DATASHEET

EL7512
®
Data Sheet
May 23, 2005
High Frequency PWM Step-Up Regulator
Features
The EL7512 is a high frequency, high efficiency step-up
DC:DC regulator operated at fixed frequency PWM mode.
With an integrated 1A MOSFET, it can deliver up to 600mA
output current at up to 90% efficiency. The adjustable
switching frequency is up to 1.2MHz, making it ideal for DSL
applications.
• 90% efficiency
FN7290.1
• Up to 600mA IOUT
• 5V < VOUT < 18V
• VIN > 2V
• Up to 1.2MHz adjustable frequency
When shut down, it draws <3µA of current. This feature,
along with the minimum starting voltage of 2V, makes it
suitable for portable equipment powered by one lithium ion
or 3 to 4 NiMH cells.
The EL7512 is available in a 10-pin MSOP package, with
maximum height of 1.1mm. With proper external
components, the whole converter takes less than 0.25in2
PCB space.
This device is specified for operation over the full -40°C to
+85°C temperature range.
• < 3µA shutdown current
• Adjustable soft-start
• Low battery detection
• Internal thermal protection
• 1.1mm max height 10-pin MSOP package
• Pb-Free available (RoHS compliant)
Applications
• 3V to 5V, 12V, and 18V converters
Pinout
• 5V to 12V and 16V converters
EL7512
(10-PIN MSOP)
TOP VIEW
• TFT-LCD
• DSL
• Portable equipment
L1
VIN
(2V9V)
D1
10µF
R3
VOUT
(12V up
to
47µF 400mA)
R4
1kΩ
10µH
C1
1 PGND
LX 10
2 SGND
VDD 9
3 RT
FB 8
4 EN
SS 7
5 LBI
LBO 6
100k
• Desktop equipment
C5
Ordering Information
C4
PACKAGE
TAPE &
REEL
PKG. DWG. #
EL7512CY
10-Pin MSOP
-
MDP0043
EL7512CY-T7
10-Pin MSOP
7”
MDP0043
EL7512CY-T13
10-Pin MSOP
13”
MDP0043
EL7512CYZ
(See Note)
10-Pin MSOP
(Pb-free)
-
MDP0043
EL7512CYZ-T7
(See Note)
10-Pin MSOP
(Pb-free)
7”
MDP0043
EL7512CYZ-T13
(See Note)
10-Pin MSOP
(Pb-free)
13”
MDP0043
0.1µF
C3
20nF
R2
80.6k
R1
10kΩ
PART NUMBER
C10
4.7nF
NOTE: Intersil Pb-free products employ special Pb-free material sets;
molding compounds/die attach materials and 100% matte tin plate
termination finish, which are RoHS compliant and compatible with
both SnPb and Pb-free soldering operations. Intersil Pb-free products
are MSL classified at Pb-free peak reflow temperatures that meet or
exceed the Pb-free requirements of IPC/JEDEC J STD-020.
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-352-6832 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2002, 2003, 2005. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
EL7512
Absolute Maximum Ratings (TA = 25°C)
EN, LBI, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+18V
LX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20V
VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12V
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
Operating Temperature . . . . . . . . . . . . . . . . . . . . . . .-40°C to +85°C
Operating Junction Temperature:. . . . . . . . . . . . . . . . . . . . . . . 135°C
CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typical values are for information purposes only. Unless otherwise noted, all tests
are at the specified temperature and are pulsed tests, therefore: TJ = TC = TA
Electrical Specifications
PARAMETER
VIN = 5V, VOUT = 12V, IOUT = 0mA, RT = 100kΩ, TA = 25°C unless otherwise specified.
DESCRIPTION
CONDITION
MIN
TYP
MAX
UNIT
3
µA
2.5
4
mA
1.35
1.39
V
0.10
µA
IQ1
Quiescent Current - Shut-down
VEN = 0
IQ2
Quiensent Current
VEN = 2V
VFB
Feedback Voltage
IB
Feedback Input Bias Current
VIN
Input Voltage Range
2
DMAX
Maximum Duty Cycle
84
90
ILIM
Current Limit - Max Average Input
Current
1000
1250
ISHDN
Shut-down Input Bias Current
VLBI
LBI Threshold Voltage
VOL-LBO
LBO Output Low
ILEAK-LBO
1.31
V
%
1500
mA
1
µA
220
250
mV
ILBO = 1mA
0.1
0.2
V
LBO Output Leakage Current
VLBI = 250mV, VLBO = 5V
0.02
1
µA
RDS-ON
Switch On Resistance
at 12V output
300
ILEAK-SWITCH
Switch Leakage Current
∆VOUT/∆VIN
Line Regulation
3V < VIN < 6V, VOUT = 12V, no load
∆VOUT/∆IOUT
Load Regulation
IOUT < 250mA
FOSC-MAX
Maximum Switching Frequency
RT = 49.9kΩ
FOSC1
Switching Frequency
530
VHI_EN
EN Input High Threshold
1.6
VLO_EN
EN Input Low Threshold
180
mΩ
1
µA
0.15
%/V
0.5
%
1200
kHz
670
800
kHz
V
0.5
V
Pin Descriptions
PIN NUMBER
PIN NAME
PIN FUNCTION
1
PGND
Power ground; connected to the source of internal N-channel power MOSFET
2
SGND
Signal ground; ground reference for all the control circuitry; needs to have only a single connection to PGND
3
RT
Timing resistor to adjust the oscillation frequency of the converter
4
EN
Chip enable; connects to logic HI (>1.6V) for chip to function
5
LBI
Low battery input; connects to a sensing voltage, or left open if function is not used
6
LBO
Low battery detection output; connected to the open drain of a MOSFET; able to sink 1mA current
7
SS
Soft-start; connects to a capacitor to control the start-up of the converter
8
FB
Voltage feedback input; needs to connect to resistor divider to decide VO
9
VDD
10
LX
Control circuit positive supply
Inductor drive pin; connected to the drain of internal N-channel power MOSFET
2
EL7512
Block Diagram
VOUT
15µF
80.6k
VIN
10kΩ
1kΩ
4.7nF
47µF
0.1µF
FB
VDD
MAX_DUTY
Thermal
Shut-down
10µF
LX
RT
Reference
Generator
100kΩ
VREF
VRAMP
PWM
Logic
PWM
Comparator
0.3Ω
EN
LBO
12µA
LBI
-
-
Start-up
Oscillator
+
+
ILOUT
7.2k
80mΩ
210mV
SGND
SS
20nF
3
PGND
EL7512
Typical Performance Curves
