LTC3025-3 LINER [Linear Technology], LTC3025-3 Datasheet - Page 12

• Manufacturer Part Number: LTC3025-3
• Description: 1A, 0.9V to 10V, Very Low Dropout Linear Regulator
• Manufacturer: LINER [Linear Technology]

LT3022/LT3022-1.2
LT3022-1.5/LT3022-1.8
APPLICATIONS INFORMATION
The LT3022 very low dropout linear regulator is capable of
0.9V input supply operation. It supplies 1A output current
and dropout voltage is typically 145mV. Quiescent current
is typically 400µA and drops to 7.5µA in shutdown. The
LT3022 incorporates several protection features, making
it ideal for use in battery-powered systems. The device
protects itself against reverse-input and reverse-output
voltages. If the output is held up by a backup battery when
the input is pulled to ground in a battery backup application,
the LT3022 behaves as if a diode is in series with its output,
preventing reverse current flow. In dual supply applications
where the regulator load is returned to a negative supply,
pulling the output below ground by as much as 10V does
not affect start-up or normal operation.
Adjustable Operation
The LT3022’s output voltage range is 0.2V to 9.5V. Figure 1
shows that the external resistor ratio sets output voltage.
The device regulates the output to maintain ADJ at 200mV
referred to ground. R1’s current equals 200mV/R1. R2’s
current is R1’s current minus the ADJ pin bias current.
The 30nA ADJ pin bias current flows out of the pin. Use
Figure 1’s formula to calculate output voltage. Given the
LT3022’s 1mA minimum load current requirement, Linear
Technology recommends choosing resistor divider values
to satisfy this requirement. A 200Ω R1 value sets a 1mA
resistor divider current. In shutdown, the output is 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.
Specifications 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 1A is typically 100µV
at V
Table 1 shows 1% resistor divider values for some common
output voltages with a resistor divider current equaling or
about 1mA.
12
200
ADJ
1 5
.
mV
= 200mV. At V
V
OUT
•
100
/200mV). For example, load regulation for
µV
=
750
OUT
µV
= 1.5V, load regulation is:
Table 1
Output Capacitance and Transient Response
The LT3022’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
capacitor of 10µF with an ESR of less than 0.1Ω to prevent
oscillations. The LT3022 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
large load current changes.
Ceramic capacitors require extra consideration. Manufac-
turers make ceramic capacitors with a variety of dielectrics;
each with a different behavior across temperature and
applied voltage. The most common dielectrics are Z5U,
Y5V, X5R and X7R. Z5U and Y5V dielectrics provide
high C-V products in a small package at low cost, but
exhibit strong voltage and temperature coefficients. X5R
and X7R dielectrics yield highly stable characteristics
V
OUT
+
V
V
I
OUTPUT RANGE: 0.2V TO 9.5V
0.9
1.0
1.2
1.5
1.8
2.5
3.3
ADJ
OUT
ADJ
(V)
: 30nA AT 25°C
: 200mV
: 200mV • (1 + R2/R1) – (I
V
IN
Figure 1. Adjustable Operation
IN
SHDN
LT3022
GND
R1 (Ω)
OUT
ADJ
200
187
200
200
187
187
200
ADJ
• R2)
R2
R1
3022 F01
R2 (Ω)
V
1000
1300
1500
2150
3090
OUT
698
750
3022fb