LTC2901-2IGN 查看數據表（PDF） - Linear Technology
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LTC2901-2IGN
Linear Technology
LTC2901-2IGN Datasheet PDF : 16 Pages
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LTC2901
APPLICATIO S I FOR ATIO
Monitoring Power Supply Controller Activity
Figure 7 demonstrates how the LTC2901 can be used to
monitor switcher activity. The monitor is configured to
supervise 3.3V, 2.5V, 1.8V and one adjustable input.
Because 2.5V does not exist in this application, the V2
input is tied to the V1 (3.3V) input. The feedback voltage
on the LTC1772 (0.8V typ) is monitored with the adjust-
able input (V4). The RST pin will go high 216ms
(CRT = 47nF) after the 3.3V and 1.8V supplies and the
feedback voltage are above threshold. Individual input
status is available at the COMPX pins.
While the voltage monitors can detect low voltage or
shorted inputs, the watchdog circuit can be used to detect
an open circuit to the primary load. With the CWT pin
unconnected, the watchdog time-out is approximately
200µs. At low load currents on the 1.8V supply, the
LTC1772 will go into Burst Mode® operation. With an
open-ciruit load, the duty cycle at the gate of M1 will drop,
and the pulse spacing will exceed the watchdog time-out
period. The WDO pin will go low indicating the low load
condition. The WDO pin will return high on the next pulse
to the gate of M1. The WDO pin will remain high if the load
is restored.
Ensuring Reset Valid for VCC Down to 0V
(LTC2901-2/LTC2901-4)
Some applications require the reset output (RST) to be
valid with VCC down to 0V. The LTC2901-2 is designed to
handle this requirement with the addition of an external
resistor from RST to ground. The resistor will provide a
path for stray charge and/or leakage currents, preventing
the RST output from floating to undetermined voltages
when connected to high impedance (such as CMOS logic
inputs). The resistor value should be small enough to
provide effective pull-down without excessively loading
the active pull-up circuitry. Too large a value may not pull
down well enough. A 100k resistor from RST to ground is
satisfactory for most applications.
Burst Mode is a registered trademark of Linear Technology Corporation.
R6
10k
C3
220pF
LTC1772
1
6
ITH PGATE
2
5
GND
VIN
3
VFB
SENSE– 4
C1: TAIYO YUDEN CERAMIC LMK325BJ106K-T
C2: SANYO POSCAP 6TPA47M
D1: MOTOROLA MBRM120T3
L1: COILTRONICS UP1B-100
M1: Si3443DV
R5: DALE 0.25W
R5
0.15Ω
M1 L1
10µH
+
D1
C1
10µF
10V
C2
47µF
6V
R3
100k
VIN
3.3V
VOUT
1.8V
0.5A
R4
80.6k
R1
28k
1%
R2
71.5k
1%
LTC2901-2
4
V1
2
COMP1
3.3V MONITOR
14
16
V2 COMP2
3
V3
1
COMP3
1.8V MONITOR
13
V4
COMP4 15 FEEDBACK MONITOR
8
WDI
6
RST
COMMON RESET OUT
12
VREF
11
VPG
10
GND
7
WDO
5
CRT
9
CWT
LOW LOAD INDICATOR
CRT
47nF
2901 F07
Figure 7. Monitor Input, Output, Feedback Voltage and Low Load Conditions on DC/DC Controller
2901fb
14
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