LINEAR TECHNOLOGY LT3582 Technical data
L DESIGN FEATURES
LOAD CURRENT (mA)
0.1
35
EFFICIENCY (%)
POWER LOSS (mW)
45
350
300
250
200
150
100
50
0
55
65
75
85
95
1 10 100
V
OUTP
V
OUTN
LT3582
V
IN
SWP
CAPP
V
NEG
–12V
85mA
CAPP
V
PP
SDA
SCL
CA
GND
SWN
SWN
V
OUTN
I2C
INTERFACE
V
OUTP
SHDN
INPUT
4.5V TO 5.5V
V
POS
12V
80mA
L1
6.8µH
D1
C2
4.7µF
C6
10nF
C5
10nF
RAMPNRAMPP
C3
C1
4.7µF
C4 1µF
D2
L2 6.8µH
OPTIONAL ON
LT3582-12
REG0/OTP0 = B0h
REG1/OTP1 = D8h
REG2/OTP2 = 03h
D1-D2: DIODES INC. B0540WS-7
L1-L2: COILCRAFT XPL2010-682
C1: 4.7µF, 6.3V, X5R, 0805
C2: 4.7µF, 16V, X5R, 0805
C3: 1s 4.7µF OR 2s 4.7µF OR 10µF
16V, X5R, 0805
C4: 1µF, 16V, X5R, 0603
C5-C6: 10nF, 0603
Space-Saving, Dual Output
DC/DC Converter Yields Plus/Minus
Voltage Outputs with (Optional)
I2C Programming
Introduction
There are many applications that require both positive and negative DC
voltages generated from a single input
supply. The LT3582 is a highly integrated dual switching regulator that
produces positive and negative voltages for AMOLEDs, CCDs, op amps, and
general ±5V and ±12V supplies. The
LT3582 uses a novel control scheme
resulting in low output voltage ripple
and high conversion efficiency over a
wide load current range. The total solution size is very small due to the tiny
3mm × 3mm 16-pin QFN package, integrated feedback resistors, integrated
loop compensation networks and the
single-inductor negative output topology (see Figure 1).
The LT3582-5 and LT3582-12 are
factory configured for accurate ±5V
and ±12V outputs respectively, making
it easy to squeeze a high performance
solution into a small space. For other
voltage combinations, the LT3582
offers I2C digitally programmable out-
puts of 3.2V to 12.775V and –1.2V to
–13.95V that can be made permanent
with on-chip OTP (One-Time-Programming) memory. The input supply range
is 2.55V to 5.5V and switch current
limits are 350mA and 600mA for the
boost and inverting switches, respectively. In addition, the LT3582 features
power up sequencing with ramping
from ground to regulation, power down
discharging, positive output disconnect and soft-start.
Accurate Output Voltages
without External Feedback
Resistors
The LT3582 series uses integrated
feedback resistors to select the output
voltages. The LT3582-5 and LT358212 are pre-configured at the factory
for ±5V and ±12V outputs with ±1.5%
accuracy or better. The LT3582 allows
other output voltages to be configured
using the I2C interface. There are
nine bits to configure the positive
output voltage from 3.2V to 12.775V
in 25mV steps and another eight bits
to configure the negative output voltage from –1.2V to –13.95V in 50mV
steps. Default settings can be stored
by Mathew Wich
Figure 1. Dual output supplies
in a small board footprint
in One-Time-Programmable memory
and, if left unlocked, the voltages can
be subsequently changed on the fly
using the I2C interface.
Great Performance
Includes Low Ripple and
High Efficiency Across
the Load Range
The LT3582 is among several novel
parts from Linear Technology that
modulate peak switch current and
switch off time to reduce ripple and
improve light load efficiency (also see
the LT3494, LT3495, LT8410 and
22
Figure 2. ±12V supplies from a single 5V input
Linear Technology Magazine • June 2009
DESIGN FEATURES L
L1
D1
SWP
C1
V
OUTP
C3
V
IN
C2
CAPP
LT3582
SERIES
DISCONNECT
CONTROL
LOAD
V
VOUTP
10mV/DIV
AC COUPLED
V
SWP
5V/DIV
I
L2
0.2A/DIV
5µs/DIV
CAPP
2V/DIV
I
L2
0.2A/DIV
V
RAMPP
0.2V/DIV
V
OUTP
2V/DIV
1ms/DIV
V
VOUTP
5V/DIV
V
VOUTN
5V/DIV
V
RAMPP
0.5V/DIV
V
RAMPN
0.5V/DIV
5ms/DIV
RAMPN
RAMPP
V
RAMPP
1V/DIV
V
RAMPN
1V/DIV
V
VOUTN
5V/DIV
V
VOUTP
5V/DIV
5ms/DIV
V
VOUTP
10mV/DIV
AC COUPLED
V
SWP
5V/DIV
I
L2
0.2A/DIV
200ns/DIV
V
VOUTP
10mV/DIV
AC COUPLED
V
SWP
5V/DIV
I
L2
0.2A/DIV
2µs/DIV
Figure 3. Switching waveforms at 1mA load
for the boost application shown in Figure 2
Figure 6. Power-Up Sequencing
(V
followed by V
OUTP
OUTN
)
LT8415). Under light load conditions,
the LT3582 chooses an optimum
combination of frequency and peak
switch current to improve efficiency
while moderating the output ripple.
Figures 3–5 show how the frequency
and peak inductor current vary from
light to heavy loads. At very light loads
(typically < 1mA), peak switching
currents are dramatically reduced to
further reduce ripple when frequencies
are in the audio band.
Figure 8. V
Linear Technology Magazine • June 2009
soft-start ramping from ground
OUTP
Figure 4. Switching waveforms at 10mA load
for the boost application shown in Figure 2
Figure 7. Output disconnect PMOS
Adjustable Power-Up
Sequencing and
Soft-Start Options
The LT3582 has digitally configurable
power-up sequencing that forces the
outputs to power up in one of four
ways:
q
V
ramps up first, followed by
OUTP
V
(shown in figure 6)
OUTN
q
V
ramps up first, followed by
OUTN
V
OUTP
q
both outputs ramp up
simultaneously
q
both outputs are disabled
The LT3582-5 and LT3582-12 are
factory configured for both outputs to
ramp up simultaneously.
The power-up ramp rates of the output voltages are also adjustable. Slowly
ramping the outputs (also known as
soft-start) reduces what would otherwise be high peak switching currents
during start-up. Without soft-start,
high start-up current is inherent in
switching regulators due to V
far from its final value. The regulator
tries to charge the output capacitors
OUT
Figure 5. Switching waveforms at 100mA load
for the boost application shown in Figure 2
as quickly as possible, which results
in large peak currents.
The output voltage ramp rates are
proportional to the ramp rates of the
RAMPP and RAMPN pin voltages. Upon
chip enable, a programmable current
(1µA, 2µA, 4µA or 8µA) linearly charges
capacitors (typically about 10nF)
connected to the RAMPP and RAMPN
pins. By varying the capacitor sizes
or charging currents, a wide range
of output voltage ramp rates can be
accommodated.
being
Figure 9. Power-down discharge waveforms
23
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