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| 型号： | MAX16955EVKIT+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 14/26页 |
| 文件大小： | 0K |
| 描述： | KIT EVALUATION FOR MAX16955 |
| 其它有关文件： | Automotive Product Guide |
| 标准包装： | 1 |
| 主要目的： | DC/DC，步降 |
| 输出及类型： | 1，非隔离 |
| 输出电压： | 5V |
| 电流 - 输出： | 5A |
| 输入电压： | 6 ~ 36 V |
| 稳压器拓扑结构： | 降压 |
| 频率 - 开关： | 400kHz |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | MAX16955 |
MAX16955
36V, 1MHz Step-Down Controller
with Low Operating Current
I LOAD ( SKIP ) [ A ] =
During the second half of the cycle, the high-side
MOSFET turns off and the low-side MOSFET turns on.
The inductor releases the stored energy as the current
ramps down, providing current to the output. The out-
put capacitor stores charge when the inductor current
exceeds the required load current and discharges
when the inductor current is lower, smoothing the volt-
age across the load. Under soft-overload conditions,
when the peak inductor current exceeds the selected
current limit, the high-side MOSFET is turned off imme-
diately. The low-side MOSFET is turned on and
remains on to let the inductor current ramp down until
the next clock cycle.
Forced Fixed-Frequency PWM Mode
The low-noise forced fixed-frequency PWM mode
(FSYNC connected to BIAS or an external clock) dis-
ables the zero-crossing comparator, which controls the
low-side switch on-time. This forces the low-side gate-
driver waveform to constantly be the complement of the
high-side gate-drive waveform. The inductor current
reverses at light loads while DH maintains a duty factor
of V OUT /V SUP .
The benefit of forced fixed-frequency PWM mode is to
keep the switching frequency fairly constant. However,
forced fixed-frequency PWM operation comes at a cost:
the no-load 5V supply current can be up to 45mA,
depending on the external MOSFETs and switching fre-
quency. Forced fixed-frequency PWM mode is most
useful for avoiding audio frequency noises and improv-
ing load-transient response.
Light-Load Low-Quiescent Operating
(Skip) Mode
The MAX16955 includes a light-load operating mode
control input (FSYNC = SGND) used to enable or dis-
able the zero-crossing comparator. When the zero-
crossing comparator is enabled, the regulator forces
DL low when the current-sense inputs detect zero
inductor current. This keeps the inductor from discharg-
ing the output capacitor and forces the regulator to skip
pulses under light-load conditions to avoid overcharg-
ing the output.
The lowest operating currents can be achieved in skip
mode. When the MAX16955 operates in skip mode with
no external load current, the overall current consump-
tion can be as low as 50μA. A disadvantage of skip
mode is that the operating frequency is not fixed.
Skip-Mode Current-Sense Threshold
When skip mode is enabled, the on-time of the step-
down controller terminates when the output voltage
exceeds the feedback threshold and when the current-
14
sense voltage exceeds the idle-mode current-sense
threshold (V CS,IDLE ). See Figure 1. Under light-load
conditions, the on-time duration depends solely on the
skip-mode current-sense threshold, which is 25mV
(typ). This forces the controller to source a minimum
amount of power with each cycle. To avoid overcharg-
ing the output, another on-time cannot begin until the
output voltage drops below the feedback threshold.
Because the zero-crossing comparator prevents the
switching regulator from sinking current, the controller
must skip pulses. Therefore, the controller regulates the
valley of the output ripple under light-load conditions.
Automatic Pulse-Skipping Crossover
In skip mode, an inherent automatic switchover to pulse
frequency modulation (PFM) takes place at light loads.
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
senses the inductor current across CS to OUT. Once
(V CS - V OUT ) drops below the 6mV zero-crossing, cur-
rent-sense threshold, the comparator forces DL low.
This mechanism causes the threshold between pulse-
skipping PFM and nonskipping PWM operation to coin-
cide 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
given by:
( V SUP ? V OUT ) V OUT
2 × V SUP × f SW [ MHz ] × L [ μH ]
The switching waveforms can appear noisy and asyn-
chronous when light-loading causes pulse-skipping
operation. This is a normal operating condition that
results in high light-load efficiency. Trade-offs in PFM
noise vs. light-load efficiency is made by varying the
inductor value. Generally, low inductor values produce
a broader efficiency versus load current, while higher
values result in higher full-load efficiency (assuming
that the coil resistance remains constant) and less out-
put-voltage ripple. Drawbacks of using higher inductor
values include larger physical size and degraded load-
transient response (especially at low input-voltage lev-
els).
MOSFET Gate Drivers (DH and DL)
The DH and DL drivers are optimized for driving logic-
level n-channel power MOSFETs. The DH high-side
n-channel MOSFET driver is powered by charge pump-
ing at BST, while the DL synchronous rectifier drivers
are powered directly by the 5V linear regulator (BIAS).
Maxim Integrated
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相关代理商/技术参数 |
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|---|---|
| MAX16955EVKIT# | 功能描述:电源管理IC开发工具 MAX16955 Eval Kit RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| MAX16955EVKIT+ | 功能描述:电源管理IC开发工具 MAX16955 Eval Kit RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| MAX16956AUBA/V+T | 制造商:Maxim Integrated Products 功能描述:36V, 300MA, MINI BUCK CONVERTER WITH 2UA IQ - Tape and Reel |
| MAX16958GEE/V+ | 功能描述:模数转换器 - ADC 500mA Hi-Speed USB Protector RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32 |
| MAX16958GEE/V+T | 功能描述:模数转换器 - ADC 500mA Hi-Speed USB Protector RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32 |
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