Datasheet

TLV1117LV Series
SBVS160A –MAY 2011– REVISED SEPTEMBER 2011 www.ti.com
APPLICATION INFORMATION
The TLV1117LV is a low quiescent current linear regulator designed for high current applications. Unlike typical
high current linear regulators, the TLV1117LV series consume significantly less quiescent current. These devices
deliver excellent line and load transient performance. The device is low noise, and exhibits a very good
power-supply rejection ratio (PSRR). As a result, it is ideal for high current applications that require very sensitive
power-supply rails.
This family of regulators offers both current limit and thermal protection. The operating junction temperature
range of the device is –40°C to +125°C.
Input and Output Capacitor Requirements
For stability, 1.0-μF ceramic capacitors are required at the output. Higher-valued capacitors improve transient
performance. X5R- and X7R-type ceramic capacitors are recommended because these capacitors have minimal
variation in value and equivalent series resistance (ESR) over temperature. Unlike traditional linear regulators
that need a minimum ESR for stability, the TLV1117LV series are ensured to be stable with no ESR. Therefore,
cost-effective ceramic capacitors can be used with these devices. Effective output capacitance that takes bias,
temperature, and aging effects into consideration must be greater than 0.5 μF to ensure stability of the device.
Although an input capacitor is not required for stability, it is good analog design practice to connect a 0.1-μF to
1.0-μF, low-ESR capacitor across the IN pin and GND pin of the regulator. This capacitor counteracts reactive
input sources and improves transient response, noise rejection, and ripple rejection. A higher-value capacitor
may be necessary if large, fast rise-time load transients are anticipated, or if the device is not located physically
close to the power source. If source impedance is greater than 2 Ω, a 0.1-μF input capacitor may also be
necessary to ensure stability.
Board Layout Recommendations to Improve PSRR and Noise Performance
Input and output capacitors should be placed as close to the device pins as possible. To improve characteristic
ac performance such as PSRR, output noise, and transient response, it is recommended that the board be
designed with separate ground planes for V
IN
and V
OUT
, with the ground plane connected only at the GND pin of
the device. In addition, the ground connection for the output capacitor should be connected directly to the GND
pin of the device. Higher value ESR capacitors may degrade PSRR performance.
Internal Current Limit
The TLV1117LV internal current limit helps to protect the regulator during fault conditions. During current limit,
the output sources a fixed amount of current that is largely independent of the output voltage. In such a case, the
output voltage is not regulated, and can be calculated by the formula: V
OUT
= I
LIMIT
× R
LOAD
. The PMOS pass
transistor dissipates (V
IN
– V
OUT
) × I
LIMIT
until thermal shutdown is triggered and the device turns off. As the
device cools down, it is turned on by the internal thermal shutdown circuit. If the fault condition continues, the
device cycles between current limit and thermal shutdown. See the Thermal Information section for more details
The PMOS pass element in the TLV1117LV device has a built-in body diode that conducts current when the
voltage at OUT exceeds the voltage at IN. This current is not limited; if extended reverse voltage operation is
anticipated, external limiting to 5% of the rated output current is recommended.
Dropout Voltage
The TLV1117LV uses a PMOS pass transistor to achieve low dropout. When (V
IN
– V
OUT
) is less than the
dropout voltage (V
DO
), the PMOS pass device is in the linear region of operation and the input-to-output
resistance is the R
DS(ON)
of the PMOS pass element. V
DO
scales approximately with output current because the
PMOS device behaves as a resistor in dropout.
As with any linear regulator, PSRR and transient response are degraded as (V
IN
– V
OUT
) approaches dropout
Transient Response
As with any regulator, increasing the size of the output capacitor reduces over-/undershoot magnitude.
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