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| 型号： | MAX8764ETP+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 13/23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
? i
? t
=
V BATT -V OUT
L
I PEAK
I PEAK
I LOAD
I LOAD = I PEAK / 2
I LIMIT
0 ON-TIME
TIME
0
TIME
Figure 3. Pulse-Skipping/Discontinuous Crossover Point
where V DROP1 is the sum of the parasitic voltage drops
in the inductor discharge path, including synchronous
rectifier, inductor, and PC board resistances; V DROP2 is
the sum of the resistances in the charging path, and t ON
is the on-time calculated by the MAX8764.
Automatic Pulse-Skipping Switchover
In skip mode ( SKIP low), an inherent automatic
switchover to PFM takes place at light loads (Table 3).
This switchover is affected by a comparator that trun-
cates the low-side switch on-time at the inductor current’s
zero crossing. This mechanism causes the threshold
between pulse-skipping PFM and nonskipping PWM
operation to coincide with the boundary between continu-
ous and discontinuous inductor-current operation (also
known as the “critical conduction ” point; see the
Continuous-to-Discontinuous Inductor Current vs. Input
Voltage graph in the Typical Operating Characteristics ).
In low-duty-cycle applications, this threshold is relatively
constant, with only a minor dependence on battery
voltage.
Figure 4. ‘‘Valley’’ Current-Limit Threshold Point
results in high light-load efficiency. Trade-offs in PFM
noise vs. light-load efficiency are made by varying the
inductor value. Generally, low inductor values produce a
broader efficiency vs. load curve, while higher values
result in higher full-load efficiency (assuming that the coil
resistance remains fixed) and less output voltage ripple.
Penalties for using higher inductor values include larger
physical size and degraded load-transient response
(especially at low-input voltage levels).
DC output accuracy specifications refer to the threshold
of the error comparator. When the inductor is in continu-
ous conduction, the output voltage has a DC regulation
level higher than the trip level by 50% of the ripple. In
discontinuous conduction ( SKIP = GND, light load), the
output voltage has a DC regulation level higher than the
error-comparator threshold by approximately 1.5% due
to slope compensation.
Forced-PWM Mode ( SKIP = High)
The low-noise, forced-PWM mode ( SKIP = high) disables
the zero-crossing comparator, which controls the low-
×
I LOAD(SKIP) ≈
KV OUT V IN -V OUT
2L V IN
side switch on-time. This causes the low-side gate-drive
waveform to become the complement of the high-side
gate-drive waveform. This in turn causes the inductor
where K is the on-time scale factor (Table 5). The load-
current level at which PFM/PWM crossover occurs,
I LOAD( SKIP ) , is equal to 1/2 the peak-to-peak ripple cur-
rent, which is a function of the inductor value (Figure 3).
For example, in the Standard Application Circuit with
K = 3.3μs (Table 5), V OUT = 2.5V, V IN = 15V, and L =
6.8μH, switchover to pulse-skipping operation occurs at
I LOAD = 0.51A or about 1/8 full load. The crossover point
occurs at an even lower value if a swinging (soft-satura-
tion) inductor is used.
The switching waveforms may appear noisy and asyn-
chronous when light loading causes pulse-skipping
operation, but this is a normal operating condition that
current to reverse at light loads while DH maintains a
duty factor of V OUT /V IN . The benefit of forced-PWM
mode is to keep the switching frequency fairly constant,
but it comes at a cost: the no-load battery current can be
10mA to 40mA, depending on the external MOSFETs.
Forced-PWM mode is most useful for reducing audio-
frequency noise, improving load-transient response, pro-
viding sink-current capability for dynamic output voltage
adjustment, and improving the cross-regulation of
multiple-output applications that use a flyback trans-
former or coupled inductor.
______________________________________________________________________________________
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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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