65V, Low-Quiescent-Current, High-Voltage Linear
Regulators with µP Reset and Watchdog Timer
BATT
BATT
V
IN
EN
V
WHEN WATCHDOG IS HELD
OV
OV
OV
WDI
OUT
HIGH AND EN = HIGH
RESET
V
OUT
POR
NORMAL OPERATION
WDI HELD HIGH
BATT
BATT
V
IN
EN
V
WHEN WATCHDOG IS HELD
OUT
OV
OV
WDI
LOW AND EN = HIGH
RESET
OV
V
OUT
POR
NORMAL OPERATION
WDI HELD LOW
Figure 2. Watchdog Operation Timing Diagram
Figure 2 shows the Watchdog Operation Timing
Diagram. To prevent the watchdog from asserting
RESET, toggle WDI with a valid rising or falling edge
Reset Output
The reset supervisor circuit is fully integrated in the
MAX5023/MAX5024 and uses the same reference volt-
age as the regulator. RESET asserts during power-
up/down and brownout conditions. RESET goes low if
prior to t
(min) = 1.12s. The watchdog counter clears
WD
when WDI toggles prior to t
The watchdog resumes counting after RESET deasserts.
or when RESET asserts.
WD
V
drops below the preset output voltage threshold,
OUT
and remains low for 200ms (reset timeout period, t
)
RP
Enable and Hold Inputs
The MAX5023/MAX5024 support two logic inputs, EN
(active high) and HOLD (active low), making these
devices “automotive friendly.” For example, the ignition
drives EN high, the regulator turns on and remains on
even if EN goes low, as long as HOLD is forced low
and stays low after initial regulator power-up. This fea-
ture makes it possible to implement a self-holding
circuit without external components. Release HOLD (an
internal current source connects HOLD to OUT) to turn
the regulator off.
after V
rises above the reset voltage threshold. For
OUT
the MAX5023 only, RESET also asserts when WDI does
not transition for 1.6s (watchdog timeout period, t ).
WD
Two supply tolerance reset thresholds, -7.5% and
-12.5%, are available for each device type.
Watchdog Timer (MAX5023 only)
A watchdog timer asserts RESET if the watchdog input
(WDI) is not toggled for 1.6s (watchdog timeout period,
t
). RESET remains low for 200ms (reset timeout peri-
RP
WD
od, t ). If the watchdog is not updated for lengthy
periods of time, the reset output appears as a pulse
train, asserted for 200ms, deasserted for 1.6s, until WDI
is toggled again. Once RESET asserts, it stays low for
the entire reset timeout period ignoring any WDI transi-
tions during the reset timeout period.
Force EN low and HOLD high to place the MAX5023/
MAX5024 into shutdown mode. Shutdown mode draws
less than 16µA of supply current. Table 1 shows the state
of the regulator output with respect to the voltage level at
8
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