DC1575A Linear Technology, DC1575A Datasheet - Page 10

• Manufacturer Part Number: DC1575A
• Description: LTC4362-1/LTC4362-2 Overvoltage/Overcurrent Protector With LatchOff/Auto-Retry
• Manufacturer: Linear Technology
• Series: -r

Specifications of DC1575A

• Design Resources: DC1575A Schematic DC1575 Design Files
• Main Purpose: Overvoltage/Overcurrent Protection
• Embedded: No
• Utilized Ic / Part: LTC4362-2
• Primary Attributes: -
• Secondary Attributes: -
• Kit Application Type: Power Management
• Application Sub Type: Overvoltage Protection
• Features: Demonstrates Two Protection Schemes Selected At JP2, Provides Connection For USB Protection
• Lead Free Status / Rohs Status: Not applicable / Not applicable

APPLICATIONS INFORMATION
LTC4362-1/LTC4362-2
Figure 5 shows an input transient after an overcurrent.
The current in L
the internal N-channel MOSFET to C
Typically, IN will be clamped to a voltage of V
BV
tive, pulse of energy (E
ing this avalanche breakdown with a peak current I
approximated by the formula:
For L
within the I
So in most instances, the LTC4362 can ride through such
transients without a bypass capacitor, transient voltage
suppressor or other external components at IN.
Figure 6 shows a particularly bad situation which can oc-
cur in a mobile device with dual power inputs. A 20V wall
10
ADAPTOR
WALL
DSS
E
USB
20V
Figure 6. Setup for Testing 20V Plugged into 5V System
AS
5V
IN
of Internal MOSFET) = 45V. The single, nonrepeti-
10V/DIV
=
= 0.7μH and I
2A/DIV
5V/DIV
+
–
+
–
I
CABLE
V
2
1
OUT
Figure 5. Input Transient After Overcurrent
V
AS
IN
• L
FIGURE 4 CIRCUIT
R
LOAD = 10Ω, C
and E
R
IN
IN
IN
IN
OVERCURRENT
= 150mΩ, L
I
CABLE
will cause V
• I
2
AS
AS
L
IN
AS
capabilities of the internal MOSFET.
OUT
AS
IN
= 3A, then E
= 0.7μH
) absorbed by the MOSFET dur-
= 10μF
2μs/DIV
B160
IN
to overshoot and avalanche
TURN-OFF
IN
OUT
AS
IN
LT4362
436212 F05
.
GND
= 3.15μJ. This is
OUT
OUT
OUT
+ 1.3•(30V
C
OUT
436212 F06
AS
LOAD
is
adaptor is mistakenly hot-plugged into the 5V device with
the USB input already live. As shown in Figure 7, a large
current can build up in L
internal MOSFET shuts off, this current is dumped into
C
this to a 1V rise in the output voltage.
If the voltage rise at V
in L
of the MOSFET is exceeded, an additional external clamp
Z1 such as the SMAJ24A can be placed between IN and
GND. Figure 8 shows the resulting waveform.
OUT
IN
, causing a large 40V transient. The LTC4362 limits
into C
Figure 8. Overvoltage Protection Waveforms When
20V Plugged into 5V System with External IN Clamp
10A/DIV
10V/DIV
10A/DIV
10V/DIV
2V/DIV
I
2V/DIV
CABLE
I
Figure 7. Overvoltage Protection Waveforms
When 20V Plugged into 5V System
V
CABLE
V
OUT
V
OUT
V
IN
OUT
IN
R
LOAD = 10Ω
C
R
LOAD = 10Ω
C
OUT
IN
IN
OUT
is not acceptable or the avalanche capability
= 150mΩ, L
= 150mΩ, L
= 10μF (16V, SIZE 1210)
= 10μF (16V, SIZE 1210)
OUT
IN
IN
due to the discharge of the energy
= 2μH
IN
= 0.7μH
1μs/DIV
1μs/DIV
to charge up C
436212 F07
436212 F08
OUT
. When the
436212fa