LTC2922IF-2.5 Linear Technology, LTC2922IF-2.5 Datasheet - Page 11

• 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
Setting the Supply Monitor Levels
The LTC2921 and LTC2922 series both feature low 0.5V
monitoring thresholds with tight 1% accuracy. To set a
supply monitoring level tightly, design a precision ratio
resistive divider to relate the lowest valid supply voltage to
the maximum specified monitor threshold voltage. Use
resistors with 1% tolerance or better to limit the error due
to mismatch. The basic resistive divider connection for
supply monitoring is shown in Figure 5.
First, divide the nominal monitor threshold voltage by an
acceptable bias current (I
dard value for resistor R
Next, calculate the bounds on the value of R
guarantee that the divided minimum supply voltage ex-
ceeds the maximum specified monitor threshold voltage,
and that the minimum specified overvoltage threshold
exceeds the divided maximum supply voltage. Use Equa-
tions 2 and 3 to calculate R
the resistor tolerance (RTOL), the supply voltage, the
monitor threshold and overvoltage specifications, and the
monitor pin leakage current specification.
When the integrated remote sensing switch is closed, the
DC/DC converter will compensate for the IR drop from
drain to source of the external N-channel FET (V
increasing the supply voltage by the same amount. Calcu-
late with V
not used.
CONVERTER
R
DC/DC
A
1
V
GND
OUT
V
FB
0 500
Q1(ON)(MAX)
.
I
A
R
R
Figure 5. Basic Monitor Connection
Y1
Z1
1
V
V
SRC1
I
V
A1
U
V1
= 0V if the remote sense switch is
R
R
I
MON
0.1 A
B1
A1
A1
A1
U
B1(MAX)
(see Equation 1).
), and choose a nearby stan-
V1
LTC2922
and R
GND
W
GATE
B1(MIN)
10
R
+
G1
V
Q1
C
–
Q1
Q1(ON)
from R
U
GATE
V
LOAD
2921/22 F05
B1
L1
that
) by
(1)
A1
,
Choose a standard resistor value for R
inequality of Equation 4.
When several standard values meet the requirement,
choose the value closest to R
monitor threshold. This also allows more headroom for
larger V
value closest to R
threshold.
All four monitor input voltages must be between the
monitor threshold and the overvoltage threshold for the
turn-on sequence to begin. Connect unneeded monitor
input pins to any of the utilized monitor input pins.
Selecting the External N-Channel MOSFETs
The GATE pin drives the gate of external N-channel
MOSFETs above V
The GATE drive voltage provided by the LTC2921/LTC2922
series is best suited to logic-level and sublogic-level
power MOSFETs. To achieve the lowest switch resistance,
the V
voltage.
Consider the application requirements for current, turnoff
speed, on-resistance, gate-source voltage specification,
etc. Refer to the Electrical Specifications and Typical
Performance Curves to determine the GATE voltages for
given V
Calculate the minimum gate drive voltage for each moni-
tored supply for use in selecting the FETs. Check the
maximum GATE voltage against the FETs’ gate-source
R
R
R
R
B1(MIN)
B MAX
B MIN
V
A
CC
1
1
SRC MAX
1
(
(
LTC2921/LTC2922 Series
•
CC
Q1(ON)(MAX)
pin must be connected to the highest supply
1
1
1
voltages over the required range of conditions.
(
)
)
–
0 665
RTOL
RTOL
.
R
R
)
B1
A
1
V
CC
V
B1(MIN)
•
Q ON MAX
. Alternatively, choose the standard
– .
R
•
1
to connect the supplies to the loads.
1
1
(
B1(MAX)
0 1
–
0 505
V
RTOL
RTOL
)(
.
SRC MIN
to set the tightest overvoltage
A R
•
1
V
(
)
B1(MAX)
A
– .
•
1
0 665
0 1
)
.
– .
0 505
B1
A R
to set the tightest
V
•
that satisfies the
A
V
1
11
29212fa
(2)
(3)
(4)