TL7700_16 Datasheet, PDF (10/23 Pages) Texas Instruments – SUPPLY-VOLTAGE SUPERVISOR

TL7700
SLVS220F – JULY 1999 – REVISED AUGUST 2011
DETAILED DESCRIPTION
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Sense-Voltage Setting
The SENSE terminal input voltage, Vs, of the TL7700 typically is 500 mV. By using two external resistors, the
circuit designer can obtain any sense voltage over 500 mV. In Figure 19, the sensing voltage, Vs', is calculated
as:
V_s' = V_s × (R1 + R2)/R2
Where:
V_s = 500 mV typ at T_A = 25°C
At room temperature, V_s has a variation of 500 mV ± 5 mV. In the basic circuit shown in Figure 19, variations of
[±5 ± (R1 + R2)/R2] mV are superimposed on V_s.
V_CC
R1
V_CC
V_s
SENSE
RESET
R_L
RESET
CT
R2
GND
C_t
GND
Figure 19.
Sense-Voltage Hysteresis Setting
If the sense voltage (V_s') does not have hysteresis in it, and the voltage on the sensing line contains ripples, the
resetting of TL7700 is unstable. Hysteresis is added to the sense voltage to prevent such problems. As shown in
Figure 20, the hysteresis (V_hys) is added, and the value is determined as:
V_hys = I_s × R1
Where:
I_s = 2.5 μA typ at T_A = 25°C
At room temperature, Is has variations of 2.5 mA ± 0.5 mA. Therefore, in the circuit shown in Figure 19, V_hys has
variations of (±0.5 × R1) mV. In circuit design, it is necessary to consider the voltage-dividing resistor tolerance
and temperature coefficient in addition to variations in V_s and V_hys.
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