View ISL97645A_4161959.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

(R)
ISL97645A
Data Sheet July 2, 2007 FN6353.0
Boost + VON Slice + VCOM
The ISL97645A represents an integrated DC/DC regulator for monitor and notebook applications with screen sizes up to 20". The device integrates a boost converter for generating AVDD, a VON slice circuit, and a high performance VCOM amplifier. The boost converter features a 2.6A FET and has user programmable soft-start and compensation. With efficiencies up to 92%, the AVDD is user selectable from 7V to 20V. The VON slice circuit can control gate voltages up to 30V. High and low levels are programmable, as well as discharge rate and timing. The supply monitor can be used to monitor the input voltage to prevent low voltage operation. The integrated VCOM features high speed and drive capability. With 30MHz bandwidth and 50V/s slew rate, the VCOM amplifier is capable of driving 400mA peaks, and 100mA continuous output current.
Features
* 2.7V to 5.5V Input * 2.6A Integrated Boost for Up to 20V AVDD * Integrated VON Slice * RESET signal generated by Supply Monitor * 600kHz/1.2MHz fS * VCOM Amplifier - 30MHz BW - 50V/s SR - 400mA Peak Output Current * UV and OT Protection * 24 Ld 4x4 QFN * Pb-Free Plus Anneal Available (RoHS Compliant)
Applications
* LCD Monitors (15"+) * Notebook Display (up to 16")
Ordering Information
PART NUMBER (Note) ISL97645AIRZ ISL97645AIRZ-T* PART MARKING TEMP. RANGE (C) PACKAGE (Pb-Free) PKG. DWG. #
Pinout
ISL97645A (24 LD 4x4 QFN) TOP VIEW
ENABLE 19 18 LX 17 VIN2 16 FREQ2 15 COMP 14 SS 13 RESET 7 OUT 8 NEG 9 POS 10 AGND 11 CD2 12 VDIV PGND 21
976 45AIRZ -40 to +85 24 Ld 4x4 QFN L24.4x4D
VGH
RE
CE
ISL97645AIRZ-TK* 976 45AIRZ -40 to +85 24 Ld 4x4 QFN L24.4x4D Tape and Reel *"-T" or "-TK" suffix for tape and reel. Please refer to TB347 for details on reel specifications. NOTE: Intersil Pb-free plus anneal 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.
GND VGH_M VFLK VDPM VDD1 VDD2 1 2 3 4 5 6
24
23
22
20
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2007. All Rights Reserved All other trademarks mentioned are the property of their respective owners.
FB
976 45AIRZ -40 to +85 24 Ld 4x4 QFN L24.4x4D Tape and Reel
ISL97645A Pin Descriptions
PIN NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 NAME GND VGH_M VFLK VDPM VDD1 VDD2 OUT NEG POS AGND CD2 VDIV RESET SS COMP FREQ VIN2 LX ENABLE FB PGND RE CE VGH Signal ground Gate Pulse Modulator Output Gate Pulse Modulator Control input Gate Pulse Modulator Enable. Connect a capacitor from VDPM to GND to set the delay time before GPM is enabled. A 20A current source charges CDPM. Power on delay time = 60.75k*CDPM. Gate Pulse Modulator Low Voltage Input VCOM Amplifier Supply VCOM Amplifier Output VCOM Amplifier Inverting input VCOM Amplifier Non-inverting input VCOM Amplifier Ground Voltage detector rising edge delay. Connect a capacitor between this pin and GND to set the rising edge delay. Voltage detector threshold. Connect to the center of a resistive divider between VIN and