DATASHEET

ISL97644
®
Data Sheet
December 14, 2007
Boost + LDO + VON Slice + VCOM
Features
The ISL97644 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, an integrated logic LDO and a high
performance VCOM amplifier.
• 3V to 5.5V Input
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 logic LDO includes a 350mA FET for driving the low
voltage needed by the external digital circuitry.
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 integrated VCOM features high speed and drive
capability. With 30MHz bandwidth and 50V/µs slew rate, the
VCOM amplifier is capable of driving 400mA peaks, and
100mA continuous output current.
FN9228.1
• 2.6A Integrated Boost for Up to 20V AVDD
• Integrated VON Slice
• 350mA VLOGIC LDO
- 2.5V, 2.85V, 3.3V Output Voltage Selectable
• 600kHz/1.2MHz fS
• VCOM Amplifier
- 30MHz BW
- 50V/µs SR
- 400mA Peak Output Current
• UV and OT Protection
• 24 Ld 4x4 QFN
• Pb-Free (RoHS Compliant)
Applications
• LCD Monitors (15”+)
Pinout
• Notebook Display (up to 16”)
ISL97644
(24 LD 4x4 QFN)
TOP VIEW
VGH
RE
CE
PGND
FB
ENABLE
Ordering Information
24
23
22
21
20
19
TEMP.
RANGE
PART NUMBER
PART
(°C)
(Note)
MARKING
PACKAGE
(Pb-Free)
PKG.
DWG. #
ISL97644IRZ
97644IRZ -40 to +85 24 Ld 4x4 QFN L24.4x4D
ISL97644IRZ-T*
97644IRZ -40 to +85 24 Ld 4x4 QFN L24.4x4D
Tape & Reel
17
VIN_2
VFLK
3
16
FREQ
ISL97644IRZ-TK* 97644IRZ -40 to +85 24 Ld 4x4 QFN L24.4x4D
Tape & Reel
VDPM
4
15
COMP
*Please refer to TB347 for details on reel specifications.
VDD_1
5
14
SS
VDD_2
6
13
VIN_1
7
8
9
1
10
11
12
LDO_OUT
2
ADJ
VGH_M
AGND
LX
POS
18
NEG
1
OUT
GND
NOTE: These Intersil Pb-free plastic packaged products employ
special Pb-free material sets; molding compounds/die attach
materials and 100% matte tin plate PLUS ANNEAL - e3 termination
finish, which is 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.
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. 2006, 2007. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
ISL97644
Pin Descriptions
PIN NUMBER
PIN NAME
1
GND
2
VGH_M
3
VFLK
Gate Pulse Modulation Control Input
4
VDPM
Gate Pulse Modulation Enable
5
VDD_1
Gate Pulse Modulation Lower Voltage Input
6
VDD_2
VCOM Amplifier Supply
7
OUT
VCOM Amplifier Output
8
NEG
VCOM Amplifier Inverting Input
9
POS
VCOM Amplifier Noninverting Input
10
AGND
VCOM Amplifier Ground
11
ADJ
LDO Output Adjust Pin
12
LDO_OUT
13
VIN_1
14
SS
15
COMP
Boost Converter Compensation Pin. Connect a series resistor and capacitor between this pin and
GND to optimize transient response.
16
FREQ
Boost Converter Frequency Select.
17
VIN_2
Boost Converter Power Supply
18
LX
19
ENABLE
20
FB
21
PGND
22
CE
Gate Pulse Modulator Delay Control. Connect a capacitor between this pin and GND to set the
delay time.
23
RE
Gate Pulse Modulator Slew Control. Connect a resistor between this pin and GND to set the falling
slew rate.
24
VGH
2
FUNCTION
Ground
Gate Pulse Modulation Output
LDO Output
LDO power supply
Boost Converter Soft-start. Connect a capacitor between this pin and GND to set the soft-start
time.
