Microsemi LQH3C-220 1.0mhz inverting dc/dc converter Datasheet

LX1734
®
TM
1.0MHz Inverting DC/DC Converter
KEY FEATURES
DESCRIPTION
Fixed frequency operation ensures a
clean output free from low frequency
noise typically present with charge pump
solutions. The low impedance output
remains within 1% of nominal during
large load steps. The 18V switch allows
high voltage outputs to be generated.
The LX1734 is available in the space
saving 6-lead 3x3 Jedec MO-229
package, which has the same footprint
and lead spacing as the SOT-23A. A
complete inverter function utilizes less
than 0.32 inches of PCB space.
ƒ Fixed Frequency 1.0MHz
Operation
ƒ Very Low Noise: 1mVP-P Output
Ripple Possible With Cuk
Topology
ƒ Stable Operation With Ceramic or
Tantalum Capacitors
ƒ -5V at 250mA from 5V Input
ƒ Uses Small Surface Mount L/C
Components
ƒ Wide Input Range: 4.2V to 8V
ƒ Low VCESAT Switch: 600mV at
600mA
ƒ 6-Lead 3x3mm JEDEC MLPM
Package
ƒ Functionally Compatible with
LT1611 or LT1931
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The LX1734 is an inverting
DC/DC current-mode controller. With
a 750mA integrated switch, the
LX1734 can generate large output
currents in a small footprint. The
LX1734 minimizes external component size and cost by implementing
a high switching frequency of
1.0MHz, while generating -5V at
250mA.
When configured in the dual
inductor inverting topology very low
output voltage ripple approaching
1mVP-P can be achieved when used in
conjunction with ceramic output
capacitors. The dual inductor can be
implemented as a coupled or separate
cores.
APPLICATIONS/BENEFITS
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
ƒ
ƒ
ƒ
ƒ
ƒ
Disk Drive MR Head Bias
Digital Camera CCD Bias
LCD Bias
GaAs FET Bias
Local -5V or -12V Supplies
PRODUCT HIGHLIGHT
L1A
22µH
C2
1µF
L1B
22µH
VIN = 5V
VIN
C1
10µF
R1
29.4k
SW
LX1734
NFB
SD
GND
R2
10k
C4
1000pF
VOUT = -5V
@ 150mA
C3
22µF
Note: L1A and L1B are shown as coupled. Individual inductors can also be used.
C1, C2, C3 are ceramic capacitors
LX1734
Figure 1
PACKAGE ORDER INFO
Plastic MLPL
LM
6-Pin
T (°C)
A
RoHS Compliant / Pb-free
Transition DC: 0452
0 to 85
LX1734CLM
Note: Available in Tape & Reel. Append the letters “TR” to the
part number. (i.e. LX1734CLM-TR)
Copyright © 2002
Rev. 3.0a, 2005-03-14
Microsemi
Microsemi Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX1734
®
TM
1.0MHz Inverting DC/DC Converter
ABSOLUTE MAXIMUM RATINGS
PACKAGE PIN OUT
SW
**
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Supply Voltage (VIN), Shutdown ( SD ).................................................... 0 to 10V
SW Voltage....................................................................................... -0.4V to 20V
NFB Voltage .................................................................................................... -2V
Current Into NFB Pin................................................................................... ±1mA
Operating Temperature Range ............................................................0°C to 85°C
Maximum Junction Temperature ................................................................. 125°C
Storage Temperature......................................................................-65°C to 150°C
Peak Package Solder Reflow Temperature
(40 second maximum exposure) ..................................................... 260°C (+0, -5)
VIN
GND
N/C*
NFB
SD
LM PACKAGE
(Top View)
* Not Internally Connected.
** Package heatsink should
be connected to ground or
left floating.
Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to
Ground. Currents are positive into, negative out of specified terminal.
RoHS / Pb-free 100% Matte Tin Lead Finish
THERMAL DATA
LM Plastic LM 6-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJC
8°C/W
Junction Temperature Calculation: TJ = TA + (PD x θJC).
The θJC numbers are guidelines for the thermal performance of the device/pc-board
system. All of the above assume no ambient airflow.
FUNCTIONAL PIN DESCRIPTION
NAME
DESCRIPTION
SW
Power Switch Pin
GND
Common ground reference
Feedback Pin - Connect to a resistive divider in order to set the output voltage. Feedback threshold is -1.235V.
Given the typical NFB bias current (INFB) of 4µA flows out of the pin, the suggested value for R2 is 10K. Given
R2, set R1 according to:
NFB
R1 =
VOUT
1 . 235
R2
VIN
Input Supply – Input pin must be locally bypassed.
SD
Shutdown, Connected to >2V, device is active.
