View EL7512_237862.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

(R)
EL7512
Data Sheet April 12, 2002 FN7290
High Frequency PWM Step-Up Regulator
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. When shut down, it draws <3A 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 -40C to +85C temperature range.
Features
* 90% efficiency * Up to 600mA IOUT * 5V < VOUT < 18V * VIN > 2V * Up to 1.2MHz adjustable frequency * < 3A shutdown current * Adjustable soft-start * Low battery detection * Internal thermal protection * 1.1mm max height 10-pin MSOP package
Applications
* 3V to 5V, 12V, and 18V converters * 5V to 12V and 16V converters * TFT-LCD
Pinout
EL7512 (10-PIN MSOP) TOP VIEW
* DSL * Portable equipment * Desktop equipment
L1 VIN (2V9V) C1 10F 1 PGND 2 SGND R3 100k 4 EN 5 LBI SS 7 3 RT LX 10 VDD 9 FB 8 10H
D1 R4 1k C4 0.1F R2 80.6k R1 10k
VOUT (12V up to 47F 400mA) C5
Ordering Information
PART NUMBER EL7512CY PACKAGE 10-Pin MSOP 10-Pin MSOP 10-Pin MSOP TAPE & REEL 7" 13" PKG. NO. MDP0043 MDP0043 MDP0043
C3 20nF LBO 6
C10 4.7nF
EL7512CY-T7 EL7512CY-T13
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 321-724-7143 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright (c) Intersil Americas Inc. 2003. All Rights Reserved. Elantec is a registered trademark of Elantec Semiconductor, Inc. All other trademarks mentioned are the property of their respective owners.
EL7512
Absolute Maximum Ratings (TA = 25C)
EN, LBI, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+18V LX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20V VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12V Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65C to +150C Operating Temperature . . . . . . . . . . . . . . . . . . . . . . .-40C to +85C Operating Junction Temperature:. . . . . . . . . . . . . . . . . . . . . . . 135C
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 IQ1 IQ2 VFB IB VIN DMAX ILIM ISHDN VLBI VOL-LBO ILEAK-LBO RDS-ON ILEAK-SWITCH VOUT/VIN VOUT/IOUT FOSC-MAX FOSC1 VHI_EN VLO_EN
VIN = 5V, VOUT = 12V, IOUT = 0mA, RT = 100k, TA = 25C unless otherwise specified. CONDITION VEN = 0 VEN = 2V 1.31 2.5 1.35 MIN TYP MAX 3 4 1.39 0.10 2 84 1000 90 1250 1500 1 180 ILBO = 1mA VLBI = 250mV, VLBO = 5V at 12V output 220 0.1 0.02 300 1 3V < VIN < 6V, VOUT = 12V, no load IOUT < 250mA RT = 49.9k 530 1.6 0.5 0.5 1200 670 800 0.15 250 0.2 1 UNIT A mA V A V % mA A mV V A m A %/V % kHz kHz V V
DESCRIPTION Quiescent Current - Shut-down Quiensent Current Feedback Voltage Feedback Input Bias Current Input Voltage Range Maximum Duty Cycle Current Limit - Max Average Input Current Shut-down Input Bias Current LBI Threshold Voltage LBO Output Low LBO Output Leakage Current Switch On Resistance Switch Leakage Current Line Regulation Load Regulation Maximum Switching Frequency Switching Frequency EN Input High Threshold EN Input Low Threshold
Pin Descriptions
PIN NUMBER 1 2 3 4 5 6 7 8 9 10 PIN NAME PGND SGND RT EN LBI LBO SS FB VDD LX PIN FUNCTION Power ground; connected to the source of internal N-channel power MOSFET Signal ground; ground reference for all the control circuitry; needs to have only a single connection to PGND Timing resistor to adjust the oscillation frequency of the converter Chip enable; connects to logic HI (>1.6V) for chip to function Low battery input; connects to a sensing voltage, or left open if function is not used Low battery detection output; connected to the open drain of a MOSFET; able to sink 1mA current Soft-start; connects to a capacitor to control the start-up of the converter Voltage feedback input; needs to connect to resistor divider to decide VO Control circuit positive supply Inductor drive pin; connected to the drain of internal N-channel power MOSFET
2
EL7512 Block Diagram
VOUT 80.6k 10k 4.7nF 1k 0.1F 47F 10F 15F VIN