100
Efficiency
VIN=3.3V, VO=12V
100
80
Efficiency (%)
Efficiency (%)
80
Efficiency
VIN=3.3V, VO=5V
60
40
20
60
40
20
0
10
FS=670kHz
60
110
0
10
210
160
FS=670kHz
110
210
IO (mA)
310
410
510
IO (mA)
FS vs VDD
1400
100
Efficiency
VIN=5V, VO=12V
RT=51.1kΩ
1200
80
RT=71.5kΩ
Efficiency (%)
FS (kHz)
1000
800
RT=100kΩ
600
60
40
400
RT=200kΩ
20
200
0
5
6
7
8
9
10
11
0
10
12
FS=670kHz
60
110
160
210
Internal VREF vs TJ
1.4
360
760
740
VDD=5V
1.3
720
1.25
FS (kHz)
VREF (V)
310
FS vs Temperature
1.35
1.2
1.15
700
VDD=10V
680
VDD=12V
1.1
660
1.05
1
-50
260
IO (mA)
VDD (V)
VDD=12V
0
50
TJ (°C)
4
100
150
640
-50
RT=100kΩ
0
50
TJ (°C)
100
150
EL7512
Typical Performance Curves
(Continued)
VFB vs VDD
FS vs RT
1.355
1400
1.35
1200
1.345
1000
FS (kHz)
VFB
VDD=10V
1.34
1.335
800
600
1.33
400
1.325
200
1.32
5
6
7
8
9
10
11
0
50
12
VDD
100
150
RT (kΩ)
Steady State Operation (inductor continuous
conduction) VIN=5V, VO=12V, IO=300mA
IDD vs FS
3.6
3.4
VDD=10V
VO=12V-18V
∆VI
IDD (mA)
3.2
3
2.8
VLX
2.6
∆VO
2.4
iL
2.2
2
650
750
850
950
1050
1150
1250
FS (kHz)
Steady State Operation (inductor discontinuous
conduction) VIN=5V, VO=12V, IO=25mA
Power-Up
VIN=5V, VO=12V, IO=300mA
∆VI
VLX
VIN
VO
∆VO
iL
iL
Load Transient Response
VIN=5V, VO=12V, IO=50mA-300mA
iO
∆VO
5
200
EL7512
Applications Information
where:
The EL7512 is a step-up regulator, operated at fixed
frequency pulse-width-modulation (PWM) control. The input
voltage is 2V-12V and output voltage is 5V-18V. The
switching frequency (up to 1.2MHz) is decided by the
resistor connected to RT pin.
∆IL is the inductor peak-to-peak current ripple and is
decided by:
Start-Up
D is the MOSFET turn-on ratio and is decided by:
After VDD reaches a threshold of about 2V, the start-up
oscillator generates fixed duty-ratio of 0.5-0.7 at a frequency
of several hundred kilohertz. This will boost the output
voltage.
When VDD reaches about 3.7V, the PWM comparator takes
over the control. The duty ratio will be decided by the
multiple-input direct summing comparator, Max_Duty signal
(about 90% duty-ratio), and the Current Limit Comparator,
whichever is the smallest.
V IN D
∆I L = --------- × ------L
FS
V O – V IN
D = ----------------------VO
FS is the switching frequency.
The following table gives typical values:
MAX CONTINUOUS OUTPUT CURRENTS
VIN (V)
VO (V)
L (µH)
FS (kHz)
IOMAX
(mA)
2
5
10
1000
360
2
9
10
1000
190
2
12
10
1000
140
3.3
5
10
1000
600
3.3
9
10
1000
310
3.3
12
10
1000
230
5
9
10
1000
470
Steady-State Operation
5
12
10
1000
340
When the output reaches the preset voltage, the regulator
operates at steady state. Depending on the input/output
conditions and component values, the inductor operates at
either continuous-conduction mode or discontinuousconduction mode.
5
15
10
1000
260
9
12
10
1000
630
9
15
10
1000
470
12
15
10
1000
670
12
18
11
1000
510
The soft-start is provided by the current limit comparator. As
the internal 12µA current source charges the external CSS,
the peak MOSFET current is limited by the voltage on the
capacitor. This in turn controls the rising rate of the output
voltage.
The regulator goes through the start-up sequence as well
after the EN signal is pulled to HI.
In the continuous-conduction mode, the inductor current is a
triangular waveform and LX voltage a pulse waveform. In the
discontinuous-conduction mode, the inductor current is
completely dried out before the MOSFET is turned on again.
The input voltage source, the inductor, and the MOSFET and
output diode parasitic capacitors forms a resonant circuit.
Oscillation will occur in this period. This oscillation is normal
and will not affect the regulation.
At very low load, the MOSFET will skip pulses sometimes.
This is normal.
Component Considerations
It is recommended that CIN is larger than 10µF.
Theoretically, the input capacitor has ripple current of ∆IL.
Due to high-frequency noise in the circuit, the input current
ripple may exceed the theoretical value. Larger capacitor will
reduce the ripple further.
The inductor has peak and average current decided by:
Current Limit
IO
I LAVG = -----------1–D
The MOSFET current limit is nominally 1.2A and guaranteed
1A. This restricts the maximum output current IOMAX based
on the following formula:
∆I
I LPK = I LAVG + --------L
2
V IN
∆I
I OMAX =  1 – --------L × --------
2  VO
The inductor should be chosen to be able to handle this
current. Furthermore, due to the fixed internal
compensation, it is recommended that maximum inductance
of 10µH and 15µH to be used in the 5V and 12V or higher
output voltage, respectively.
The output diode has average current of IO, and peak
current the same as the inductor's peak current. Schottky
6
EL7512
diode is recommended and it should be able to handle those
currents.
Output voltage ripple is the product of peak inductor current
times the ESR of output capacitor. Low ESR capacitor is to
be used to reduce the output ripple. The minimum output
capacitance of 330µF, 47µF, and 33µF is recommended for
5V, 12V, and 16V for 600kHz switching frequency,
respectively. For 1MHz switching frequency, 220µF, 33µF,
and 22µF capacitor can be used for the output voltages. In
addition to the voltage rating, the output capacitor should
also be able to handle the rms current is given by:
I CORMS =
2