− 1 . 235
(
+ I NFB
)
PACKAGE DATA
Copyright © 2002
Rev. 3.0a, 2005-03-14
Microsemi
Microsemi Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
LX1734
®
TM
1.0MHz Inverting DC/DC Converter
ELECTRICAL CHARACTERISTICS
Parameter
Symbol
Minimum Operating Voltage
VIN Under Voltage Lockout
Reference Voltage
Reference Voltage Line Regulation
NFB Pin Bias Current
Quiescent Current
VIN
UVLO
VNFB
Quiescent Current
Test Conditions
Min
VIN rising, regulator remains off
4.5V < VIN < 5.5V, TAMB > 25°C
INFB
IQ
ISHDN
(Regulator Not Switching, VNFB = -2V)
V < 0.28V
SD
IOUT = 5mA to 250mA
Switching Frequency
Maximum Duty Cycle
Switch VCESAT
ISW = 600mA
VSW = 10V
Duty Cycle < 50%
Device Active
Device Disabled
V = 0.28V
Switch Leakage Current
Switch Circuit Current Limit
Shutdown Input Voltage
High
Low
VSDH
VSDL
Bias
Current
ISD
SD
LX1734
Typ
Max
Units
4.25
3.2
4.25
-1.205 -1.235 -1.255
18
-4
-8
9
12
300
0.8
1.4
82
650
800
0.02
1
700
2
0.8
-5
0.4
1.0
V
V
V
mV
µA
mA
µA
MHz
%
mV
µA
mA
V
V
µA
30
µA
VSD = 5V
50
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Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C ≤ TA ≤ 85°C and the following
test conditions: VIN = 5V
BLOCK DIAGRAM
VIN
SD
SW
UVLO
BIAS
+
Q1
R
100k
Q2
40pF
+
S
SET
CLR
Q
Q3
Q
Σ
+
Ramp
Generator
0.1Ω
-
ELECTRICALS
1.1MHz
Oscillator
R1 (External)
NFB
R2 (External)
GND
VOUT
CPL
Figure 2 – Simplified Block Diagram
Copyright © 2002
Rev. 3.0a, 2005-03-14
Microsemi
Microsemi Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
LX1734
®
TM
1.0MHz Inverting DC/DC Converter
CONDITIONS: VIN @ 5V, VOUT @ -5V, CIN=COUT=10uF Ceramic, L1=L2=10uH
STEP LOAD RESPONSE 0 – 250mA
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STEP LOAD RESPONSE 0 – 100mA
VOUT
VOUT
ISTEP LOAD
ISTEP LOAD
POWER ON RESPONSE, IOUT @ 200mA
OUTPUT VOLTAGE RIPPLE, IOUT @ 10mA and 150 mA
VOUT
IOUT = 10Ma
VIN
IOUT = 150mA
Inductor, 2A/div
LX1734 TEMPERATURE STABILITY
IL = 132mA
TEMP, °C -15
Copyright © 2002
Rev. 3.0a, 2005-03-14
1070
1040
1010
980
950
920
890
860
830
800
Vout, Volts
FREQ, Khz
0
15
30
45
60
75
90
105
WAVEFORMS
-4.84
-4.88
-4.92
-4.96
-5
-5.04
-5.08
-5.12
-5.16
-5.2
120
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Microsemi Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
LX1734
®
TM
1.0MHz Inverting DC/DC Converter
THEORY OF OPERATION
The bandgap control circuit keeps Q1 biased on and produces a
reference current (IREF) that produces a voltage drop across the
internal resistance that has a positive temperature coefficient.
When this resistor voltage drop is added to the negative temperature
coefficient of the base-emitter voltage drop of Q1, the result is a
temperature compensated reference voltage (VREF) at the NFB pin.
The summing node from the external feedback network is
connected directly to NFB pin, which is relatively high impedance
(typically 150k). The feedback loop minimizes the error current,
(IERROR) which effectively regulates the voltage at the NFB pin. As
with a conventional error amplifier, the error signal is proportional
to the difference between the temperature compensated reference
voltage (VREF) and the summing node voltage. A slight correction
factor is necessary to account for the added summing node voltage
due to the reference current (IREF, typically 4µADC) flowing
through the Thevenin equivalent summing node external resistance.
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The LX1734 is a fixed frequency current mode controller
designed to develop a negative output voltage from a positive
input voltage. The switching transistor and current sense resistor
are integrated into the part. The PWM functions in a peak current
regulation mode using the amplified error signal to determine the
peak switch current each cycle. Slope compensation is added to
provide stable operation at high duty cycles. A current limit
detector overrides the regulation loop and prevents the switch
current from exceeding the over current threshold level.
APPLICATION NOTE
The LX1734 can be used in several topologies that generate a
negative output voltage from a positive input voltage. The
LX1734 can be used in a dual inductor converter with coupled or
uncoupled inductors (see Figure 1); this topology is required if
the absolute value of the output voltage is less than or equal to
the input voltage but can also be used for higher voltage outputs.
