SP6641 Sipex, SP6641 Datasheet - Page 11

• Manufacturer Part Number: SP6641
• Description: 500mA Alkaline DC/DC Boost Regulator in SOT-23
• Manufacturer: Sipex

APPLICATION INFORMATION: continued
Low Battery Circuit for SP6641
Application
The circuit in figure 17 uses the Sipex SPX432
shunt regulator as a reference and comparator
circuit to detect a low battery condition and give
a high level, typically 1.7V output. When the
battery is good, the SPX432 output is low, but
not at ground but at 0.8V or about one Vbe
below the 1.24V reference. To translate that
level to a CMOS Low of less than 0.4V, an NPN
and 2 signal diodes can be added to the SPX432
Figure 16. SP6641A 3.3V with SuperCap Switch
Figure 17. SP6641A 3.3V with Low Battery Detection
Rev. 3/5/02, *Patent Pending
Diode
Schottky
Diode
Schottky
D1
22 F
C2
V
BATT
V
BATT
22 F
C2
1
2
3
LX
GND
V
OUT
SP6641
22 H
1
2
3
SP6641A/6641B 500mA Alkaline DC/DC Boost Regulator in SOT-23
L1
U1
LX
GND
V
22 F
OUT
SHDN
C1
V
®
®
22 H
SP6641
BATT
L1
U1
22 F
5
4
C1
SHDN
V
BATT
®
®
5
4
1
2
3
SHDN
J1
1.8V THRES.
R1
44k
R2
100k
11
R3
20k
output, as shown.
SPX432 and 2N3904 bipolar transistor and di-
odes are small and inexpensive to add to the
SP6641 circuit and work well to add a Battery
Low detection circuit, with the addition of about
130 A current from 3.3V out. As a bonus, the
output of this circuit can be used to drive the
SP6641 SHDN_N pin 3 to GND when the bat-
tery is removed, which would reset the SP6641
and eliminate the need for the SuperCap Switch
shown in figure 16.
V
+3.3V
1
2
OUT
REF
K
100k
SPX432M
SOT23-3
R4
U2
VTHRES = 1.24V(1 + R1/R2)
SOT23-3 IRLML6302
1N4148
2.7V, 0.9 PMOS
A
3
D2
3
1
Q1
1
3
2
1N4148
Q2 SOT23-3 IRLML2402
D3
2
2.7V NMOS
R1
1M
The small SOT23-3pin
© Copyright 2002 Sipex Corporation
Q2
2N3904
3.3V to
Nonvolatile Function
C3
.22F Supercap
2V = BATT GOOD
0V = LOW BATT
R5
100k
V
BATT GOOD
OUT
3.3V