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參數(shù)資料
| 型號(hào)： | SP3249EEY-L/TR |
| 廠商： | Exar Corporation |
| 文件頁(yè)數(shù)： | 15/16頁(yè) |
| 文件大?。?/td> | 0K |
| 描述： | IC TXRX RS232 INTELLIGNT 24TSSOP |
| 產(chǎn)品變化通告： | Packaging Change 15/Jul/2010 |
| 標(biāo)準(zhǔn)包裝： | 1,500 |
| 類型： | 收發(fā)器 |
| 驅(qū)動(dòng)器/接收器數(shù)： | 5/3 |
| 規(guī)程： | RS232 |
| 電源電壓： | 3 V ~ 5.5 V |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 24-TSSOP（0.173"，4.40mm 寬） |
| 供應(yīng)商設(shè)備封裝： | 24-TSSOP |
| 包裝： | 帶卷 (TR) |
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Exar Corporation 48720 Kato Road, Fremont CA, 94538 510-668-7017 www.exar.com
SP3249E_100_013111
Charge Pump
The charge pump is an Exar–patented design
(U.S. 5,306,954) and uses a unique approach
compared to older less–efficient designs.
The charge pump still requires four external
capacitors, but uses a four–phase voltage
shifting technique to attain symmetrical 5.5V
power supplies. The internal power supply
consists of a regulated dual charge pump that
provides output voltages 5.5V regardless of
the input voltage (V
CC) over the +3.0V to +5.5V
range. This is important to maintain compli-
ant RS-232 levels regardless of power supply
fluctuations.
The charge pump operates in a discontinuous
mode using an internal oscillator. If the output
voltages are less than a magnitude of 5.5V, the
charge pump is enabled. If the output voltages
exceed a magnitude of 5.5V, the charge pump
is disabled. This oscillator controls the four
phases of the voltage shifting. A description of
each phase follows.
Phase 1
— V
SS charge storage — During this phase of the
clock cycle, the positive side of capacitors C
1 and
C
2 are initially charged to VCC. Cl
+
is then switched
to GND and the charge in C
1
–
is transferred to C
2
–
.
SinceC
2
+
isconnectedtoV
CC, the voltage potential
across capacitor C
2 is now 2 times VCC.
Figure 7. Loopback Test Circuit for RS-232 Driver
Data Transmission Rates
Figure 9. Loopback Test results at 250Kbps
(All Drivers Fully Loaded)
Figure 8. Loopback Test results at 120kbps
(All Drivers Fully Loaded)
SP3249E
TxIN
TxOUT
C1+
C1-
C2+
C2-
V+
V-
VCC
0.1F
+
C2
C5
C1
+
C3
C4
+
LOGIC
INPUTS
VCC
5k
RxIN
RxOUT
LOGIC
OUTPUTS
GND
1000pF
0.1F
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