The following components or their equivalents can be used to
implement the converter in Figure 1, which produces a –5V
output at 150mA from a +5V input. The reference design has an
efficiency of greater than 72% and an input ripple voltage of less
than 6mVP-P and an output ripple voltage of less than 300µVP-P.
Ref
C1
C2
C3
C4
D1
L1
Description
Ceramic, 4.7uF,
6.3V (0805)
Ceramic, 1uF, 16V
(0805)
Ceramic, 22uF,
6.3V (1210)
Ceramic, 470pF,
50V (0402)
Diode, 0.5A, 30V
Inductor, Coupled,
22uH
Part Number
JMK212BJ475MG
Manufacturer
Taiyo Yuden
GRM40X7R105M16
Murata
JMK325BJ226MM
Taiyo Yuden
GRM36X7R471K050
Murata
UPS530
CLS62-220NC
Microsemi
Sumida
Table 1 - Part List for Figure 1 (All Parts Are Surface Mount).
Table 2 - Part List For Alternative Inductors
Ref.
Designator
L1, L2
Description
Part Number
Manufacturer
Inductor, 47uH,
(1812)
LQH4C470K04M00
Murata
Copyright © 2002
Rev. 3.0a, 2005-03-14
When the LX1734 is used in a dual inductor converter with coupled
inductors, a parallel winding inductor value of 22µH works well for
a 5V input and a -5V output at 150mA. The inductor value can be
scaled to the particular set of operating conditions based on the
input voltage, output voltage, and output current. The new value of
coupled inductor parallel inductance can be calculated using the
following equation:
⎛ V ⎞ ⎛ 150 mA ⎞⎟ ⎛⎜ − 5 V ⎞⎟
L NEW = 22 µH× ⎜ IN ⎟ × ⎜⎜
×
⎝ 5 V ⎠ ⎝ I OUT ⎟⎠ ⎜⎝ VOUT ⎟⎠
The inductor value should be rounded to the nearest available value.
The parallel saturation current rating of a coupled inductor should
be sized to carry the summation of the peak input and peak output
inductor currents.
When the LX1734 is used in a dual inductor converter with two
separate (uncoupled) inductors or when using the boost converter
with an inverting charge pump output configuration, the inductance
value for each inductor should be about twice the value
recommended for a coupled inductor.
The peak current in the inductor is the DC current plus ½ of the
peak-to-peak ripple current. The saturation current rating of the
inductors should be sized to carry the peak inductor current. The
peak-to-peak ripple current can be calculated based on the inductor
value, the terminal voltage (input or output), and the duty cycle.
The DC inductor current is the same as the DC output current on the
output inductor. The DC input current includes the power for the
LX1734, but is still a good approximation for the DC inductor
current for higher power applications.
For simplicity, the
calculations below ignore the voltage drops of the switch and diode.
The duty cycle, D, for the dual inductor topology (assuming
continuous inductor current mode operation) is approximately:
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Microsemi Integrated Products
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APPLICATION
Separate inductors (not on a common core) can be used in place
of the coupled inductor (L1) of Figure 1. In this case the only
component that changes in the parts list is L1, which now would
be two separate inductors (L1, formerly L1A, and L2, formerly
L1B). With the separate inductors the peak-to-peak voltage
ripple on the input the output were less the 2mVP-P and less than
500µVP-P, respectively.
Inductor Selection
LX1734
®
TM
1.0MHz Inverting DC/DC Converter
APPLICATION NOTE (CONTINUED)
VOUT
(VOUT − VIN )
where VOUT < 0
Capacitor Selection
For example, the duty cycle for +5V = VIN and –3.3V = VOUT
is 40%.
The duty cycle for the Inverting Charge Pump Output topology
(assuming continuous inductor current mode operation) is
approximately:
⎛ V ⎞
D = 1 + ⎜⎜ IN ⎟⎟
⎝ VOUT ⎠
where VOUT < 0
To minimize ripple voltage, only capacitors with low series
resistance (ESR) are recommended. Mutli-layer ceramic capacitors
with X5R or X7R dielectric are an excellent choice featuring small
size, very low ESR, and a temperature stable dielectric. The level
shifting capacitor, C2 (of Figure 1), should have a value of 1µF and
a voltage difference between the input and output voltages. The
input and output capacitors (C1 and C2, respectively) should have
values in the range of 1µF or larger. If the inductor ripple current is
known, the ripple voltage can be estimated by the following
equation:
For example, the duty cycle for +5V = VIN and –12V = VOUT is
58%.
The peak-to-peak ripple current in the input inductor is
approximately:
I RIPPLEpp =
(VIN × D )
(L IN × Fsw )
where Fsw = 1.0MHz (the switching frequency)
For example, with a +5V input and a-12V output in an Inverting
Charge Pump Output topology with a 47µH inductor, the peak-topeak input ripple is 52mA.