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 High Voltage Input
FN9228.1
December 14, 2007
ISL97644
Absolute Maximum Ratings
Thermal Information
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 Resistance
Recommended Operating Conditions
Input Voltage Range, VS . . . . . . . . . . . . . . . . . . . . . . . . . 3V to 5.5V
Boost Output Voltage Range, AVDD . . . . . . . . . . . . . . . . . 8V to 20V
Input Capacitance, CIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22µF
Boost Inductor, L1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3µH to 10µH
LDO Output Capacitance. . . . . . . . . . . . . . . . . . . . . . .2.2µF to 10µF
Output Capacitance, COUT . . . . . . . . . . . . . . . . . . . . . . . . . . 2x22µF
Operating Ambient Temperature Range . . . . . . . . . .-40°C to +85°C
Operating Junction Temperature . . . . . . . . . . . . . . .-40°C to +125°C
θJA (°C/W)
θJC (°C/W)
4x4 QFN Package (Notes 1, 2) . . . . . .
39
2.5
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . See Curves
Maximum Continuous Junction Temperature . . . . . . . . . . . +125°C
Power Dissipation
TA ≤ +25°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.44W
TA = +70°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.34W
TA = +85°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.98W
TA = +100°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.61W
Pb-free reflow profile . . . . . . . . . . . . . . . . . . . . . . . . . .see link below
http://www.intersil.com/pbfree/Pb-FreeReflow.asp
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. θJA 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 θJC, the “case temp” location is the center of the exposed metal pad on the package underside.
Electrical Specifications
SYMBOL
VIN1 = VIN2 = ENABLE = 5V, VDD1 = VDD2 = 14V, VGH = 25V, AVDD = 10V, TA = -40°C to +85°C
Unless Otherwise Noted.
PARAMETER
TEST CONDITION
MIN
TYP
MAX
UNIT
3.0
5.0
5.5
V
0.2
2
µA
GENERAL
VS
VIN1, VIN2 Input Voltage Range
See separate LDO specifications
IS_DIS
Sum of VIN1, VIN2 Supply Currents
when Disabled
ENABLE = 0V
IS
Sum of VIN1, VIN2 Supply Currents
ENABLE = 5V, LX not switching, LDO
not loaded
UVLO
Undervoltage Lockout Threshold
VIN2 Rising
2.3
2.45
2.6
V
VIN2 Falling
2.2
2.35
2.5
V
OTR
Thermal Shutdown Temperature
OTF
1
mA
Temperature Rising
140
C
Temperature Falling
100
C
LOGIC INPUT CHARACTERISTICS - ENABLE, VFLK, FREQ, VDPM
VIL
Low Voltage Threshold
VIH
High Voltage Threshold
RIL
Pull-Down Resistor
0.8
2.2
Enabled, Input at VIN2
150
V
V
250
400
kΩ
20
V
STEP-UP SWITCHING REGULATOR
AVDD
Output Voltage Range
ΔAVDD/ΔIOUT
Load Regulation
50mA < ILOAD < 250mA
0.2
ΔAVDD/ΔVIN
Line Regulation
