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LT1121HVIS8#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
LT1121/LT1121-3.3/LT1121-5
10
1121fg
APPLICATIONS INFORMATION
Table 1. N8 Package*
COPPER AREA
THERMAL RESISTANCE
JUNCTION TO AMBIENTTOPSIDE BACKSIDE BOARD AREA
2500 sq mm 2500 sq mm 2500 sq mm 80ºC/W
1000 sq mm 2500 sq mm 2500 sq mm 80ºC/W
225 sq mm 2500 sq mm 2500 sq mm 85ºC/W
1000 sq mm 1000 sq mm 1000 sq mm 91ºC/W
* Device is mounted on topside. Leads are through hole and are
soldered to both sides of board.
NC leads were connected to the ground plane.
Table 2. S8 Package
COPPER AREA
THERMAL RESISTANCE
JUNCTION TO AMBIENT
TOPSIDE* BACKSIDE BOARD AREA
2500 sq mm 2500 sq mm 2500 sq mm 120ºC/W
1000 sq mm 2500 sq mm 2500 sq mm 120ºC/W
225 sq mm 2500 sq mm 2500 sq mm 125ºC/W
100 sq mm 1000 sq mm 1000 sq mm 131ºC/W
* Device is mounted on topside.
Table 3. AS8 Package*
COPPER AREA
THERMAL RESISTANCE
JUNCTION TO AMBIENT
TOPSIDE** BACKSIDE BOARD AREA
2500 sq mm 2500 sq mm 2500 sq mm 60ºC/W
1000 sq mm 2500 sq mm 2500 sq mm 60ºC/W
225 sq mm 2500 sq mm 2500 sq mm 68ºC/W
100 sq mm 2500 sq mm 2500 sq mm 74ºC/W
* Pins 3, 6 and 7 are ground.
** Device is mounted on topside.
Table 4. SOT-223 Package
(Thermal Resistance Junction-to-Tab 20ºC/W)
COPPER AREA
THERMAL RESISTANCE
JUNCTION TO AMBIENT
TOPSIDE* BACKSIDE BOARD AREA
2500 sq mm 2500 sq mm 2500 sq mm 50ºC/W
1000 sq mm 2500 sq mm 2500 sq mm 50ºC/W
225 sq mm 2500 sq mm 2500 sq mm 58ºC/W
100 sq mm 2500 sq mm 2500 sq mm 64ºC/W
1000 sq mm 2500 sq mm 1000 sq mm 57ºC/W
1000 sq mm 0 1000 sq mm 60ºC/W
* Tab of device attached to topside copper.
Table 5. TO-92 Package THERMAL RESISTANCE
Package alone 220ºC/W
Package soldered into PC board with plated through
holes only
175ºC/W
Package soldered into PC board with 1/4 sq. inch of
copper trace per lead
145ºC/W
Package soldered into PC board with plated through
holes in board, no extra copper trace, and a clip-on type
heat sink: Thermalloy type 2224B
160ºC/W
Aavid type 5754 135ºC/W
Calculating Junction Temperature
Example: given an output voltage of 3.3V, an input voltage
range of 4.5V to 7V, an output current range of 0mA to
100mA, and a maximum ambient temperature of 50°C,
what will the maximum junction temperature be?
Power dissipated by the device will be equal to:
I
OUT MAX
• (V
IN MAX
– V
OUT
) + (I
GND
• V
IN
)
where
, I
OUT MAX
= 100mA
V
IN MAX
= 7V
I
GND
at (I
OUT
= 100mA, V
IN
= 7V) = 5mA
so
, P = 100mA • (7V – 3.3V) + (5mA • 7V)
= 0.405W
If we use an SOT-223 package, then the thermal resistance
will be in the range of 50°C/W to 65°C/W depending on
copper area. So the junction temperature rise above ambi-
ent will be less than or equal to:
0.405W • 60°C/W = 24°C
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
T
JMAX
= 50°C + 24°C = 74°C
Output Capacitance and Transient Performance
The LT1121 is designed to be stable with a wide range of
output capacitors. The minimum recommended value is 1µF
with an ESR of 3Ω or less. For applications where space
is very limited, capacitors as low as 0.33µF can be used if
combined with a small series resistor. Assuming that the
ESR of the capacitor is low (ceramic)
the suggested series
LT1121/LT1121-3.3/LT1121-5
11
1121fg
APPLICATIONS INFORMATION
resistor is shown in Table 6. The LT1121 is a micropower
device and output transient response will be a function of
output capacitance. See the Transient Response curves
in the Typical Performance Characteristics. Larger values
of output capacitance will decrease the peak deviations
and provide improved output transient response. Bypass
capacitors, used to decouple individual components
powered by the LT1121, will increase the effective value
of
the output capacitor.
Protection Features
The LT1121 incorporates several protection features
which make it ideal for use in battery-powered circuits.
In addition to the normal protection features associated
with monolithic regulators, such as current limiting and
thermal limiting, the device is protected against reverse
input voltages, reverse output voltages, and reverse volt-
ages from output to input.
Current limit protection and thermal overload protection
are intended
to protect the device against current overload
conditions at the output of the device. For normal opera-
tion, the junction temperature should not exceed 125°C.
The input of the device will withstand reverse voltages of
30V. Current flow into the device will be limited to less
than 1mA (typically less than 100µA) and no negative
voltage will appear at the output. The device will protect
both
itself and the load. This provides protection against
batteries that can be plugged in backwards.
For fixed voltage versions of the device, the output can
be pulled below ground without damaging the device. If
the input is open circuit or grounded the output can be
pulled below ground by 20V. The output will act like an
open circuit, no current will flow out of the pin. If
the input
is powered by a voltage source, the output will source the
Table 6. Suggested Series Resistor Values
OUTPUT CAPACITANCE SUGGESTED SERIES RESISTOR
0.33µF
2Ω
0.47µF
1Ω
0.68µF
1Ω
>1µF None Needed
short-circuit current of the device and will protect itself by
thermal limiting. For the adjustable version of the device,
the output pin is internally clamped at one diode drop
below ground. Reverse current for the adjustable device
must be limited to 5mA.
In circuits where a backup battery is
required, several
different input/output conditions can occur. The output
voltage may be held up while the input is either pulled
to ground, pulled to some intermediate voltage, or is left
open circuit. Current flow back into the output will vary
depending on the conditions. Many battery-powered cir-
cuits incorporate some form of power management. The
following information will help optimize battery life. Table
7 summarizes the
following information.
The reverse output current will follow the curve in Figure
2 when the input pin is pulled to ground. This current
flows through the output pin to ground. The state of the
shutdown pin will have no effect on output current when
the input pin is pulled to ground.
In some applications it may be necessary to leave the
input to the LT1121 unconnected when
the output is held
high. This can happen when the LT1121 is powered from
a rectified AC source. If the AC source is removed, then
the input of the LT1121 is effectively left floating. The
reverse output current also follows the curve in Figure 2
if the input pin is left open. The state of the shutdown pin
will have no effect on the reverse output current
when the
input pin is floating.
Figure 2. Reverse Output Current
OUTPUT VOLTAGE (V)
0
OUTPUT PIN CURRENT (μA)
100
90
80
70
60
50
40
30
20
10
0
8
1121• F02
2
4
6
10
1 3 5 7 9
T
J
= 25°C
V
IN
< V
OUT
CURRENT FLOWS
INTO OUTPUT PIN
TO GROUND
LT1121-3.3
LT1121
(V
OUT
= V
ADJ
)
LT1121-5
LT1121/LT1121-3.3/LT1121-5
12
1121fg
APPLICATIONS INFORMATION
Table 7. Fault Conditions
INPUT PIN SHDN PIN OUTPUT PIN
<V
OUT
(Nominal) Open (Hi) Forced to V
OUT
(Nominal) Reverse Output Current ≈ 15µA (See Figure 2)
Input Current ≈ 1µA (See Figure 3)
<V
OUT
(Nominal) Grounded Forced to V
OUT
(Nominal) Reverse Output Current ≈ 15µA (See Figure 2)
Input Current ≈ 1µA (See Figure 3)
Open Open (Hi) Forced to V
OUT
(Nominal) Reverse Output Current ≈ 15µA (See Figure 2)
Open Grounded Forced
to V
OUT
(Nominal) Reverse Output Current ≈ 15µA (See Figure 2)
≤0.8V Open (Hi) ≤0V Output Current = 0
≤0.8V Grounded ≤0V Output Current = 0
>1.5V Open (Hi) ≤0V Output Current = Short-Circuit Current
–30V < V
IN
< 30V Grounded ≤0V Output Current = 0
When the input of the LT1121 is forced to a voltage below
its nominal output voltage and its output is held high, the
reverse output current will still follow the
curve in Figure
2. This condition can occur if the input of the LT1121 is
connected to a discharged (low voltage) battery and the
output is held up by either a backup battery or by a second
regulator circuit. When the input pin is forced below the
output pin or the output pin is pulled above the input pin,
the input current will typically drop to less
than 2µA (see
Figure 3). The state of the shutdown pin will have no effect
on the reverse output current when the output is pulled
above the input.
Figure 3. Input Current
INPUT VOLTAGE (V)
0
INPUT CURRENT (μA)
5
4
3
2
1
0
4
1121 F03
1
2
3
5
V
OUT
= 3.3V (LT1121-3.3)
V
OUT
= 5V (LT1121-5)
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

LT1121HVIS8#TRPBF

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Buy LT1121HVIS8#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
LDO Voltage Regulators HV Adj Low Dropout uP Regulator
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