generate VDD
參數(shù)資料
型號: LTC1544CG
廠商: Linear Technology
文件頁數(shù): 5/20頁
文件大小: 0K
描述: IC TXRX SOFTWARE SELECTBL 28SSOP
標準包裝: 47
類型: 收發(fā)器
驅(qū)動器/接收器數(shù): 4/4
電源電壓: 4.75 V ~ 5.25 V
安裝類型: 表面貼裝
封裝/外殼: 28-SSOP(0.209",5.30mm 寬)
供應(yīng)商設(shè)備封裝: 28-SSOP
包裝: 管件
13
LTC1544
Charge Pump
The LTC1543 uses an internal capacitive charge pump to
generate VDD and VEE as shown in Figure 21. A voltage
doubler generates about 8V on VDD and a voltage inverter
generates about – 7.5V for VEE. Four 1F surface mounted
tantalum or ceramic capacitors are required for C1, C2, C3
and C4. The VEE capacitor C5 should be a minimum of
3.3
F.Allcapacitorsare16Vandshouldbeplacedasclose
as possible to the LTC1543 to reduce EMI.
The generator differential impedance must be 50
to
150
and the impedance between shorted terminals (A
and B) and ground C must be 150
±15. For the
generator termination, switches S1 and S2 are both on and
the top side of the center resistor is brought out to a pin so
it can be bypassed with an external capacitor to reduce
common mode noise as shown in Figure 20.
Figure 20. V.35 Driver Using the LTC1344A
V.35 DRIVER
A
B
C
51.5
S2
ON
S1
ON
1544 F20
51.5
LTC1344A
124
C1
100pF
28
27
26
25
1544 F21
3
2
1
4
C3
1
F
C4
1
F
5V
C1
1
F
C2
1
F
C5
3.3
F
LTC1543
VDD
C1+
C1
VCC
C2+
C2
VEE
GND
+
Figure 21. Charge Pump
Any mismatch in the driver rise and fall times or skew in
the driver propagation delays will force current through
the center termination resistor to ground, causing a high
frequency common mode spike on the A and B terminals.
The common mode spike can cause EMI problems that are
reduced by capacitor C1 which shunts much of the com-
mon mode energy to ground rather than down the cable.
No-Cable Mode
The no-cable mode (M0 = M1 = M2 = 1) is intended for the
case when the cable is disconnected from the connector.
The charge pump, bias circuitry, drivers and receivers are
turned off, the driver outputs are forced into a high
impedance state, and the supply current drops to less than
200
A.
Receiver Fail-Safe
All LTC1543/LTC1544 receivers feature fail-safe opera-
tion in all modes. If the receiver inputs are left floating or
shorted together by a termination resistor, the receiver
output will always be forced to a logic high.
DTE vs DCE Operation
The DCE/DTE pin acts as an enable for Driver 3/Receiver
1 in the LTC1543, and Driver 3/Receiver 1 and Driver 4/
Receiver 4 in the LTC1544. The INVERT pin in the LTC1544
allows the Driver 4/Receiver 4 enable to be high or low true
polarity.
APPLICATIONS INFORMATION
WU
U
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