参数资料
| 型号： | MAX8741EAI+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 24/34页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR PWR SUP 28-SSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 46 |
| 应用： | 控制器，笔记本电脑电源系统 |
| 输入电压： | 4.2 V ~ 30 V |
| 输出数： | 2 |
| 输出电压： | 3.3V，5V，2.5 V ~ 5.5 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SSOP（0.209"，5.30mm 宽） |
| 供应商设备封装： | 28-SSOP |
| 包装： | 管件 |
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500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
Rectifier Diode (Transformer Secondary Diode)
The secondary diode in coupled-inductor applications
must withstand flyback voltages greater than 60V,
which usually rules out most Schottky rectifiers.
Common silicon rectifiers, such as the 1N4001, are also
prohibited because they are too slow. This often makes
fast silicon rectifiers such as the MURS120 the only
choice. The flyback voltage across the rectifier is relat-
ed to the V IN - V OUT difference, according to the trans-
former turns ratio:
V FLYBACK = V SEC + (V IN - V OUT ) ? N
where:
N = the transformer turns ratio SEC/PRI
V SEC = the maximum secondary DC output voltage
V OUT = the primary (main) output voltage
Subtract the main output voltage (V OUT ) from
V FLYBACK in this equation if the secondary winding is
returned to V OUT and not to ground. The diode reverse-
breakdown rating must also accommodate any ringing
due to leakage inductance. The rectifier diode’s current
rating should be at least twice the DC load current on
the secondary output.
Low-Voltage Operation
Low input voltages and low input-output differential volt-
ages each require extra care in their design. Low
absolute input voltages can cause the V L 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). Also, low V IN - V OUT differentials can
also cause the output voltage to sag when the load cur-
rent changes abruptly. The amplitude of the sag is a
and the ESR requirements do not 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(tran) = transition losses
? P(gate) = gate-charge losses
? P(diode) = diode-conduction losses
? P(cap) = input capacitor ESR losses
? P(IC) = losses due to the IC’s operating supply current
Inductor core losses are fairly low at heavy loads
because the inductor’s AC current component is small.
Therefore, they are not 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 ? 100% = P OUT /(P OUT + P TOTAL )
? 100%
P TOTAL = P(I 2 R) + P(tran) + P(gate) + P(diode) +
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-
sense resistor value. The R DS(ON) term assumes identi-
cal MOSFETs for the high-side and low-side switches
because they time-share the inductor current. If the
MOSFETs are not identical, their losses can be estimat-
ed by averaging the losses according to duty factor:
P ( tran ) = V IN × I LOAD ×
[
f × × ( V IN RSS GATE ) - 20 ns
× C
function of inductor value and maximum duty factor (an
Electrical Characteristics parameter, 97% guaranteed
over temperature at f = 333kHz), as follows:
3
2
/ I
]
V SAG =
2 × C OUT
I STEP 2 × L
× ( V IN ( MIN ) × D MAX - V OUT )
where C RSS is the reverse transfer capacitance of the
high-side MOSFET (a data sheet parameter), I GATE is
the DH gate-driver peak output current (1.5A typ), and
20ns is the rise/fall time of the DH driver (20ns typ):
The cure for low-voltage sag is to increase the output
capacitor’s value. Take a 333kHz/6A application circuit
as an example, at V IN = +5.5V, V OUT = +5V, L = 6.7μH,
f = 333kHz, I STEP = 3A (half-load step), a total capaci-
tance of 470μF keeps the sag less than 200mV. The
capacitance is higher than that shown in the Typical
Application Circuit because of the lower input voltage.
Note that only the capacitance requirement increases
P(gate) = Q G ? f ? V L
where V L is the internal-logic-supply voltage (5V), and
Q G is the sum of the gate-charge values for low-side
and high-side switches. For matched MOSFETs, Q G is
twice the data sheet value of an individual MOSFET. If
V OUT is set to less than 4.5V, replace V L in this equa-
tion with V BATT . In this case, efficiency can be
24
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8741EAI+ | 功能描述:电流和电力监控器、调节器 500kHz Multi-Out Pwr Supply Controller RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| MAX8741EAI+T | 功能描述:电流和电力监控器、调节器 500kHz Multi-Out Pwr Supply Controller RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| MAX8741EAI-T | 功能描述:电流和电力监控器、调节器 RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| MAX8742EAI | 功能描述:电流和电力监控器、调节器 RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| MAX8742EAI+ | 功能描述:电流和电力监控器、调节器 500kHz Multi-Out Pwr Supply Controller RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
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