ILOAD = 150mA, 3.0 < VIN1 < 5.5V
0.15
ACCAVDD
Overall Accuracy (Line, Load,
Temperature)
10mA < ILOAD < 300mA, 3.0 < VIN1
< 5.5V, 0°C < TA < +85°C
3
VIN*1.25
-3
%
0.25
%/V
3
%
FN9228.1
December 14, 2007
ISL97644
Electrical Specifications
SYMBOL
VFB
VIN1 = VIN2 = ENABLE = 5V, VDD1 = VDD2 = 14V, VGH = 25V, AVDD = 10V, TA = -40°C to +85°C
Unless Otherwise Noted. (Continued)
PARAMETER
Feedback Voltage (VFB)
TEST CONDITION
MIN
TYP
MAX
UNIT
ILOAD = 100mA, TA = +25°C
1.20
1.21
1.22
V
ILOAD = 100mA, TA = -40°C to +85°C
1.19
1.21
1.23
V
IFB
FB Input Bias Current
250
500
nA
RDS(ON)
Switch On Resistance
150
300
mΩ
EFF
Peak Efficiency
92
%
ILIM
Switch Current Limit
2.1
2.6
A
DMAX
Max Duty Cycle
85
90
%
FOSC
Oscillator Frequency
FREQ = 0V
550
650
800
kHz
FREQ = VIN2
1.0
1.2
1.4
MHz
ISS
Soft-Start Slew Current
SS < 1V, TA = +25°C
2.75
µA
LDO REGULATOR
VSL
VLDO
Input Voltage Range VIN1
Output Voltage
ADJ = LDO_OUT
3.0
5.5
V
ADJ OPEN
3.35
5.5
V
ADJ = 0V
3.8
5.5
V
ADJ = GND, ILDO = 1mA
3.31
V
ADJ = GND, ILDO = 350mA
3.29
V
ADJ OPEN, ILDO = 1mA
2.86
V
ADJ OPEN, ILDO = 350mA
2.84
V
ADJ = LDO_OUT, ILDO = 1mA
2.51
V
ADJ = LDO_OUT, ILDO = 350mA
2.49
V
ACCLDO
Overall Accuracy
1mA < ILDO < 350mA
ΔVLDO/ΔVIN
Line Regulation
ILDO = 1mA, 3.0V < VIN1 < 5.5V
ΔVLDO/ΔIOUT
Load Regulation
VDO
ILIML
-4
4
%
2
mV/V
1mA < ILDO < 350mA
0.75
%
Dropout Voltage
Output drops by 2%, ILDO = 350mA
300
Current Limit
Output drops by 2%
350
500
400
mV
mA
VCOM AMPLIFIER RLOAD = 10k, CLOAD = 10pF, Unless Otherwise Stated
VSAMP
Supply Voltage
4.5
ISAMP
Supply Current
3
VOS
Offset Voltage
3
20
mV
IB
Noninverting Input Bias Current
0
100
nA
CMIR
Common Mode Input Voltage
Range
0
VDD2
V
CMRR
Common-Mode Rejection Ratio
50
70
dB
PSRR
Power Supply Rejection Ratio
70
85
dB
VOH
Output Voltage Swing High
Iout(source) = 5mA
VDD2 - 50
mV
VOH
Output Voltage Swing High
Iout(source) = 50mA
VDD2 - 450
mV
VOL
Output Voltage Swing Low
Iout(sink) = 5mA
50
mV
VOL
Output Voltage Swing Low
Iout(sink) = 50mA
450
mV
4
20
V
mA
FN9228.1
December 14, 2007
ISL97644
Electrical Specifications
SYMBOL
VIN1 = VIN2 = ENABLE = 5V, VDD1 = VDD2 = 14V, VGH = 25V, AVDD = 10V, TA = -40°C to +85°C
Unless Otherwise Noted. (Continued)
PARAMETER
ISC
Output Short Circuit Current
SR
Slew Rate
BW
Gain Bandwidth
TEST CONDITION
MIN
TYP
250
400
mA
50
V/µs
30
MHz
-3dB gain point
MAX
UNIT
GATE PULSE MODULATOR
VGH
VGH Voltage
7
IVGH
VGH Input Current
30
V
VFLK = 0
260
µA
RE = 33kΩ, VFLK = VDD1
40
µA
VDD1
VDD1 Voltage
3
IVDD1
VDD1 Input Current
-2
RONVGH
VGH to VGH_M On Resistance
70
Ω
IDIS_VGH
VGH_M Discharge Current (Note 1) RE = 33kΩ
8
mA
TDEL
DELAY Time (Note 2)
1.9
µs
CE = 470pF, RE = 33kΩ
0.1
VGH - 2
V
2
µA
NOTES:
