参数资料
型号: LTC4267CGN-1#PBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: Power over Ethernet IEEE 802.3af PD Interface with Integrated Switching Regulator; Package: SSOP; No of Pins: 16; Temperature Range: 0°C to +70°C
中文描述: 1 A SWITCHING CONTROLLER, 240 kHz SWITCHING FREQ-MAX, PDSO16
封装: 0.150 INCH, LEAD FREE, PLASTIC, SSOP-16
文件页数: 17/32页
文件大小: 925K
代理商: LTC4267CGN-1#PBF
LTC4267-1
24
42671f
virtually all the supply current required by the LTC4267-1
switching regulator. CPVCC should be sized sufciently to
handle the switching current needed to drive NGATE while
maintaining minimum switching voltage.
The external preregulator has improved efciency over
the simple resistor-shunt regulator method mentioned
previously. RB can be selected so that it provides a small
current necessary to maintain the zener diode voltage and
the maximum possible base current Q1 will encounter. The
actual current needed to power the LTC4267-1 switching
regulator goes through Q1 and PVCC sources current on
an “as-needed” basis. The static current is then limited
only to the current through RB and D1.
Compensating the Main Loop
In an isolated topology, the compensation point is typically
chosen by the components congured around the external
error amplier. Shown in Figure 14, a series RC network
APPLICATIO S I FOR ATIO
WU
UU
Figure 12. Powering the LTC4267-1 Switching
Regulator via the Shunt Regulator
Figure 13. Powering the LTC4267-1 Switching
Regulator with an External Preregulator
preregulator consists of a series pass transistor Q1, zener
diode D1, and a bias resistor RB. The preregulator holds
PVCC at 7.6V nominal, well above the maximum rated PVCC
turn-off threshold of 6.8V. Resistor RSTART momentarily
charges the PVCC node up to the PVCC turn-on threshold,
enabling the switching regulator. The voltage on CPVCC
begins to decline as the switching regulator draws its
normal supply current, which exceeds the delivery of
RSTART. After some time, the output voltage approaches
the desired value. By this time, the pass transistor Q1
catches the declining voltage on the PVCC pin, and provides
is connected from the compare voltage of the error am-
plier to the error amplier output. In PD designs where
transient load response is not critical, replace RZ with a
short. The product of R2 and CC should be sufciently large
to ensure stability. When fast settling transient response
is critical, introduce a zero set by RZCC. The PD designer
must ensure that the faster settling response of the output
voltage does not compromise loop stability.
Figure 14. Main Loop Compensation for an Isolated Design
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