Rainbow Electronics MAX5093 - Manual (Page 13)

MAX5092/MAX5093
4V to 72V Input LDOs with Boost Preregulator
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Internal Regulator (VL)
An internal regulator (VL) is used to supply all internal
low-voltage blocks. Bypass VL to SGND with a 1µF
ceramic capacitor placed as close to the IC as possi-
ble. V
VL regulates to 5.5V when V BSOUT is above 5.5V.
V VL tracks the voltage at BSOUT when V BSOUT is
below 5.5V.
Power-On-Reset Output (
RESET)
The MAX5092_/MAX5093_ contain an open-drain output
(RESET) that indicates when the LDO output (V
OUT
) is
out of regulation. If the output of the LDO falls below 90%
of the nominal output voltage, RESET pulls low after a
short delay. Once the output rises above 92% of the
nominal output voltage, RESET goes high impedance
after the programmed reset timeout period. Connect a
100kΩ pullup resistor from OUT to RESET. See the
CT
Capacitor Selection section for details on setting the
RESET timeout period.
Enable and Hold Inputs
The MAX5092_/MAX5093_ utilize two logic inputs, EN
(active-high) and HOLD (active low), to implement a
self-holding circuit with no additional components. For
example, an automotive ignition switch drives EN high
and the regulator turns on. If HOLD is then driven low,
the regulator remains on even if EN goes low. As long
as HOLD is forced low and remains low after initial reg-
ulator power-up, the regulator remains on. From this
state, release HOLD (an internal current source con-
nects HOLD to OUT), or connect HOLD to OUT to turn
the regulator off. Drive EN low and HOLD high to place
the IC into shutdown mode. Shutdown mode reduces
supply current to 5µA. Figure 3 shows the timing dia-
gram for the enable and hold functions. Table 1 shows
the state of the regulator output with respect to the volt-
age level at EN and HOLD with reference to Figure 3.
Connect HOLD to OUT or leave unconnected to dis-
able the hold feature and use EN as a standard on/off
control input.
3 1
HOLD
EN
OUT
ORDER 2 4 5 6
Figure 3. Enable and Hold Timing Diagram
ORDER EN
HOLD
OUT COMMENTS
1 Low X Off
Initial State. EN has a 500nA pulldown to GND. HOLD has an internal current source to OUT.
HOLD follows OUT.
2 High Released On
Regulator output is active when EN is pulled high. HOLD is in release state, and it follows
OUT.
3 Low Released Off HOLD is in release state. OUT follows EN.
4 High Low On
HOLD is pulled low externally after OUT turns on. The regulator output is forced on
regardless of the state of EN. A self-holding state.
5 Low Released Off HOLD is released after EN is pulled low. Output turns off.
5 High X On Regulator enabled. Normal turn-on behavior. Regulator follows EN and HOLD follows OUT.
Table 1. Truth Table for Enable and Hold Timing Diagram