LT3021EDH#PBF Linear Technology, LT3021EDH#PBF Datasheet - Page 10

• Manufacturer Part Number: LT3021EDH#PBF
• Description: IC REG LDO ADJ 500MA 16-DFN
• Manufacturer: Linear Technology

Specifications of LT3021EDH#PBF

• Regulator Topology: Positive Adjustable
• Voltage - Output: 0.2 ~ 9.5 V
• Voltage - Input: 0.9 ~ 10 V
• Voltage - Dropout (typical): 0.155V @ 500mA
• Number Of Regulators: 1
• Current - Output: 500mA
• Current - Limit (min): 550mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-DFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LT3021/LT3021-1.2/
LT3021-1.5/LT3021-1.8
APPLICATIONS INFORMATION
The LT3021 is a very low dropout linear regulator capable
of 1V input supply operation. Devices supply 500mA of
output current and dropout voltage is typically 155mV.
Quiescent current is typically 120μA and drops to 3μA in
shutdown. The LT3021 incorporates several protection
features, making it ideal for use in battery-powered sys-
tems. The device protects itself against reverse-input and
reverse-output voltages. In battery backup applications
where the output is held up by a backup battery when the
input is pulled to ground, the LT3021 acts as if a diode is
in series with its output which prevents reverse current
fl ow. In dual supply applications where the regulator
load is returned to a negative supply, the output can be
pulled below ground by as much as 10V without affecting
start-up or normal operation.
Adjustable Operation
The LT3021’s output voltage range is 0.2V to 9.5V. Figure
1 shows that the output voltage is set by the ratio of two
external resistors. The device regulates the output to main-
tain the ADJ pin voltage at 200mV referenced to ground.
The current in R1 equals 200mV/R1 and the current in R2
is the current in R1 minus the ADJ pin bias current. The
ADJ pin bias current of 20nA fl ows out of the pin. Use
the formula in Figure 1 to calculate output voltage. An R1
value of 20k sets the resistor divider current to 10μA. Note
that in shutdown the output is turned off and the divider
current is zero. Curves of ADJ Pin Voltage vs Temperature
and ADJ Pin Bias Current vs Temperature appear in the
Typical Performance Characteristics section.
Specifi cations for output voltages greater than 200mV
are proportional to the ratio of desired output voltage to
200mV; (V
an output current change of 1mA to 500mA is typically
10
OUT
/200mV). For example, load regulation for
Figure 1. Adjustable Operation
V
IN
V
V
I
OUTPUT RANGE = 0.2V TO 9.5V
ADJ
OUT
ADJ
= 20nA AT 25°C
= 200mV
= 200mV
IN
SHDN
LT3021
GND
( )
1 +
R2
R1
OUT
ADJ
– I
ADJ
(R2)
R2
R1
3021 F01
+
V
OUT
0.4mV at V
Output Capacitance and Transient Response
The LT3021’s design is stable with a wide range of output
capacitors, but is optimized for low ESR ceramic capacitors.
The output capacitor’s ESR affects stability, most notably
with small value capacitors. Use a minimum output ca-
pacitor of 3.3μF with an ESR of 0.2Ω or less to prevent
oscillations. The LT3021 is a low voltage device, and output
load transient response is a function of output capacitance.
Larger values of output capacitance decrease the peak
deviations and provide improved transient response for
larger load current changes. For output capacitor values
greater than 22μF a small feedforward capacitor with a
value of 300pF across the upper divider resistor (R2 in
Figure 1) is required. Under extremely low output current
conditions (I
oscillation (200Hz/8mV
A minimum load of 100μA is recommended to prevent
this instability.
Give extra consideration to the use of ceramic capacitors.
Manufacturers make ceramic capacitors with a variety of
dielectrics, each with a different behavior across tempera-
ture and applied voltage. The most common dielectrics
are Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics
provide high C-V products in a small package at low cost,
but exhibit strong voltage and temperature coeffi cients.
The X5R and X7R dielectrics yield highly stable character-
isitics and are more suitable for use as the output capacitor
at fractionally increased cost. The X5R and X7R dielectrics
both exhibit excellent voltage coeffi cient characteristics.
The X7R type works over a larger temperature range and
exhibits better temperature stability whereas X5R is less
expensive and is available in higher values. Figures 2 and
3 show voltage coeffi cient and temperature coeffi cient
comparisons between Y5V and X5R material.
Voltage and temperature coefficients are not the only
sources of problems. Some ceramic capacitors have a
piezoelectric response. A piezoelectric device generates
voltage across its terminals due to mechanical stress,
similar to the way a piezoelectric accelerometer or micro-
phone works. For a ceramic capacitor, the stress can be
induced by vibrations in the system or thermal transients.
The resulting voltages produced can cause appreciable
(1.5V/200mV) • (0.4mV) = 3mV
ADJ
LOAD
= 200mV. At V
< 30μA) a low frequency small signal
P-P
OUT
at 1.2V output) can occur.
= 1.5V, load regulation is:
3021fc