参数资料
型号: MAX761ESA+
厂商: Maxim Integrated Products
文件页数: 9/12页
文件大小: 0K
描述: IC REG BOOST 12V/ADJ 0.15A 8SOIC
标准包装: 100
类型: 升压(升压)
输出类型: 两者兼有
输出数: 1
输出电压: 12V,5 V ~ 16.5 V
输入电压: 2 V ~ 16.5 V
频率 - 开关: 300kHz
电流 - 输出: 150mA
同步整流器:
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 8-SOIC(0.154",3.90mm 宽)
包装: 管件
供应商设备封装: 8-SOIC
12V/15V or Adjustable, High-Efficiency,
Low I Q , Step-Up DC-DC Converters
1A
500mA
Figure 4a. CCM, Heavy Load Current Waveform (500mA/div)
used in a bootstrapped circuit (Figure 5), undervoltage
lockout prevents start-up at low input voltages; but
once started, operation can continue down to a lower
voltage that depends on the load.
There is no undervoltage lockout when the internal feed-
back resistors are used (Figure 2), and special circuitry
guarantees start-up at 2.0V. The start-up circuitry fixes
the duty cycle at 50% until V+ is driven to 2.5V, above
which the normal control system takes over.
Shutdown Mode
The MAX761/MAX762 enter shutdown mode when
SHDN is high. In this mode, the internal biasing circuitry
is turned off (including the reference) and V OUT equals
V+ minus a diode drop (due to the DC path from the
input to the output). In shutdown mode, the supply cur-
rent drops to less than 5μA. SHDN is a TTL/CMOS logic
level input. Connect SHDN to GND for normal operation.
LBO is high impedance during shutdown.
Modes of Operation
When delivering high output currents, the MAX761/
MAX762 operate in CCM. In this mode, current always
flows in the inductor, and the control circuit adjusts the
switch’s duty cycle on a cycle-by-cycle basis to maintain
regulation without exceeding the switch-current capabili-
ty. This provides excellent load-transient response and
high efficiency.
In discontinuous-conduction mode (DCM), current
through the inductor starts at zero, rises to a peak value,
then ramps down to zero on each cycle. Although effi-
ciency is still excellent, the switch waveforms contain
1A
500mA
0A
Figure 4b. Light/Medium Load Current Waveform (500mA/div)
ringing (the inductor's self-resonant frequency). This
ringing is normal and poses no operational problems.
Low-Battery Detector
The MAX761/MAX762 provide a low-battery comparator
that compares the voltage on LBI to the 1.5V reference
voltage. When the LBI voltage is below V REF , LBO (an
open-drain output) goes low. The low-battery compara-
tor’s 20mV of hysteresis adds noise immunity, prevent-
ing repeated triggering of LBO. Use a resistor-divider
network between V+, LBI, and GND to set the desired
trip voltage V TRIP (Figure 3). When SHDN is high, LBI is
ignored and LBO is high impedance. The value of
resistor R3 should be no larger than 500k ? to ensure
the LBI leakage current does not cause inaccuracies in
V TRIP .
__________________Design Procedure
Setting the Output Voltage
The MAX761/MAX762’s output voltage can be adjusted
from 5V to 16.5V using external resistors R1 and R2
configured as shown in Figures 3 and 5. For adjustable-
output operation, select feedback resistor R1 in the
10k ? to 250k ? range. Higher R1 values within this
range give lowest supply current and best light-load
efficiency. R2 is given by:
R2 = (R1)( V OUT - 1)
V REF
where V REF = 1.5V.
Note: Tie FB to GND for fixed-output operation
(bootstrapped mode only).
_______________________________________________________________________________________
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