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| 型号： | MAX1992ETG+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 31/36页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 24-TQFN |
| 标准包装： | 75 |
| 系列： | Quick-PWM™ |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 600kHz |
| 占空比： | 100% |
| 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： | 24-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
PD ( N L Re sistive ) = ? 1 ? ? OUT ? ? ( I LOAD ) R DS ( ON )
V IN ? ? ?
? ?
I LOAD = I VALLEY ( MAX ) + ? ?
? ?
? + V DROP 2 ? V DROP 1
V IN ( MIN ) = ?
? 1 ? ?
? ?
? ?
?
?
? + 0 . 1 V ? 0 . 1 V = 3 . 47 V
V IN ( MIN ) = ?
? 1 . 5 × 500 ns ? ?
? 1 ? ? ? ?
? ?
? ? ?
If the high-side MOSFET chosen for adequate R DS(ON)
at low battery voltages becomes extraordinarily hot
when subjected to V IN(MAX) , consider choosing another
MOSFET with lower parasitic capacitance.
For the low-side MOSFET (N L ) the worst-case power
dissipation always occurs at maximum battery voltage:
? ? V ? ? 2
?
The absolute worst case for MOSFET power dissipation
occurs under heavy overload conditions that are
greater than I LOAD(MAX) but are not high enough to
exceed the current limit and cause the fault latch to trip.
To protect against this possibility, “overdesign” the cir-
cuit to tolerate:
? I LOAD(MAX) LIR ?
2
where I VALLEY(MAX) is the maximum valley current
allowed by the current-limit circuit, including threshold
tolerance and sense-resistance variation. The
MOSFETs must have a relatively large heatsink to han-
dle the overload power dissipation.
Choose a Schottky diode (D L ) with a forward voltage
drop low enough to prevent the low-side MOSFET’s
body diode from turning on during the dead time. As a
general rule, select a diode with a DC current rating
equal to 1/3 the load current. This diode is optional and
can be removed if efficiency is not critical.
Applications Information
Dropout Performance
The output voltage adjustable range for continuous-con-
duction operation is restricted by the nonadjustable mini-
mum off-time one-shot. For best dropout performance,
use the slower (200kHz) on-time setting. When working
with low input voltages, the duty-factor limit must be cal-
culated 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 3). Also, keep in
mind that transient response performance of buck regula-
tors operated too close to dropout is poor, and bulk out-
put capacitance must often be added (see the V SAG
equation in the Design Procedure section).
The absolute point of dropout is when the inductor cur-
rent ramps down during the minimum off-time ( Δ I DOWN )
as much as it ramps up during the on-time ( Δ I UP ). The
ratio h = Δ I UP / Δ I DOWN indicates the controller’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 cannot increase as much 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 adjusting
this up or down allows trade-offs between V SAG , output
capacitance, and minimum operating voltage. For a
given value of h, the minimum operating voltage can be
calculated as:
? ?
? ?
? V OUT + V DROP 1 ?
? ? h × t OFF ( MIN ) ? ?
K
where V DROP1 and V DROP2 are the parasitic voltage
drops in the discharge and charge paths (see the On-
Time One-Shot (TON) section), t OFF(MIN) is from the
Electrical Characteristics , and K is taken from Table 3.
The absolute minimum input voltage is calculated with h
= 1.
If the calculated V IN(MIN) is greater than the required
minimum input voltage, then 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.
A dropout design example follows:
V OUT = 2.5V
f SW = 300kHz
K = 3.3μs, worst-case K MIN = 3.0μs
t OFF(MIN) = 500ns
V DROP1 = V DROP2 = 100mV
h = 1.5
? ?
? ?
? 2 . 5 V + 0 . 1 V
? 3 . 0 μ s
______________________________________________________________________________________
31
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1992ETG+ | 功能描述:电压模式 PWM 控制器 Step-Down w/Inductor RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX1992ETG+T | 功能描述:电压模式 PWM 控制器 Step-Down w/Inductor RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX1992ETG-T | 功能描述:电压模式 PWM 控制器 RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX1993ETG | 功能描述:电压模式 PWM 控制器 RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX1993ETG+ | 功能描述:电压模式 PWM 控制器 Step-Down w/Inductor RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
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