DC1555A Linear Technology, DC1555A Datasheet - Page 9

• Manufacturer Part Number: DC1555A
• Description: LTC4365 High Voltage UV, OV And Reverse Supply Protection Controller
• Manufacturer: Linear Technology
• Series: -r

Specifications of DC1555A

• Design Resources: DC1555 Design Files DC1555A Schematic
• Main Purpose: Power Management, Voltage Protection, Over, Under
• Embedded: No
• Utilized Ic / Part: LTC4365
• Primary Attributes: -
• Secondary Attributes: -
• Kit Application Type: Power Management
• Application Sub Type: Overvoltage Protection
• Features: Board Intended To Demonstrate Performance Of The LTC4365 High Voltage, Undervoltage Controller
• Lead Free Status / Rohs Status: Not applicable / Not applicable

APPLICATIONS INFORMATION
Figure 2 highlights the dependence of the gate drive on V
and V
low to high, V
values of V
heavy loads by ensuring that there is enough gate drive
to support the load.
As V
voltage remains fixed until V
of (V
gate drive begins to increase up to a maximum of 9.8V
(for V
a GATE load of –1μA. If there were no load on GATE, the
gate drive for each V
Note that when V
range, the external N-channel MOSFET must be selected
with a corresponding lower threshold voltage.
Table 1 lists some external MOSFETs compatible with
different V
Table 1. Dual MOSFETs for Various Supply Ranges
≤30V
≤60V
2.5V
3.3V
OUT
V
5V
IN
IN
OUT
IN
–1V) or 6V. Once V
ramps up from 0V, the absolute value of the GATE
≥ 12V). The curves of Figure 2 were taken with
Figure 2. Gate Drive (GATE – V
. When system power is first turned on (SHDN
IN
IN
12
10
8
6
2
0
4
supply voltages.
. This helps prevent start-up problems into
OUT
MOSFET
0
SiB914
Si5920
Si7940
Si4230
Si9945
= 0V), gate drive is at a maximum for all
IN
V
IN
3
is at the lower end of the operating
IN
= 2.5V
V
IN
would be slightly higher.
= 3.3V
V
V
IN
6
TH(MAX)
V
0.8V
1.0V
1.5V
3.0V
3.0V
= 5V
OUT
V
IN
OUT
OUT
(V)
= 12V
9
is greater than the lower
crosses this threshold,
I
GATE
V
OUT
V
IN
12
GS(MAX)
T = 25°C
20V
20V
= 30V
5V
5V
8V
) vs V
= –1μA
4365 F02
15
OUT
V
DS(MAX)
60V
12V
30V
8V
8V
IN
Overvoltage and Undervoltage Protection
The LTC4365 provides two accurate comparators to moni-
tor for overvoltage (OV) and undervoltage (UV) conditions
at V
OV threshold, the gate of the external MOSFET is quickly
turned off, thus disconnecting the load from the input.
Similarly, if the input supply falls below the user adjust-
able UV threshold, the gate of the external MOSFET also
is quickly turned off. Figure 3 shows a UV/OV application
for an input supply of 12V.
UV
The external resistive divider allows the user to select
an input supply range that is compatible with the load at
V
leakage currents (typically < 1nA at 100°C), allowing for
large values in the external resistive divider. In the applica-
tion of Figure 3, the load is connected to the supply only if
V
above 18V or below 3.5V, the gate of the external N-channel
MOSFET is immediately discharged with a 50mA current
sink, thus isolating the load from the supply.
OV
OUT
IN
TH
TH
IN
= 3.5V
lies between 3.5V and 18V. In the event that V
12V
= 18V
. Furthermore, the UV and OV inputs have very low
. If the input supply rises above the user adjustable
Figure 3. UV, OV Comparators Monitor 12V Supply
R3
1820k
R2
243k
R1
59k
UV
OV
V
IN
0.5V
0.5V
–
+
+
–
COMPARATOR
COMPARATOR
UV
25mV
OV
25mV
LTC4365
LTC4365
DISCHARGE GATE
WITH 50mA SINK
IN
goes
4365 F03
9
4365f