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PDF LT1534IS-1 Data sheet ( Hoja de datos )
| Número de pieza | LT1534IS-1 | |
| Descripción | Ultralow Noise 2A Switching Regulators | |
| Fabricantes | Linear Technology | |
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LT1534/LT1534-1
Ultralow Noise
2A Switching Regulators
FEATURES
s Greatly Reduced Conducted and Radiated EMI
s Low Switching Harmonic Content
s Independent Control of Switch Voltage and
Current Slew Rates
s 2A Current Limited Power Switch
s Regulates Positive and Negative Voltages
s 20kHz to 250kHz Oscillator Frequency
s Easily Synchronized to External Clock
s Wide Input Voltage Range: 2.7V to 23V
s Low Shutdown Current: 12µA Typical
s Easier Layout than with Conventional Switchers
U
APPLICATIO S
s Precision Instrumentation Systems
s Isolated Supplies for Industrial Automation
s Medical Instruments
s Wireless Communications
s Single Board Data Acquisition Systems
DESCRIPTIO
The LT®1534/LT1534-1 are a new class of switching regula-
tor designed to reduce conducted and radiated electromag-
netic interference (EMI). Ultralow noise and EMI are achieved
by providing user control of the output switch slew rates.
Voltage and current slew rates can be independently pro-
grammed to optimize switcher harmonic content versus
efficiency. The LT1534/LT1534-1 can reduce high frequency
harmonic power by as much as 40dB with only minor losses
in efficiency.
The LT1534/LT1534-1 utilize a current mode architecture
optimized for low noise boost topologies. The ICs include a
2A power switch along with all necessary oscillator, control
and protection circuitry. Unique error amp circuitry can
regulate both positive and negative voltages. The internal
oscillator may be synchronized to an external clock for more
accurate placement of switching harmonics. Protection fea-
tures include cycle-by-cycle current limit protection, under-
voltage lockout and thermal shutdown.
Low minimum supply voltage and low supply current during
shutdown make the LT1534/LT1534-1 well suited for por-
table applications. The LT1534/LT1534-1 are available in the
16-pin narrow SO package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
L1
3.3V 50µH
1N5817
A
L3
50µH B
+ CIN
15
33µF
6.3V
12
SHDN
VIN
2
COL
4
SYNC
3300pF
5 CT
16.9k 6 RT
PGND
LT1534-1
RVSL
3
14
13
RCSL
10Ω
L2
24k
24k
220pF
11
VC GND
6.8k 1,8,
15nF
9,16
FB
NFB
10
7
2.49k
+ C1
47µF
6.3V
×2
1nF
+
OPTIONAL
C2
47µF
7.5k
1534 TA01
CIN: MATSUSHITA ECGCOJB330
C1, C2: MATSUSHITA ECGCOJB47O
L1, L3: COILTRONICS CTX50-4
L2: COILCRAFT B08T (28nH) OR PC TRACE
5V
650mA
A
50mV/DIV
B
2mV/DIV
Figure 1. Low Noise 3.3V to 5V Boost Converter
5V Output Noise (BW = 100MHz)
10µs/DIV
1534 TA02
1
1 page  
LT1534/LT1534-1
TYPICAL PERFORMANCE CHARACTERISTICS
VC Pin Threshold and Clamp
Voltage vs Temperature
1.6
1.4
1.2 VC PIN CLAMP
VOLTAGE
1.0
0.8
0.6
0.4 VC PIN
THRESHOLD
0.2
0
–50 –25
0 25 50 75 100 125
TEMPERATURE (°C)
1534 G09
Load Transient Response
ILOAD
0.5A/DIV
VOUT
100mV/DIV
VIN = 3.3V
500µs/DIV
VOUT = 5V (NODE A)
ILOAD = 0.1A TO 0.5A
FIGURE 1 CIRCUIT
1534 G10
Typical Output Switch Voltage
and Current Slew Rates vs Slew
Setting Resistance (RVSL = RCSL)
40
35 IRISE
IFALL
30 VRISE
25 VFALL
TA = 25°C
4
3
20 2
15
10 1
5
00
0
1/20k
1/10k 1/6.7k
1/5k
1/R (mmho)
1534 G11
Percent Change in Oscillator
Frequency vs Temperature (NPO
Cap and Metal Film R)
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1534 G12
Load Regulation
2.0
FIGURE 1 CIRCUIT
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
0
100 200 300 400 500 600 700
LOAD CURRENT (mA)
1534-1 G13
5
5 Page 
LT1534/LT1534-1
APPLICATIONS INFORMATION
where ∆I is the ripple current in the switch, RCSL and
RVSL are the slew resistors and fOSC is the oscillator
frequency.
