SS8014-18GTR SSC [Silicon Standard Corp.], SS8014-18GTR Datasheet - Page 8

• Manufacturer Part Number: SS8014-18GTR
• Description: 300mA Low-Noise LDO Regulators
• Manufacturer: SSC [Silicon Standard Corp.]

1/12/2005 Rev.2.10
Over Current Protection
The SS8014 uses a current mirror to monitor the output
current. A small portion of the PMOS output transistor’s
current is mirrored onto a resistor such that the voltage
across this resistor is proportional to the output current.
This voltage is compared against the 1.25V reference.
Once the output current exceeds the limit, the PMOS
output transistor is turned off. Once the output transistor is
turned off, the current monitoring voltage decreases to
zero, and the output PMOS is turned on again. If the over
current condition persist, the over current protection cir-
cuit will be triggered again. Thus, when the output is
shorted to ground, the output current will be alternating
between 0 and the over current limit. The typical over
current limit of the SS8014 is set to 350mA. Note that
the input bypass capacitor of 1µF must be used in this
case to filter out the input voltage spike caused by the
surge current due to the inductive effect of the package
pin and the printed circuit board’s routing wire. Otherwise,
the actual voltage at the IN pin may exceed the absolute
maximum rating.
Over Temperature Protection
To prevent abnormal temperature from occurring, the
SS8014 has a built-in temperature monitoring circuit.
When it detects the temperature is above 150
output transistor is turned off. When the IC is cooled
down to below 135
this way, the SS8014 will be protected against abnor-
mal junction temperature during operation.
Shutdown Mode
When the SHDN pin is connected a logic low voltage,
the SS8014 enters shutdown mode. All the analog cir-
cuits are turned off completely, which reduces the current
consumption to only the leakage current. The output is
disconnected from the input. When the output has no load
at all, the output voltage will be discharged to ground
through the internal resistor voltage divider.
Operating Region and Power Dissipation
Since the SS8014 is a linear regulator, its power dissi-
pation is always given by P = I
maximum power dissipation is given by:
where (T
SS8014 die and the ambient air, and
resistance of the chosen package to the ambient air. For
surface mount devices, heat sinking is accomplished by
using the heat spreading capabilities of the PC board and
its copper traces. In the case of a SOT23-5 package, the
thermal resistance is typically 240
ommended Minimum Footprint) [Figure 2]. Refer to Fig-
ure 3 for the SS8014 valid operating region (Safe Op-
erating Area) & refer to Figure 4 for the maximum power
dissipation of the SOT-23-5.
P
DMAX
= (T
J
– T
J
– T
A
) is the temperature difference between the
A
)/
o
JA
C, the output is turned on again. In
= (150-25) / 240 = 520mW
OUT
o
C/Watt. (See Rec-
(V
www.SiliconStandard.com
JA
IN
, is the thermal
– V
OUT
o
C, the
). The
The die attachment area of the SS8014’s lead frame is
connected to pin 2, which is the GND pin. Therefore, the
GND pin of SS8014 can carry away the heat of the
SS8014 die very effectively. To improve the power
dissipation, connect the GND pin to ground using a large
ground plane near the GND pin.
Applications Information
Capacitor Selection and Regulator Stability
Normally, use a 1µF capacitor on the input and a 1µF
capacitor on the output of the SS8014. Larger input
capacitor values and lower ESR provide better sup-
ply-noise rejection and transient response. A higher-
value input capacitor (10µF) may be necessary if large,
fast transients are anticipated and the device is located
several inches from the power source. For stable opera-
tion over the full temperature range, with load currents up
to 120mA, a minimum of 1µF is recommended.
Power-Supply
Sources Other than Batteries
The SS8014 is designed to deliver low dropout volt-
ages and low quiescent currents in battery powered sys-
tems. Power-supply rejection is 57dB at low frequencies
as the frequency increases above 20 kHz; the output
capacitor is the major contributor to the rejection of
power-supply noise.
When operating from sources other than batteries, im-
prove supply-noise rejection and transient response by
increasing the values of the input and output capacitors,
and using passive filtering techniques.
Load Transient Considerations
The SS8014 load-transient response graphs show two
components of the output response: a DC shift of the
output voltage due to the different load currents, and the
transient response. Typical overshoot for step changes in
the load current from 0mA to 100mA is 12mV. Increasing
the output capacitor's value and decreasing its ESR at-
tenuates transient spikes.
Input-Output (Dropout) Voltage
A regulator's minimum input-output voltage differential (or
dropout voltage) determines the lowest usable supply
voltage. In battery-powered systems, this will determine
the useful end-of-life battery voltage. Because the
SS8014 uses a P-channel MOSFET pass transistor, the
dropout voltage is a function of R
load current.
Rejection
and
DS(ON)
SS8014-xxG
Operation
multiplied by the
8 of 10
from