APL5910 Anpec Electronics Coropration, APL5910 Datasheet - Page 10

• Manufacturer Part Number: APL5910
• Description: 1A, Ultra Low Dropout (0.12v Typical) Linear Regulator
• Manufacturer: Anpec Electronics Coropration

Function Description
Thermal Shutdown
APL5910
Copyright
Rev. A.2 - Aug., 2008
Power-On-Reset
A Power-On-Reset (POR) circuit monitors both of supply
voltages on VCNTL and VIN pins to prevent wrong logic
controls. The POR function initiates a soft-start process
after both of the supply voltages exceed their rising POR
voltage thresholds during powering on. The POR func-
tion also pulls low the POK voltage regardless of the
output status when one of the supply voltages falls below
its falling POR voltage threshold.
Internal Soft-Start
An internal soft-start function controls rise rate of the out-
put voltage to limit the current surge during start-up. The
typical soft-start interval is about 0.6ms.
Output Voltage Regulation
An error amplifier working with a temperature-compen-
sated 0.8V reference and an output NMOS regulates out-
put to the preset voltage. The error amplifier is designed
with high bandwidth and DC gain provides very fast tran-
sient response and less load regulation. It compares the
reference with the feedback voltage and amplifies the dif-
ference to drive the output NMOS which provides load
current from VIN to VOUT.
Current-Limit Protection
The APL5910 monitors the current flowing through the
output NMOS and limits the maximum current to prevent
load and APL5910 from damages during current over-
load conditions.
Short Current-Limit Protection
The short current-limit function reduces the current-limit
level down to 0.4A (typical) when the voltage on FB pin
falls below 0.2V (typical) during current overload or short-
circuit conditions.
The short current-limit function is disabled for success-
ful start-up during soft-start interval.
A thermal shutdown circuit limits the junction tempera-
ture of APL5910. When the junction temperature exceeds
+170
lowing the device to cool down. The regulator regulates
the output again through initiation of a new soft-start pro-
cess after the junction temperature cools by 50
o
C, a thermal sensor turns off the output NMOS, al-
ANPEC Electronics Corp.
o
C,
10
resulting in a pulsed output during continuous thermal
overload conditions. The thermal shutdown is designed
with a 50
perature during continuous thermal overload conditions,
extending lifetime of the device.
For normal operation, the device power dissipation should
be externally limited so that junction temperatures will
not exceed +125 C.
Enable Control
The APL5910 has a dedicated enable pin (EN). A logic
low signal applied to this pin shuts down the output. Fol-
lowing a shutdown, a logic high signal re-enables the
output through initiation of a new soft-start cycle. When
left open, this pin is pulled up by an internal current source
(5 A typical) to enable normal operation. It’ s not neces-
sary to use an external transistor to save cost.
Power-OK and Delay
The APL5910 indicates the status of the output voltage by
monitoring the feedback voltage (V
V
old (V
end of the delay time, the IC turns off the internal NMOS of
the POK to indicate that the output is ok. As the V
and reaches the falling Power-OK voltage threshold, the
IC turns on the NMOS of the POK (after a debounce time
of 10 s typical).
FB
rises and reaches the rising Power-OK voltage thresh-
THPOK
o
C hysteresis to lower the average junction tem-
), an internal delay function starts to work. At the
FB
www.anpec.com.tw
) on FB pin. As the
FB
falls