LTC2931 Linear Technology, LTC2931 Datasheet - Page 12

• Manufacturer Part Number: LTC2931
• Description: Confi gurable Six Supply Monitor
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
LTC2931
12
Supply and Temperature Monitor
Figure 5 illustrates how to confi gure 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:
V1 is the nominal operating voltage at input V1, V
1.210V, V
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.
RBIAS = (RHOT/V
RHYST =
RTA
V
= 0.5V, and RPU < RHYST. The closest 1%
RTA
V1
MANUAL RESET
5V
3.3V
12V
28V
–5.2V
PUSH BUTTON
•
5110k 1%
(
(
RTA
RCOLD−RHOT
RCOLD • RHOT
) • (V
2150k 1%
467k 1%
Figure 5. Supply and Temperature Monitor (5V, 3.3V, 28V, -5.2V, 12V, 115°C)
10k**
REF
100k
1%
– V
100k
1%
RHYST
RTA
)
)
280k
1%
RNTC*
) = 1.42 • RHOT
470k
RBIAS
15.8k
1%
0.1μF
93.1k
9.53k
121k
1%
1%
1%
R1
R2
REF
=
V1
V2
V3
V5
V4
VREF
V6
VPG GND CRT
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 confi gured to mode 13 (see Table 1). When
the threshold is reached on V1, COMP1 pulls high. COMP1
then enables the 3.3V converter fi rst. 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 fi ve 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.
LTC2931
t
t
RST
WD
= 940ms
= 94ms
C
47nF
RT
COMP1
COMP2
COMP3
COMP4
COMP5
COMP6
CWT
WDO
WDI
RST
C
47nF
WT
10k
*PANASONIC ERTJOEV474J
**OPTIONAL FOR ESD PROTECTION
RPU
10k
10k
POWER GOOD
TEMP GOOD
SYSTEM
LOGIC
2931 F05
2931fb