GND. Voltage detector reset output. Boost Converter Soft-Start. Connect a capacitor between this pin and GND to set the soft-start time. Boost Converter Compensation pin. Connect a series resistor and capacitor between this pin and GND to optimize transient response. Boost Converter frequency select Boost Converter power supply Boost Converter Switching Node Chip Enable pin. Connect to VIN1 for normal operation, GND for shutdown. Boost Converter Feedback Boost Converter Power Ground Gate Pulse Modulator Slew Control. Connect a resistor between this pin and GND to set the falling slew rate. Gate Pulse Modulator Delay Control. Connect a capacitor between this pin and GND to set the delay time. Gate Pulse Modulator High Voltage Input DESCRIPTION
2
FN6353.0 July 2, 2007
ISL97645A
Absolute Maximum Ratings
Lx to GND, AGND and PGND . . . . . . . . . . . . . . . . . . . . -0.5 to +25V VDD2, OUT, NEG and POS to GND, AGND and PGND. . . . . . . . . . . . . . . . . . . . . -0.5 to +25V VDD1, VGH and VGH_M to GND, AGND and PGND. . . . . . . . . . . . . . . . . . . . . -0.5 to +32V Differential Voltage Between POS and NEG . . . . . . . . . . . . . . . 6V Voltage Between GND, AGND and PGND . . . . . . . . . . . . . . . 0.5V All Other Pins to GND, AGND and PGND . . . . . . . . . . -0.5 to +6.5V Input, Output, or I/O Voltage . . . . . . . . . . . GND -0.3V to VIN + 0.3V
Thermal Information
Thermal Resistance JA (C/W) JC (C/W) 4x4 QFN Package (Notes 1, 2) . . . . . . 39 2.5 Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65C to +150C Maximum Continuous Junction Temperature . . . . . . . . . . . +125C Power Dissipation TA +25C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.44W TA = +70C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.34W TA = +85C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.98W TA = +100C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.61W Pb-free reflow profile . . . . . . . . . . . . . . . . . . . . . . . . . .see link below http://www.intersil.com/pbfree/Pb-FreeReflow.asp
Recommended Operating Conditions
Input Voltage Range, VS . . . . . . . . . . . . . . . . . . . . . . . . 2.7V to 5.5V Boost Output Voltage Range, AVDD . . . . . . . . . . . . . . . . . 8V to 20V Input Capacitance, CIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22F Boost Inductor, L1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3H to 10H Output Capacitance, COUT . . . . . . . . . . . . . . . . . . . . . . .2F x 22F Operating Ambient Temperature Range . . . . . . . . . .-40C to +85C Operating Junction Temperature . . . . . . . . . . . . . . .-40C to +125C
CAUTION: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to such conditions may adversely impact product reliability and result in failures not covered by warranty.
NOTES: 1. JA is measured in free air with the component mounted on a high effective thermal conductivity test board with "direct attach" features. See Tech Brief TB379. 2. For JC, the "case temp" location is the center of the exposed metal pad on the package underside.
