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参数资料
| 型号： | MAX1844EEP+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 13/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 20-QSOP |
| 标准包装： | 50 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 600kHz |
| 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： | 20-SSOP（0.154"，3.90mm 宽） |
| 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 MAX1844.
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 effected 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 will have a DC regu-
lation level higher than the trip level by 50% of the ripple.
In discontinuous conduction ( SKIP = GND, light load),
the output voltage will have 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 |
|---|---|
| MAX1844EEP+ | 功能描述:电流型 PWM 控制器 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 |
| MAX1844EEP+T | 功能描述:电流型 PWM 控制器 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 |
| MAX1844EEP-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 |
| MAX1844EGP | 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 |
| MAX1844EGP+ | 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 |
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