參數(shù)資料
型號(hào)： SC4901
廠商： Semtech Corporation
英文描述： COMBI-SYNC Secondary Side Synchronous Rectifier and Regulator
中文描述： 客貨兩用，同步二次側(cè)同步整流和穩(wěn)壓器
文件頁(yè)數(shù)： 13/20頁(yè)
文件大?。?/td> 598K
代理商： SC4901
13
2005 Semtech Corp.
www.semtech.com
SC4901
POWER MANAGEMENT
Application Information (Cont.)
Layout Guidelines
The Combi Sync topology and SC4901 are intended for
use in multi output convertors and demand careful
attention to good layout practices. The topology has an
inherent advantage in that all switching circuits naturally
operate at the same frequency set by the primary controller.
But the operating duty ratio is different for different outputs
and this may cause unexpected interferences. Make sure
that the currents in the RTN path are kept separate and
returned to a single node at the transformer end. High
current returns from one output should be isolated from
the signal current returns going into the AGND pins of other
outputs. A dedicated ground plane is strongly
recommended to improve noise immunity.
SC4901 requires a clean synchronising signal at the ZCD
pin to ensure proper operation. There are several sources
that may contribute to the noise at this pin. The traces
from the transformer terminals to the corresponding QS
drain and QR source pins must be kept to the absolute
minimum. When the FETs are turned ON or OFF, the current
in the transformer secondary winding is subjected to a rapid
rate of di/dt. Long traces that encompass wide areas have
higher parasitic lead inductances. The combination of a
rapid di/dt and large parasitic inductance is a dip or spike
in the transformer waveform which can confuse the ZCD
pin and lead to random transitions at the output. The series
resistor RZ shown in the Typical Application Circuit should
have a separate connection to the transformer secondary
terminal where the source waveform is relatively free of
distortions.
The primary side layout also requires special attention.
Excessive ringing or spikes on the primary side will be
reflected to the secondary and interfere with the controller
operation. It is important to physically separate the primary
and secondary circuits and use separate ground planes to
minimise interference.
The drive transformer for the forward FETs can contribute
significantly to the overall performance. For fast rise and
fall times and low switching losses, choose a driver with
low inductances. The traces from the transformer to OUTA
and XFRA pins must be kept short to minimise the overall
inductance in the drive path.
Reference Design and Typical Waveforms
The complete schematic of a secondary channel delivering
3.3V/10A is shown in Fig 4). Typical waveforms are shown
in Figs 5) to Fig 8) These waveforms were taken on a dual
output convertor with 48V input and a transformer turns
ratio of 6:1. Both outputs were generated off a single
secondary winding. The primary topology was a free
running, active reset, forward convertor operating at 225
kHz. Volt second control was implemented using input
feedforward with a maximum duty ratio of 65% at 40V
input. The two outputs were rated at 3.3V/13A and 2.5V/
13A for a total of 75W power. Of special interest are the
primary side waveforms shown in Fig 8). The zero current
turn on can be clearly seen. During turn off, the current
decreases as 2.5V forward FETs turn off first, followed by
3.3V output. The last small step at final turn off represents
the magnetising current in transformer primary.
相關(guān)PDF資料
PDF描述
SC4901ITSTRT COMBI-SYNC Secondary Side Synchronous Rectifier and Regulator
SC4905A_06 High Performance Voltage Mode PWM Controller
SC4905AIMSTR High Performance Voltage Mode PWM Controller
SC4905AIMSTRT High Performance Voltage Mode PWM Controller
SC4905B High Performance Voltage Mode PWM Controller
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
SC4901ITSTRT 制造商:Semtech Corporation 功能描述:Secondary Side PWM Cntrlr SYNC POST REGUL 1MHz 16-Pin TSSOP T/R 制造商:Semtech Corporation 功能描述:Controller IC
SC4905A 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:HIGH PERFORMANCE VOLTAGE MODE PWM CONTROLLER
SC4905A_06 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Voltage Mode PWM Controller
SC4905AIMSTR 制造商:Semtech Corporation 功能描述:IC, VOLTAGE MODE PWM CTRL, 12V, MSOP-10; Input Voltage:48V; Output Voltage:500mV; Output Current:1mA; Supply Voltage Min:0V; Supply Voltage Max:12V; Digital IC Case Style:MSOP; No. of Pins:10; Frequency:1MHz; Control Mode:Voltage ;RoHS Compliant: No
SC4905AIMSTRT 制造商:Semtech Corporation 功能描述:Voltage Mode PWM Controller 10-Pin MSOP T/R
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