- 您现在的位置：买卖IC网 > Sheet目录342 > MC34848EPR2 (Freescale Semiconductor)IC LED DVR BACKLIGHT 8CH 48QFN
TYPICAL APPLICATIONS
the value of the C COMP2 capacitor, until acquiring an
appropriate stability of the converter. For the previous design
a 56 pF capacitor was used.
G(s) H(s)
Compensated system
G(s)
Boost converter
H(s)
Compensation network
Figure 24. Plotting the Results for the Transconductance Op-amp Based Compensation Example.
SELECTING THE SLEW RATE OF THE SWITCHING
RATE
The SLEW pin is used to limit the slew on the OUT_SW pin
to reduce noise and avoid EMI problems. If the slew rate is
reduced too much, it will reduce the efficiency of the device.
The slew rate can be changed by tying a resistor from the
SLEW pin to GND. The lower the value of this resistor, the
steeper the rising and the falling times of the switching
frequency. The value of this resistor could be within three
different ranges:
? R SLEW < 10 k Ω.
? 10 k Ω ≤ R SLEW < 20 k Ω.
? R SLEW > 20 k Ω.
SELECTING THE CS LOW PASS FILTER TO
REDUCE NOISE.
Since any changes in the PCB layout (track length,
grounding, component connections, etc.) around the
switching FET and the current sense circuitry has an impact
on the PCB parasitics, a low pass RC filter is recommended
to be added at the CS pin for noise reduction.
The selection of this filter should be made based on the
amplitude and frequency of the ringing across the sense
resistor, so the noise can be attenuated properly while the
current sense signal is kept as close as possible to its original
shape (a trapezoid in CCM or a triangle in DCM). The ringing
frequency should be attenuated by 20 dB at least through the
selection of the proper low pass RC filter.
An example: let’s assume that the sense signal (CS)
shows a ringing of 60 MHz, and you want to attenuate it at a
rate of 20 dB per decade. Based on these conditions, the cut-
off frequency (-3.0 dB) of the low pass filter should be set to
6.0 MHz which still allows passing the maximum boost
switching frequency signal of 1.2 MHz. The following formula
is used for calculating the RC components:
f_3 db = 1 / (2 π RC)
It is important to consider that the value of the resistor (R)
should be no higher than 200 ohms, to avoid adding a
significant offset in the CS signal. A resistor of 180 ohms is
selected for this example. The capacitor (C) of the filter is
then selected as follows:
C = 1 / (2 π *180*6E6)
C = 147 pf
Once the filter is added on the CS pin, as shown on figures
20 and 21, measurements should be performed again to
confirm that the noise has been reduced.
34848
Analog Integrated Circuit Device Data
32
Freescale Semiconductor
发布紧急采购，3分钟左右您将得到回复。
相关PDF资料
MC56F8006DEMO-T
BOARD DEMO FOR MC56F8006 DSP
MCB1114
BOARD EVALUATION FOR NXP LPC1114
MCB11C14
BOARD EVAL FOR NXP LPC11C14
MCB2470
BOARD EVAL NXP LPC247X SERIES
MCBSTM32EXL
BOARD EVALUATION FOR STM32F103ZE
MCBTMPM330
BOARD EVAL TOSHIBA TMPM330 SER
MCIMX25WPDKJ
KIT DEVELOPMENT WINCE IMX25
MCIMX53-START-R
KIT DEVELOPMENT I.MX53
相关代理商/技术参数
MC34849
制造商:SPC Multicomp 功能描述:HEADER VERTICAL 16WAY 制造商:SPC Multicomp 功能描述:WIRE-BOARD CONN, RECEPTACLE, 16POS, 3MM; Series:2261(5561); Pitch Spacing:3mm; Contact Termination:Through Hole Vertical; No. of Contacts:16; No. of Rows:2; Connector Mounting:PCB; Gender:Receptacle; Contact Material:Copper Alloy ;RoHS Compliant: Yes
MC34851
制造商:SPC Multicomp 功能描述:HEADER VERTICAL 18WAY 制造商:SPC Multicomp 功能描述:HEADER, VERTICAL, 18WAY
MC34853
制造商:SPC Multicomp 功能描述:HEADER R/ANGLE 16WAY 制造商:SPC Multicomp 功能描述:HEADER, R/ANGLE, 16WAY 制造商:SPC Multicomp 功能描述:WIRE-BOARD CONN, RECEPTACLE, 16POS, 3MM; Series:2261(5561); Pitch Spacing:3mm; Contact Termination:Through Hole Right Angle; No. of Contacts:16; No. of Rows:2; Connector Mounting:PCB; Gender:Receptacle; Contact Material:Copper Alloy ;RoHS Compliant: Yes
MC34855
制造商:SPC Multicomp 功能描述:HEADER R/ANGLE 18WAY 制造商:SPC Multicomp 功能描述:HEADER, R/ANGLE, 18WAY
MC34857
制造商:SPC Multicomp 功能描述:HEADER VERTICAL SMT 2WAY 制造商:SPC Multicomp 功能描述:HEADER, VERTICAL, SMT, 2WAY 制造商:SPC Multicomp 功能描述:WIRE-BOARD CONN, RECEPTACLE, 2POS, 3MM; Series:2261(5561)R; Pitch Spacing:3mm; Contact Termination:Surface Mount Vertical; No. of Contacts:2; No. of Rows:2; Connector Mounting:PCB; Gender:Receptacle; Contact Material:Copper Alloy ;RoHS Compliant: Yes
MC34859
制造商:SPC Multicomp 功能描述:HEADER VERTICAL SMT 4WAY 制造商:SPC Multicomp 功能描述:HEADER, VERTICAL, SMT, 4WAY 制造商:SPC Multicomp 功能描述:WIRE-BOARD CONN, RECEPTACLE, 4POS, 3MM; Series:2261(5561)R; Pitch Spacing:3mm; Contact Termination:Surface Mount Vertical; No. of Contacts:4; No. of Rows:2; Connector Mounting:PCB; Gender:Receptacle; Contact Material:Copper Alloy ;RoHS Compliant: Yes
MC3486
制造商:Panasonic Industrial Company 功能描述:I.C. (I)
MC34861
制造商:SPC Multicomp 功能描述:HEADER VERTICAL SMT 6WAY 制造商:SPC Multicomp 功能描述:HEADER, VERTICAL, SMT, 6WAY 制造商:SPC Multicomp 功能描述:WIRE-BOARD CONN, RECEPTACLE, 6POS, 3MM; Series:2261(5561)S; Pitch Spacing:3mm; Contact Termination:Surface Mount Vertical; No. of Contacts:6; No. of Rows:2; Connector Mounting:PCB; Gender:Receptacle; Contact Material:Copper Alloy ;RoHS Compliant: Yes