LTC2931HF 데이터 시트보기 (PDF) - Linear Technology
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LTC2931HF
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LTC2931HF Datasheet PDF : 16 Pages
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LTC2931
APPLICATIONS INFORMATION
Supply and Temperature Monitor
Figure 5 illustrates how to configure the LTC2931 to
monitor temperature. Temperature is sensed by a
thermistor, RNTC, as part of a voltage divider driving
adjustable input V6. Output COMP6 goes low when the
temperature is higher than the trip point, and is fed back
through RHYST to provide hysteresis.
Assume a thermistor (RNTC) with values RHOT at the up-
per threshold and RCOLD at the lower threshold. Minimize
errors arising from V6 input current (15nA maximum)
by choosing RCOLD ≤ 100kΩ, and to limit the loading
on VREF, choose RHOT ≥ 1kΩ. RBIAS and RHYST are
calculated from:
RBIAS = (RHOT/VRTA) • (VREF – VRTA) = 1.42 • RHOT
RHYST =
V1
VRTA
•
(RCOLD •RHOT)
(RCOLD − RHOT)
V1 is the nominal operating voltage at input V1, VREF =
1.210V, VRTA = 0.5V, and RPU < RHYST. The closest 1%
value was chosen for RHYST.
In Figure 5, the trip points are 115°C with RHOT = 11.1kΩ
(COMP6 goes low) and 100°C with RCOLD = 18.5kΩ
(COMP6 goes high). A reset is generated in the event of
an over-temperature condition. COMP6 (Temp Good) and
COMP5 (Power Good) distinguish over-temperature and
undervoltage faults.
Five Supply Power-up Sequencer
In Figure 6, the LTC2931’s real-time COMP outputs are
used to enable DC/DC converters sequentially. The system
is powered by a 12V source.
The system is started when the push-button is pressed and
the LTC2950-1 brings the RUN pin of the LTM4600 high.
Subsequently, the LTM4600 generates a 5V output which
applies power to each of the 4 DC/DC converters.
The LTC2931 is configured to mode 13 (see Table 1). When
the threshold is reached on V1, COMP1 pulls high. COMP1
then enables the 3.3V converter first. When the threshold
is reached on V2, COMP2 pulls high and enables the 1.8V
converter next. When all the converters have been enabled
and are good, COMP5 pulls high. RST pulls high 9.4ms
after COMP5. Figure 7 shows the power-up sequence of
the five supplies and the DONE and RST outputs.
If the KILL input on the LTC2950-1 does not receive a logic
high within 512ms of initial power-up, EN pulls low and
the LTM4600 is powered down.
In the event that the external 12V supply drops below
9.6V, COMP6 and RST will pull low. The LTC2950-1 then
receives a logic low on the KILL input, which powers down
the LTM4600 and the sequencing circuit.
12
5V
0.1μF
3.3V
12V
28V
–5.2V
2150k 1%
5110k 1%
467k 1%
RHYST
280k
1%
RBIAS
15.8k
1%
MANUAL RESET
PUSH BUTTON
10k**
100k
1%
RNTC*
100k 470k
1%
121k
1%
R1
93.1k
1%
R2
9.53k
1%
LTC2931
10k
RPU
10k
10k
V1
COMP1
V2
COMP2
V3
COMP3
V5
COMP4
V4
COMP5
COMP6
POWER GOOD
TEMP GOOD
VREF
RST
WDO
V6
VPG GND CRT
WDI
CWT
*PANASONIC ERTJOEV474J
**OPTIONAL FOR ESD PROTECTION
CRT
47nF
CWT
47nF
SYSTEM
LOGIC
2931 F05
tRST = 94ms
tWD = 940ms
Figure 5. Supply and Temperature Monitor (5V, 3.3V, 28V, -5.2V, 12V, 115°C)
2931fb
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