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| 型号： | ADP1871-1.0-EVALZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 22/44页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL FOR ADP1871-1.0 |
| 标准包装： | 1 |
| 系列： | * |
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ADP1870/ADP1871
SYNCHRONOUS RECTIFIER
The ADP1870/ADP1871 employ an internal lower-side MOSFET
driver to drive the external upper- and lower-side MOSFETs.
The synchronous rectifier not only improves overall conduction
efficiency, but also ensures proper charging to the bootstrap
capacitor located at the upper-side driver input. This is beneficial
during startup to provide sufficient drive signal to the external
upper-side MOSFET and to attain fast turn-on response, which is
essential for minimizing switching losses. The integrated upper-
and lower-side MOSFET drivers operate in complementary
fashion with built-in anticross conduction circuitry to prevent
unwanted shoot-through current that may potentially damage the
Data Sheet
As soon as the forward current through the lower-side
MOSFET decreases to a level where
10 mV = I Q2 × R ON(Q2)
the zero-cross comparator (or I REV comparator) emits a signal to
turn off the lower-side MOSFET. From this point, the slope of the
as the body diode of the lower-side MOSFET begins to conduct
current and continues conducting current until the remaining
energy stored in the inductor has been depleted.
ANOTHER t ON EDGE IS
TRIGGERED WHEN V OUT
FALLS BELOW REGULATION
MOSFETs or reduce efficiency as a result of excessive power loss.
POWER SAVING MODE (PSM) VERSION (ADP1871)
The power saving mode version of the ADP1870 is the ADP1871.
The ADP1871 operates in the discontinuous conduction mode
(DCM) and pulse skips at light load to mid load currents. It
outputs pulses as necessary to maintain output regulation. Unlike
the continuous conduction mode (CCM), DCM operation
prevents negative current, thus allowing improved system
efficiency at light loads. Current in the reverse direction through
this pathway, however, results in power dissipation and therefore
a decrease in efficiency.
SW
LS
I LOAD
0A
t ON
HS AND LS
IN IDLE MODE
ZERO-CROSS COMPARATOR
DETECTS 10mV OFFSET AND
TURNS OFF LS
10mV = R ON × I LOAD
HS
t ON
Figure 76. 10 mV Offset to Ensure Prevention of Negative Inductor Current
The system remains in idle mode until the output voltage drops
below regulation. A PWM pulse is then produced, turning on the
upper-side MOSFET to maintain system regulation. The
LS
t OFF
HS AND LS ARE OFF
OR IN IDLE MODE
ADP1871 does not have an internal clock, so it switches purely
as a hysteretic controller as described in this section.
TIMER OPERATION
The ADP1870/ADP1871 employ a constant on-time architecture,
AS THE INDUCTOR
CURRENT APPROACHES
which provides a variety of benefits, including improved load
I LOAD
0A
ZERO CURRENT, THE STATE
MACHINE TURNS OFF THE
LOWER-SIDE MOSFET.
and line transient response when compared with a constant
(fixed) frequency current-mode control loop of comparable
loop design. The constant on-time timer, or t ON timer, senses
Figure 74. Discontinuous Mode of Operation (DCM)
To minimize the chance of negative inductor current buildup,
an on-board zero-cross comparator turns off all upper- and
lower-side switching activities when the inductor current
approaches the zero current line, causing the system to enter
the high input voltage (V IN ) and the output voltage (V OUT ) using
SW waveform information to produce an adjustable one-shot
PWM pulse that varies the on-time of the upper-side MOSFET in
response to dynamic changes in input voltage, output voltage, and
load current conditions to maintain regulation. It then generates
an on-time (t ON ) pulse that is inversely proportional to V IN.
idle mode, where the upper- and lower-side MOSFETs are
turned off. To ensure idle mode entry, a 10 mV offset, connected
t ON ? K ?
V OUT
V IN
ZERO-CROSS
COMPARATOR
SW
I Q2
where:
K is a constant that is trimmed using an RC timer product for
LS
10mV
Q2
the 300 kHz, 600 kHz, and 1.0 MHz frequency options.
Figure 75. Zero-Cross Comparator with 10 mV of Offset
Rev. B | Page 22 of 44
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| ADP1871ACPZ-0.3-R7 | 功能描述:IC REG CTRLR BUCK PWM CM 10LFCSP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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 ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| ADP1871ACPZ-0.6-R7 | 功能描述:IC REG CTRLR BUCK PWM CM 10LFCSP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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 ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| ADP1871ACPZ-1.0-R7 | 功能描述:IC REG CTRLR BUCK PWM CM 10LFCSP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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 ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| ADP1871ARMZ-0.3-R7 | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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 ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| ADP1871ARMZ-0.6-R7 | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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 ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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