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| 型号： | SP7648EB |
| 厂商： | Exar Corporation |
| 文件页数： | 7/13页 |
| 文件大小： | 0K |
| 描述： | EVAL BOARD FOR SP7648 |
| 标准包装： | 1 |
| 系列： | * |
S P 7 6 4 8
L o w R e f e r e n c e H i g h E f f i c i e n c y B o o s t R e g u l a t o r
THEORY OF OPERATION
D ETAILED D ESCRIPTION
The SP7648 is a step-up DC-DC converter with
an input voltage operation range from 2.7V to
4.7V. In addition to the main 0.3 ? internal
NMOSFET switch the SP7648 has an internal
synchronous rectifier, thereby increasing
efficiency and reducing the space and cost of
an external diode. An internal inductive-
damping switch significantly reduces inductive
ringing for low noise-high efficiency operation.
If the supply voltage drops below 0.61V the
SP7648 goes into under voltage lockout, thus
opening both internal switches. The inductor
peak current is externally programmable to
allow for a range of inductor values.
C IRCUIT L AYOUT
Printed circuit board layout is a critical part of
a power supply design. Poor designs can result
in excessive EMI on the feedback paths and on
the ground planes with applications involving
high switching frequencies and large peak
currents. Excessive EMI can result in instability
or regulation errors. All power components
should be placed on the PC board as closely as
possible with the traces kept short, direct, and
wide (>50mils or 1.25mm). Extra copper on
the PC board should be integrated into ground
as a pseudo-ground plane. On a multilayer PC
board, route the star ground using
component-side copper fill, then connect it to
the internal ground plane using vias. For the
SP7648 devices, the inductor and input &
output filter capacitors should be soldered with
their ground pins as close together as possible
in a star-ground configuration. The V OUT pin
must be bypassed directly to ground as close
to the SP7648 devices as possible (within
0.2in or 5mm). The DC-DC converter and any
digital circuitry should be placed on the
opposite corner of the PC board as far away
from sensitive RF and analog input stages.
Noisy traces, such as from the LX pin, should
be kept away from the voltage-feedback V FB
node and separated from it using grounded
copper to minimize EMI. See the SP7648EB
Evaluation Board Manual for PC Board Layout
design details.
C ONTROL S CHEME
A minimum off-time, current limited pulse
frequency modulation (PFM) control scheme
combines the high output power and efficiency
of a pulse width modulation (PWM) device with
the ultra low quiescent current of the
traditional PFM. At low to moderate output
loads the PFM control provides higher
efficiency than traditional PWM converters are
capable of delivering. At these loads the
switching frequency is determined by a
minimum off-time (T OFF , MIN) and a maximum
on-time (T ON , MAX) where:
T OFF ≤ K OFF / (V OUT - V BATT )
T ON ≥ K ON / V BATT
K OFF = 1.0Vμs
K ON = 3.5 Vμs
At light loads (as shown in plot A in Figure 14)
the charge cycle will last the maximum value
for t ON : For a 3V battery this would be as
follows: T ON = K ON / V BATT = 3.5VμS/ 3V
=1.17μS. The current built up in the coil
during the charge cycle gets fully discharged
in the discontinuous conduction mode (DCM).
When the current in the coil has reached zero,
the synchronous rectifier switch is opened and
the voltage across the coil (from V BATT to LX) is
shorted internally to eliminate inductive
ringing. With increasing load (as shown in plot
B in Figure 14) this inductor damping time
becomes shorter, because the output will
quickly drop below its regulation point due to
heavier load. If the load current increases
further, the SP7648 enters continuous
conduction mode (CCM) where there is always
current flowing in the inductor. The charge
time remains at maximum T ON as long as the
inductor peak current limit is not reached as
shown in plot C in Figure 14. The inductor
peak current limit can be programmed by
tying a resistor R LIM from the R LIM pin to
ground where:
I PEAK = 1600 / R LIM
When the peak current limit is reached the
charge time is short-cycled. In plot D of Figure
14, the switch current reaches the peak
current limit during the charge period which
ends the charge cycle and starts the discharge
? 2012 Exar Corporation
7/13
Rev. 2.0.0
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相关代理商/技术参数 |
参数描述 |
|---|---|
| SP7648ER | 制造商:SIPEX 制造商全称:Sipex Corporation 功能描述:Low Reference High Efficiency Boost Regulator |
| SP7648ER/TR | 制造商:SIPEX 制造商全称:Sipex Corporation 功能描述:PackageLow Reference High efficiency Boost Regulator |
| SP7648ER-L | 功能描述:LED照明驱动器 Efficiency Boost Regulator RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N |
| SP7648ER-L/TR | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| SP7648EU | 制造商:SIPEX 制造商全称:Sipex Corporation 功能描述:Evaluation Board Manual |
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