Datasheet

MAX6469–MAX6484
300mA LDO Linear Regulators with Internal
Microprocessor Reset Circuit
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Detailed Description
The MAX6469–MAX6484 are ultra-low, quiescent cur-
rent, low-dropout linear regulators with an integrated
microprocessor reset circuit. These devices guarantee
300mA (min) drive capabilities and are available with
preset output voltages in 100mV increments between
+1.5V and +3.3V. The internal reset circuit monitors the
regulator output voltage and asserts the reset output
when the regulator output is below the microprocessor
supply tolerance.
Regulator
The regulator core operates with +2.5V to +5.5V input
voltage range. The output voltage is offered in 100mV
increments between +1.5V and +3.3V (contact factory
for other output voltage options). The MAX6469–
MAX6472/MAX6477–MAX6480 offer an adjustable out-
put voltage implemented with an external resistor-
divider network between OUT, SET, and GND (Figure
1). SET must be connected to either GND for fixed
V
OUT
or to an external divider for adjustable V
OUT
. The
MAX6469–MAX6472/MAX6477–MAX6480 automatically
determine the feedback path depending on the con-
nection of SET. The Typical Operating Circuit shows a
typical connection for the MAX6469. OUT is an internal-
ly regulated low-dropout (LDO) linear regulator that
powers a microprocessor.
Reset Circuit
The reset supervisor circuit is fully integrated in the
MAX6469–MAX6484 and uses the same reference volt-
age as the regulator. Two supply tolerance reset
thresholds, -7.5% and -12.5%, are provided for each
type of device.
-7.5% Reset: Reset does not assert until the regulator
output voltage is at least -5% out of tolerance and
always asserts before the regulator output voltage is
-10% out of tolerance.
-12.5% Reset: Reset does not assert until the regulator
output voltage is at least -10% out of tolerance and
always asserts before the regulator output voltage is
-15% out of tolerance.
RESET Output
A µP’s reset input starts the µP in a known state. The
MAX6469–MAX6484 µP supervisory circuits assert
RESET during power-up, power-down, and brownout
conditions. RESET asserts when the input voltage is
below the undervoltage lockout threshold. RESET
asserts when V
OUT
is below the reset threshold and
remains asserted for at least the minimum selected reset
timeout period (t
RP
, Table 3) after V
IN
rises above the
undervoltage lockout threshold and V
OUT
rises above
the reset threshold. RESET asserts when MR is pulled
low (MAX6471–MAX6474/MAX6479–MAX6482). RESET
asserts when SHDN is pulled low (MAX6469/
MAX6470/MAX6473–MAX6478/MAX6481–MAX6484).
Shutdown
(MAX6469/MAX6470/MAX6473–MAX6478/MAX6481–
MAX6484 only)
SHDN allows the regulator to shut down, thereby reduc-
ing the total I
IN
consumption of the device. SHDN pro-
vides a digitally controlled active-low shutdown. In
shutdown mode, the pass transistor, control circuit, and
reference turn off to reduce the supply current to below
0.1µA. Connect SHDN to IN for normal operation.
Manual Reset Input
(MAX6471–MAX6474/MAX6479–MAX6482 only)
Many µP-based products require manual reset capabil-
ity, allowing the operator, a test technician, or external
logic circuitry to initiate a reset. A logic low on MR
asserts reset while the regulator output voltage is still
within tolerance.
Reset remains asserted while MR is low and for the
reset timeout period (t
RP
) after MR returns high. The
MR input has an internal pullup of 40kΩ (typ) to OUT.
MR can be driven with TTL/CMOS logic levels or with
open-drain/collector outputs. Connect a normally open
switch from MR to GND to create a manual reset func-
tion; external debounce circuitry is not required. If MR
is driven from long cables or the device is used in a
noisy environment, connect a 0.1µF capacitor from MR
to GND to provide additional noise immunity.
Feedback Input
(MAX6475/MAX6476/MAX6483/MAX6484 only)
The feedback input (FB) connects to an internal resistor-
divider network ( Functional Diagram ). FB is not internally
connected to V
OUT
, and as a result can be used to
MAX6469–MAX6472
MAX6477–MAX6480
R1
R2
C
OUT
MANUAL
RESET
GND
IN
OUT
SET
2.5V TO 5.5V
(MR)
( ) ARE FOR MAX6471/MAX6472/MAX6479/MAX6480 ONLY
Figure 1. Adjustable Output Voltage Configuration