Datasheet
SLVS167C − SEPTEMBER 1998 − REVISED − MAY 1999
22
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
SENSE connection
The SENSE terminal of fixed-output devices must be connected to the regulator output for proper functioning
of the regulator. Normally, this connection should be as short as possible; however, the connection can be made
near a critical circuit (remote sense) to improve performance at that point. Internally, SENSE connects to a
high-impedance wide-bandwidth amplifier through a resistor-divider network, and noise pickup feeds through
to the regulator output. It is essential to route the SENSE connection in such a way as to minimize/avoid noise
pickup. Adding an RC network between SENSE and OUT to filter noise is not recommended because it can
cause the regulator to oscillate.
external capacitor requirements
An input capacitor is not required; however, a ceramic bypass capacitor (0.047 pF to 0.1 µF) improves load
transient response and noise rejection when the TPS73HD3xx is located more than a few inches from the power
supply. A higher-capacitance electrolytic capacitor may be necessary if large (hundreds of milliamps) load
transients with fast rise times are anticipated.
As with most LDO regulators, the TPS73HD3xx requires an output capacitor for stability. A low-ESR 10-µF
solid-tantalum capacitor connected from the regulator output to ground is sufficient to ensure stability over the
full load range (see Figure 44). Adding high-frequency ceramic or film capacitors (such as power-supply bypass
capacitors for digital or analog ICs) can cause the regulator to become unstable unless the ESR of the tantalum
capacitor is less than 1.2 Ω over temperature. Capacitors with published ESR specifications such as the
AVX TPSD106M035R0300 and the Sprague 593D106X0035D2W work well because the maximum ESR at
25°C is 300 mΩ (typically, the ESR in solid-tantalum capacitors increases by a factor of 2 or less when the
temperature drops from 25°C to −40°C). Where component height and/or mounting area is a problem,
physically smaller, 10-µF devices can be screened for ESR. Figures 23 through 28 show the stable regions of
operation using different values of output capacitance with various values of ceramic load capacitance.
Due to the reduced stability range available when using output capacitors smaller than 10 µF, capacitors in this
range are not recommended. Larger capacitors provide a wider range of stability and better load transient
response. Because capacitor minimum ESR is seldom if ever specified, it may be necessary to add a 0.5-Ω to
1-Ω resistor in series with the capacitor and limit ESR to 1.5 Ω maximum. As shown in the CSR graphs
(Figures 23 through 28), minimum ESR is not a problem when using 10-µF or larger output capacitors.
Below is a partial listing of surface-mount capacitors usable with the TPS73HD3xx. This information, along with
the CSR graphs, is included to assist in selection of suitable capacitance for the user’s application. When
necessary to achieve low height requirements along with high output current and/or high ceramic load
capacitance, several higher ESR capacitors can be used in parallel to meet the guidelines above.