- 您现在的位置：买卖IC网 > PDF目录383338 > MAX1855EEG (MAXIM INTEGRATED PRODUCTS INC) Replaced by TMS320C6202B : Fixed-Point Digital Signal Processor 352-FCBGA PDF资料下载
参数资料
| 型号： | MAX1855EEG |
| 厂商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | Replaced by TMS320C6202B : Fixed-Point Digital Signal Processor 352-FCBGA |
| 中文描述： | SWITCHING CONTROLLER, 550 kHz SWITCHING FREQ-MAX, PDSO24 |
| 封装： | 0.150 INCH, 0.025 INCH PITCH, QSOP-24 |
| 文件页数： | 17/33页 |
| 文件大小： | 840K |
| 代理商： | MAX1855EEG |
第1页第2页第3页第4页第5页第6页第7页第8页第9页第10页第11页第12页第13页第14页第15页第16页当前第17页第18页第19页第20页第21页第22页第23页第24页第25页第26页第27页第28页第29页第30页第31页第32页第33页
M
High-Speed, Adjustable, Synchronous Step-Down
Controllers with Integrated Voltage Positioning
______________________________________________________________________________________
17
switching frequency. The on-time guaranteed in the
Electrical Characteristics
table is influenced by switch-
ing delays in the external high-side MOSFET. Resistive
losses
—
including the inductor, both MOSFETs, output
capacitor ESR, and PC board copper losses in the out-
put and ground
—
tend to raise the switching frequency
at higher output currents. Switch dead-time can
increase the effective on-time, reducing the switching
frequency. This effect occurs only in PWM mode (
SKIP
= high) 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.
When the controller operates in continuous mode, the
dead-time is no longer a factor and the actual switching
frequency is:
= (V
OUT
+ V
DROP1
) / [t
ON
×
(V+ + V
DROP1
–
V
DROP2
)]
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 high-side switch, inductor, and PC board resis-
tances; and t
ON
is the on-time calculated by the
MAX1716/MAX1854/MAX1855.
Automatic Pulse-Skipping Switchover
In skip mode (
SKIP
= low), an inherent automatic
switchover to PFM takes place at light loads (Figure 3).
This switchover is controlled by a comparator that trun-
cates the low-side switch on-time at the inductor cur-
rent
’
s zero crossing. This mechanism causes the
threshold between pulse-skipping PFM and nonskip-
ping PWM operation to coincide with the boundary
between continuous and discontinuous inductor-cur-
rent operation. For an input voltage (V+) range of 7V to
24V, this threshold is relatively constant, with only a
minor dependence on the input voltage:
where K is the on-time scale factor (Table 3). 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 (300kHz), V
BATT
= 12V, V
OUT
= 1.6V, and
L = 0.68μH, switchover to pulse-skipping operation
occurs at I
LOAD
= 2.3A or about 1/4 full load. The
crossover point occurs at an even lower value if a
swinging (soft-saturation) inductor is used.
The switching waveforms may appear noisy and asyn-
chronous when light loading causes pulse-skipping
operation; this is a normal operating condition that
improves light-load efficiency. Trade-offs in PFM noise
vs. light-load efficiency are made by varying the induc-
tor 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-tran-
sient response (especially at low input voltage levels).
Forced-PWM Mode (
SKIP
= High)
The low-noise, forced-PWM mode (
SKIP
driven high)
disables the zero-crossing comparator that controls the
I
I
LIMIT
I
LOAD
0
TIME
-I
PEAK
Figure 4.
“
Valley
”
Current-Limit Threshold Point
I
I
LOAD
= I
PEAK
/2
ON-TIME
0
TIME
-I
PEAK
L
V
BATT
- V
OUT
i
t
=
Figure 3. Pulse-Skipping/Discontinuous Crossover Point
I
K
V
L
V
V
V
LOAD SKIP
OUT
OUT
(
)
+
≈
×
+
2
相关PDF资料 |
PDF描述 |
|---|---|
| MAX1854 | High-Speed, Adjustable, Synchronous Step-Down Controllers with Integrated Voltage Positioning |
| MAX1857EUA47 | 500mA, Low-Dropout, Ripple-Rejecting LDO in MAX |
| MAX1857 | Replaced by TMS320C6202B : Fixed-Point Digital Signal Processor 352-FCBGA |
| MAX1858 | Dual 180∑ Out-of-Phase Buck Controllers with Sequencing/Prebias Startup and POR |
| MAX1858EEG | Dual 180∑ Out-of-Phase PWM Step-Down Controller with Power Sequencing and POR |
相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1855EEG+ | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1855EEG-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 |
| MAX1855EVKIT | 功能描述:DC/DC 开关控制器 Evaluation Kit for the MAX1716 MAX1854 MAX1855 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 |
| MAX1856EUB | 功能描述:电信线路管理 IC RoHS:否 制造商:STMicroelectronics 产品:PHY 接口类型:UART 电源电压-最大:18 V 电源电压-最小:8 V 电源电流:30 mA 最大工作温度:+ 85 C 最小工作温度:- 40 C 安装风格:SMD/SMT 封装 / 箱体:VFQFPN-48 封装:Tray |
| MAX1856EUB+ | 功能描述:电信线路管理 IC Synchronizable PWM SLIC Power Supply RoHS:否 制造商:STMicroelectronics 产品:PHY 接口类型:UART 电源电压-最大:18 V 电源电压-最小:8 V 电源电流:30 mA 最大工作温度:+ 85 C 最小工作温度:- 40 C 安装风格:SMD/SMT 封装 / 箱体:VFQFPN-48 封装:Tray |
发布紧急采购，3分钟左右您将得到回复。