∆I L
1
( 1 – D ) ×  D + ------------------- × ------  × I LAVG

2 12 
I LAVG


Output Voltage
An external resistor divider is required to divide the output
voltage down to the nominal reference voltage. The current
drawn by the resistor network should be limited to maintain
the overall converter efficiency. The maximum value of the
resistor network is limited by the feedback input bias current
and the potential for noise being coupled into the feedback
pin. A resistor network less than 300kΩ is recommended.
The boost converter output voltage is determined by the
relationship:
R 

V OUT = V FB ×  1 + ------2-
R 1

where VFB slightly changes with VDD. The curve is shown in
this data sheet.
RC Filter
The maximum voltage rating for the VDD pin is 12V and is
recommended to be about 10V for maximum efficiency to
drive the internal MOSFET. The series resistor R4 in the RC
filter connected to VDD can be utilized to reduce the voltage.
If VO is larger than 10V, then:
V O – 10
R 4 = -------------------I DD
where IDD is shown in IDD vs FS curve. Otherwise, R4 can
be 10Ω to 51Ω with C4 = 0.1µF.
Thermal Performance
The EL7512 uses a fused-lead package, which has a
reduced θJA of 100°C/W on a four-layer board and 115°C/W
on a two-layer board. Maximizing copper around the ground
pins will improve the thermal performance.
This chip also has internal thermal shut-down set at around
135°C to protect the component.
7
Layout Considerations
The layout is very important for the converter to function
properly. Power Ground (
) and Signal Ground (--)
should be separated to ensure that the high pulse current in
the Power Ground never interferes with the sensitive signals
connected to Signal Ground. They should only be connected
at one point.
The trace connected to pin 8 (FB) is the most sensitive trace.
It needs to be as short as possible and in a “quiet” place,
preferably between PGND or SGND traces.
In addition, the bypass capacitor connected to the VDD pin
needs to be as close to the pin as possible.
The heat of the chip is mainly dissipated through the SGND
pin. Maximizing the copper area around it is preferable. In
addition, a solid ground plane is always helpful for the EMI
performance.
The demo board is a good example of layout based on these
principles. Please refer to the EL7512 Application Brief for
the layout.
EL7512
Package Outline Drawing
NOTE: The package drawing shown here may not be the latest version. To check the latest revision, please refer to the Intersil website at
<http://www.intersil.com/design/packages/index.asp>
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.
Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and
reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com
8
Similar pages