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| 型号： | MAX1846EUB+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 15/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK INV CM 10UMAX |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 345kHz |
| 占空比： | 98% |
| 电源电压： | 3 V ~ 16.5 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 反相： | 是 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 管件 |
| 产品目录页面： | 1410 (CN2011-ZH PDF) |
High-Efficiency, Current-Mode,
Inverting PWM Controller
The ESR-induced ripple usually dominates this last
(
) (
)
( )
equation, so typically output capacitor selection is
based mostly upon the capacitor’s ESR, voltage rating,
and ripple current rating. Use the following formula to
determine the maximum ESR for a desired output ripple
voltage (V RIPPLE-D ):
Z RHP =
? ?
? 2 ?
? ? 1 ? D MAX x V IN ( MIN ) ? V OUT xR LOAD ?
? ?
2 π x V OUT × L
R ESR = V RIPPLE-D / I LPP
Select a capacitor with ESR rating less than R ESR . The
value of this capacitor is highly dependent on dielectric
type, package size, and voltage rating. In general, when
choosing a capacitor, it is recommended to use low-ESR
capacitor types such as ceramic, organic, or tantalum
capacitors. Ensure that the selected capacitor has suffi-
cient margin to safely handle the maximum RMS ripple
current.
For continuous inductor current the maximum RMS ripple
current in the output filter capacitor is:
The calculations for p OUT2 are very complex. For most
applications where V OUT does not exceed -48V (in a
negative sense), the p OUT2 will not be lower than 1/8th
of the oscillator frequency and is generally at a higher
frequency than z RHP . Therefore:
p OUT2 ≥ 0.125 f OSC
A pole is created by the output capacitor and the load
resistance. This pole must also be compensated and
its center frequency is given by the formula:
p OUT1 = 1 / (2 π R LOAD C OUT )
Finally, there is a zero introduced by the ESR of the out-
I RMS =
I LOAD
I ? D MAX
x
D MAX
?
D MAX
2
put capacitor. This zero is determined from the follow-
ing equation:
z ESR = 1 / (2 π C OUT R ESR )
Choosing Compensation Components
The MAX1846/MAX1847 are externally loop-compen-
sated devices. This feature provides flexibility in
designs to accommodate a variety of applications.
Proper compensation of the control loop is important to
Calculating the Required Pole Frequency
To ensure stability of the MAX1846/MAX1847, the gain
of the error amplifier must roll-off the total loop gain to 1
before Z RHP or P OUT2 occurs. First, calculate the DC
open-loop gain, A DC :
prevent excessive output ripple and poor efficiency
caused by instability. The goal of compensation is to
cancel unwanted poles and zeros in the DC-DC con-
verter’s transfer function created by the power-switch-
A DC =
B x G M
x
R O x ( 1 ? D MAX ) R LOAD
A CS x R CS
ing and filter elements. More precisely, the objective of
compensation is to ensure stability by ensuring that the
DC-DC converter’s phase shift is less than 180° by a
safe margin, at the frequency where the loop gain falls
below unity. One method for ensuring adequate phase
margin is to introduce corresponding zeros and poles
in the feedback network to approximate a single-pole
response with a -20dB/decade slope all the way to
unity-gain crossover.
Calculating Poles and Zeros
The MAX1846/MAX1847 current-mode architecture
takes the double pole caused by the inductor and out-
put capacitor and shifts one of these poles to a much
higher frequency to make loop compensation easier.
To compensate these devices, we must know the cen-
ter frequencies of the right-half plane zero (z RHP ) and
the higher frequency pole (p OUT2 ). Calculate the z RHP
where:
A CS is the current sense amplifier gain = 3.3
B is the feedback-divider attenuation factor =
R 2
R 1 + R 2
G M is the error-amplifier transconductance =
400 μA/V
R O is the error-amplifier output resistance = 3 M ?
R CS is the selected current-sense resistor
Determining the Compensation Component Values
Select a unity-gain crossover frequency (f CROS ), which
is lower than z RHP and p OUT2 and higher than p OUT1 .
Using f CROS , calculate the compensation resistor
(R COMP ).
frequency with the following formula:
R COMP =
f CROS x R O
A DC xP OUT 1 ? f CROS
______________________________________________________________________________________
15
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1846EUB+ | 功能描述:电流型 PWM 控制器 Current-Mode Invert PWM Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1846EUB+T | 功能描述:电流型 PWM 控制器 Current-Mode Invert PWM Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1846EUB-T | 功能描述:电流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1846EVKIT | 功能描述:电流型 PWM 控制器 Evaluation Kit for the MAX1846 MAX1847 RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1847EEE | 功能描述:电流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
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