Electrical Specifications
SYMBOL GENERAL VS IS_DIS IS UVLO
VIN = ENABLE = 5V, VDD1 = VDD2 = 14V, VGH = 25V, AVDD = 10V, TA = -40C to +85C Unless Otherwise Noted. PARAMETER TEST CONDITION MIN TYP MAX UNIT
VIN Input Voltage Range VIN Supply Currents when Disabled VIN Supply Currents Under Voltage Lockout Threshold ENABLE = 0V ENABLE = 5V, LX not switching VIN2 Rising VIN2 Falling
2.7
3.3 1 1
5.5 3.5
V A mA
2.3 2.2
2.45 2.35 140 100
2.6 2.5
V V C C
OTR OTF
Thermal Shutdown Temperature
Temperature Rising Temperature Falling
LOGIC INPUT CHARACTERISTICS - ENABLE, VFLK, FREQ, VDPM VIL VIH RIL Low Voltage Threshold High Voltage Threshold Pull-Down Resistor Enabled, Input at VIN 2.2 150 250 400 0.8 V V k
STEP-UP SWITCHING REGULATOR AVDD Output Voltage Range 50mA < ILOAD < 250mA ILOAD = 150mA, 3.0 < VIN < 5.5V 10mA < ILOAD < 300mA, 3.0 < VIN < 5.5V, 0C < TA < +85C ILOAD = 100mA, TA = +25C ILOAD = 100mA, TA = -40C to +85C IFB FB Input Bias Current -3 1.20 1.19 1.21 1.21 250 VIN*1.25 0.2 0.15 0.25 3 1.22 1.23 500 20 V % % % V V nA
VBOOST/IOUT Load Regulation VBOOST/VIN ACCAVDD VFB Line Regulation Overall Accuracy (Line, Load, Temperature) Feedback Voltage (VFB)
3
FN6353.0 July 2, 2007
ISL97645A
Electrical Specifications
SYMBOL rDS(ON) EFF ILIM DMAX fOSC VIN = ENABLE = 5V, VDD1 = VDD2 = 14V, VGH = 25V, AVDD = 10V, TA = -40C to +85C Unless Otherwise Noted. (Continued) PARAMETER Switch On Resistance Peak Efficiency Switch Current Limit Max Duty Cycle Oscillator Frequency FREQ = 0V FREQ = VIN2 ISS Soft-Start Slew Current SS < 1V, TA = +25C 85 550 1.0 TEST CONDITION MIN TYP 150 92 2.9 90 650 1.2 2.75 800 1.4 MAX 300 UNIT m % A % kHz MHz A
VCOM AMPLIFIER RLOAD = 10k, CLOAD = 10pF, Unless Otherwise Stated VSAMP ISAMP VOS IB CMIR CMRR PSRR VOH VOH VOL VOL ISC SR BW Supply Voltage Supply Current Offset Voltage Noninverting Input Bias Current Common Mode Input Voltage Range Common-Mode Rejection Ratio Power Supply Rejection Ratio Output Voltage Swing High Output Voltage Swing High Output Voltage Swing Low Output Voltage Swing Low Output Short Circuit Current Slew Rate Gain Bandwidth -3dB gain point IOUT(source) = 5mA IOUT(source) = 50mA IOUT(sink) = 5mA IOUT(sink) = 50mA 250 0 50 70 70 85 VDD2 - 50 VDD2 - 450 50 450 400 50 30 4.5 3 3 0 20 100 VDD2 20 V mA mV nA V dB dB mV mV mV mV mA V/s MHz
GATE PULSE MODULATOR VGH VIH_VDPM IVGH VGH Voltage VDPM Enable Threshold VGH Input Current VFLK = 0 RE = 33k, VFLK = VDD1 VDD1 IVDD1 RONVGH IDIS_VGH IDPM tDEL SUPPLY MONITOR VIH_VDIV VIL_VDIV VDIV High Threshold VDIV Low Threshold CD2 Charge Current RESET Pull-Down Resistance RESET Delay on the Rising Edge VDIV rising VDIV falling 10 750 121.5k*CD 1.18 1.05 V V A s VDD1 Voltage VDD1 Input Current VGH to VGH_M On Resistance VGH_M Discharge Current VDPM Charge Current DELAY Time CE = 470pF, RE = 33k RE = 33k 3 -2 0.1 70 8 20 1.9 7 1.18 1.215 260 40 VGH - 2 2 30 1.25 V V A A V A mA A s
ICD2
RIL_RESET
TDELAY_RESET
4
FN6353.0 July 2, 2007
ISL97645A
I
Typical Performance Curves
