LT1640AH LINER [Linear Technology], LT1640AH Datasheet - Page 12

• Manufacturer Part Number: LT1640AH
• Description: Negative Voltage Hot Swap Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LT1640AL/LT1640AH
The new threshold voltage when the input moves from low
to high is:
where V
The new threshold voltage when the input moves from
high to low is:
where V
The new hysteresis value will be:
With R1 = 562k, R2 = 16.9k and R3 = 1.62M, V
and V
(from low to high) and 37.6V (from high to low). The
hysteresis is 5.4V. A separate resistor divider should be
used to set the overvoltage threshold given by:
12
V
V
UV HL
HYS
V
UV LH
,
UVHY
,
UVH
UVL
V
UVHY
V
= 20mV, the undervoltage threshold will be 43V
UVL
V
UVH
is typically 1.223V.
is typically 1.243V.
R
R
R
2
2
2
•
•
U
R
R
•
R
3
3
3
R
R
R R
R R
* DIODES INC. SMAT70A
– 48V
U
R
2
2
1
1
GND
R R
2
•
•
•
•
1
R
R
•
•
*
R
3
3
3
3
GND
3
3
R4
R5
R6
(SHORT PIN)
R R
R R
W
R R
1
1
•
•
1
3
2
•
2
2
LT1640AH
UV
OV
2
3
+
–
–
Figure 11. Active High Enable Module
4
V
1
EE
V
GATE
PG
V
V
R1
GATE
U
GATE
SENSE
2
= 13.5V
–
+
4
•
•
5
R
R
R
R
3
1
1
3
V
DD
C1
6.5k
8
R7
GATE
Q1
V
EE
With R4 = 506k, R5 = 8.87k and V
overvoltage threshold will be 71V.
PWRGD/PWRGD Output
The PWRGD/PWRGD output can be used to directly en-
able a power module when the input voltage to the module
is within tolerance. The LT1640AL has a PWRGD output
for modules with an active low enable input, and the
LT1640AH has a PWRGD output for modules with an
active high enable input.
When the DRAIN voltage of the LT1640AH is high with
respect to V
turned off and R7 and Q2 clamp the PWRGD pin one diode
drop ( 0.7V) above the DRAIN pin. Transistor Q2 sinks
the module’s pull-up current and the module turns off.
When the DRAIN voltage drops below V
shorting the bottom of R7 to DRAIN and turning Q2 off.
The pull-up current in the module then flows through R7,
pulling the PWRGD pin high and enabling the module.
Q3
6
R2
PWRGD
Q2
V
R3
DRAIN
OV
C2
1
7
V
OVH
+
EE
1640A F11
R
(Figure 11), the internal transistor Q3 is
C3
4
R
ENABLE MODULE
V
ON/OFF
V
5
ACTIVE HIGH
IN
IN
R
+
–
5
V
V
OUT
OUT
+
–
OVH
PG
, Q3 will turn on,
= 1.223V, the