參數(shù)資料
型號: LTC1421-2.5CG
廠商: LINEAR TECHNOLOGY CORP
元件分類: 電源管理
英文描述: 14-bit, 5V, 200KSPS, 4-Channel Unipolar ADC 20-SOIC 0 to 70
中文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO24
封裝: 0.209 INCH, PLASTIC, SSOP-24
文件頁數(shù): 9/24頁
文件大?。?/td> 464K
代理商: LTC1421-2.5CG
9
LTC1421/LTC1421-2.5
APPLICATIO
S I
N
FOR
ATIO
U
PWRGD and RESET
The LTC1421 uses a 1.232V bandgap reference, internal
resistive divider and a precision voltage comparator to
monitor V
OUTLO
(Figure 6).
The reset threshold voltage for V
OUTLO
is determined by
the FB pin connection as summarized in Table 1.
W
U
When V
OUTLO
drops below its reset threshold, the com-
parator output goes high, and PWRGD is immediately
pulled low (time point 2). After a 32
μ
s delay, RESET is
pulled low. The RESET delay allows the PWRGD signal to
be used as an early warning that a reset is about to occur.
If the PWRGD signal is used as a interrupt input to a
microprocessor, a short power-down routine can be run
before the reset occurs.
If V
OUTLO
rises above the reset threshold for less than
200ms, the PWRGD output will trip, but the RESET output is
not affected (time point 3). If V
OUTLO
drops below the reset
threshold for less than 32
μ
s, the PWRGD output will trip, but
again the RESET output will not be affected (time point 5).
Voltage Comparator
The uncommitted voltage comparator (COMP2) can be
used to monitor output voltages other than V
OUTLO
. Figure
8a shows how the comparator can be used to monitor a
12V supply (V
OUTHI
), while the 5V supply (V
OUTLO
) gener-
ates a reset when it dips below 4.65V. When the 12V
supply drops below 10.8V, COMPOUT will pull low. The FB
pin is left floating.
Figure 8b shows how the comparator can be used to
monitor the 5V supply (V
OUTHI
) while the 3.3V supply
(V
OUTLO
) generates a reset when it dips below 2.9V. When
the 5V supply drops below 4.65V, COMPOUT will pull low.
The FB pin is tied to V
OUTLO
.
Figure 6. Supply Monitor Block Diagram
+
V
CCLO
V
CCLO
V
OUTLO
FB
1421 F06
1.232V
20
μ
A
20
μ
A
26.7k
PWRGD
RESET
COMP1
RESET
TIMING
REF
73.5k
71.5k
V
OUTLO
PWRGD
RESET
64
μ
s
V2
V2
V2
V2
V1
V1
V1
1
2
3
4
5
200ms
<200ms
200ms
1421 F07
<64
μ
s
Table 1
FEEDBACK PIN
Floating
V
OUTLO
GND
V
OUTLO
RESET VOLTAGE
4.65V
2.90V
5.88V
When the V
OUTLO
voltage rises above its reset threshold
voltage, the comparator output goes low, and PWRGD is
immediately pulled high to V
CCLO
by a weak pull-up
current source or external resistor (Figure 7, time points
1 and 4). After a 200ms delay, RESET is pulled high. The
weak pull-up current source to V
CCLO
on PWRGD and
RESET have a series diode so the pins can be pulled above
V
CCLO
by an external pull-up resistor without forcing
current back into V
CCLO
.
Figure 7. Power Monitor Waveforms
Figure 8a. Monitor 12V, Reset 5V at 4.65V
1421 F08a
10k
5%
1%
13.7k
1%
5V
12V
+
+
V
CCLO
V
CCLO
1.232V
LTC1421
20
μ
A
20
μ
A
8
14
13
15
11
16
20
26.7k
COMP1
COMP2
RESET
TIMING
73.5k
107k
6
7
71.5k
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