SP690SEN-L Datasheet, PDF (15/20 Pages) Sipex Corporation – 3.0V/3.3V Low Power Microprocessor Supervisory with Battery Switch-Over

A.)
VIN
R1
R2
VCC
PFI
+
*C1
R3
SP690T/S/R
SP802T/S/R
SP804T/S/R
SP805T/S/R
TOµP
PFO
GND
*OPTIONAL
B.)
VIN
R1
R2
VCC
PFI
+
*C1
R3
SP690T/S/R
SP802T/S/R
SP804T/S/R
SP805T/S/R
TOµP
PFO
GND
PFO
0V
0V
VL
VTRIP
VH
VIN
( ) ^VTRIP ^{= V}PFT
R1 + R2
R2
( )( )( ₎ ^{V = H}
VPFT + VPFH
R1
1 +1 +1
R1 R2 R3
[ ( ) ] ^VL ^{= R1}
VPFT
1 +1 +1
R1 R2 R3
- VCC
R3
WHERE VPFT = 1.25V
VPFH = 10mV
Figure 22A. Adding Additional Hysteresis to the Power-Fail Comparator.
Figure 22B. Shifting the Additional Hysteresis above V_PFT
PFO
0V
0V
VTRIP
VH
VIN
( ) ^VTRIP ^{= V}PFT
R1 + R2
R2
[( )( ) ] ^VL ^{= R1}
VPFT + VPFH
1 + 1 + 1 - (VCC - VD)
R1 R2 R3
R3
WHERE VPFT = 1.25V
VPFH = 10mV
VD = DIOD FORWARD VOLTAGE DROP
Connecting an ordinary signal diode in series
with R3, as in Figure 22B, causes the lower trip
point (V_L) to coincide with the trip point without
hysteresis (V_TRIP), so the entire hysteresis
window occurs above V_TRIP. This method pro-
vides additional noise margin without compro-
mising the accuracy of the power-fail threshold
when the monitored voltage is falling. It is
useful for accurately detecting when a voltage
falls past a threshold.
The current through R1 and R2 should be at least
1µA to ensure that the 25nA (max over extended
temperature range) PFI input current does not
shift the trip point. R3 should be larger than
10kΩ so it does not load down the PFO pin.
Capacitor C1 adds additional noise rejection.
R1
R2
V-
VCC
SP690T/S/R
SP802T/S/R
PFI
PFO
SP804T/S/R
SP805T/S/R
GND
VIN
R1
R2
3.0V OR 3.3V
VCC
SP690T/S/R
SP802T/S/R
PFI
PFO
SP804T/S/R
SP805T/S/R
GND
VCC
PFO
VCC
PFO
V-
VL
VTRIP
0V
VTRIP
VH
VIN
[( )( ₎ ] ^VTRIP ^{= R2}
VPFT + VPFH
1 +1
R1 R2
- VCC
R1
[ ( ) ] ^VL ^{= R2 V}PFT
1 +1
R1 R2
- VCC
R3
WHERE VPFT = 1.25V
VPFH = 10mV
NOTE: VTRIP IS NEGATIVE
( ) ^VTRIP ^{= V}PFT
R1 + R2
R2
( )( ) ^{V =} H
VPFT + VPFH
R1 + R2
R2
Figure 23. Using the Power-Fail Comparator to Monitor an Additional Power Supply
SP690T/S/R JAN 30-06 SP690T/S/R, 802/T/S/R, 804T/S/R, 805T/S/R Low Power Microprocessor Supervisory
15
© 2006 Sipex Corporation