100 90 LOAD REGULATION (%) 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 200 400 600 800 IAVDD (mA) 1000 1200 fOSC = 1.2MHz fOSC = 650kHz 0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 -0.9 0 200 400 600 800 IAVDD (mA) 1000 1200 fOSC = 1.2MHz fOSC = 650kHz
FIGURE 1. AVDD EFFICIENCY vs IAVDD
FIGURE 2. AVDD LOAD REGULATION vs IAVDD
10.5 10.45 AVDD 150mA 10.4 AVDD (V) 10.35 10.3 10.25 10.2 10.15 3 3.5 4.0 4.5 VIN (V) 5.0 5.5 6.0 AVDD 500mA
L = 10H, COUT = 40F, CCOMP = 2.2nF, RCOMP = 10k IAVDD
AVDD (AC COUPLED)
FIGURE 3. LINE REGULATION AVDD vs VIN
FIGURE 4. BOOST CONVERTER TRANSIENT RESPONSE
CE = 1pF, RE = 100k
CE = 1000pF, RE = 100k
VGH_M
VGH_M
VFLK
VFLK
FIGURE 5. GPM CIRCUIT WAVEFORM
FIGURE 6. GPM CIRCUIT WAVEFORM
5
FN6353.0 July 2, 2007
ISL97645A Typical Performance Curves (Continued)
CE = 10pF, RE = 100k CE = 10pF, RE = 150k
VGH_M
VGH_M
VFLK
VFLK
FIGURE 7. GPM CIRCUIT WAVEFORM
FIGURE 8. GPM CIRCUIT WAVEFORM
INPUT SIGNAL
OUTPUT SIGNAL
FIGURE 9. VGHM FOLLOWS VGH WHEN THE SYSTEM POWERS OFF
FIGURE 10. VCOM RISING SLEW RATE
INPUT SIGNAL
OUTPUT SIGNAL (-3dB ATTENTUATION FROM INPUT SIGNAL)
FIGURE 11. VCOM BANDWIDTH MEASUREMENT
6
FN6353.0 July 2, 2007
ISL97645A Block Diagram
FREQ LX
OSCILLATION GENERATOR SLOPE COMPENSATION COMP FB + SUMMING AMPLIFIER PWM LOGIC
+
2.5A PGND
SS VIN REFERENCE GENERATOR START-UP AND FAULT CONTROL 20A VDPM
ENABLE 10A CD2 VREF + -
RESET
OUT
VDIV VREF
+ 750 + -
VDD2 POS NEG GND
GPM CIRCUIT
VDD1
VFLK
VGH VGH_M CE
RE
FIGURE 12. ISL97645A BLOCK DIAGRAM
7
FN6353.0 July 2, 2007
ISL97645A Functional Block Diagram
VIN VIN AVDD
LX
COMP
BOOST
FB
SS
PGND
VSHDN V ON FREQVGH VDPM VFLK CE VGH_M RE VDD2 POS OUT NEGVIN RESET AGND VDIV REF CD2 VIN VGATE GPM CIRCUIT VDD1
GND
FIGURE 13. FUNCTIONAL BLOCK DIAGRAM
Applications Information
The ISL97645A provides a complete power solution for TFT LCD applications. The system consists of one boost converter to generate AVDD voltage for column drivers, one integrated VCOM buffer which can provide up to 400mA peak current, and one supply monitor to generate the reset signal when the input voltage is low. This part also integrates Gate Pulse Modulator circuit that can help to optimize the picture quality.
Boost Converter
Frequency Selection
The ISL97645A switching frequency can be user selected to operate at either constant 650kHz or 1.2MHz. Lower switching frequency can save power dissipation, while higher switching frequency can allow smaller external components like inductor and output capacitors, etc. Connecting the FREQ pin to GND sets the PWM switching frequency to 650MHz, or connecting FREQ pin to VIN for 1.2MHz.
Enable Control
When enable pin is pulling down, the ISL97645A is shut down reducing the supply current to <10A. When the voltage at enable pin reaches 2.2V, the ISL97645A is on.
Soft-Start
The soft-start is provided by an internal 2.5A current source to charge the external soft-start capacitor. The ISL97645A ramps up current limit from 0A up to full value, as the voltage at SS pin ramps from 0 to 1.2V. Hence the soft-start time is 4.8ms when the soft-start capacitor is 10nF, 22.6ms for 47nF and 48ms for 100nF.
