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參數(shù)資料
| 型號： | TPS9125PW |
| 廠商： | Texas Instruments, Inc. |
| 英文描述： | 5 V/3 V SIM SUPPLY AND LEVEL SHIFTERS |
| 中文描述： | 5伏/ 3伏SIM卡供應(yīng)及電平轉(zhuǎn)換器 |
| 文件頁數(shù)： | 13/24頁 |
| 文件大?。?/td> | 338K |
| 代理商： | TPS9125PW |
TPS9125
5 V/3 V SIMSUPPLY AND LEVEL SHIFTERS
SLVS244A – SEPTEMBER 1999 – REVISED NOVEMBER 1999
13
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
charge pump terminal
The charge pump can be used to generate a negative voltage from a positive supply voltage, or to
voltage-double, triple, or otherwise multiply the supply voltage. In the TSP9125, a charge pump is used to
generate a 5-V supply rail from an input voltage of 3 V.
Figure 11 is used to explain the principle of a charge pump when configured as a voltage doubler.
Figure 11. Principal of a Charge Pump Configured as a Voltage Doubler
VDD
VCAP1
VCAP2
OSC
VDD
SIMVCC
S1
S2
S3
S4
C1
1
C2
GND
GND
During the first half of the oscillator period, switches S1 and S2 are closed, switches S3 and S4 are open, and
the pump capacitor C1 is charged. In the second half of the oscillator period, switches S3 and S4 are closed
and switches S1 and S2 are open. Immediatetly after closing the switches S3 and S4, the voltage at Node 1
is:
V1
VDD
VC1
≈
2
VDD
assuming C1 was charged up to V
DD
. In this half of the period, the pump capacitor C1 charges the output
capacitor C2. After the start-up time, the output capacitor C2 is charged up to V
1
and the voltage at SIMVCC
is stable at this value, with only a small amount of ripple, which is normally around 1% of the supply voltage.
The ripple depends on the oscillator frequency, the load on SIMVCC, and the size of output capacitor C2.
In practice, the voltage V
1
is a little bit less than 2
×
V
DD
because of conduction losses across the switches and
switching losses in capacitor C1.
An unregulated charge pump generates an output voltage that is only dependent on the supply voltage and the
output current.
voltage generator
The charge pump used in the TSP9125 is regulated in such a way that the output voltage stays at 5 V
±
10%,
independently of the supply voltage and output current. A two-point regulator scheme was used to control the
output voltage. In addition, it reduces power consumption. The charge pump is active and enabled as long as
an oscillator frequency is applied. Figure 11 shows the functional block diagram of the voltage generator.
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