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| 型号： | MAX1993ETG+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 18/36页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 24-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 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
I LOAD ( SKIP ) ≈ ? OUT ? ? IN OUT ?
? = 0 . 76 A
? 2 . 5 V × 3 . 3 μ s ? ? 12 V ? 2 . 5 V ?
? 2 × 4 . 3 μ H ? ?
? ? ?
where K (switching period) is set by the TON pin-strap
connection (Table 3), and 0.075V is an approximation to
accommodate the expected drop across the low-side
MOSFET switch. This algorithm results in a nearly con-
stant switching frequency despite the lack of a fixed-fre-
quency clock generator. The benefits of a constant
switching frequency are twofold: 1) the frequency can
be selected to avoid noise-sensitive regions such as the
455kHz IF band; 2) the inductor ripple-current operating
point remains relatively constant, resulting in easy design
methodology and predictable output voltage ripple.
The on-time one-shot has good accuracy at the operat-
ing points specified in the Electrical Characteristics
(approximately ±12.5% at 600kHz and 450kHz and
±10% at 200kHz and 300kHz). On-times at operating
points far removed from the conditions specified in the
Electrical Characteristics can vary over a wider range.
For example, the 600kHz setting typically runs approxi-
mately 10% slower with inputs much greater than 5V
due to the very short on-times required.
The constant on-time translates only roughly to a constant
switching frequency. The on-times guaranteed in the
Electrical Characteristics are influenced by resistive loss-
es and by switching delays in the high-side MOSFET.
Resistive losses—including the inductor, both MOSFETs,
output capacitor ESR, and PC board copper losses in the
output and ground—tend to raise the switching frequency
as the load increases. The dead-time effect increases the
effective on-time, reducing the switching frequency as
one or both dead times are added to the effective on-
time. It occurs only in PWM mode ( SKIP = V CC ) and
during dynamic output voltage transitions when the
inductor current reverses at light or negative load
currents. With reversed inductor current, the inductor’s
EMF causes LX to go high earlier than normal, extending
the on-time by a period equal to the DH-rising dead time.
For loads above the critical conduction point, where the
dead-time effect is no longer a factor, the actual switch-
ing frequency is:
Automatic Pulse-Skipping Mode
( SKIP = GND)
In skip mode ( SKIP = GND), an inherent automatic
switchover to PFM takes place at light loads (Figure 3).
This switchover is affected by a comparator that trun-
cates the low-side switch on-time at the inductor cur-
rent ’s zero crossing. The zero-crossing comparator
differentially senses the inductor current across the cur-
rent-sense resistor (CSP to CSN). Once V CSP - V CSN
drops below 5% of the current-limit threshold (2.5mV
for the default 50mV current-limit threshold), the com-
parator forces DL low (Figure 2). This mechanism caus-
es the threshold between pulse-skipping PFM and
nonskipping PWM operation to coincide with the
boundary between continuous and discontinuous
inductor-current operation (also known as the critical
conduction point). The load-current level at which
PFM/PWM crossover occurs, I LOAD(SKIP) , is equal to
one-half the peak-to-peak ripple current, which is a
function of the inductor value (Figure 3). This threshold
is relatively constant, with only a minor dependence on
battery voltage:
? V K ? ? V ? V ?
? 2 L ? ? V IN ?
where K is the on-time scale factor (Table 3). For exam-
ple, in the standard application circuit (K = 3.3μs, V OUT =
2.5V, V IN = 12V, and L = 4.3μH), the pulse-skipping
switchover occurs at:
12 V ?
The crossover point occurs at an even lower value if a
swinging (soft-saturation) inductor is used. The switch-
ing waveforms can appear noisy and asynchronous
when light loading causes pulse-skipping operation,
but this is a normal operating condition that results in
high light-load efficiency. Trade-offs in PFM noise vs.
f SW =
V OUT + V DROP 1
t ON ( V IN + V DROP 2 )
light-load efficiency are made by varying the inductor
value. Generally, low inductor values produce a broad-
er efficiency vs. load curve, while higher values result in
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, includ-
ing the high-side switch, inductor, and PC board resis-
tances; and t ON is the on-time calculated by the
MAX1992/MAX1993.
higher full-load efficiency (assuming that the coil resis-
tance 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).
18
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相关代理商/技术参数 |
参数描述 |
|---|---|
| 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 |
| MAX1993ETG+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 |
| MAX1993ETG+TG40 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1993ETG-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 |
| MAX1993EVKIT | 制造商:Maxim Integrated Products 功能描述:EVALUATION KIT FOR THE MAX1992 MAX1993 - Bulk |
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