MAX16999 데이터 시트보기 (PDF) - Maxim Integrated
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MAX16999 Datasheet PDF : 11 Pages
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MAX16999
Ultra-Low Output Voltage, Low-Quiescent-Current
Linear Regulator for High-Temperature Applications
Detailed Description
The MAX16999 is a low-quiescent-current linear regula-
tor designed for applications requiring high reliability. This
device can supply loads up to 100mA and is available in
factory-preset output voltages from 0.5V to 3.3V (see the
Selector Guide). As illustrated in Figure 1, the MAX16999
linear regulator consists of a reference, an error amplifier,
a p-channel MOSFET pass transistor, and an internal
feedback voltage-divider. A power-on reset section signals
if the output voltage has come out of regulation. The reset
signal timeout is defined by the charging time of an exter-
nal capacitor attached to CRES.
To increase system reliability, the MAX16999 features a
POR reset timeout along with overcurrent and overtem-
perature protection. A power-on reset timeout guarantees
startup even with a faulty timing capacitor. Parameters
are guaranteed up to +125°C junction temperature. The
EN signal is latched in its last state even if the signal line
becomes disconnected.
Logic-Controlled Enable
The MAX16999 provides a logic-enable input (EN). For
normal operation drive EN to logic-high. When EN is driv-
en high, the linear regulator starts to regulate by increas-
ing the output voltage up to the preset value. To disable
the device, drive EN low to set OUT to high impedance—
this enables a pulldown current from CRES to discharge
the capacitor. Once the device is disabled, the input sup-
ply current reduces to less than 0.3μA. The EN input is
latched into its last state by a 120kΩ internal resistor. To
change state, the latch needs to be overridden. When EN
is low, the RESET output is high impedance.
POR Timer
Once the output voltage rises above the threshold
VRES, two internal timers are simultaneously activated.
The reset timer is realized by means of a pullup current
ICRES,UP that charges the capacitor connected to CRES.
As soon as the voltage on CRES rises above the threshold
of 600mV (typ), RESET goes high impedance.
The internal reset timer is set by the value of the external
capacitance (CCRES). Calculate the reset time using the
following formula:
t POR_DELAY
=
C CRES
x
60
x
10 3
V
A
where CCRES is in Farads and the delay to GND is given
in seconds.
The second timer is an internal fault timer and ensures the
regulator does not stay off indefinitely because of a fault
on CRES such as a short. The fault timer runs for a maxi-
mum of 100ms. A logic block monitors both internal timers
to determine the shortest timeout. If the first timeout is the
fault timer, the pullup current is switched off in order to
avoid unnecessary current consumption and a resistive
pulldown is also activated. If tPOR_DELAY exceeds 100ms
(typ) the fault timer defines the timeout behavior.
Current Limit
Once the output voltage reaches regulation, the output
current is limited to 150mA (typ). If the output current
exceeds the current limit, the output voltage begins to
decrease.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipa-
tion in the MAX16999. When the junction temperature
exceeds +165°C, a thermal sensor turns off the pass tran-
sistor, allowing the IC to cool. The thermal sensor turns
the pass transistor on again after the junction temperature
cools by 15°C, resulting in a pulsed output during con-
tinuous thermal-overload conditions. Thermal-overload
protection safeguards the MAX16999 in the event of fault
conditions. For continuous operation, do not exceed the
absolute maximum junctiontemperature rating of +150°C.
Table 1 lists maximum DC output currents (milliamps) that
are allowed for operation at TA = +125°C without causing
thermal shutdown of the MAX16999.
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