AS1364-BTDT-33-1k ams, AS1364-BTDT-33-1k Datasheet - Page 14

• Manufacturer Part Number: AS1364-BTDT-33-1k
• Description: Low Dropout Controllers - LDO
• Manufacturer: ams

Specifications of AS1364-BTDT-33-1k

• Rohs: yes
• Input Voltage Max: 5.5 V
• Output Voltage: 3.3 V
• Output Current: 1 A
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: TDFN-8
• Input Voltage Min: 2 V
• Minimum Operating Temperature: - 40 C

AS1364
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9.6 Explanation of Dynamic Specifications
9.6.1 Power Supply Rejection Ratio (PSRR)
Known also as Ripple Rejection, this specification measures the ability of the regulator to reject noise and ripple beyond DC. PSRR is a
summation of the individual rejections of the error amplifier, reference and AC leakage through the series pass transistor. The specification, in
the form of a typical attenuation plot with respect to frequency, shows up the gain bandwidth compromises forced upon the designer in low
quiescent current conditions. Generally:
Power supply rejection ratio is fixed by the internal design of the regulator. Additional rejection must be provided externally.
9.6.2 Output Capacitor ESR
The series regulator is a negative feedback amplifier, and as such is conditionally stable. The ESR of the output capacitor is usually used to
cancel one of the open loop poles of the error amplifier in order to produce a single pole response. Excessive ESR values may actually cause
instability by excessive changes to the closed loop unity gain frequency crossover point. The range of ESR values for stability is usually shown
either by a plot of stable ESR versus load current, or a limit statement in the datasheet.
Some ceramic capacitors exhibit large capacitance and ESR variations with temperature. Z5U and Y5V capacitors may be required to ensure
stability at temperatures below T
Larger output capacitor values (10µF max) help to reduce noise and improve load transient-response, stability and power-supply rejection.
9.6.3 Input Capacitor
An input capacitor at V
input pin V
of not more than 1cm from the V
at the input.
9.6.4 Noise
The regulator output is a DC voltage with noise superimposed on the output. The noise comes from three sources; the reference, the error
amplifier input stage, and the output voltage setting resistors. Noise is a random fluctuation and if not minimized in some applications, will
produce system problems.
9.6.5 Transient Response
The series regulator is a negative feedback system, and therefore any change at the output will take a finite time to be corrected by the error
loop. This “propagation time” is related to the bandwidth of the error loop. The initial response to an output transient comes from the output
capacitance, and during this time, ESR is the dominant mechanism causing voltage transients at the output. More generally:
Thus an initial +50mA change of output current will produce a -12mV transient when the ESR=240m. Remember to keep the ESR within
stability recommendations when reducing ESR by adding multiple parallel output capacitors.
After the initial ESR transient, there follows a voltage droop during the time that the LDO feedback loop takes to respond to the output change.
This drift is approx. linear in time and sums with the ESR contribution to make a total transient variation at the output of:
Where:
C
T = Propagation delay of the LDO
This shows why it is convenient to increase the output capacitor value for a better support for fast load changes. Of course the formula holds for
t < “propagation time”, so that a faster LDO needs a smaller cap at the load to achieve a similar transient response. For instance 50mA load
current step produces 50mV output drop if the LDO response is 1usec and the load cap is 1µF.
There is also a steady state error caused by the finite output impedance of the regulator. This is derived from the load regulation specification
discussed above.
www.austriamicrosystems.com
LOAD
is output capacitor
IN
and ground (capacitance value may be increased without limit subject to ESR limits). This capacitor must be located at a distance
V
TRANSIENT
IN
is required for stability. It is recommended that a 4.7µF capacitor be connected between the AS1364 power supply
V
PSSR =
IN
AMB
TRANSIENT
pin and returned to a clean analog ground. Any good quality ceramic, tantalum, or film capacitor may be used
=
= -10ºC. With X7R or X5R capacitors, a 4.7µF capacitor should be sufficient at all operating temperatures.
I
OUTPUT
20Log
=
V
--------------- -
V

I
OUT


OUTPUT
IN
R
ESR
dB using lower case
+

--------------- -
C
R
LOAD
T
ESR
Revision 1.8


Units are Volts, Amps, Ohms.
Units are Volts, Seconds, Farads, Ohms.

to indicate AC values
(EQ 16)
(EQ 17)
(EQ 15)
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