LTC4261 LINER [Linear Technology], LTC4261 Datasheet - Page 18

• Manufacturer Part Number: LTC4261
• Description: Negative Voltage Hot Swap Controllers with ADC and I2C Monitoring
• Manufacturer: LINER [Linear Technology]

LTC4261/LTC4261-2
APPLICATIONS INFORMATION
to turn on again immediately (without delay) unless the
overvoltage auto-retry has been disabled by clearing reg-
ister bit D0.
Undervoltage Comparator and Undervoltage Fault
The LTC4261/LTC4261-2 provide two undervoltage pins,
UVH and UVL, for adjustable UV threshold and hyster-
esis. The UVH and UVL pins have the following accurate
thresholds:
Both UVH and UVL pins have a minimum hysteresis of
δV
supply, the undervoltage comparator works in such a way
that both the UVH and the UVL pins have to cross their
thresholds for the comparator output to change state.
The UVH, UVL, and OV threshold ratio is designed to
match the standard telecom operating range of 43V to
71V and UV hysteresis of 4.5V when UVH and UVL are
tied together as in Figure 1, where the built-in UV hyster-
esis referred to the UVL pin is:
Using R1 = 11.8k, R2 = 16.9k and R3 = 453k as in Figure 1
gives a typical operating range of 43.0V to 70.7V, with
18
For UVH rising, V
For UVL falling, V
UV
ΔV
UV(HYST)
(15mV typical). In either a rising or a falling input
= V
UVH(TH)
UVH(TH)
UVL(TH)
RTN – V
– V
SENSE
GATE
PGIO
V
TMR
= 2.291V, turn off
OUT
= 2.56V, turn on
PG
SS
EE
UVL(TH)
V
2.56V
LOAD
GATEH
36V
0V
0V
0V
= 0.269V
Figure 6. –36V to –72V Step Response
50mV
LOAD + INRUSH
FET V
72V
TH
an undervoltage shutdown threshold of 38.5V and an
overvoltage shutdown threshold of 72.3V.
The UV hysteresis can be adjusted by separating the
UVH and the UVL pins with a resistor R
increase the UV hysteresis, the UVL tap should be placed
above the UVH tap as in Figure 7a. To reduce the UV hys-
teresis, place the UVL tap under the UVH tap as in Figure
7b. UV hysteresis referred to the UVL pin is given by:
For V
the minimum hysteresis at UVH and UVL: δV
when R
The design of the LTC4261/LTC4261-2 protects the UV
comparator from chattering even when R
R
An undervoltage fault occurs when the UVL pin falls be-
low 2.291V and the UVH pin falls below 2.56V – δV
This activates the FET turn-off and sets the undervoltage
H(MAX)
for V
∆
or for V
∆
V
V
UVL
UVL HYST
UVL HYST
H(MAX)
UVL
.
< V
(
(
UVL
≥
UVH
V
= 0.11 • (R1 + R2)
)
)
<
UVH
=
=
, the minimum UV hysteresis allowed is
V
UVH
∆
∆
LOAD
,
V
V
UV HYST
UV
,
(
(
H H YST
42612 F06
)
)
+
– .
2 56
2 56
.
V
V
•
•
H
R
R
H
(Figure 7). To
1
1
is larger than
R R
+
+
H
UV
R
R
R
2
2
H
= 15mV
+
R
42612fb
H
UV
.