In the dual inductor topology with separate inductors, the peakto-peak ripple current in the output inductor is approximately:
[− VOUT × (1 − D )]
I RIPPLE pp =
(L OUT × Fsw )
For example, with a +5V input and a -3.3V output in a dual
inductor topology with a 47µH output inductor, the peak-to-peak
output ripple is 35mA.
There are many inductor models from many different
manufacturers that work well with the LX1734. Some sources
are listed in Table 5. Ferrite core inductors are recommended to
reduce core losses due to the high operating frequency of the
LX7134. Using inductors with low DC resistance will further
reduce efficiency losses.
Phone
URL
Sumida
(847)
956-0666
www.sumida.com
Murata
(404)
436-1300
www.murata.com
LQH3C-220
Coiltronics
(407)
241-7876
www.coiltronics.com
CTX20-1
CLS62-22022
CD43-470
Table 5 – List of Inductor Vendors
Copyright © 2002
Rev. 3.0a, 2005-03-14
Part
Comments
22µH
Coupled
47µH
22µH, 2mm
Height
20µH,
Coupled,
Low DCR
(I
2
×L
(2 × C× V )
PPRIPPLE
)
Since ripple voltage is inversely proportional to the capacitor value,
larger value ceramic capacitors will result in lower ripple voltages.
When using a ceramic capacitor for the output capacitor, it is
recommended that a phase lead network be inserted in the feedback
loop to improve the transient response. This can be accomplished
by placing a capacitor in parallel with resistor R1 (see Figure 1).
The corner frequency for the phase lead zero is between 20KHz and
60KHz. C4 can be calculated using the following equation:
fz =
1
(2 π× R 1× C 4)
Electrolytic capacitors such as solid tantalum or OS-CON types can
also be used with consideration for the ESR. Since ESR adds to the
capacitor reactive impedance, ESR will increase the ripple voltage.
The electrolytic output capacitor impedance has a built in zero, so
adding C4 is usually not required when using an electrolytic
capacitor.
Diode Selection
A Schottky diode is recommended for use with the LX1734. The
Microsemi UPS530 (30V @ 0.5A) or Microsemi UPS5817 (20V @
1A) are good choices.
Layout Considerations
In operation, current is transferred between the LX1734 and D1 so
to minimize ground noise it is recommended that the D1 cathode be
connected directly to the ground pin pad for the LX1734 (refer to
figure 1). When laying out the converter, to minimize EMI, it is
important to minimize the area enclosed within the main current
loops. It is also important to minimize the length of etch connecting
to pin 3 (NFB) and to minimize the total trace area on both sides of
C2. A ceramic bypass capacitor should be connected between pin 5
(VIN) and pin 2 (GND) and located in close proximity to the
LX1734.
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11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
APPLICATION
Vendor
VPP(RIPPLE) =
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D=
LX1734
®
TM
1.0MHz Inverting DC/DC Converter
PACKAGE DIMENSIONS
6-Pin Plastic Exposed Pad JEDEC MO-229 Reference
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LM
D
Dim
A
A1
A2
A3
b
D
E
e
D2
E2
L
L2
K
E
TOP VIEW
θ
A2
A
.08
SIDE VIEW
A3
b
θ
A1
MILLIMETERS
MIN
MAX
0.80
1.05
*
0.05
0.65
0.75
0.15
0.25
0.33
0.45
2.90
3.10
2.90
3.10
0.95 BSC
1.78
2.34
1.01
1.57
0.20
0.45
--0.13
0.20
*
0°
12°
INCHES
MIN
MAX
0.031 0.041
0.002
0.025 0.295
0.006 0.010
0.012 0.017
0.114 0.122
0.114 0.122
0.037 BSC
0.070 0.092
0.039 0.061
0.007 0.017
--0.005
0.007
*
0°
12°
e
L2
Note:
1. Dimensions do not include mold flash or protrusions;
these shall not exceed 0.155mm(.006”) on any side.
Lead dimension shall not include solder coverage.
D2
E2
L
BOTTOM VIEW
MECHANICAL
Copyright © 2002
Rev. 3.0a, 2005-03-14
Microsemi
Microsemi Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
LX1734
TM
®
1.0MHz Inverting DC/DC Converter
NOTES
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NOTES
PRODUCTION DATA – Information contained in this document is proprietary to
Microsemi and is current as of publication date. This document may not be modified in
any way without the express written consent of Microsemi. Product processing does not
necessarily include testing of all parameters. Microsemi reserves the right to change the
configuration and performance of the product and to discontinue product at any time.
Copyright © 2002
Rev. 3.0a, 2005-03-14
Microsemi
Microsemi Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
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