1. Nominal discharge current = 300/(RE+5kΩ).
2. Nominal delay time = 4000*CE.
5
FN9228.1
December 14, 2007
ISL97644
I
Typical Performance Curves
100
0
FOSC = 650kHz
90
-0.1
EFFICIENCY (%)
LOAD REGULATION (%)
FOSC = 1.2MHz
80
70
60
50
40
30
20
-0.3
FOSC = 650kHz
-0.4
-0.5
FOSC = 1.2MHz
-0.6
-0.7
-0.8
10
0
-0.2
0
200
400
600
800
IAVDD (mA)
1000
-0.9
1200
FIGURE 1. AVDD EFFICIENCY vs IAVDD
0
200
400
600
800
IAVDD (mA)
1000
1200
FIGURE 2. AVDD LOAD REGULATION vs IAVDD
10.5
L = 10µH, COUT = 40µF, CCOMP = 2.2nF, RCOMP = 10k
10.45
AVDD 150mA
IAVDD
AVDD (V)
10.4
AVDD 500mA
10.35
10.3
10.25
AVDD (AC COUPLED)
10.2
10.15
3
3.5
4.0
4.5
5.0
5.5
6.0
VIN (V)
FIGURE 3. LINE REGULATION AVDD vs VIN
FIGURE 4. BOOST CONVERTER TRANSIENT RESPONSE
0
3.4
3.3
LDO LOAD REGULATION (%)
3.3V OUTPUT, 100mA
3.3V OUTPUT, 350mA
3.2
LDO_OUT (V)
3.1
3.0
2.9
2.85V OUTPUT, 100mA
2.8
2.85V OUTPUT, 350mA
2.7
2.6
2.5V OUTPUT, 100mA
2.5
2.4
2.5V OUTPUT, 350mA
-0.2
-0.6
ADJ = OPEN
4
5
VIN (V)
FIGURE 5. LINE REGULATION LDO_OUT vs VIN
6
6
ADJ = LDO_OUT
-0.8
-1.0
-1.2
3
ADJ = 0
-0.4
0
100
200
300
400
IO (mA)
FIGURE 6. LDO LOAD REGULATION vs IO
FN9228.1
December 14, 2007
ISL97644
Typical Performance Curves (Continued)
CE = 1pF, RE = 100k
CE = 1000pF, RE = 100k
VGH_M
VGH_M
VFLK
VFLK
FIGURE 7. GPM CIRCUIT WAVEFORM
FIGURE 8. GPM CIRCUIT WAVEFORM
CE = 10pF, RE = 100k
CE = 10pF, RE = 150k
VGH_M
VGH_M
VFLK
VFLK
FIGURE 9. GPM CIRCUIT WAVEFORM
FIGURE 10. GPM CIRCUIT WAVEFORM
INPUT
SIGNAL
INPUT SIGNAL
OUTPUT SIGNAL
OUTPUT
SIGNAL
(-3dB ATTENTUATION
FROM INPUT SIGNAL)
FIGURE 11. VCOM RISING SLEW RATE
7
FIGURE 12. VCOM BANDWIDTH MEASUREMENT
FN9228.1
December 14, 2007
ISL97644
Block Diagram
FREQ
LX
OSCILLATION
GENERATOR
SLOPE
COMPENSATION
COMP
FB
SUMMING
AMPLIFIER
+
PWM
LOGIC
+
2.5µA
PGND
SS
REFERENCE
GENERATOR
VIN2
START-UP AND
FAULT CONTROL
VDPM
ENABLE
LDO
CONTROLLER
ADJ
VIN1
LDO_OUT
VDD2
POS
+
-
OUT
NEG
GND
GPM
CIRCUIT
VFLK
VGH VGH_M CE
VDD1
RE
FIGURE 13. ISL97644 BLOCK DIAGRAM
8
FN9228.1
December 14, 2007
ISL97644
Typical Application Diagram
L1
10µH
VIN
VIN2
C1
22µF
C3
2.2nF
D1
LX
AVDD
R1
10k
C2
47µF
C9 (OPTIONAL)
COMP
BOOST
R5
C4 10k
10nF SS
FB
R2
1.3k
PGND
ENABLE
FREQ-
VON
VGH
VDPM
VDD_1
VFLK
GPM
C5
470P CE
CIRCUIT
AVDD
R7
80k
R3
2k
TO ROW DRIVER
VDD2
RE
R6
130k
VGH_M
C10
2.2µF
POS
C11
1µF
NEGOUT
VCOM
+4.0V
VLOGIC
VIN1
C6
0.1µF
LDO_OUT
C7
4.7µF
AGND
LDO
GND
CONTROLLER
ADJ
FIGURE 14. TYPICAL APPLICATION DIAGRAM
Applications Information
Boost Converter
The ISL97644 provides a complete power solution for TFT
LCD applications. The system consists of one boost
converter to generate AVDD voltage for column drivers, one
logic LDO regulator to provide voltage to logic circuit in the
LCD panel, one integrated VCOM buffer which can provide
up to 400mA peak current. This part also integrates Gate
Pulse Modulator circuit that can help to optimize the picture
quality.