8
FN6353.0 July 2, 2007
ISL97645A
Operation
The boost converter is a current mode PWM converter operating at either a 650kHz or 1.2MHz. It can operate in both discontinuous conduction mode (DCM) at light load and continuous mode (CCM). In continuous current mode, current flows continuously in the inductor during the entire switching cycle in steady state operation. The voltage conversion ratio in continuous current mode is given by Equation 1:
V Boost 1 ------------------ = -----------1-D V IN (EQ. 1)
The current through the MOSFET is limited to 2.6APEAK. This restricts the maximum output current (average) based on Equation 3:
I L V IN I OMAX = I LMT - -------- x -------- 2 VO (EQ. 3)
Where IL is peak to peak inductor ripple current, and is set by Equation 4:
V IN D I L = --------- x --L fs (EQ. 4)
Where D is the duty cycle of the switching MOSFET. Figure 12 shows the block diagram of the boost regulator. It uses a summing amplifier architecture consisting of gm stages for voltage feedback, current feedback and slope compensation. A comparator looks at the peak inductor current cycle by cycle and terminates the PWM cycle if the current limit is reached. An external resistor divider is required to divide the output voltage down to the nominal reference voltage. 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 in the order of 60k is recommended. The boost converter output voltage is determined by Equation 2:
R1 + R2 V Boost = -------------------- x V FB R2 (EQ. 2)
where fS is the switching frequency (650kHz or 1.2MHz). Table 2 gives typical values (margins are considered 10%, 3%, 20%, 10% and 15% on VIN, VO, L, fS and IOMAX).
Capacitor
An input capacitor is used to suppress the voltage ripple injected into the boost converter. The ceramic capacitor with capacitance larger than 10F is recommended. The voltage rating of input capacitor should be larger than the maximum input voltage. Some capacitors are recommended in Table 1 for input capacitor.
TABLE 1. BOOST CONVERTER INPUT CAPACITOR RECOMMENDATION CAPACITOR 10F/16V 10F/10V 22F/10V SIZE 1206 0805 1210 MFG TDK Murata Murata PART NUMBER C3216X7R1C106M GRM21BR61A106K GRB32ER61A226K
TABLE 2. MAXIMUM OUTPUT CURRENT CALCULATION VIN (V) 3 3 3 5 5 5 5 3 3 3 5 5 5 5 VO (V) 9 12 15 9 12 15 18 9 12 15 9 12 15 18 L (H) 10 10 10 10 10 10 10 10 10 10 10 10 10 10 FS (MHz) 0.65 0.65 0.65 0.65 0.65 0.65 0.65 1.2 1.2 1.2 1.2 1.2 1.2 1.2 IOMAX (mA) 636 419 289 1060 699 482 338 742 525 395 1236 875 658 514
9
FN6353.0 July 2, 2007
ISL97645A
Inductor
The boost inductor is a critical part which influences the output voltage ripple, transient response, and efficiency. Values of 3.3H to 10H are used to match the internal slope compensation. The inductor must be able to handle the following average and peak current are in Equation 5:
IO I LAVG = -----------1-D I L I LPK = I LAVG + -------2 (EQ. 5)
For low ESR ceramic capacitors, the output ripple is dominated by the charging and discharging of the output capacitor. The voltage rating of the output capacitor should be greater than the maximum output voltage. Note: Capacitors have a voltage coefficient that makes their effective capacitance drop as the voltage across then increases. COUT in the equation above assumes the effective value of the capacitor at a particular voltage and not the manufacturer's stated value, measured at 0V. Table 5 shows some selections of output capacitors.
TABLE 5. BOOST OUTPUT CAPACITOR RECOMMENDATION CAPACITOR 10F/25V 10F/25V SIZE 1210 1210 MFG TDK Murata PART NUMBER C3225X7R1E106M GRM32DR61E106K
Some inductors are recommended in Table 3.
