- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄358818 > LM2485 (National Semiconductor Corporation) 220V Triple Bias Clamp with G1 Blank Amplifier PDF資料下載
參數(shù)資料
| 型號(hào)： | LM2485 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 220V Triple Bias Clamp with G1 Blank Amplifier |
| 中文描述： | 220三偏置與G1期空白鉗放大器 |
| 文件頁(yè)數(shù)： | 4/8頁(yè) |
| 文件大?。?/td> | 858K |
| 代理商： | LM2485 |
Theory of Operation
The pinout and internal block diagram of the LM2485 is
shown in
Figure 1
.
The LM2485 is a triple channel bias clamp amplifier used to
DC restore the AC coupled outputs of a DTV CRT driver and
for cut-off adjustment. The clamp circuit amplifies the DC
inputs, V
IN
, by the internally fixed gain of –25. Each DC
clamp output, V
OUT
, will require a pull-up resistor to V
CC
.
The clamp DC transfer function is shown in
Figure 4
.
The LM2485 also has an integrated blanking amplifier that
takes a positive-going 5V input pulse, VB
IN
, and outputs a
negative-going pulse, VB
OUT
, with a selectable amplitude of
either 20V
P-P
or 40V
P-P
via the Pin 13 (S40) option. If Pin 13
is floated, the VB
OUT
pulse amplitude is 20V
P-P
; if Pin 13 is
grounded, the amplitude is 40V
(see
Figure 5
). With a
simple clamp circuit, this inverted pulse can be used to drive
the G1 grid of a CRT negative to blank the horizontal retrace
lines during the vertical flyback period. The input pulse can
be generated from a vertical flyback pulse or by a microcon-
troller.
The LM2485 can operate with a V
supply of up to 220V
and a selectable V
supply of either 8V or 12V via the Pin
12 (S12) option. If Pin 12 is floated, then 8V is expected at
the V
pin; if Pin 12 is grounded, then 12V is expected. This
V
option ensures the LM2485 is compatible with any
National Semiconductor DTV CRT driver sharing the same
operating voltages in the application. Note that using a V
supply of 12V will increase the input offset of the clamp
circuit, which would have the effect of shifting the DC trans-
fer function slightly to the right. Also, if the V
option is
incorrectly matched to the actual V
supply voltage, an
incorrect VB
OUT
amplitude will be produced. Therefore, it is
important to ensure that the appropriate V
BB
option is used
and the V
BB
supply is within the range stated in the
Section
Operating Ranges
.
Application Information
INTRODUCTION
National Semiconductor (NSC) is committed to provide ap-
plication information that assists our customers in obtaining
the best performance possible from our products. The fol-
lowing information is provided in order to support this com-
mitment. The reader should be aware that the optimization of
performance was done using a specific printed circuit board
designed at NSC. Variations in performance can be realized
due to physical changes in the printed circuit board and the
application. Therefore, the designer should know that com-
ponent value changes may be required in order to optimize
performance in a given application. The values shown in this
document can be used as a starting point for evaluation
purposes.
POWER SUPPLY BYPASS
The LM2485 should have proper power supply bypassing for
optimal arc protection and performance. A 0.1 μF capacitor
should be connected from each of the supply pins, V
and
V
BB
, to ground, as close to the supply and ground pins as
possible. Additionally, a 1 μF electrolytic capacitor should be
connected from each supply to the LM2485 ground and
placed reasonably close to both supply pins.
ARC PROTECTION
During normal CRT operation, internal arcing may occasion-
ally occur. To protect the LM2485 against arcing, it is impor-
tant that the recommended applications circuit is used and
good layout practices are followed. Please refer to the
Sec-
tion NSC Demonstration Board
for a detailed example on arc
protection and PCB layout considerations.
THERMAL CONSIDERATIONS
Determining Maximum Power Dissipation and Ambient
Temperature
Power dissipation within an integrated circuit package is a
very important parameter. An incorrect maximum power dis-
sipation calculation may result in excessive thermal stress to
the device, affecting its reliability and performance. To esti-
mate the maximum power dissipation of the LM2485, the
following system parameters should be determined first.
Maximum V
CC
and V
BB
supply voltages
Average CRT cut-off voltages
Maximum average beam currents
Highest duty cycle
Once these parameters are known, the system designer can
then calculate the maximum ambient temperature surround-
ing the LM2485 without a heat sink. A small, low-cost heat
sink may be used if the calculated maximum ambient tem-
perature does not satisfy the worst-case operating tempera-
ture inside the TV.
The following example shows how to determine the maxi-
mum power dissipation and maximum ambient temperature
and assumes the recommended application circuit is used
(see
Figure 6
).
Example
The LM2485 uses 1.0W of static power from the 220V and
8V supplies, assuming the worst-case supply currents. If the
average CRT cut-off voltage of all channels is 180V and
each LM2485 output sinks a maximum average beam cur-
rent of 1.0 mAat 77% duty cycle (480p format) at the highest
brightness setting, the LM2485 will dissipate:
P
DISS
= P
STATIC
+ 3 x (V
CUT-OFF
x I
AVG
MAX
) x
δ
, or
P
DISS
= 1.0W + 3 x (180V x 1.0 mA) x 0.77 = 1.42W.
The maximum thermal resistance from junction-to-air,
θ
,
and maximum junction temperature, T
, are stated in the
Section Absolute Maximum Ratings
. Therefore, the maxi-
mum ambient temperature surrounding the LM2485 can be
calculated:
T
A
MAX
= T
J
MAX
- (P
DISS
x
θ
JA
), or
T
A
MAX
= 150C - (1.42W x 68C/W) = 53C.
TYPICAL APPLICATION
Used in conjunction with NSC’s LM12XX Preamplifier and
LM24XX CRT Driver, a complete analog video solution from
the preamplifier input to the CRT cathode can be achieved.
The LM2485 can support any AC coupled DTV application
using formats up to 1080i with proper selection of a pream-
plifier and CRT drivers.
L
www.national.com
4
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM2485NA | RES 9.1 OHM 1/2W 5% CARBON FILM |
| LM24P20 | Medium Size Graphic Type LCD Module |
| LM2501 | Mobile Pixel Link (MPL) Camera Interface Serializer and Deserializer |
| LM2501SL | Mobile Pixel Link (MPL) Camera Interface Serializer and Deserializer |
| LM2502 | Mobile Pixel Link (MPL) Display Interface Serializer and Deserializer |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2485NA | 制造商:Rochester Electronics LLC 功能描述:220V BIAS CLAMP W/G1 BLANK - Bulk |
| LM2485NA/NOPB | 功能描述:IC TRIPLE BIAS CLAMP 220V 24-DIP RoHS:是 類別:集成電路 (IC) >> PMIC - 顯示器驅(qū)動(dòng)器 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:- 顯示器類型:真空熒光 (VF) 配置:5 x 7（矩陣） 接口:串行 數(shù)字或字符:- 電流 - 電源:3.5mA 電源電壓:2.7 V ~ 3.6 V 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:16-SSOP（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:16-QSOP 包裝:帶卷 (TR) |
| LM248D | 功能描述:運(yùn)算放大器 - 運(yùn)放 Quad Op Amp RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LM248DE4 | 功能描述:運(yùn)算放大器 - 運(yùn)放 Quadruple Oper Amplifier RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LM248DG4 | 功能描述:運(yùn)算放大器 - 運(yùn)放 Quad Op Amp RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。