Frequency Selection
Enable Control
When enable pin is pulling down, the ISL97644 is shut down
reducing the supply current to <10µA. When the voltage at
enable pin reaches 2.2V, the ISL97644 is on.
9
The ISL97644 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 FREQ pin to ground sets the PWM switching
frequency to 650MHz, or connecting FREQ pin to VIN for
1.2MHz.
Soft-Start
The soft-start is provided by an internal 2.5µA current source
to charge the external soft start capacitor. The ISL97644
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.
FN9228.1
December 14, 2007
ISL97644
Operation
The current through the MOSFET is limited to 2.6APEAK.
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:
This restricts the maximum output current (average) based
on the following equation:
V Boost
1
------------------- = ------------1–D
V IN
ΔI L
V IN
I OMAX = ⎛ I LMT – --------⎞ × --------⎝
2 ⎠ VO
(EQ. 3)
Where ΔIL is peak to peak inductor ripple current, and is set
by:
V IN D
ΔI L = --------- × ---L
fs
(EQ. 1)
(EQ. 4)
Where D is the duty cycle of the switching MOSFET.
where fS is the switching frequency (650kHz or 1.2MHz).
Figure 13 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.
The 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 10µF 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.
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 60kΩ is recommended.
The boost converter output voltage is determined by the
following equation:
R1 + R2
V Boost = --------------------- × V FB
R2
TABLE 1. BOOST CONVERTER INPUT CAPACITOR
RECOMMENDATION
CAPACITOR
(EQ. 2)
SIZE
MFG
PART NUMBER
10µF/16V
1206
TDK
C3216X7R1C106M
10µF/10V
0805
Murata
GRM21BR61A106K
22µF/10V
1210
Murata
GRB32ER61A226K
TABLE 2. MAXIMUM OUTPUT CURRENT CALCULATION
VIN (V)
VO (V)
L (µH)
Fs (MHz)
IOMAX (mA)
3
9
10
0.65
636
3
12
10
0.65
419
3
15
10
0.65
289
5
9
10
0.65
1060
5
12
10
0.65
699
5
15
10
0.65
482
5
18
10
0.65
338
3
9
10
1.2
742
3
12
10
1.2
525
3
15
10
1.2
395
5
9
10
1.2
1236
5
12
10
1.2
875
5
15
10
1.2
658
5
18
10
1.2
514
10
FN9228.1
December 14, 2007
ISL97644
Inductor
The boost inductor is a critical part which influences the
output voltage ripple, transient response, and efficiency.
Values of 3.3µH to 10µH are used to match the internal
slope compensation. The inductor must be able to handle
the following average and peak current:
IO
I LAVG = ------------1–D
ΔI L
I LPK = I LAVG + -------2
(EQ. 5)
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 zero volts.
The following table shows some selections of output
capacitors.
TABLE 5. BOOST OUTPUT CAPACITOR RECOMMENDATION
Some inductors are recommended in Table 3.
CAPACITOR
TABLE 3. BOOST INDUCTOR RECOMMENDATION
INDUCTOR
DIMENSIONS
(mm)
MFG
PART NUMBER
6.8µH/3APEAK
7.3x6.8x3.2
TDK
RLF7030T-6R8N3R0
10µH/4APEAK
8.3X8.3X4.5
Sumida
CDR8D43-100NC
5.2µH/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.
SIZE
MFG
PART NUMBER
10µF/25V
1210
TDK
C3225X7R1E106M
10µF/25V
1210
Murata
GRM32DR61E106K
Compensation
The boost converter of ISL97644 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.
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 15. The voltage rating of the external
MOSFET should be greater than AVDD.
AVDD
VIN
TABLE 4. BOOST CONVERTER RECTIFIER DIODE
RECOMMENDATION
DIODE
VR/IAVG RATING
PACKAGE
SS23
30V/2A
SMB
Fairchild
Semiconductor
MBRS340
40V/3A
SMC
International
Rectifier
SL23
30V/2A
SMB
Vishay
Semiconductor
MFG
LX
FB
Intersil
ISL97644
Output Capacitor
The output capacitor supplies the load directly and reduces
the ripple voltage at the output. Output ripple voltage
consists of two components: the voltage drop due to the
inductor ripple current flowing through the ESR of output
capacitor, and the charging and discharging of the output
capacitor.
