LTC2921IGN-3.3 Linear Technology, LTC2921IGN-3.3 Datasheet - Page 15

• Manufacturer Part Number: LTC2921IGN-3.3
• Description: IC 5 POWER SUPPLY MONITOR 16SSOP
• Manufacturer: Linear Technology

Specifications of LTC2921IGN-3.3

• Applications: Five Power Supply Monitor
• Voltage - Supply: 2.97 V ~ 3.63 V
• Current - Supply: 2mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Input: -

APPLICATIO S I FOR ATIO
Before Q1 closes to connect the load, the actual supply
voltage relative to V
After both Q1 and the internal remote sense switch have
closed, the load voltage relative to V
13.
A small part of the load current will flow through the
remote sense switch. Use Equation 14 to calculate the
current, and do not exceed the switch current Absolute
Maximum Rating when choosing the value of R
In addition, once the remote sensing is active, the supply
voltage V
the external FET. The effect on the monitor resistive divider
design has already been accounted for in the previous
section, Setting the Supply Monitor Levels.
The terminals of each switch are interchangeable; choose
the connections to optimize the board layout. Ground all
unused switch pins.
Design Example
Consider the design of a three-supply monitoring system,
as shown in Figure 12, with specifications as listed in
Table 1.
I
V
DS
V
SRC
V
SRC
1
L
1
1
1
SRC1
I
L
V
1
V
V
L
•
V
S
S
1
SRC
1
1
will rise by approximately the drop across
–
R
V
Q ON
R
I
1
V
S
L
1
X
Q ON
1
(
–
1
U
S1
1
1
•
( )
V
R
)
S
is given by Equation 12.
–
Q ON
1
I
1
L
( )
U
1
V
•
S
R
1
• –
Q ON
•
1
(
1
R
S1
W
)
X
R
1
•
is given by Equation
FB ON
R
R
1
X
R
R
( )
FB ON
1
R
X
Y
1
1
1
X
(
1
U
R
)
X1
Z
1
.
(12)
(13)
(14)
(15)
Table 1. Design Example Electrical Specifications
Supply Specifications
5V 7.5%
3.3V 7.5%
2.5V 7.5%
External N-channel FET Drain-Source Voltage Specification
5V Supply
3.3V Supply
2.5V Supply
Timing Specification
TIMER Delay
GATE Ramp Time
Bias Current Specification
Monitor Resistive
Divider Current
The LTC2921 suits this application because the largest
supply in the system is 5V, and only three remote sense
switches are required.
Start with the design of the resistive dividers that set the
monitor levels. As the largest supply voltage, the 5V
supply must be connected to the V
resistive divider sets that monitor level. Consult the
Electrical Characteristics table to confirm that V
>V
The bias current in the lower resistor for the 3.3V supply’s
dividers yields a standard 1% value of R
Other Requirements
• Remote Sense all 3 Load Voltages
• Tight Monitoring Levels
• Use Circuit Breaker Function
• DC/DC Converter Feedback Resistive Divider >100k
CC(MON)(MAX)
R
A1
LTC2921/LTC2922 Series
0 500
10
.
A
V
V
V
V
V
V
V
V
V
V
t
t
I
I
and V
DLY
RAMP
A1
A2
SRC0(MAX)
SRC0(MIN)
SRC1(MAX)
SRC1(MIN)
SRC2(MAX)
SRC2(MIN)
Q0(ON)(MAX)
Q1(ON)(MAX)
Q2(ON)(MAX)
= 10 A (nom)
= 10 A (nom)
= 150ms (nom)
50
= 500ms (nom)
SRC0(MAX)
k
= 4.625V
= 3.0525V
= 2.3125V
= 5.375V
= 3.5475V
= 2.6875V
< 250mV
< 250mV
< 150mV
49 9
.
k
<V
CC(OV)(MIN)
CC
I
I
I
A1
pin; an internal
L0
L1
L2
= 0.8A (max)
= 1.6A (max)
= 0.4A (max)
= 49.9k:
.
SRC0(MIN)
15
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