FB
VDD
LX
MAX_DUTY RT 100k Reference Generator VREF VRAMP PWM Comparator
Thermal Shut-down
PWM Logic
0.3
EN LBO 12A LBI
+
Start-up Oscillator
+ ILOUT 7.2k 80m
210mV SGND SS 20nF PGND
3
EL7512 Typical Performance Curves
100
Efficiency VIN=3.3V, VO=12V
100
Efficiency VIN=3.3V, VO=5V
80 Efficiency (%) Efficiency (%) FS=670kHz 60 110 IO (mA) FS vs VDD 1400 1200 1000 FS (kHz) 800 600 400 RT=200k 200 0 5 6 7 8 9 10 11 12 VDD (V) Internal VREF vs TJ 1.4 1.35 1.3 VREF (V) FS (kHz) 1.25 1.2 1.15 1.1 1.05 1 -50 VDD=12V 0 50 TJ (C) 100 150 RT=100k RT=51.1k 160 210
80
60
60
40
40
20
20 FS=670kHz 110 210 310 410 510
0 10
0 10
IO (mA) Efficiency VIN=5V, VO=12V
100
80 Efficiency (%) RT=71.5k
60
40
20 FS=670kHz 60 110 160 210 260 310 360
0 10
IO (mA) FS vs Temperature 760 740 720 700 680 VDD=12V 660 640 -50 RT=100k 0 50 TJ (C) 100 150 VDD=10V VDD=5V
4
EL7512 Typical Performance Curves
VFB vs VDD 1.355 1.35 1.345 VFB 1.34 1.335 1.33 1.325 1.32 5 6 7 8 VDD IDD vs FS 3.6 3.4 3.2 IDD (mA) 3 2.8 2.6 2.4 2.2 2 650 750 850 950 FS (kHz) Steady State Operation (inductor discontinuous conduction) VIN=5V, VO=12V, IO=25mA Power-Up VIN=5V, VO=12V, IO=300mA 1050 1150 1250 VLX VO iL VDD=10V VO=12V-18V VI 9 10 11 12 FS (kHz) 1400 VDD=10V 1200 1000 800 600 400 200 0 50
(Continued)
FS vs RT
100 RT (k)
150
200
Steady State Operation (inductor continuous conduction) 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
EL7512 Applications Information
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. where: IL is the inductor peak-to-peak current ripple and is decided by:
V IN D I L = --------- x -----L FS
Start-Up
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. The soft-start is provided by the current limit comparator. As the internal 12A 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.
D is the MOSFET turn-on ratio and is decided by:
V O - V IN D = ----------------------VO
FS is the switching frequency. The following table gives typical values:
MAX CONTINUOUS OUTPUT CURRENTS VIN (V) 2 2 2 3.3 3.3 3.3 5 5 5 9 9 12 12 VO (V) 5 9 12 5 9 12 9 12 15 12 15 15 18 L (H) 10 10 10 10 10 10 10 10 10 10 10 10 11 FS (kHz) 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 IOMAX (mA) 360 190 140 600 310 230 470 340 260 630 470 670 510
Steady-State Operation
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. 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 10F. 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:
IO I LAVG = -----------1-D I L I LPK = I LAVG + -------2
Current Limit
The MOSFET current limit is nominally 1.2A and guaranteed 1A. This restricts the maximum output current IOMAX based on the following formula:
V IN I L I OMAX = 1 - -------- x -------- 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 10H and 15H 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 330F, 47F, and 33F is recommended for 5V, 12V, and 16V for 600kHz switching frequency, respectively. For 1MHz switching frequency, 220F, 33F, and 22F 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:
2 I L 1( 1 - D ) x D + ------------------- x ----- x I LAVG 2 12 I LAVG
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.
I CORMS =
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 300k is recommended. The boost converter output voltage is determined by the relationship:
R 2 V OUT = V FB x 1 + ------ 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 10 to 51 with C4 = 0.1F.
Thermal Performance
The EL7512 uses a fused-lead package, which has a reduced JA of 100C/W on a four-layer board and 115C/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 135C to protect the component.
7
EL7512 Package Outline Drawing
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

▲Up To Search▲

Price & Availability of EL7512

	To Download EL7512 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .