參數(shù)資料
型號: MAX6768TTLD2+
廠商: MAXIM INTEGRATED PRODUCTS INC
元件分類: 電源管理
英文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, DSO8
封裝: 3 X 3 MM, 0.80 MM HIEGHT, LEAD FREE, MO-229WEEC, TDFN-8
文件頁數(shù): 8/23頁
文件大?。?/td> 300K
代理商: MAX6768TTLD2+
MAX6765–MAX6774
Automotive Micropower Linear Regulators
with Supervisor
16
______________________________________________________________________________________
Watchdog Timer (MAX6773/MAX6774)
The MAX6773/MAX6774 include a watchdog timer that
asserts RESET if the watchdog input (WDI) does not
toggle within the watchdog timeout period tWD (1.6s,
typ). RESET remains low for the reset timeout period,
tRP. If the watchdog is not updated for lengthy periods
of time, the reset output appears as a pulse train,
asserted for the reset timeout period and deasserted
for the watchdog timeout period, until WDI is toggled
again. When RESET asserts, it stays low for the entire
reset timeout period ignoring any WDI transitions. To
prevent the watchdog from asserting RESET, toggle
WDI with a valid rising or falling edge prior to tWD (min)
= 1.12s. The watchdog counter clears when WDI tog-
gles prior to tWD or when RESET asserts. The watchdog
resumes counting after RESET deasserts. The watch-
dog timer cannot be disabled.
Thermal Protection
When the junction temperature exceeds TJ = +160°C
(typ), an internal thermal sensor signals the shutdown
logic that turns off the pass transistor and allows the IC
to cool. The thermal sensor turns the pass transistor on
again after the IC’s junction temperature cools by 20°C
(typ), resulting in a cycled output during continuous
thermal-overload conditions. Thermal protection pro-
tects the MAX6765–MAX6774 in the event of a fault con-
dition. Never exceed the absolute maximum junction
temperature rating of TJ = +150°C. See Figures 3 and 4
for the safe operating area.
Applications Information
Output Voltage Selection
The MAX6767–MAX6774 feature dual-mode operation:
these devices operate in either a preset or adjustable
voltage mode. In preset voltage mode, internal trimmed
feedback resistors set the internal linear regulator to
+1.8V, +2.5V, +3.3V, or +5V (see Table 2). Select pre-
set-voltage mode by connecting SET to ground. In
adjustable mode, select an output voltage between
+1.8V and +11V using two external resistors connected
as a voltage-divider to SET (see Figure 1). Set the out-
put voltage using the following equation:
VOUT = VSET (1 + R1 / R2)
where VSET = 1.233V and the recommended value for
R2 is 50k (maximum 100k).
RESETIN Threshold Selection
The MAX6769/MAX6770 feature an adjustable reset
threshold to monitor the voltage on RESETIN using a
resistive divider between the monitored voltage,
RESETIN and GND. See Figure 2. Use the following for-
mula to set the desired reset threshold:
VMON = VTH (1 + R3 / R4)
where VTH is 1.085V for the M/S/Y/V versions and
1.147V for L/T/Z/W versions.
MAX6769
MAX6770
RESET
RESETIN
R3
R4
GND
IN
VIN
VMON
Figure 2. RESETIN Threshold Selection
OPERATING
STATE
ENABLE
HOLD
REGULATOR
OUTPUT
COMMENT
Initial State
Low
Don’t care
Off
ENABLE is pulled to GND through an internal pulldown. HOLD is
floating (pulled up to OUT). Regulator output is disabled.
Turn-On State
High
Don’t care
On
ENABLE is externally driven high turning the regulator output on.
HOLD is pulled up by OUT.
Hold
Setup State
High
Low
On
HOLD is externally pulled low while ENABLE remains high (latches
HOLD state).
Hold State
Low
On
ENABLE is driven low (or allowed to float low by an internal pulldown).
HOLD remains externally pulled low keeping the regulator output on.
Off-State
Low
High
(floats high)
Off
HOLD is driven high (or allowed to float high by an internal pullup)
while ENABLE is low. Regulator output is shut off and ENABLE/
HOLD logic returns to the initial state.
Table 3. ENABLE/HOLD Truth Table/State Table
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