參數(shù)資料
型號: TL7700CPSE4
廠商: TEXAS INSTRUMENTS INC
元件分類: 電源管理
英文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8
封裝: PLASTIC, SO-8
文件頁數(shù): 2/11頁
文件大小: 147K
代理商: TL7700CPSE4
TL7700
SUPPLY-VOLTAGE SUPERVISOR
SLVS220B – JULY 1999 – REVISED AUGUST 2000
10
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
sense-voltage hysteresis setting
If the sense voltage, Vs’, does not have hysteresis in it and the voltage on the sensing line contains ripples, the
resetting of TL7700 will be unstable. Hysteresis is added to the sense voltage to prevent such problems. As
shown in Figure 20, the hysteresis, Vhys, is added, and the value is determined as:
Vhys = Is × R1
Where:
Is = 2.5 A, typically at TA = 25°C
At room temperature, Is has variations of 2.5 A ± 0.5 A. Therefore, in the circuit shown in Figure 19, Vhys has
variations of (
±0.5 × R1) V. In circuit design, it is necessary to consider the voltage-dividing resistor tolerance
and temperature coefficient in addition to variations in Vs and Vhys.
tpo
RESET
Vhys
VCC
1.5 V
T
Vs’
NOTE A: The sense voltage, Vs’, is different from the SENSE terminal input voltage, Vs. Vs is normally 500 mV for
triggering.
Figure 20. VCC-RESET Timing Chart
output pulse-duration setting
Constant-current charging starts on the timing capacitor when the sensing-line voltage reaches the TL7700
sense voltage. When the capacitor voltage exceeds the threshold level of the output drive comparator, RESET
changes from a low to a high level. The output pulse duration is the time between the point when the sense-pin
voltage exceeds the threshold level and the point when the RESET output changes from a low level to a high
level. When the TL7700 is used for system power-on reset, the output pulse duration, tpo, must be set longer
than the power rise time. The value of tpo is:
tpo = Ct × 105 seconds
Where:
Ct is the timing capacitor in farads
There is a limit on the device response speed. Even if Ct = 0, tpo is not 0, but approximately 5 s to 10 s.
Therefore, when the TL7700 is used as a comparator with hysteresis, without connecting Ct, switching speeds
(tr/tf, tpo/tpd, etc.) must be considered.
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