Power dissipation PD is the sum of these three terms. Die
junction temperature is then computed as:
TJ = TAMB + (PD)(θJA)
where TAMB is ambient temperature and θJA is the package
thermal resistance. For the 16-pin SO with fused leads the
θJA is 50°C/W.
For example, with fOSC = 40kHz, 0.4A average current and
0.1A of ripple, the maximum duty cycle is 88%. Assume
slew resistors are both 17k and VSAT is 0.26V, then:
PD = 0.176W + 0.094W + 0.158W = 0.429W
In an S16 fused lead package the die junction temperature
would be 21°C above ambient.
Frequency Compensation
Loop frequency compensation is accomplished by way of
a series RC network on the output of the error amplifier (VC
pin). Referring to Figure 4, the main pole is formed by
capacitor CVC and the output impedance of the error
amplifier (approximately 400kΩ). The series resistor RVC
creates a “zero” which improves loop stability and tran-
sient response. A second capacitor CVC2, typically one-
tenth the size of the main compensation capacitor, is
sometimes used to reduce the switching frequency ripple
on the VC pin. VC pin ripple is caused by output voltage
ripple attenuated by the output divider and multiplied by
the error amplifier. Without the second capacitor, VC pin
ripple is:
( )( )( )( )VCPIN RIPPLE =
1.25
VRIPPLE gm
VOUT
RVC
where VRIPPLE = Output ripple (VP-P)
gm = Error amplifier transconductance
RVC = Series resistor on VC pin
VOUT = DC output voltage
To prevent irregular switching, VC pin ripple should be
kept below 50mVP-P. Worst-case VC pin ripple occurs at
maximum output load current and will also be increased if
poor quality (high ESR) output capacitors are used. The
addition of a 0.0047µF capacitor on the VC pin reduces
switching frequency ripple to only a few millivolts. A low
value for RVC will also reduce VC pin ripple, but loop phase
margin may be inadequate.
RVC
2k
CVC
0.01µF
VC PIN
CVC2
4.7nF
1534 F03
Figure 4
Capacitors
While the IC reduces the source of switcher noise, it is
essential for the lowest noise, that the filter capacitors
should have low parasitic impedance. Sanyo OS-CON,
Panasonic Specialty Polymer and tantalum capacitors are
the preferred types. Aluminum electrolytics are not suit-
able for this application. In general, ESR is more critical
than capacitance. At higher frequencies, ESL can also be
important. Paralleling capacitors can reduce both ESR and
ESL.
Design Note 95 offers more information about capacitor
selection. The following is a brief summary:
Solid tantalum capacitors have small size and low
impedance. Typically they are available for voltages
below 50V. They may have a problem with surge
currents (AVX TPS line addresses this issue).
OS-CON capacitors have very low impedance but are
only available for 25V or less. Form factor may be a
problem. Sometimes their very low ESR can cause loop
stability problems.
Ceramic capacitors are generally used for high fre-
quency and high voltage bypass. They too can have
such a low ESR as to cause loop stability problems.
Often they can resonate with their ESL before ESR
becomes effective.
Specialty Polymer Aluminum: Panasonic has come out
with their series CD capacitors. While they are only
available for voltages below 16V, they have very low
ESR and good surge capability.
11
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