IO
V O – V IN
1
V RIPPLE = I LPK × ESR + ------------------------ × ---------------- × ---C OUT f s
VO
(EQ. 6)
For low ESR ceramic capacitors, the output ripple is
dominated by the charging and discharging of the output
11
FIGURE 15. CASCADED MOSFET TOPOLOGY FOR HIGH
OUTPUT VOLTAGE APPLICATIONS
Linear-Regulator (LDO)
The ISL97644 includes a LDO with adjustable output, and it
can supply current up to 350mA. The output voltage is
adjusted by connection of ADJ pin. When ADJ pin is
connected to ground, the output voltage is set to 3.3V; when
ADJ pin is floating, the output voltage is set to 2.85V, and
when ADJ pin is connected to LDO_OUT pin, the output
voltage is set to 2.5V.
FN9228.1
December 14, 2007
ISL97644
Gate Pulse Modulator Circuit
The efficiency of LDO is depended on the difference
between input voltage and output voltage, as well as the
output current:
η ( % ) = ( V IN1 – V LDO_OUT ) × I LDO_OUT × 100%
(EQ. 7)
The less difference between input and output voltage, the
higher efficiency it is. The minimum dropout voltage of LDO
of ISL97644 is 300mV.
The ceramic capacitors are recommended for the LDO input
and output capacitor. Larger capacitors help reduce noise
and deviation during transient load change.
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 VDPM is HIGH, the output is determined
by VFLK. When VFLK goes high, VGHM is pulled to VGH by
a 70Ω 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.
VGH
VGH_M
EnGPM1
+
VDD1
-
x240
VREF
+
RE
200µA
VFLK
-
+
CE
CONTROL AND
TIMING
FIGURE 16. GATE PULSE MODULATOR CIRCUIT BLOCK DIAGRAM
12
FN9228.1
December 14, 2007
ISL97644
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)*Load Capacitance.
TO INDUCTOR
INPUT
ENABLE
FIGURE 19. CIRCUIT TO DISCONNECT THE DC PATH OF
BOOST CONVERTER
VDPM
0
VFLK
SLOPE CONTROLLED
BY RE AND LOAD
CAPACITANCE
0
VGH
VGH_M
VDD_1
0
DELAY TIME
CONTROLLED BY CE
FIGURE 17. GATE PULSE MODULATOR TIMING DIAGRAM
Start-Up Sequence
Figure 18 shows a detailed start up sequence waveform.
VIN
0
ENABLE
0
VDPM
and inductor to disconnect the DC path when the part is
disabled.
VIN THRESHOLD
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 ISL97644 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 µs 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.
Fault Protection
0
ISL97644 provides the overall fault protections including
over current protection and over-temperature protection.
AVDD
VGH_M
LDO OUTPUT
0
FIGURE 18. START-UP SEQUENCE
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
+140°C and +100°C respectively.
When VIN exceeds 2.5V and ENABLE reaches the VIH
threshold value, Boost converter and LDO start up, and gate
pulse modulator circuit output holds until VDPM goes to
high. 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
13
FN9228.1
December 14, 2007
ISL97644
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.
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
FN9228.1
December 14, 2007
ISL97644
Package Outline Drawing
L24.4x4D
24 LEAD QUAD FLAT NO-LEAD PLASTIC PACKAGE
Rev 2, 10/06
4X 2.5
4.00
A
20X 0.50
B
PIN 1
INDEX AREA
PIN #1 CORNER
(C 0 . 25)
24
19
1
4.00
18
2 . 50 ± 0 . 15
13
0.15
(4X)
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
C
0 . 90 ± 0 . 1
BASE PLANE
( 3 . 8 TYP )
SEATING PLANE
0.08 C
SIDE VIEW
(
2 . 50 )
( 20X 0 . 5 )
C
0 . 2 REF
5
( 24X 0 . 25 )
0 . 00 MIN.
0 . 05 MAX.
( 24X 0 . 6 )
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 indentifier may be
either a mold or mark feature.
15
FN9228.1
December 14, 2007
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