lt3022emse Linear Technology Corporation, lt3022emse Datasheet - Page 11

• Manufacturer Part Number: lt3022emse
• Description: Lt3022 1a, 0.9v To 10v, Very Low Dropout Linear Regulator Features
• Manufacturer: Linear Technology Corporation

applicaTions inForMaTion
No-Load/Light-Load Recovery
A possible transient load step that occurs is where the
output current changes from its maximum level to zero
current or a very small load current. The output voltage
responds by overshooting until the regulator lowers the
amount of current it delivers to the new level. The regulator
loop response time and the amount of output capacitance
control the amount of overshoot. Once the regulator has
decreased its output current, the current provided by
the resistor divider (which sets V
remaining to discharge the output capacitor from the level
to which it overshot. The amount of time it takes for the
output voltage to recover easily extends to milliseconds
with minimum divider current and many microfarads of
output capacitance.
To eliminate this problem, the LT3022 incorporates a
no-load or light load recovery circuit. This circuit is a
voltage-controlled current sink that significantly improves
the light load transient response time by discharging the
output capacitor quickly and then turning off. The current
sink turns on when the output voltage exceeds 6.5% of
the nominal output voltage. The current sink level is then
proportional to the overdrive above the threshold up to a
maximum of about 24mA. Consult the curve in the Typical
Performance Characteristics for the No-Load Recovery
Threshold.
Figure 4. Noise Resulting from Tapping on a Ceramic Capacitor
1mV/DIV
V
C
I
LOAD
OUT
OUT
= 1.3V
= 10µF
= 0
1ms/DIV
OUT
) is the only current
3022 F04
If external circuitry forces the output above the no-load
recovery circuit’s threshold, the current sink turns on in
an attempt to restore the output voltage to nominal. The
current sink remains on until the external circuitry releases
the output. However, if the external circuitry pulls the output
voltage above the input voltage or the input falls below the
output, the LT3022 turns the current sink off and shuts
down the bias current/reference generator circuitry.
Thermal Considerations
The LT3022’s maximum rated junction temperature of
125°C limits its power handling capability. Two components
comprise the power dissipation of the device:
1. Output current multiplied by the input-to-output voltage
2. GND pin current multiplied by the input voltage:
GND pin current is found by examining the GND pin current
curves in the Typical Performance Characteristics. Power
dissipation equals the sum of the two components listed.
The LT3022’s internal thermal limiting (with hysteresis)
protects the device during overload conditions. For nor-
mal continuous conditions, do not exceed the maximum
junction temperature rating of 125°C. Carefully consider
all sources of thermal resistance from junction to ambi-
ent including other heat sources mounted in proximity to
the LT3022.
The underside of the LT3022 DHC and MSE packages
has exposed metal from the lead frame to the die attach-
ment. Heat transfers directly from the die junction to the
printed circuit board metal, allowing maximum junction
temperature control. The dual-in-line pin arrangement
allows metal to extend beyond the ends of the package
on the topside (component side) of a PCB. Connect this
metal to GND on the PCB. The multiple IN and OUT pins
of the LT3022 also assist in spreading heat to the PCB.
Copper board stiffeners and plated throughholes can also
be used to spread the heat generated by power devices.
differential:
(I
(I
LOAD
GND
) • (V
) • (V
IN
IN
)
– V
OUT
) and
LT3022

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