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| 型号： | MAX1802EHJ+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 14/28页 |
| 文件大小： | 0K |
| 描述： | IC PWR SPLY STEP DOWN 32-TQFP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 360 |
| 应用： | 控制器，数字式相机 |
| 输入电压： | 2.5 V ~ 11 V |
| 输出数： | 5 |
| 输出电压： | 1.25 V ~ 5.5 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-TQFP |
| 供应商设备封装： | 32-TQFP（5x5） |
| 包装： | 托盘 |
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Digital Camera Step-Down
Power Supply
Detailed Description
The MAX1802 typical application circuit is shown in
Figure 1. It features two step-down DC-DC converters
(main and core), three auxiliary step-up DC-DC con-
trollers, and control capability for multiple external
MAX1801 slave DC-DC controllers. Together, these
provide a complete high-efficiency power-supply solu-
tion for digital still cameras. Figures 2 and 3 show the
MAX1802 functional block diagrams.
Master-Slave Configuration
The MAX1802 supports MAX1801 “ slave ” controllers
that obtain input power, a voltage reference, and an
oscillator signal directly from the MAX1802 “ master ”
DC-DC converter. The master-slave configuration
reduces system cost by eliminating redundant circuitry
and controlling the harmonic content of noise with syn-
chronized converter switching.
Main DC-DC Converter
The MAX1802 main step-down DC-DC converter gen-
erates a 2.7V to 5.5V output voltage from a 2.5V to 11V
battery input voltage. When the battery voltage is lower
than the main regulation voltage, the regulator goes
into dropout and the P-channel switch remains on. In
this condition, the output voltage is slightly lower than
the input voltage. The converter drives an external P-
channel MOSFET power switch and an external N-
channel MOSFET synchronous rectifier. The converter
operates in a low-noise, constant-frequency PWM cur-
rent mode to regulate the voltage across the load.
drain of the external P-channel MOSFET. The MAX1802
main output switches to Idle Mode at light loads to
improve efficiency by leaving the P-channel switch on
until the voltage across the MOSFET reaches the 20mV
Idle Mode threshold. The Idle Mode current is 20mV
divided by the MOSFET on-resistance. By forcing the
inductor current above the Idle Mode threshold, more
energy is supplied to the output capacitor than is
required by the load. The switch and synchronous rec-
tifiers then remain off until the output capacitor dis-
charges to the regulation voltage. This causes the
converter to operate at a lower effective switching fre-
quency at light loads, thus improving efficiency.
An internal comparator turns off the N-channel synchro-
nous rectifier as the inductor current drops near zero,
by measuring the voltage across the MOSFET. If the N-
channel MOSFET on-resistance is low (less than that of
the P-channel switch), it may cause the MOSFET to turn
off prematurely, degrading efficiency. This is especially
critical for high input voltage applications, such as with
2 series Li+ cells. In this case, use an N-channel MOS-
FET with greater on-resistance than the P-channel
switch, and/or place a Schottky recitifier across the N-
channel MOSFET gate-source.
The voltage at COMPM is typically clamped to
V COMPM(MAX) = 2.14V, thereby limiting the inductor
current. The peak inductor current (I LIM ) and the maxi-
mum average output current (I OUT(MAX) ) are deter-
mined by the following equations:
V COMPM ( MAX ) ? V REF ? 1 + OUT VSWM ?
Switching harmonics generated by fixed-frequency
operation are consistent and easily filtered.
The external P-channel MOSFET switch turns on during
the first part of each cycle, allowing current to ramp up
in the inductor and store energy in a magnetic field
I LIM =
? V A ?
? V IN ?
A VCSM R DSP
? ? 1 ?
I OUT ( MAX ) = I LIM ? ??
V OUT ?
? V OUT ?
?
?
while supplying current to the load. During the second
part of each cycle, the P-channel MOSFET turns off and
the voltage across the inductor reverses, forcing cur-
rent through the external N-channel synchronous rectifi-
er to the output filter capacitor and load. As the energy
stored in the inductor is depleted, the current ramps
down. The synchronous rectifier turns off when the
? ?
?
?
? ?
V IN ? ?
2 f OSC L
?
? ?
inductor current approaches zero or at the beginning of
a new cycle, at which time the P-channel switch turns
on again.
The current-mode PWM converter uses the voltage at
COMPM to program the inductor current and regulate
the output voltage. The converter detects inductor cur-
rent by sensing the voltage across the source and
where A VSWM is the main slope compensation gain
(0.20V/V), A VCSM is the voltage gain of the main cur-
rent-sense amplifier (9.3V/V), R DSP is the on-resistance
of the external P-channel MOSFET switch, and L is the
inductor value. Note that the current limit increases as
the input/output voltage ratio increases.
14
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相关代理商/技术参数 |
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| MAX1802EHJ+ | 功能描述:直流/直流开关转换器 Step-Up Slave DC/DC Controller RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX1802EHJ+T | 功能描述:直流/直流开关转换器 Step-Up Slave DC/DC Controller RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX1802EHJ-T | 功能描述:直流/直流开关转换器 Step-Up Slave DC/DC Controller RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX1804EUB | 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 |
| MAX1804EUB+ | 功能描述:电流和电力监控器、调节器 Feedback Integrator for Power Supply 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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