lt2940 Linear Technology Corporation, lt2940 Datasheet - Page 15

• Manufacturer Part Number: lt2940
• Description: Power And Current Monitor
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
When the LATCH pin voltage exceeds 2.5V, the next high
result from the comparator also enables the comparator
latch. The CMPOUT pin goes open (high), and the CMPOUT
pin sinks current (low) regardless of the changes to the
CMP
level sensitive, not edge sensitive, so if CMP
when LATCH is brought above 2.5V, the comparator result
is high, and the latch is set immediately. The LATCH pin
voltage may be taken safely to 80V regardless of the V
pin voltage.
The latch is released and the comparator reports a low
when LATCH ≤ 0.5V or when V
CMP
current (low), while the CMPOUT pin goes open (high).
As with latching, clearing is level-sensitive: comparator
outputs react to the input signal as soon as LATCH ≥ 1.25V
and V
+
+
CC
level until the latch is cleared. Latch activation is
pin voltage. In this state, the CMPOUT pin sinks
> 2.7V.
OVERPOWER (OVP) GOES HIGH
WHEN LOAD POWER > 40W
k
k
V
I
= 150mΩ
=
Figure 7. Supply Resistor Reduces Package Heating by Reducing V
30V TO 80V
15
1
CC
< 2.3V regardless of the
OVP
36V MAX
6.19k
R3
R14
20k
13.7k
+
R4
> 1.24V
LATCH
CMPOUT
CMPOUT
CMP
5mA
MAX
+
100V MAX
PMON
V
CC
CC
R12
3.9k
10% 1/8W
V
PMON
LT2940
GND
Thermal Considerations
If operating at high supply voltages, do not ignore package
dissipation. At 80V the dissipation could reach 400mW;
more if IMON or PMON current exceeds full-scale. Pack-
age thermal resistance is shown in the Pin Confi guration
section. Package dissipation can be reduced by simply
adding a dropping resistor in series with the V
shown in Figure 7. The operating range of the current sense
input pins I
of V
V
Consult Table 1 during design. Operating an open-col-
lector output pin with simultaneously large current and
large voltage bias also contributes to package heating and
must be avoided.
–
SCALE = 10
40W FULL-SCALE
, PMON and IMON pins are, however, limited by V
I
+
CC
150mΩ
1/2W
R
, make this possible. The voltage ranges of the V
IMON
S
I
–
W
0A TO 1.3A
V
+
2940 F07
V
V
and I
+
–
–
, which extends to 80V independent
R2
140k
R1
10.0k
CC
LOAD
Voltage
LT2940
CC
15
pin, as
2940f
CC
+
,
.