB
< V
EXTREF
/ 4.
Synchronous Rectification
In a stepdown regulator without synchronous rectification,
an external Schottky diode provides a path for current to
flow when the inductor is discharging. Replacing the
Schottky diode with a low-resistance NMOS synchro-
nous switch reduces conduction losses and improves
efficiency.
The NMOS synchronous-rectifier switch turns on follow-
ing a short delay (approximately 50ns) after the PMOS
power switch turns off, thus preventing cross-conduc-
tion or
“
shoot-through.
”
In constant-off-time mode, the
synchronous-rectifier switch turns off just prior to the
PMOS power switch turning on. While both switches
are off, inductor current flows through the internal body
diode of the NMOS switch.
Current Sourcing and Sinking
By operating in a constant-off-time, pseudo-fixed-fre-
quency mode, the MAX1809 can both source and sink
current. Depending on the output current requirement,
the circuit operates in two modes. In the first mode the
output draws current and the MAX1809 behaves as a
regular buck controller, sourcing current to the output
from the input supply rail. However, when the output is
supplied by another source, the MAX1809 operates in
a second mode as a synchronous boost, taking power
from the output and returning it to the input.
Thermal Resistance
Junction-to-ambient thermal resistance,
θ
JA
, is highly
dependent on the amount of copper area immediately
surrounding the IC leads. The MAX1809 QFN package
has 1in
2
of copper area and a thermal resistance of
50
°
C/W with no forced airflow. The MAX1809 16-pin
QSOP evaluation kit has 0.5in
2
of copper area and a
thermal resistance of 80
°
C/W with no forced airflow.
Airflow over the board significantly reduces the junction-
to-ambient thermal resistance. For heat sinking pur-
poses, it is essential to connect the exposed backside
pad of the QFN package to a large analog ground plane.
Shutdown
Drive
SHDN
to a logic-level low to place the MAX1809 in
low-power shutdown mode and reduce supply current to
less than 1μA. In shutdown, all circuitry and internal
MOSFETs turn off, so the LX node becomes high imped-
ance. Drive
SHDN
to a logic-level high or connect to V
CC
for normal operation.
Power Dissipation
Power dissipation in the MAX1809 is dominated by
conduction losses in the two internal power switches.
Power dissipation due to charging and discharging the
gate capacitance of the internal switches (i.e., switch-
ing losses) is approximately:
P
D(CAP)
= C
V
IN
2
f
SW
MAX1809
IN
V
CC
V
IN
V
SET
SHDN
EXTREF
TOFF
33
μ
F
10
10k
10k
R
TOFF
R
DROOP
V
(2.5V)
V
SSQ
0.01
μ
F
1
μ
F
270
μ
F
2V
15m
2.2
μ
F
1000pF
1000pF
LX
L
PGND
GND
FB
REF
SS
FOR V
IN
= 5V: L = 1
μ
H, R
TOFF
= 130k
FOR V
IN
= 3.3V: L = 0.68
μ
TOFF
= 73.2k
V
DDQ
2
( )
V
OUT
=
Figure 1. Typical Application Circuit
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參數(shù)描述
MAX1809EEE 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
MAX1809EEE+ 功能描述:電壓模式 PWM 控制器 3A 1MHz DDR Memory Termination Supply RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開關(guān)頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
MAX1809EEE+T 功能描述:電壓模式 PWM 控制器 3A 1MHz DDR Memory Termination Supply RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開關(guān)頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
MAX1809EEE-T 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
MAX1809EGI 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
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