Datasheet

REV. 0–14–
ADM1070
Figure 13 shows the behavior of ADM1070 when a temporary
current fault occurs followed by a permanent current fault.
When the first overcurrent fault occurs, the first 100 mV spike
on the sense line can be seen. During the t
OFF
time, this current
fault corrects itself. After this time period, a no fault condition is
detected and the limited consecutive counter is reset. GATE is
reasserted. When the overcurrent fault returns permanently, the
limited consecutive retry counter detects seven consecutive
faults and the part latches off.
GATE
SENSE
5.00VCH2100mV M 500ms
CH1
B
N
T
Figure 13. Illustration of the PWM Ratio (t
ON
/t
OFF
)
In this way, the ADM1070 prevents nuisance shutdowns from
transient shorts of up to three seconds (typically), but will provide
latched shut-down protection from permanently shorted loads.
KELVIN SENSE RESISTOR CONNECTION
When using a low value sense resistor for high current measure-
ment, the problem of parasitic series resistance can arise. The
lead resistance can be a substantial fraction of the rated resis-
tance, making the total resistance a function of lead length. This
problem can be avoided by using a Kelvin sense connec
tion.
This type of connection separates the current path
through
the resistor and the voltage drop across the resistor. Figure 14
shows the correct way to connect the sense resistor between the
SENSE and V
EE
Pins of the ADM1070.
KELVIN SENSE TRACES
CURRENT
FLOW FROM
LOAD
CURRENT
FLOW TO –48V
BACKPLANE
SENSE RESISTOR
SENSE V
EE
ADM1070
Figure 14. Kelvin Sensing with the ADM1070
UV/OV AS ENABLE PIN
Connecting an open collector output to the UV/OV Pin means
that a TTL signal can be used to disable the part. In Figure 15,
the open collector output connects to EN. Driving the base of
the open collector device high enough to cause the UV/OV Pin
to be pulled below the undervoltage falling threshold of 0.86 V
typical will cause the pass transistor Q1 to be turned off.
EN
ADM1070
0V
–48V
R1
R2
R
DROP
V
IN
UV/OV
TIMER
GATE
SENSE
V
EE
C
LOAD
V
OUT
Q1
R
SENSE
Figure 15. UV/OV Used as Enable Input