Datasheet

MINIMUM LOAD REQUIREMENTS
FB-PIN CONNECTION (ADJUSTABLE VERSION ONLY)
EXTERNAL CAPACITOR REQUIREMENTS
PROGRAMMING THE TPS767D301 ADJUSTABLE LDO REGULATOR
V
OUT
+ V
REF
ǒ
1)
R
1
R
2
Ǔ
(1)
TPS767D3xx
www.ti.com ......................................................................................................................................................... SLVS209H – JULY 1999 – REVISED AUGUST 2008
The TPS767D3xx family also features a shutdown mode that places the output in the high-impedance state
(essentially equal to the feedback-divider resistance) and reduces quiescent current to under 2 µ A. If the
shutdown feature is not used, EN should be tied to ground. Response to an enable transition is quick; regulated
output voltage is typically re-established in 120 µ s.
The TPS767D3xx family is stable even at zero load; no minimum load is required for operation.
The FB pin is an input pin to sense the output voltage and close the loop for the adjustable option. The output
voltage is sensed through a resistor divider network as is shown in Figure 26 to close the loop. Normally, this
connection should be as short as possible; however, the connection can be made near a critical circuit to
improve performance at that point. Internally, FB connects to a high-impedance, wide-bandwidth amplifier and
noise pickup feeds through to the regulator output. Routing the FB connection to minimize/avoid noise pickup is
essential. In fixed output options, this pin is not connected.
An input capacitor is not required; however, a ceramic bypass capacitor (0.047pF to 0.1 µ F) improves load
transient response and noise rejection when the TPS767D3xx 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.
Like all low dropout regulators, the TPS767D3xx requires an output capacitor connected between OUT and GND
to stabilize the internal control loop. The minimum recommended capacitance value is 10 µ F and the ESR
(equivalent series resistance) must be between 60m Ω and 1.5 Ω . Capacitor values of 10 µ F or larger are
acceptable, provided the ESR is less than 1.5 Ω . Solid tantalum electrolytic, aluminum electrolytic, and multilayer
ceramic capacitors are all suitable, provided they meet the requirements described previously.
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 previous guidelines.
The output voltage of the TPS767D301 adjustable regulator is programmed using an external resistor divider as
shown in Figure 26 . The output voltage is calculated using:
Resistors R
1
and R
2
should be chosen for approximately 40 µ A divider current. Lower-value resistors can be used
but offer no inherent advantage and waste more power. Higher values should be avoided as leakage currents at
FB increase the output voltage error.
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