LTC2922IF-2.5 Linear Technology, LTC2922IF-2.5 Datasheet - Page 17

• Manufacturer Part Number: LTC2922IF-2.5
• Description: IC 5 PWR SUPPLY MONITOR 20TSSOP
• Manufacturer: Linear Technology

Specifications of LTC2922IF-2.5

• Applications: Five Power Supply Monitor
• Voltage - Supply: 2.37 V ~ 2.63 V
• Current - Supply: 2mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Input: -

APPLICATIO S I FOR ATIO
Next, consider the supply ramping N-channel MOSFETs
Q0, Q1 and Q2. Transistor Q0 will have >4.5V of gate-
source voltage, even at maximum supply voltage (5.375V)
and minimum GATE pin voltage (10V). Considering the
voltages, temperatures, and currents involved, the maxi-
mum on-resistance (R
Si2316DS is about 150m . Switches Q1 and Q2 will see
even higher gate-source voltages, implying even smaller
R
V
across R
Table 2. External MOSFET Drain-Source Voltage Drops
Supply
Voltage
5V
3.3V
2.5V
The 20V absolute maximum gate-source voltage rating
of the Si2316DS easily accommodates this design.
Next, calculate the necessary capacitance on the GATE pin
to realize the desired ramp rate. Use the nominal value of
V
standard value.
Include drain bypass capacitors of 0.1 F and series gate
resistors of 10 on each external power FET to damp turn-
on oscillations.
Find the capacitance at the TIMER pin required to set the
delays in the power-on sequence:
The application requires the use of the circuit breaker
function on the V
sense resistor value:
Q(ON)(MAX)
GATE
Q(ON)(MAX)
R
C
C
SENSE
GATE
TIMER
from the Electrical Specification, and choose a
SENSE
MOSFET
External
Q0
Q1
Q2
10
voltages. Include the additional 50mV drop
values. Table 2 summarizes the calculated
45
1 2
2
0 8
.
when budgeting for the V
.
mV
CC
A
10 8
A
V
A
•
supply. First, find the upper limit on the
•
.
U
~150m
<150m
<150m
500
150
R
V
Max
Q(ON)
Q(ON)(MAX)
53 25
ms
ms
.
U
m
0 463
0 25
0.8A
1.6A
0.4A
Max
.
.
I
L
) of the Vishay Siliconix
W
F
F
(+50mV = 170mV)
0 22
CC
0 47
.
.
<240mV
supply path.
120mV
<60mV
V
Max
Q(ON)
U
F
F
Select a precision power sense resistor, such as the
Vishay Dale WSL1206 series. They can be specified to 1%,
and exhibit <1% variation over the LTC2921/LTC2922
operating range; choose R
ances, the circuit breaker trip current threshold variation
will be:
The PG pin is configured as a 2.5V negative-logic reset
signal for the microcontroller. The minimum pull-up resis-
tance for proper operation is:
Figure 13 shows R
arbitrarily chosen, but it does limit the pull-down current
to <500 A. Trade off lower pull-down currents against
faster pull-up edge rates in other applications.
Recall that proper operation of the remote load sensing
function requires:
In this example, the operating conditions and the Si2316DS
give R
table guarantees R
specification requires that (R
= R
Before the loads are connected to the supplies, the voltage
error due to the R
supplies:
After the remote sense switches close, the load voltage
errors due to R
R
I
I
R
X1
TRIP MIN
TRIP MAX
Q(ON)
PG MIN
V
SRC
Q(ON)(MAX)
= R
(
LTC2921/LTC2922 Series
(
(
, R
X2
)
)
FB(ON)
)
= 100 satisfies the inequality.
V
SRC
2 6875
X
51
45
.
49
55
at maximum loads will be:
= 150m , the Electrical Characteristics
m
•
mV
X
<< R
FB(ON)
m
mV
PG
resistors will be <0.1% for all three
5
100
100
mA
V
X
= 4.7k. The value is somewhat
– .
0 88
< 10 , and the example design
<< (R
k
SENSE
1 12
0 4
.
.
Y
V
A
+ R
A
Y
V
1000
= 50m . Including toler-
+R
SRC
Z
460
) <100k. Selecting R
Z
)
0 1
. %
of V
17
SRC
29212fa
X0