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参数资料
| 型号： | MAX1655EEE |
| 厂商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP |
| 中文描述： | SWITCHING CONTROLLER, 350 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | 0.150 INCH, 0.025 INCH PITCH, QSOP-16 |
| 文件页数： | 18/28页 |
| 文件大小： | 265K |
| 代理商： | MAX1655EEE |
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M
High-Effic ienc y, PWM, S tep-Down
DC-DC Controllers in 16-Pin QS OP
18
______________________________________________________________________________________
With high input voltages, the required duty factor is
approximately (V
OUT
+ V
Q2
)/ V
IN
, where V
Q2
is the volt-
age drop across the synchronous rectifier. The
MAX1652’s minimum duty factor is determined by
delays through the feedback network, error comparator,
internal logic gate drivers, and the external MOSFETs,
which typically total 400ns. This delay is about 12% of
the switching period at 300kHz and 6% at 150kHz, limit-
ing the typical minimum duty factor to these values.
Even if the circuit can not attain the required duty factor
dictated by the input and output voltages, the output
voltage will remain in regulation. However, there may be
intermittent or continuous half-frequency operation. This
can cause a factor-of-two increase in output voltage rip-
ple and current ripple, which will increase noise and
reduce efficiency. Choose 150kHz operation for high-
input-voltage/low-output-voltage circuits.
S ec ondary Feedbac k-Regulation Loop
(S ECFB Pin)
A flyback winding control loop regulates a secondary
winding output (MAX1652/MAX1654 only), improving
cross-regulation when the primary is lightly loaded
or when there is a low input-output differential voltage.
If SECFB crosses its regulation threshold, a 1μs one-
shot is triggered that extends the low-side switch’s
on-time beyond the point where the inductor current
crosses zero (in discontinuous mode). This causes the
inductor (primary) current to reverse, which in turn pulls
current out of the output filter capacitor and causes the
flyback transformer to operate in the forward mode. The
low impedance presented by the transformer secondary
in the forward mode dumps current into the secondary
output, charging up the secondary capacitor and bring-
ing SECFB back into regulation. The SECFB feedback
loop does not improve secondary output accuracy in
normal flyback mode, where the main (primary) output is
heavily loaded. In this mode, secondary output accura-
cy is determined (as usual) by the secondary rectifier
drop, turns ratio, and accuracy of the main output volt-
age. Hence, a linear post-regulator may still be needed
in order to meet tight output accuracy specifications.
The secondary output voltage-regulation point is deter-
mined by an external resistor-divider at SECFB. For neg-
ative output voltages, the SECFB comparator is
referenced to GND (MAX1654); for positive output volt-
ages, SECFB regulates at the 2.50V reference
(MAX1652). As a result, output resistor-divider connec-
tions and design equations for the two device types dif-
fer slightly (Figure 7). Ordinarily, the secondary
regulation point is set 5% to 10% below the voltage nor-
mally produced by the flyback effect. For example, if the
MAX1654
NEGATIVE
SECONDARY
OUTPUT
MAIN
OUTPUT
DH
V+
SECFB
R3
R2
1-SHOT
TRIG
DL
0.33
μ
F
REF
MAX1652
POSITIVE
SECONDARY
OUTPUT
MAIN
OUTPUT
DH
V+
SECFB
2.5V REF
R3
R2
1-SHOT
TRIG
DL
+V
TRIP
WHERE V
REF
(NOMINAL) = 2.5V
= V
REF
(
1 + R3
)
-V
TRIP
R3 = 100k
(RECOMMENDED)
= -V
REF
(
R3
)
Figure 7. Secondary-Output Feedback Dividers
相关PDF资料 |
PDF描述 |
|---|---|
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| MAX1658 | 350mA, 16.5V Input, Low-Dropout Linear Regulators |
| MAX1658ESA | 350mA, 16.5V Input, Low-Dropout Linear Regulators |
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1655EEE+ | 功能描述:DC/DC 开关控制器 PWM Step-Down RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1655EEE+T | 功能描述:DC/DC 开关控制器 PWM Step-Down RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1655EEE-T | 功能描述:DC/DC 开关控制器 PWM Step-Down RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1655ESE | 功能描述:DC/DC 开关控制器 PWM Step-Down RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1655ESE+ | 功能描述:DC/DC 开关控制器 PWM Step-Down RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
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