8
LTC1841/LTC1842/LTC1843
Figure 3a. Power Supply Transient Test Circuit
APPLICATIONS INFORMATION
WU
U
8V
V +
5V
VREF
OUT
2mV/
DIV
2ms/DIV
1841/1843 F03b
Figure 3b. Power Supply Transient Rejection
Hysteresis
Hysteresis can be added to the LTC1842/LTC1843 by
connecting a resistor (R1) between the REF and HYST pins
and a second resistor (R2) from HYST to V – (Figure 4).
The difference between the upper and lower threshold
voltages, or hysteresis voltage band (VHB), is equal to twice
the voltage difference between the REF and HYST pins.
As more hysteresis is added, the upper threshold in-
creases the same amount as the low threshold decreases.
The maximum voltage allowed between REF and HYST
pins is 50mV, producing a maximum hysteresis voltage
band of 100mV. The hysteresis band may vary by up to
Figure 4. Programmable Hysteresis
15%. If hysteresis is not wanted, the HYST pin should be
shorted to REF. Acceptable values for IREF range are from
0.1
A to 5A. If 2.4M is chosen for R2, then the value of
R1 is equal to the value of VHB.
Window Detector
The LTC1843 is ideal for use as a micropower window
detector as shown in Figure 5. The values of R1, R2 and R3
are selected for a 4.5V undervoltage threshold and a 5.5V
overvoltage threshold. R4 and R5 set the hysteresis volt-
age. The following design procedure can be used to select
the component values:
–
+
–
+
IN A+
VOTH = 5.5V
VUTH = 4.5V
R4
2.4M
R1
294k
R2
62.2k
R3
1M
R5
10k
HYST
3
5V
5
IN B–
V –
V +
VIN
LTC1843
2
4
OUT B
1841/43 F05
8
OUT A 1
7
REF
6
Figure 5. Dual Level Detector
6
R2
5
R1
1841/43 F04
2
IREF
R1 =
VHB
(2)(IREF)
R2 =
IREF
1.182V –
()
VHB
2
HYST
V–
REF
LTC1843
V +
R1
430
R2
10k
C1
1
F
5V
TO
8V
OUT A
V –
2
7
5V
1
LTC1843
1841/43 F03a
IN A+
HYST
REF
3
5
6
1M
R3
2.4M
–
+