參數(shù)資料
型號: CS5157
廠商: ZF Electronics Corporation
英文描述: CPU 5-Bit Synchronous Buck Controller
中文描述: CPU的5位同步降壓控制器
文件頁數(shù): 10/14頁
文件大小: 316K
代理商: CS5157
Applications Information: continued
C
10
Figure 13: OVP response to an input-to-output short circuit by pulling
the input voltage to ground.
External Output Enable Circuit
On/off control of the regulator can be implemented
through the addition of two additional discrete compo-
nents (see Figure 14). This circuit operates by pulling the
soft start pin high, and the V
FFB
pin low, emulating a short
circuit condition.
Figure 14: Implementing shutdown with the CS5157.
External Power Good Circuit
An optional Power Good signal can be generated through
the use of four additional external components (see Figure
15). The threshold voltage of the Power Good signal can be
adjusted per the following equation:
V
Power Good
=
This circuit provides an open collector output that drives
the Power Good output to ground for regulator voltages
less than V
Power Good
.
Figure 15: Implementing Power Good with the CS5157.
Figure 16: CS5157 demonstration board during power up. Power Good
signal is activated when output voltage reaches 1.70V.
Selecting External Components
The CS5157 can be used with a wide range of external
power components to optimize the cost and performance of
a particular design. The following information can be used
as general guidelines to assist in their selection.
NFET Power Transistors
Both logic level and standard MOSFETs can be used. The
reference designs derive gate drive from the 12V supply
which is generally available in most computer systems and
utilize logic level MOSFETs. Multiple MOSFETs may be
paralleled to reduce losses and improve efficiency and ther-
mal management.
Voltage applied to the MOSFET gates depends on the
application circuit used. Both upper and lower gate driver
outputs are specified to drive to within 1.5V of ground
when in the low state and to within 2V of their respective
bias supplies when in the high state. In practice, the MOS-
FET gates will be driven rail to rail due to overshoot caused
by the capacitive load they present to the controller IC. For
the typical application where V
CC1
= V
CC2
= 12V and 5V is
Trace 3 = 12V Input (V
) and V
CC2
) (10V/div.)
Trace 4 = 5V Input (2V/div.)
Trace 1 = Regulator Output Voltage (1V/div.)
Trace 2 = Power Good Signal (2V/div.)
Ch 1 High
2.80V
V
OUT
CS5157
R1
10k
R2
6.2k
R3
10k
Power Good
5V
PN3904
PN3904
(R1 + R2)
×
0.65V
R2
Shutdown
Input
5V
V
FFB
CS5157
SS
5
8
IN4148
MMUN2111T1 (SOT-23)
Trace 4 = 5V from PC Power Supply (2V/div.)
Trace 1 = Regulator Output Voltage (1V/div.)
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