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LTC699 Datasheet(PDF) 3 Page - Linear Technology

Part No. LTC699
Description  Microprocessor Supervisory Circuit
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Maker  LINER [Linear Technology]
Homepage  http://www.linear.com
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LTC699 Datasheet(HTML) 3 Page - Linear Technology

   
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LTC699
but not serviced prior to the time-out period, the reset
pulse generator also forces RESET to active low for a mini-
mum of 140ms for every time-out period (see Figure 2).
WDI: Watchdog Input, WDI, is a three level input. Driving
WDI either high or low for longer than the watchdog time-
out period forces RESET low. Floating WDI disables the
Watchdog Timer. The timer resets itself with each transition
of the Watchdog Input (see Figure 2).
VCC: +5V supply input. The VCC pin should be bypassed
with a 0.1
µF capacitor.
GND: Ground pin.
RESET: Open drain output for
µP reset control. When VCC
falls below the reset voltage threshold (4.65V typically),
RESET goes active low. After VCC returns to 5V, the reset
pulse generator forces RESET to remain active low for a
minimum of 140ms . When the watchdog timer is enabled
PI FU CTIO S
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of circuits as described herein will not infringe on existing patent rights.
SUPPLY VOLTAGE (V)
0
3
4
5
4
2
1
0
1
2
3
5
LTC699 G01
TA = 25°C
EXTERNAL PULLUP = 10
µA
TEMPERATURE (
°C)
–50
216
224
232
25
75
LTC699 G02
208
200
–25
0
50
100
125
192
184
VCC = 5V
Reset Voltage Threshold vs
Temperature
CC
HARA TERISTICS
A
TYPICALPERFOR
CE
down, the RESET signal remains active low even with VCC
as low as 1V. This capability helps hold the microproces-
sor in stable shutdown condition. Figure 1 shows the
timing diagram of the RESET signal.
The precision voltage comparator, C1, typically has 40mV
of hysteresis which ensures that glitches at VCC pin do not
activate the RESET output. Response time is typically
10
µs.Tohelppreventmistriggeringduetotransientloads,
VCC pin should be bypassed with a 0.1µF capacitor with the
leads trimmed as short as possible.
Microprocessor Reset
The LTC699 uses a bandgap voltage reference and a
precision voltage comparator C1 to monitor the 5V supply
input VCC (see BLOCK DIAGRAM). When VCC falls below
the reset voltage threshold, the RESET output is forced to
active low state. The reset voltage threshold accounts for
a 5% variation on VCC, so the RESET output becomes
active low when VCC falls below 4.65V typical. On power-
up, the RESET signal is held active low for a minimum of
140ms after reset voltage threshold is reached to allow the
power supply and microprocessor to stabilize. On power-
S
APPLICATI
I FOR ATIO
RESET Output Voltage vs
Supply Voltage
Reset Active Time vs
Temperature
TEMPERATURE (
°C)
–50
4.64
4.65
4.66
25
75
LTC699 G03
4.63
4.62
–25
0
50
100
125
4.61
4.60


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