zldo1117 Diodes, Inc., zldo1117 Datasheet - Page 6

• Manufacturer Part Number: zldo1117
• Description: 1a Low Dropout Positive Regulator 1.2v, 1.5v, 1.8v, 2.5v, 3.3v, 5.0v And Adjustable Outputs
• Manufacturer: Diodes, Inc.

Pin Descriptions
Applications information
The ZLDO1117 family of quasi-LDO regulators is easy to use. They are protected against short circuit and
thermal overloads. (see block diagram).
Thermal protection circuitry will shut down the regulator should the junction temperature exceed 150°C at the
sense point. The ZLDO1117 is pin compatible with similar ‘1117 regulators and offers extended temperature
range and improved regulation specifications.
Operation
The ZLDO1117 develops a 1.25V reference voltage between the output and the adjust terminal (see block
diagram). By placing a resistor between these two terminals, a constant current is caused to flow through R1
and down through R2. For fixed output variants Resistors R1 and R2 are internal.
Stability
The ZLDO1117 requires an output capacitor as part of the device frequency compensation. As part of its
improved performance over industry standard 1117 the ZLDO1117 is suitable for use with MLCC (Multi Layer
Ceramic Chip) capacitors. A minimum of 4.7µF ceramic X7R, 4.7µF tantalum, or 47 µF of aluminum electrolytic
is required. The ESR of the output capacitor should be less than 0.5Ω. Surface mount tantalum capacitors,
which have very low ESR, are available from several manufacturers. When using MLCC capacitors avoid the
use of Y5V dielectrics.
Load Regulation
For improved load regulation the ZLDO1117-ADJ should have the upper feedback resistor, R
close as possible to V
This helps reduce any parasitic resistance in series with the load.
Thermal Considerations
ZLDO1117 series regulators have internal thermal limiting circuitry designed to protect the device during
overload conditions. For continuous normal load conditions however, the maximum junction temperature rating
of 125°C must not be exceeded.
It is important to give careful consideration to all sources of thermal resistance from junction to ambient. For the
SOT-223 and TO-252 packages, which are designed to be surface mounted, additional heat sources mounted
near the device must also be considered. Heat sinking is accomplished using the heat spreading capability of
the PCB and its copper traces. The θ
respectively.
Issue 1
NAME
Adj (GND)
V
V
OUT
IN
I/O
O
I
I
OUT
Pin #
1
2
3
and the lower resistor, R2, connected as close as possible to the load GND return.
The input pin of regulator. Typically a large storage capacitor (0.05Ω ≤ ESR ≤
0.5Ω) is connected from this pin to ground to ensure that the input voltage
does not sag below the minimum dropout voltage during the load transient
response. This pin must always be 1.3V higher than V
device to regulate properly.
A resistor divider from this pin to the V
The output of the regulator. A minimum of 4.7µF capacitor (0.05Ω ≤ ESR ≤
voltage (Ground only for Fixed-Mode).
0.5Ω) must be connected from this pin to ground to insure stability. For
improved ac load response a larger output capacitor is recommended.
JC
(junction to tab) of the TO-252 and SOT223 are 12°C/W and 16°C/W
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6 of 12
FUNCTION
OUT
pin and ground sets the output
OUT
©
Diodes Incorporated
1
in order for the
, connected as
ZLDO1117
June 2009