Datasheet

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 powerup/
down and brownout conditions. RESET goes low if V
OUT
drops below the preset output voltage threshold, and
remains low for 200ms (reset timeout period, t
RP
) after
V
OUT
rises above the reset voltage threshold. For 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
WD
). RESET remains low for 200ms (reset timeout
period, t
RP
). 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-
tion during the reset timeout period. Figure 2 shows the
Watchdog Operation Timing Diagram. To prevent the
watchdog from asserting RESET, toggle WDI with a
valid rising or falling edge prior to t
WD
(min) = 1.12s. The
watchdog counter clears when WDI toggles prior to t
WD
or when RESET asserts. The watchdog resumes counting
after RESET deasserts.
Enable and Hold Inputs
The MAX5023/MAX5024 support two logic inputs, EN
(active high) and HOLD (active low), making these devic-
es “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 feature makes it pos-
sible to implement a self-holding circuit without external
components. Release HOLD (an internal current source
connects HOLD to OUT) to turn the regulator off.
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
Figure 2. Watchdog Operation Timing Diagram
V
OUT
WHEN WATCHDOG IS HELD
HIGH AND EN = HIGH
V
OUT
WHEN WATCHDOG IS HELD
LOW AND EN = HIGH
BATT
BATT
BATT
BATT
POR NORMAL OPERATION WDI HELD HIGH
POR NORMAL OPERATION WDI HELD LOW
EN
WDI
RESET
V
OUT
OV
OV
OV
OV
OV
OV
V
IN
EN
WDI
RESET
V
OUT
V
IN
MAX5023/MAX5024 65V, Low-Quiescent-Current, High-Voltage Linear
Regulators with μP Reset and Watchdog Timer
www.maximintegrated.com
Maxim Integrated │ 9