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参数资料
| 型号： | MAX1791EUB+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 17/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 10-UMAX |
| 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： | 300kHz |
| 电源电压： | 5 V ~ 20 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： | 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, 10-Pin μMAX, Step-Down
Controllers for Notebooks
side switching losses do not usually become an issue
until the input is greater than approximately 15V.
Switching losses in the high-side MOSFET can become
an insidious heat problem when maximum battery volt-
age is applied, due to the squared term in the CV 2 f
switching loss equation. If the high-side MOSFET cho-
sen for adequate R DS(ON) at low battery voltages
becomes extraordinarily hot when subjected to
V VP(MAX) , reconsider your choice of high-side MOS-
FET.
Calculating the power dissipation in Q1 due to switch-
ing losses is difficult since it must allow for difficult
quantifying factors that influence the turn-on and turn-
off times. These factors include the internal gate resis-
tance, gate charge, threshold voltage, source induc-
tance, and PC board layout characteristics. The follow-
ing switching loss calculation provides only a very
rough estimate and is no substitute for breadboard
evaluation, preferably including a verification using a
thermocouple mounted on Q1:
unchanged, this voltage is approximately 0.7V (a diode
drop) at both transition edges while both switches are
off. In between the edges, the low-side switch con-
ducts; the drop is I L ? R DS(ON) . If a Schottky clamp is
connected across the low-side switch, the initial and
final voltage drops is reduced, improving efficiency
slightly.
Choose a Schottky diode (D1) having a forward voltage
low enough to prevent the Q2 MOSFET body diode
from turning on during the dead time. As a general rule,
a diode having a DC current rating equal to 1/3 of the
load current is sufficient. This diode is optional and can
be removed if efficiency isn’t critical.
Applications Issues
Dropout Performance
The output voltage adjust range for continuous-conduc-
tion operation is restricted by the nonadjustable 500ns
(max) minimum off-time one-shot. When working with
low input voltages, the duty-factor limit must be calcu-
PD (Q1 switching) = ?
?
?
? C
?
RSS × V VP(MAX) 2 × ? × I LOAD
I GATE
?
?
?
lated using worst-case values for on- and off-times.
Manufacturing tolerances and internal propagation
delays introduce an error to the t ON K-factor. Also,
keep in mind that transient response performance of
where C RSS is the reverse transfer capacitance of Q1,
and I GATE is the peak gate-drive source/sink current.
For the low-side MOSFET, the worst-case power dissi-
pation always occurs at maximum battery voltage:
buck regulators operating close to dropout is poor, and
bulk output capacitance must often be added.
Dropout design example: V IN = 7V (min), V OUT = 5V, f
= 300kHz. The required duty cycle is :
PD(Q2) = ? 1 -
?
?
? × I LOAD 2 × R DS
DC REQ = = = 0 . 74
?
?
V OUT
V VP(MAX) ? ?
V OUT +V SW 5V + 0.1V
V VP - V SW 7V - 0.1V
t ON(MIN) = × K = ×
Duty =
=
= 0 . 82 ,
The absolute worst case for MOSFET power dissipation
occurs under heavy overloads that are greater than
I LOAD(MAX) but are not quite high enough to exceed
the current limit and cause the fault latch to trip. To pro-
tect against this possibility, the circuit must be overde-
signed to tolerate:
I LOAD = I LIMIT(HIGH) + (LIR / 2 ) ? I LOAD(MAX)
where I LIMIT(HIGH) is the maximum valley current
allowed by the current-limit circuit, including threshold
tolerance and on-resistance variation. This means that
the MOSFET must be very well heatsinked. If short-cir-
cuit protection without overload protection is enough, a
normal I LOAD value can be used for calculating compo-
nent stresses.
During the period when the high-side switch is off, cur-
rent circulates from ground to the junction of both FETs
and the inductor. As a consequence, the polarity of the
switching node is negative with respect to ground. If
The worst-case on-time is:
V OUT + 0.075 5V + 0.075
V VP 7V
3 . 35 μ s × 90 % = 2 . 18 μ s
The maximum IC duty factor based on timing con-
straints of the MAX1762/MAX1792 is:
t ON(MIN) 2 . 18 μ s
t ON(MIN) + t OFF(MAX) 2 . 18 μ s + 0 . 5 μ s
which meets the required duty cycle. Remember to
include inductor resistance and MOSFET on-state volt-
age drops (V SW ) when doing worst-case dropout duty-
factor calculations.
Fixed Output Voltages
The MAX1762/MAX1791 Dual Mode operation allows
the selection of common voltages without requiring
external components (Figure 9). Connect FB to GND for
______________________________________________________________________________________
17
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1791EUB+ | 功能描述:DC/DC 开关控制器 Step-Down for Notebook 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 |
| MAX1791EUB+ | 制造商:Maxim Integrated Products 功能描述:CONTROLLER ((NW)) |
| MAX1791EUB+T | 功能描述:DC/DC 开关控制器 Step-Down for Notebook 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 |
| MAX1791EUB-T | 功能描述:DC/DC 开关控制器 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 |
| MAX1791EVKIT | 功能描述:DC/DC 开关控制器 Evaluation Kit for the MAX1791 MAX1762 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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