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参数资料
| 型号： | MAX797ESE+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 23/32页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-SOIC |
| 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，混合 |
| 输出数： | 1 |
| 频率 - 最大： | 330kHz |
| 占空比： | 96% |
| 电源电压： | 5 V ~ 30 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： | 16-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 产品目录页面： | 1409 (CN2011-ZH PDF) |
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Step-Down Controllers with
Synchronous Rectifier for CPU Power
____________Low-Voltage Operation
Low input voltages and low input-output differential volt-
ages each require some extra care in the design. Low
absolute input voltages can cause the VL linear regulator
to enter dropout, and eventually shut itself off. Low input
voltages relative to the output (low V IN -V OUT differential)
can cause bad load regulation in multi-output flyback
applications. See the design equations in the Transformer
Design section. Finally, low V IN -V OUT differentials can also
cause the output voltage to sag when the load current
changes abruptly. The amplitude of the sag is a function
of inductor value and maximum duty factor (an Electrical
Characteristics parameter, 93% guaranteed over temper-
ature at f = 150kHz) as follows:
(I STEP ) 2 x L
V SAG = ———————————————
2 x C F x (V IN(MIN) x D MAX - V OUT )
The cure for low-voltage sag is to increase the value of
the output capacitor. For example, at V IN = 5.5V, V OUT
= 5V, L = 10μH, f = 150kHz, a total capacitance of
660μF will prevent excessive sag. Note that only the
capacitance requirement is increased and the ESR
requirements don ’t change. Therefore, the added
capacitance can be supplied by a low-cost bulk
capacitor in parallel with the normal low-ESR capacitor.
__________Applications Information
Heavy-Load Efficiency Considerations
The major efficiency loss mechanisms under loads are,
in the usual order of importance:
? P(I 2 R), I 2 R losses
? P(gate), gate-charge losses
? P(diode), diode-conduction losses
? P(tran), transition losses
? P(cap), capacitor ESR losses
? P(IC), losses due to the operating supply current
of the IC
Inductor-core losses are fairly low at heavy loads
because the inductor’s AC current component is small.
Therefore, they aren’t accounted for in this analysis.
Ferrite cores are preferred, especially at 300kHz, but
powdered cores such as Kool-mu can work well.
Efficiency = P OUT / P IN x 100%
= P OUT / (P OUT + P TOTAL ) x 100%
P TOTAL = P(I 2 R) + P(gate) + P(diode) + P(tran) +
P(cap) + P(IC)
P(I 2 R) = (I LOAD ) 2 x (R DC + R DS(ON) + R SENSE )
where R DC is the DC resistance of the coil, R DS(ON) is
the MOSFET on-resistance, and R SENSE is the current-
Table 4. Low-Voltage Troubleshooting
SYMPTOM
CONDITION
ROOT CAUSE
SOLUTION
Sag or droop in V OUT
Low V IN -V OUT differential, Limited inductor-current slew
Increase bulk output capacitance per
under step load change
<1.5V
rate per cycle.
formula above. Reduce inductor value.
Dropout voltage is too
high (V OUT follows V IN as
V IN decreases)
Low V IN -V OUT differential, Maximum duty-cycle limits
<1V exceeded.
Reduce f to 150kHz. Reduce MOSFET
on-resistance and coil DCR.
Unstable—jitters between
two distinct duty factors
Secondary output won’t
support a load
High supply current,
poor efficiency
Low V IN -V OUT differential,
<1V
Low V IN -V OUT differential,
V IN < 1.3 x V OUT (main)
(MAX796/MAX799 only)
Low input voltage, <5V
Inherent limitation of fixed-fre-
quency current-mode SMPS
slope compensation.
Not enough duty cycle left to
initiate forward-mode operation.
Small AC current in primary can’t
store energy for flyback operation.
VL linear regulator is going into
dropout and isn’t providing
good gate-drive levels.
Reduce L value. Tolerate the remaining
jitter (extra output capacitance helps
somewhat).
Reduce f to 150kHz. Reduce secondary
impedances—use Schottky if possible.
Stack secondary winding on main output.
Use a small 20mA Schottky diode for
boost diode D2. Supply VL from an
external source.
Won’t start under load or
quits before battery is
completely dead
Low input voltage, <4.5V
VL output is so low that it hits the Supply VL from an external source other
VL UVLO threshold at 4.2V max. than V BATT , such as the system 5V supply.
______________________________________________________________________________________
23
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| MAX797HESE+ | IC REG CTRLR BUCK PWM 16-SOIC |
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX797ESE/GG8 | 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 |
| MAX797ESE/GG8-T | 制造商:Maxim Integrated Products 功能描述:STEP DOWN CONTROLLER - Tape and Reel |
| MAX797ESE/GH9 | 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 |
| MAX797ESE/GH9-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 |
| MAX797ESE+ | 功能描述:DC/DC 开关控制器 Step-Down Controller for CPU Power 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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