TABLE 3. BOOST INDUCTOR RECOMMENDATION INDUCTOR 6.8H/3APEAK 10H/4APEAK DIMENSIONS (mm) 7.3x6.8x3.2 8.3x8.3x4.5 MFG TDK Sumida PART NUMBER RLF7030T-6R8N3R0 CDR8D43-100NC
Compensation
The boost converter of ISL97645A can be compensated by a RC network connected from CM1 pin to ground. 4.7nF and 10k RC network is used in the demo board. The larger value resistor and lower value capacitor can lower the transient overshoot, however, at the expense of stability of the loop.
5.2H/4.55APEAK 10x10.1x3.8
Cooper CD1-5R2 Bussmann
Rectifier Diode
A high-speed diode is necessary due to the high switching frequency. Schottky diodes are recommended because of their fast recovery time and low forward voltage. The reverse voltage rating of this diode should be higher than the maximum output voltage. The rectifier diode must meet the output current and peak inductor current requirements. The following table is some recommendations for boost converter diode.
TABLE 4. BOOST CONVERTER RECTIFIER DIODE RECOMMENDATION DIODE SS23 MBRS340 SL23 VR/IAVG RATING 30V/2A 40V/3A 30V/2A PACKAGE SMB SMC SMB MFG Fairchild Semiconductor International Rectifier Vishay Semiconductor
Cascaded MOSFET Application
An 20V N-Channel MOSFET is integrated in the boost regulator. For the applications where the output voltage is greater than 20V, an external cascaded MOSFET is needed as shown in Figure 14. The voltage rating of the external MOSFET should be greater than AVDD.
VIN AVDD
LX FB INTERSIL ISL97645A
Output Capacitor
The output capacitor supplies the load directly and reduces the ripple voltage at the output. Output ripple voltage consists of two components: 1. the voltage drop due to the inductor ripple current flowing through the ESR of output capacitor. 2. charging and discharging of the output capacitor.
IO V O - V IN 1 V RIPPLE = I LPK x ESR + ----------------------- x --------------- x --C OUT f s VO (EQ. 6) FIGURE 14. CASCADED MOSFET TOPOLOGY FOR HIGH OUTPUT VOLTAGE APPLICATIONS
10
FN6353.0 July 2, 2007
ISL97645A Supply Monitor Circuit
The Supply Monitor circuit monitors the voltage on VDIV, and sets open-drain output RESET low when VDIV is below 1.15V (rising) or 1.1V (falling). There is a delay on the rising edge, controlled by a capacitor on CD2. When VDIV exceeds 1.15V (rising), CD2 is charged up from 0V to 1.215V by a 10A current source. Once CD2 exceeds 1.215V, RESET will go tri-state. When VDIV falls below 1.1V, RESET will become low with a 750 pull-down resistance. The delay time is controlled by Equation 7:
t delay = 121.5k x CD2 (EQ. 7)
Low to high transition is determined primarily by the switch resistance and the external capacitive load. High to low transition is more complex. Take the case where the block is already enabled (VDPM is H). When VFLK is H, pin CE is grounded. On the falling edge of VFLK, a current is passed into pin CE, to charge an external capacitor to 1.2V. This creates a delay, equal to CE*4200. At this point, the output begins to pull down from VGH to VDD1. The slew current is equal to 300/(RE + 5000), and the dv/dt slew rate is Isl/CLOAD. where CLOAD is the load capacitance applied to VGHM. When RESET signal changes to low, and VGH voltage is above 2.5V, the VGH_M will be tied to VGH voltage until the VGH voltage falls down to 2.5V. If the VGH voltage is lower than 2.5V, GPM block will not work properly, and there is no active control for VGH_M output. The following table shows the VGH_M status based on Vin, VGH and RESET:
For example, the delay time is 12.15ms if the CD2 = 100nF. Figure 15 is the Supply Monitor Circuit timing diagram.
