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| 型号： | MAX1993ETG+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 30/36页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 24-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 75 |
| 系列： | Quick-PWM™ |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 600kHz |
| 占空比： | 100% |
| 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： | 24-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
PD ( N H Re sistive ) = ? OUT ? ( I LOAD DS ( ON )
) 2 R
Double pulsing is more annoying than harmful, result-
ing in nothing worse than increased output ripple.
However, it can indicate the possible presence of loop
instability due to insufficient ESR. Loop instability can
result in oscillations at the output after line or load
steps. Such perturbations are usually damped but can
cause the output voltage to rise above or fall below the
tolerance limits.
The easiest method for checking stability is to apply a
very fast zero-to-max load transient and carefully
observe the output voltage ripple envelope for over-
shoot and ringing. It can help 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/overshoot.
Input Capacitor Selection
The input capacitor must meet the ripple current
requirement (I RMS ) imposed by the switching currents:
Choose a low-side MOSFET (N L ) that has the lowest
possible on-resistance (R DS(ON) ), comes in a moderate-
sized package (i.e., 8-pin SO, DPAK, or D 2 PAK), and is
reasonably priced. Ensure that the MAX1992/MAX1993
DL gate driver can supply sufficient current to support the
gate charge and the current injected into the parasitic
drain-to-gate capacitor caused by the high-side MOSFET
turning on; otherwise, cross-conduction problems can
occur. Switching losses are not an issue for the low-side
MOSFET since it is a zero-voltage switched device when
used in the step-down topology.
Power MOSFET Dissipation
Worst-case conduction losses occur at the duty factor
extremes. For the high-side MOSFET (N H ), the worst-
case power dissipation due to resistance occurs at
minimum input voltage:
? V ?
? V IN ?
I RMS = I LOAD ?
?
?
? V OUT ( V IN ? V OUT )
? V IN
?
?
?
Generally, use a small high-side MOSFET to reduce
switching losses at high-input voltages. However, the
R DS(ON) required to stay within package power-dissi-
pation limits often limits how small the MOSFET can be.
For most applications, nontantalum chemistries (ceram-
ic, aluminum, or OSCON) are preferred due to their
resistance to power-up surge currents typical of sys-
tems with a mechanical switch or connector in series
with the input. If the MAX1992/MAX1993 are operated
as the second stage of a two-stage power conversion
system, tantalum input capacitors are acceptable. In
either configuration, choose a capacitor that has less
than 10°C temperature rise at the RMS input current for
optimal reliability and lifetime.
Power MOSFET Selection
Most of the following MOSFET guidelines focus on the
challenge of obtaining high load-current capability
when using high-voltage (>20V) AC adapters. Low-cur-
The optimum efficiency occurs when the switching
losses equal the conduction (R DS(ON) ) losses. High-
side switching losses do not become an issue until the
input is greater than approximately 15V.
Calculating the power dissipation in high-side
MOSFETs (N H ) due to switching losses is difficult, since
it must allow for difficult-to-quantify factors that influ-
ence the turn-on and turn-off times. These factors
include the internal gate resistance, gate charge,
threshold voltage, source inductance, and PC board
layout characteristics. The following switching loss cal-
culation provides only a very rough estimate and is no
substitute for breadboard evaluation, preferably includ-
ing verification using a thermocouple mounted on N H :
rent applications usually require less attention.
The high-side MOSFET (N H ) must be able to dissipate
the resistive losses plus the switching losses at both
PD ( N H
Switching ) =
( V IN ( MAX ) )
2
C RSS f SW I LOAD
I GATE
V IN(MIN) and V IN(MAX) . Ideally, the losses at V IN(MIN)
should be roughly equal to the losses at V IN(MAX) , with
lower losses in between. If the losses at V IN(MIN) are
significantly higher, consider increasing the size of N H .
Conversely, if the losses at V IN(MAX) are significantly
higher, consider reducing the size of N H . If V IN does
not vary over a wide range, maximum efficiency is
achieved by selecting a high-side MOSFET (N H ) that
has conduction losses equal to the switching losses.
where C RSS is the reverse transfer capacitance of N H ,
and I GATE is the peak gate-drive source/sink current
(1A typ).
Switching losses in the high-side MOSFET can become
a heat problem when maximum AC adapter voltages
are applied, due to the squared term in the switching-
loss equation (C x V IN 2 x f SW ).
30
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1993ETG+ | 功能描述:电压模式 PWM 控制器 Step-Down w/Inductor RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX1993ETG+T | 功能描述:电压模式 PWM 控制器 Step-Down w/Inductor RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX1993ETG+TG40 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1993ETG-T | 功能描述:电压模式 PWM 控制器 RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX1993EVKIT | 制造商:Maxim Integrated Products 功能描述:EVALUATION KIT FOR THE MAX1992 MAX1993 - Bulk |
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