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参数资料
| 型号： | ADP1871-0.6-EVALZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 23/44页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL FOR ADP1871-0.6 |
| 标准包装： | 1 |
| 系列： | * |
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Data Sheet
ADP1870/ADP1871
t ON
C
SW
INFORMATION
VREG
I
R (TRIMMED)
V IN
To illustrate this feature more clearly, this section describes
one such load transient event—a positive load step—in detail.
During load transient events, the high-side driver output pulse
width stays relatively consistent from cycle to cycle; however,
the off-time (DRVL on-time) dynamically adjusts according to
the instantaneous changes in the external conditions mentioned.
When a positive load step occurs, the error amplifier (out of phase
of the output, V OUT ) produces new voltage information at its output
Figure 77. Constant On-Time Time
The constant on-time (t ON ) is not strictly “constant” because it
varies with V IN and V OUT . However, this variation occurs in such
a way as to keep the switching frequency virtually independent
of V IN and V OUT .
The t ON timer uses a feedforward technique, applied to the constant
on-time control loop, making it a pseudo-fixed frequency to a first
order. Second-order effects, such as dc losses in the external power
MOSFETs (see the Efficiency Consideration section), cause some
variation in frequency vs. load current and line voltage. These
effects are shown in Figure 23 to Figure 34. The variations in
frequency are much reduced compared with the variations
generated when the feedforward technique is not utilized.
The feedforward technique establishes the following relationship:
(COMP). In addition, the current-sense amplifier senses new
inductor current information during this positive load transient
event. The error amplifier’s output voltage reaction is compared
with the new inductor current information that sets the start of
the next switching cycle. Because current information is produced
from valley current sensing, it is sensed at the down ramp of the
inductor current, whereas the voltage loop information is sensed
through the counter action upswing of the error amplifier’s
output (COMP).
which allows an instantaneous increase in switching frequency
during the positive load transient event. In summary, a positive
load step causes V OUT to transient down, which causes COMP to
transient up and therefore shortens the off-time. This resulting
increase in frequency during a positive load transient helps to
f SW ?
1
K
quickly bring V OUT back up in value and within the regulation
window.
where f SW is the controller switching frequency (300 kHz,
600 kHz, and 1.0 MHz).
The t ON timer senses V IN and V OUT to minimize frequency
variation as previously explained. This provides a pseudo-fixed
frequency as explained in the Pseudo-Fixed Frequency section.
To allow headroom for V IN and V OUT sensing, adhere to the
following equations:
V REG ≥ V IN /8 + 1.5
V REG ≥ V OUT /4
For typical applications where V REG is 5 V, these equations are
not relevant; however, for lower V REG inputs, care may be
required.
PSEUDO-FIXED FREQUENCY
The ADP1870/ADP1871 employ a constant on-time control
scheme. During steady state operation, the switching frequency
stays relatively constant, or pseudo-fixed. This is due to the one-
shot t ON timer that produces a high-side PWM pulse with a
“fixed” duration, given that external conditions such as input
Similarly, a negative load step causes the off-time to lengthen in
response to V OUT rising. This effectively increases the inductor
demagnetizing phase, helping to bring V OUT within regulation.
In this case, the switching frequency decreases, or experiences a
foldback, to help facilitate output voltage recovery.
Because the ADP1870/ADP1871 has the ability to respond rapidly
to sudden changes in load demand, the recovery period in which
the output voltage settles back to its original steady state operating
point is much quicker than it would be for a fixed-frequency
equivalent . Therefore, using a pseudo-fixed frequency results in
significantly better load transient performance than using a
fixed frequency.
LOAD CURRENT
DEMAND
CS AMP
OUTPUT
voltage, output voltage, and load current are also at steady state.
During load transients, the frequency momentarily changes for
ERROR AMP
OUTPUT
VALLEY
TRIP POINTS
the duration of the transient event so that the output comes
PWM OUTPUT
f SW
> f SW
back within regulation more quickly than if the frequency were
fixed or if it were to remain unchanged. After the transient
event is complete, the frequency returns to a pseudo-fixed
frequency value to a first order.
Rev. B | Page 23 of 44
Figure 78. Load Transient Response Operation
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| ADP1871-1.0-EVALZ | 功能描述:BOARD EVAL FOR ADP1871-1.0 RoHS:是 类别:编程器，开发系统 >> 评估板 - DC/DC 与 AC/DC（离线）SMPS 系列:* 产品培训模块:Obsolescence Mitigation Program 标准包装:1 系列:True Shutdown™ 主要目的:DC/DC，步升 输出及类型:1，非隔离 功率 - 输出:- 输出电压:- 电流 - 输出:1A 输入电压:2.5 V ~ 5.5 V 稳压器拓扑结构:升压 频率 - 开关:3MHz 板类型:完全填充 已供物品:板 已用 IC / 零件:MAX8969 |
| 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) |
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