1.15V VDIV 1.1V 1.215V CD2
RESET
RESET DELAY TIME IS CONTROLLED BY CD2 CAPACITOR
FIGURE 15. SUPPLY MONITOR CIRCUIT TIMING DIAGRAM
Gate Pulse Modulator Circuit
The gate pulse modulator circuit functions as a three way multiplexer, switching VGHM between ground, VDD1 and VGH. Voltage selection is provided by digital inputs VDPM (enable) and VFLK (control). High to low delay and slew control is provided by external components on pins CE and RE, respectively. A block diagram of the gate pulse modulator circuit is shown in Figure 16. When VDPM is LOW, the block is disabled and VGHM is grounded. When the input voltage exceeds UVLO threshold, VDPM starts to drive an external capacitor with 20A. Once VDPM exceeds 1.215V, the GPM circuit is enabled, and the output VGH_M is determined by VFLK, RESET signal and VGH voltage. If RESET signal is high, and when VFLK goes high, VGHM is pulled to VGH by a 70 switch. When VFLK goes low, there is a delay controlled by capacitor CE, following which VGHM is driven to VDD1, with a slew rate controlled by resistor RE. Note that VDD1 is used only as a reference voltage for an amplifier, thus does not have to source or sink a significant DC current.
11
FN6353.0 July 2, 2007
ISL97645A
.
VGH
VGH_M VGH_M EnGPM1
VDD1
x240 VREF
RE
200A
CE
VFLK
CONTROL AND TIMING
FIGURE 16. GATE PULSE MODULATOR CIRCUIT BLOCK DIAGRAM
12
FN6353.0 July 2, 2007
ISL97645A
V in U V LO T hreshold 0 VGH
RESET
VDPM
1.215V
V FL K
VGH V G H _M VGL S lope is controlled by RE P ow er on dela y tim e is co ntrolled b y C D P M D ela y tim e is controlled b y C E
V G H _M is forced to V G H w h en R E S E T goes to low A N D V G H >2.5V
FIGURE 17. GATE PULSE MODULATOR TIMING DIAGRAM TABLE 6. VGH_M STATUS TABLE VIN x VDPM x RESET x VGH <2.5V VGH_M GROUND COMMENT Will be grounded if VIN is above a logic threshold. Could occur at power up or power down Startup only condition:If either VIN> VLOR or reset is H, but VDPM < 1.215V, GND VGHM
>VLOR x >VLOR
<1.215V <1.215V >1.215V
x High High
>2.5V >2.5V >2.5V
GROUND GROUND Switching controlled by VFLK VGH
x
x
Low
>2.5V
Power down state. Could occur at power up if part starts with VGH > 2.5V
Start-Up Sequence
When VIN exceeds VLOR and ENABLE reaches the VIH threshold value, Boost converter starts up, and gate pulse modulator circuit output holds until VDPM is charged to 1.215V. Note that there is a DC path in the boost converter from the input to the output through the inductor and diode, hence the input voltage will be seen at output with a forward voltage drop of diode before the part is enabled. If this voltage is not desired, the following circuit can be inserted between input and inductor to disconnect the DC path when the part is disabled.
.
TO INDUCTOR
INPUT
ENABLE
FIGURE 18. CIRCUIT TO DISCONNECT THE DC PATH OF BOOST CONVERTER
13
FN6353.0 July 2, 2007
ISL97645A VCOM Amplifier
The VCOM amplifier is designed to control the voltage on the back plate of an LCD display. This plate is capacitively coupled to the pixel drive voltage which alternately cycles positive and negative at the line rate for the display. Thus the amplifier must be capable of sourcing and sinking capacitive pulses of current, which can occasionally be quite large (a few 100mA for typical applications). The ISL97645A VCOM amplifier's output current is limited to 400mA. This limit level, which is roughly the same for sourcing and sinking, is included to maintain reliable operation of the part. It does not necessarily prevent a large temperature rise if the current is maintained. (In this case the whole chip may be shut down by the thermal trip to protect functionality.) If the display occasionally demands current pulses higher than this limit, the reservoir capacitor will provide the excess and the amplifier will top the reservoir capacitor back up once the pulse has stopped. This will happen on the s time scale in practical systems and for pulses 2 or 3 times the current limit, the VCOM voltage will have settled again before the next line is processed.
