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| 型号： | MAX8764ETP+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 19/23页 |
| 文件大小： | 0K |
| 描述： | IC CNTRL STP DWN HS 20-TQFN |
| 标准包装： | 60 |
| 应用： | 控制器，笔记本电脑电源系统 |
| 输入电压： | 2 V ~ 28 V |
| 输出数： | 1 |
| 输出电压： | 1.8V，2.5V，1 V ~ 5.5 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-WQFN 裸露焊盘 |
| 供应商设备封装： | 20-TQFN-EP（5x5） |
| 包装： | 管件 |
High-Speed, Step-Down Controller with
Accurate Current Limit for Notebook Computers
C RSS × V IN(MAX)2 × f × I LOAD
pation limits often limits how small the MOSFET can be.
Again, the optimum occurs when the switching (AC)
losses equal the conduction (R DS(ON) ) losses. High-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 AC adapter
voltages are applied, due to the squared term in the
CV 2 f switching loss equation. If the high-side MOSFET
chosen for adequate R DS(ON) at low battery voltages
becomes extraordinarily hot when subjected to
V IN(MAX) , reconsider the choice of MOSFET.
Calculating the power dissipation in Q1 due to switching
losses is difficult, since it must allow for difficult-to-quanti-
fy factors that influence 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
calculation provides only a very rough estimate and is no
substitute for breadboard evaluation, preferably including
a sanity check using a thermocouple mounted on Q1:
PD(Q1 switching) =
I GATE
where C RSS is the reverse transfer capacitance of Q1,
and I GATE is the peak gate-drive source/sink current (1A
typ).
For the low-side MOSFET, Q2, the worst-case power dis-
sipation always occurs at maximum battery voltage:
Applications Information
Dropout Performance
The output voltage adjust range for continuous-conduc-
tion operation is restricted by the nonadjustable 500ns
(max) minimum off-time one-shot. For best dropout per-
formance, use the slower (200kHz) on-time settings.
When working with low input voltages, the duty-factor
limit must be calculated using worst-case values for on-
and off-times. Manufacturing tolerances and internal
propagation delays introduce an error to the TON K-
factor. This error is greater at higher frequencies (Table
5). Also, keep in mind that transient response perfor-
mance of buck regulators operated close to dropout is
poor, and bulk output capacitance must often be
added (see the V SAG equation in the Transient
Response section).
The absolute point of dropout is when the inductor cur-
rent ramps down during the minimum off-time ( ? I DOWN )
as much as it ramps up during the on-time ( ? I UP ). The
ratio h = ? I UP / ? I DOWN indicates the circuit’s ability to
slew the inductor current higher in response to
increased load, and must always be greater than 1. As
h approaches 1, the absolute minimum dropout point,
the inductor current is less able to increase during
each switching cycle, and V SAG greatly increases
unless additional output capacitance is used.
A reasonable minimum value for h is 1.5, but this can
be adjusted up or down to allow trade-offs between
V SAG , output capacitance, and minimum operating
voltage. For a given value of h, the minimum operating
( V OUT DROP 1 )
? t
V IN ( MIN ) =
OFF ( MIN ) × h
?
?
?
?
PD(Q2) = (1 - V OUT / V IN(MAX) ) ? I LOAD2 ? R DS(ON)
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. To protect against this possibility, you must
“overdesign” the circuit to tolerate I LOAD = I LIMIT(HIGH) +
voltage can be calculated as:
+ V
1- ? ?
K
?
+ V DROP 2 - V DROP 1
[(LIR / 2) ? I LOAD(MAX) ], where I LIMIT(HIGH) is the maxi-
mum valley current allowed by the current-limit circuit,
including threshold tolerance and sense-resistance vari-
ation. If short-circuit protection without overload protec-
tion is adequate, enable undervoltage protection, and
use I LOAD(MAX ) to calculate component stresses.
Choose a Schottky diode D1 having a forward voltage
drop 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 if
efficiency is not critical it can be removed.
where V DROP1 and V DROP2 are the parasitic voltage
drops in the discharge and charge paths, t OFF(MIN) is
from the Electrical Characteristics table, and K is taken
from Table 5. The absolute minimum input voltage is cal-
culated with h = 1.
If the calculated V IN(MIN) is greater than the required
minimum input voltage, operating frequency must be
reduced or output capacitance added to obtain an
acceptable V SAG . If operation near dropout is anticipat-
ed, calculate V SAG to be sure of adequate transient
response.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8764ETP+ | 功能描述:电流型 PWM 控制器 High-Speed Step Down 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 |
| MAX8764ETP+T | 功能描述:电流型 PWM 控制器 High-Speed Step Down 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 |
| MAX8764ETP-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 |
| MAX8765AETI+ | 功能描述:电池管理 Multichemistry Battery Charger RoHS:否 制造商:Texas Instruments 电池类型:Li-Ion 输出电压:5 V 输出电流:4.5 A 工作电源电压:3.9 V to 17 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:VQFN-24 封装:Reel |
| MAX8765AETI+T | 功能描述:电池管理 Multichemistry Battery Charger RoHS:否 制造商:Texas Instruments 电池类型:Li-Ion 输出电压:5 V 输出电流:4.5 A 工作电源电压:3.9 V to 17 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:VQFN-24 封装:Reel |
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