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| 型号： | MAX1845ETX+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 19/27页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 36-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 540kHz |
| 电源电压： | 4.5 V ~ 5.5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 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： | 36-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
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Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
Table 4. Frequency Selection Guidelines
SIDE 1
SIDE 1
SIDE 2
SIDE 2
APPROXIMATE
TON SETTING
V CC
FLOAT
REF
AGND
FREQUENCY
(kHz)
235
345
485
620
K-FACTOR
(μs)
4.24
2.96
2.08
1.63
FREQUENCY
(kHz)
170
255
355
460
K-FACTOR
(μs)
5.81
4.03
2.81
2.18
K-FACTOR
ERROR (%)
±10
±10
±12.5
±12.5
f ESR ≤ SW
The actual microfarad capacitance value required
relates to the physical size needed to achieve low ESR,
as well as to the chemistry of the capacitor technology.
Thus, the capacitor is usually selected by ESR and volt-
age rating rather than by capacitance value (this is true
of tantalums, OS-CONs?, and other electrolytics).
When using low-capacity filter capacitors such as
ceramic or polymer types, capacitor size is usually
determined by the capacity needed to prevent V SAG
and V SOAR from causing problems during load tran-
sients. Also, the capacitance must be great enough to
prevent the inductor’s stored energy from launching the
output above the overvoltage protection threshold.
Generally, once enough capacitance is added to meet
the overshoot requirement, undershoot at the rising
load edge is no longer a problem (see the V SAG and
V SOAR equations in the Transient Response section).
Output Capacitor Stability
Considerations
Stability is determined by the value of the ESR zero rel-
ative to the switching frequency. The point of instability
is given by the following equation:
f
π
where:
10m Ω (max) ESR. Their typical combined ESR results in
a zero at 11.3kHz, well within the bounds of stability.
Do not put high-value ceramic capacitors directly
across the outputs without taking precautions to ensure
stability. Large ceramic capacitors can have a high-
ESR zero frequency and cause erratic, unstable opera-
tion. However, it is easy to add enough series
resistance by placing the capacitors a couple of inches
downstream from the inductor and connecting OUT_ or
the FB_ divider close to the inductor.
Unstable operation manifests itself in two related but
distinctly different ways: double-pulsing and feedback-
loop instability.
Double-pulsing occurs due to noise on the output or
because the ESR is so low that there is not enough volt-
age ramp in the output voltage signal. This “fools” the
error comparator into triggering a new cycle immedi-
ately after the 400ns minimum off-time period has
expired. Double-pulsing is more annoying than harmful,
resulting in nothing worse than increased output ripple.
However, it can indicate the possible presence of loop
instability, which is caused by insufficient ESR.
Loop instability can result in oscillations at the output
after line or load perturbations that can trip the overvolt-
age protection latch or cause the output voltage to fall
below the tolerance limit.
f ESR =
1
2 × π × R ESR × C F
The easiest method for checking stability is to apply a
very fast zero-to-max load transient (refer to the
MAX1845 EV kit manual) and carefully observe the out-
put voltage ripple envelope for overshoot and ringing. It
For a typical 300kHz application, the ESR zero frequen-
cy must be well below 95kHz, preferably below 50kHz.
Tantalum and OS-CON capacitors in widespread use
at the time of publication have typical ESR zero fre-
quencies of 15kHz. In the design example used for
inductor selection, the ESR needed to support 20mV P-P
ripple is 20mV/2A = 10m Ω . Three 470μF/6V Kemet
T510 low-ESR tantalum capacitors in parallel provide
OS-CON is a trademark of Sanyo.
helps to simultaneously monitor the inductor current
with an AC current probe. Do not allow more than one
cycle of ringing after the initial step-response under- or
overshoot.
______________________________________________________________________________________
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相关代理商/技术参数 |
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| MAX1845ETX-TG068 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1845EVKIT | 功能描述:电源管理IC开发工具 Evaluation Kit for the MAX1845 RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| MAX1846EUB | 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 |
| 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 |
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