Layout Recommendation
The device's performance including efficiency, output noise, transient response and control loop stability is dramatically affected by the PCB layout. PCB layout is critical, especially at high switching frequency. There are some general guidelines for layout: 1. Place the external power components (the input capacitors, output capacitors, boost inductor and output diodes, etc.) in close proximity to the device. Traces to these components should be kept as short and wide as possible to minimize parasitic inductance and resistance. 2. Place VIN and VDD bypass capacitors close to the pins. 3. Reduce the loop area with large AC amplitudes and fast slew rate. 4. The feedback network should sense the output voltage directly from the point of load, and be as far away from LX node as possible. 5. The power ground (PGND) and signal ground (SGND) pins should be connected at only one point. 6. The exposed die plate, on the underneath of the package, should be soldered to an equivalent area of metal on the PCB. This contact area should have multiple via connections to the back of the PCB as well as connections to intermediate PCB layers, if available, to maximize thermal dissipation away from the IC. 7. To minimize the thermal resistance of the package when soldered to a multi-layer PCB, the amount of copper track and ground plane area connected to the exposed die plate should be maximized and spread out as far as possible from the IC. The bottom and top PCB areas especially should be maximized to allow thermal dissipation to the surrounding air. 8. A signal ground plane, separate from the power ground plane and connected to the power ground pins only at the exposed die plate, should be used for ground return connections for control circuit. 9. Minimize feedback input track lengths to avoid switching noise pick-up. A demo board is available to illustrate the proper layout implementation.
Fault Protection
ISL97645A provides the overall fault protections including over current protection and over-temperature protection. An internal temperature sensor continuously monitors the die temperature. In the event that die temperature exceeds the thermal trip point, the device will shut down and disable itself. The upper and lower trip points are typically set to +140C and +100C respectively.
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 14
FN6353.0 July 2, 2007
ISL97645A
Package Outline Drawing
L24.4x4D
24 LEAD QUAD FLAT NO-LEAD PLASTIC PACKAGE Rev 2, 10/06
4X 2.5 4.00 A B 19 20X 0.50 24 PIN #1 CORNER (C 0 . 25)
PIN 1 INDEX AREA
18
1
4.00
2 . 50 0 . 15
13
(4X)
0.15 12 7 0.10 M C A B 0 . 07 24X 0 . 23 + 0 . 05 4 24X 0 . 4 0 . 1
TOP VIEW
BOTTOM VIEW
SEE DETAIL "X"
0.10 C
0 . 90 0 . 1
( 3 . 8 TYP )
C BASE PLANE
SIDE VIEW
SEATING PLANE 0.08 C
(
2 . 50 ) ( 20X 0 . 5 )
C ( 24X 0 . 25 ) ( 24X 0 . 6 )
0 . 2 REF
5
0 . 00 MIN. 0 . 05 MAX.
DETAIL "X"
TYPICAL RECOMMENDED LAND PATTERN
NOTES: 1. Dimensions are in millimeters. Dimensions in ( ) for Reference Only. 2. Dimensioning and tolerancing conform to AMSE Y14.5m-1994. 3. Unless otherwise specified, tolerance : Decimal 0.05 4. Dimension b applies to the metallized terminal and is measured between 0.15mm and 0.30mm from the terminal tip. 5. Tiebar shown (if present) is a non-functional feature. 6. The configuration of the pin #1 identifier is optional, but must be located within the zone indicated. The pin #1 identifier may be either a mold or mark feature.
15
FN6353.0 July 2, 2007

▲Up To Search▲

Price & Availability of ISL97645A

	To Download ISL97645A Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .