DATASHEET

EL7585A
®
Data Sheet
March 9, 2006
FN7523.3
TFT-LCD Power Supply
Features
The EL7585A represents a multiple output regulators for use
in all large panel, TFT-LCD applications. It features a single
boost converter with integrated 3.5A FET, two positive LDOs
for VON and VLOGIC generation, and a single negative LDO
for VOFF generation. The boost converter can be
programmed to operate in either P-mode or PI-mode for
improved load regulation.
• 3.5A current limit FET options
The EL7585A also integrates fault protection for all four
channels. Once a fault is detected, the device is latched off
until the input supply or EN is cycled. This device also
features an integrated start-up sequence for VBOOST, VOFF,
then VON or for VOFF, VBOOST, and VON sequencing. The
latter requires a single external transistor. The timing of the
start-up sequence is set using an external capacitor. The
VLOGIC output is constantly enabled, but does shut down
when a fault condition is detected.
• 3V to 5V input
• Up to 20V boost out
• 1% regulation on all outputs
• VOFF-VBOOST-VON or
VBOOST-VOFF-VON sequence control
- VLOGIC is on from start-up for EL7585A
• Programmable sequence delay
• Fully fault protected
• Thermal shutdown
• Internal soft-start
• 20 Ld QFN packages
• Pb-free plus anneal available (RoHS compliant)
The EL7585A is specified for operation over the -40°C to
+85°C temperature range.
Applications
Pinout
• LCD monitors (15”+)
• LCD-TV (up to 40”+)
• Notebook displays (up to 16”)
• Industrial/medical LCD displays
16 FBB
17 SGND
18 EN
19 VDD
20 PG
EL7585A
(20 LD QFN)
TOP VIEW
CDLY 1
Ordering Information
15 CINT
PART NUMBER
14 VREF
DELB 2
THERMAL
PAD
LX1 3
13 PGND
12 PGND
LX2 4
DRVP 5
1
DRVN 10
SGND 9
FBL 8
DRVL 7
FBP 6
11 FBN
PART
MARKING
PACKAGE
TAPE &
REEL
PKG.
DWG. #
EL7585AILZ
(Note)
7585AIL Z
20 Ld 4x4 QFN
(Pb-free)
-
MDP0046
EL7585AILZ-T7
(Note)
7585AIL Z
20 Ld 4x4 QFN
(Pb-free)
7”
MDP0046
EL7585AILZ-T13 7585AIL Z
(Note)
20 Ld 4x4 QFN
(Pb-free)
13”
MDP0046
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.
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. 2005-2006. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
EL7585A
Absolute Maximum Ratings (TA = 25°C)
Thermal Information
VDRVP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36V
VDRVN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -20V
VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5V
VDELB, VLX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24V
Thermal Resistance (Typical, Notes 1, 2) θJA (°C/W) θJC (°C/W)
QFN Package. . . . . . . . . . . . . . . . . . . .
39
2.5
VDRVL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5V
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
Ambient Operating Temperature . . . . . . . . . . . . . . . .-40°C to +85°C
Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . See Curves
Maximum continuous junction temperature . . . . . . . . . . . . . . 125°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.
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.
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
VDD = 5V, VBOOST = 11V, ILOAD = 200mA, VON = 15V, VOFF = -5V, VLOGIC = 2.5V, over temperature from
-40°C to 85°C, unless otherwise specified.
DESCRIPTION
CONDITION
MIN
TYP
MAX
UNIT
5.5
V
SUPPLY
VS
Supply Voltage
IS
Quiescent Current
3
Enabled, LX not switching
1.7
2.5
mA
Disabled
700
900
µA
1000
1100
kHz
20
V
CLOCK
Oscillator Frequency
900
VBOOST
Boost Output Range
5.5
VFBB
Boost Feedback Voltage
FOSC
BOOST
VF_FBB
FBB Fault Trip Point
VREF
Reference Voltage
TA = 25°C
1.192
1.205
1.218
V
1.188
1.205
1.222
V
0.9
TA = 25°C
1.19
1.215
1.235
V
1.187
1.215
1.238
V
100
CREF
VREF Capacitor
22
DMAX
Maximum Duty Cycle
85
ILXMAX
Switch Current Limit
ILEAK
Switch Leakage Current
rDS(ON)
Switch On-Resistance
Eff
Boost Efficiency
I(VFBB)
Feedback Input Bias Current
Pl mode, VFBB = 1.35V
∆VBOOST/
∆VIN
Line Regulation
CINT = 4.7nF, IOUT = 100mA, VIN = 3V to 5.5V
∆VBOOST/
∆IBOOST
Load Regulation - “P” mode
CINT pin strapped to VDD,
50mA < ILOAD < 250mA
∆VBOOST/
∆IBOOST
Load Regulation - “PI” mode
CINT = 4.7nF, 50mA < IO < 250mA
VCINT_T
CINT Pl Mode Select Threshold
nF
%
3.5
VLX = 16V
See curves
2
V
A
10
µA
160
mΩ
92
%
50
500
nA
0.05
%/V
3
%
0.1
%
4.7
4.8
V
FN7523.3
March 9, 2006
EL7585A
Electrical Specifications
PARAMETER
VDD = 5V, VBOOST = 11V, ILOAD = 200mA, VON = 15V, VOFF = -5V, VLOGIC = 2.5V, over temperature from
-40°C to 85°C, unless otherwise specified. (Continued)
DESCRIPTION
CONDITION
MIN
TYP
MAX
UNIT
IDRVP = 0.2mA, TA = 25°C
1.176
1.2
1.224
V
IDRVP = 0.2mA
1.172
1.2
1.228
V
0.87
0.92
V
250
nA
VON LDO
VFBP
FBP Regulation Voltage
VF_FBP
FBP Fault Trip Point
VFBP falling
0.82
IFBP
FBP Input Bias Current
VFBP = 1.35V
-250
GMP
FBP Effective Transconductance
VDRVP = 25V, IDRVP = 0.2 to 2mA
∆VON/∆I(VON) VON Load Regulation
50
I(VON) = 0mA to 20mA
2
ms
-0.5
%
4
mA
IDRVP
DRVP Sink Current Max
VFBP = 1.1V, VDRVP = 25V
IL_DRVP
DRVP Leakage Current
VFBP = 1.5V, VDRVP = 35V
VFBN
FBN Regulation Voltage
IDRVN = 0.2mA, TA = 25°C
VF_FBN
FNN Fault Trip Point
IFBN
FBN Input Bias Current
VFBN = 0.2V
-250
GMN
FBN Effective Transconductance
VDRVN = -6V, IDRVN = 0.2mA to 2mA
∆VOFF/
∆I(VOFF)
VOFF Load Regulation
I(VOFF) = 0mA to 20mA
IDRVN
DRVN Source Current Max
VFBN = 0.3V, VDRVN = -6V
IL_DRVN
DRVN Leakage Current
VFBN = 0V, VDRVN = -20V
FBL Regulation Voltage
IDRVL = 1mA, TA = 25°C
1.176
1.2
1.224
V
IDRVL = 1mA
1.174
1.2
1.226
V
0.87
0.92
V
500
nA
0.1
5
µA
0.173
0.203
0.233
V
IDRVN = 0.2mA
0.171
0.203
0.235
V
VFBN rising
0.38
0.43
0.48
V
250
nA
VOFF LDO
2
50
ms
-0.5
%
4
mA
0.1
5
µA
VLOGIC LDO
VFBL
VF_FBL
FBL Fault Trip Point
VFBL falling
0.82
IFBL
FBL Input Bias Current
VFBL = 1.35V
-500
GML
FBL Effective Transconductance
VDRVL = 2.5V, IDRVL = 1mA to 8mA
200
ms
∆VLOGIC/
∆I(VLOGIC)
VLOGIC Load Regulation
I(VLOGIC) = 100mA to 500mA
0.5
%
IDRVL
DRVL Sink Current Max
VFBL = 1.1V, VDRVL = 2.5V
16
mA
IL_DRL
IL_DRVL
VFBL = 1.5V, VDRVL = 5.5V
0.1
tON
Turn On Delay
CDLY = 0.22µF
30
ms
tSS
Soft-start Time
CDLY = 0.22µF
2
ms
tDEL1
Delay Between AVDD and VOFF
CDLY = 0.22µF
10
ms
tDEL2
Delay Between VON and VOFF
CDLY = 0.22µF
17
ms
tDEL3
Delay Between VOFF and Delayed
VBOOST
CDLY = 0.22µF
10
ms
IDELB
DELB Pull-down Current
VDELB > 0.6V
50
µA
VDELB < 0.6V
1.4
mA
220
nF
50
ms
8
5
µA
SEQUENCING
CDEL
Delay Capacitor
10
FAULT DETECTION
tFAULT
Fault Time Out
CDLY = 0.22µF
3
FN7523.3
March 9, 2006
EL7585A
Electrical Specifications
PARAMETER
VDD = 5V, VBOOST = 11V, ILOAD = 200mA, VON = 15V, VOFF = -5V, VLOGIC = 2.5V, over temperature from
-40°C to 85°C, unless otherwise specified. (Continued)
DESCRIPTION
CONDITION
OT
Over-temperature Threshold
IPG
PG Pull-down Current
MIN
TYP
MAX
UNIT
140
°C
VPG>0.6V
15
µA
VPG<0.6V
1.7
mA
LOGIC ENABLE
VHI
Logic High Threshold
VLO
Logic Low Threshold
ILOW
Logic Low bias Current
IHIGH
Logic High bias Current
2.2
at VEN = 5V
V
0.8
V
0.2
1
µA
18
24
µA
12
Pin Descriptions
PIN NAME
PIN NUMBER
DESCRIPTION
1
CDLY
A capacitor connected from this pin to GND sets the delay time for start-up sequence and sets the fault
timeout time
2
DELB
Open drain output for gate drive of optional VBOOST delay FET
3, 4
LX1, LX2
5
DRVP
6
FBP
7
DRVL
Logic LDO base drive; open drain of an internal N channel FET
8
FBL
Logic LDO voltage feedback input pin; regulates to 1.2V nominal
9, 17
SGND
Low noise signal ground
10
DRVN
Negative LDO base drive; open drain of an internal P channel FET
11
FBN
Negative LDO voltage feedback input pin; regulates to 0.2V nominal
12, 13
PGND
Power ground, connected to source of internal N channel boost FET
14
VREF
Bandgap voltage bypass, connect a 0.1µF to SGND
15
CINT
VBOOST integrator output, connect capacitor to SGND for PI mode or connect to VDD for P mode
operation
16
FBB
Boost regulator voltage feedback input pin; regulates to 1.2V nominal
18
EN
Enable pin, High=Enable; Low or floating=Disable
19
VDD
20
PG
Drain of the internal N channel boost FET; for EL7586, pin 4 is not connected
Positive LDO base drive; open drain of an internal N channel FET
Positive LDO voltage feedback input pin; regulates to 1.2V nominal
Positive supply
Push-pull gate drive of optional fault protection FET, when chip is disabled or when a fault has been
detected, this is high
4
FN7523.3
March 9, 2006
EL7585A
Typical Performance Curves
100
100
VO=9V
90
80
VO=12V
70
EFFICIENCY (%)
EFFICIENCY (%)
80
VO=15V
60
50
40
30
50
40
30
20
10
0.1
0.2
0.3
0.4
0.5
0
0.6
0
0.5
IOUT (A)
100
VO=9V
90
80
70
VO=12V
VO=15V
60
EFFICIENCY (%)
EFFICIENCY (%)
VO=9V
90
80
50
40
30
60
50
40
30
20
20
10
10
0
0.1
0.2
0.3
0.4
0.5
0.6
0
0.7
VO=12V
VO=15V
70
0
0.5
1
1.5
IOUT (A)
IOUT (A)
FIGURE 3. VBOOST EFFICIENCY AT VIN=3V (P MODE)
FIGURE 4. VBOOST EFFICIENCY AT VIN=5V (P MODE)
0
0
-0.1
-0.2
LOAD REGULATION (%)
LOAD REGULATION (%)
1.5
FIGURE 2. VBOOST EFFICIENCY AT VIN=5V (PI MODE)
100
VO=9V
-0.3
VO=15V
-0.4
-0.5
1
IOUT (A)
FIGURE 1. VBOOST EFFICIENCY AT VIN=3V (PI MODE)
0
VO=12V
60
10
0
VO=15V
70
20
0
VO=9V
90
VO=12V
0
0.1
0.2
0.3
IOUT (A)
0.4
0.5
0.6
FIGURE 5. VBOOST LOAD REGULATION AT VIN=3V (PI MODE)
5
-0.1
VO=9V
-0.2
-0.3
-0.4
VO=12V
-0.5
-0.6
VO=15V
0
0.2
0.4
0.6
0.8
IOUT (A)
1
1.2
1.4
FIGURE 6. VBOOST LOAD REGULATION AT VIN=5V (PI MODE)
FN7523.3
March 9, 2006
EL7585A
Typical Performance Curves
(Continued)
0
0
LOAD REGULATION (%)
LOAD REGULATION (%)
-1
-2
-3
VO=9V
-4
-5
VO=15V
-6
-7
-8
VO=12V
0
0.2
0.4
0.6
-2
-4
VO=9V
-6
-8
VO=15V
0.8
0
0.5
0
0
-0.1
-0.2
-0.2
-0.3
-0.4
-0.5
20
40
1.5
FIGURE 8. VBOOST LOAD REGULATION AT VIN=5V (P MODE)
LOAD REGULATION (%)
LOAD REGULATION (%)
FIGURE 7. VBOOST LOAD REGULATION AT VIN=3V (P MODE)
0
1
IOUT (A)
IOUT (A)
-0.6
VO=12V
-10
60
80
-0.4
-0.6
-0.8
-1
-1.2
-1.4
0
IOUT (mA)
20
40
60
80
100
IOUT (mA)
FIGURE 9. VON LOAD REGULATION
FIGURE 10. VOFF LOAD REGULATION
LOAD REGULATION (%)
0
-0.2
-0.4
VCDLY
-0.6
VLOGIC
-0.8
VIN
-1
-1.2
EN
0
100
200
300
400
500
600
IOUT (mA)
FIGURE 11. VLOGIC LOAD REGULATION
6
CDLY=220nF
700
TIME (10ms/DIV)
FIGURE 12. START-UP SEQUENCE
FN7523.3
March 9, 2006
EL7585A
Typical Performance Curves
(Continued)
AVDD
VCDLY
VLOGIC
VLOGIC
VOFF
VIN
VON
CDLY=220nF
VREF
TIME (10ms/DIV)
CDLY=220nF
TIME (10ms/DIV)
FIGURE 13. START-UP SEQUENCE
FIGURE 14. START-UP SEQUENCE
AVDD
VLOGIC
VOFF
VON
VIN=5V
VOUT=13V
IOUT=30mA
CDLY=220nF
TIME (400ns/DIV)
TIME (10ms/DIV)
FIGURE 15. START-UP SEQUENCE
FIGURE 16. LX WAVEFORM - DISCONTINUOUS MODE
VIN=5V
VOUT=13V
IOUT=200mA
TIME (400ns/DIV)
FIGURE 17. LX WAVEFORM - CONTINUOUS MODE
7
FN7523.3
March 9, 2006
EL7585A
EN
REFERENCE
GENERATOR
VREF
SGND
OSCILLATOR
SLOPE
COMPENSATION
COMP
OSC
LX
PWM
LOGIC
CONTROLLER
Σ
BUFFER
VOLTAGE
AMPLIFIER
FBB
GM
AMPLIFIER
CINT
PGND
CURRENT
AMPLIFIER
UVLO
COMPARATOR
EN
CURRENT REF
CURRENT
LIMIT COMPARATOR
VDD
SHUTDOWN
& START-UP
CONTROL
PG
VREF
DRVP
BUFFER
THERMAL
SHUTDOWN
FBP
UVLO
COMPARATOR
CDLY
SS
+
-
DRVN
+
-
0.2V
VREF
DELB
SS
+
-
DRVL
BUFFER
BUFFER
FBN
0.4V
FBL
UVLO
COMPARATOR
UVLO
COMPARATOR
FIGURE 18. BLOCK DIAGRAM
Applications Information
The EL7585A is a highly integrated multiple output power
solution for TFT-LCD applications. The system consists of
one high efficiency boost converter and three linearregulator controllers (VON, VOFF, and VLOGIC) with multiple
protection functions. A block diagram is shown in Figure 18.
Table 1 lists the recommended components.
The EL7585A integrates an N-channel MOSFET boost
converter to minimize external component count and cost.
The AVDD, VON, VOFF, and VLOGIC output voltages are
independently set using external resistors. VON, VOFF
voltages require external charge pumps which are post
regulated using the integrated LDO controllers.
TABLE 1. RECOMMENDED COMPONENTS (Continued)
DESIGNATION
D1
DESCRIPTION
C1, C2, C3
10µF, 16V X5R ceramic capacitor (1206)
TDK C3216X5R0J106K
C20, C31
4.7µF, 25V X5R ceramic capacitor (1206)
TDK C3216X5R1A475K
8
1A 20V low leakage Schottky rectifier (CASE 45704) ON SEMI MBRM120ET3
D11, D12, D21 200mA 30V Schottky barrier diode (SOT-23)
Fairchild BAT54S
L1
6.8µH 1.3A Inductor
TDK SLF6025T-6R8M1R3-PF
Q1
-2.4 -20V P-channel 1.8V specified PowerTrench
MOSFET (SuperSOT-3) Fairchild FDN304P
Q4
-2A -30V single P-channel logic level PowerTrench
MOSFET (SuperSOT-3) Fairchild FDN360P
Q3
200mA 40V PNP amplifier (SOT-23)
Fairchild MMBT3906
Q2
200mA 40V NPN amplifier (SOT-23)
Fairchild MMBT3904
Q5
1A 30V PNP low saturation amplifier (SOT-23)
Fairchild FMMT549
TABLE 1. RECOMMENDED COMPONENTS
DESIGNATION
DESCRIPTION
FN7523.3
March 9, 2006
EL7585A
Boost Converter
The main boost converter is a current mode PWM converter at
a fixed frequency of 1MHz which enables the use of low profile
inductors and multilayer ceramic capacitors. This results in a
compact, low cost power system for LCD panel design.
The EL7585A is designed for continuous current mode, but
they can also operate in discontinuous current mode at light
load. 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:
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
A VDD = --------------------- × V REF
R1
A VDD
1
---------------- = ------------1–D
V IN
The current through the MOSFET is limited to 3.5A peak.
This restricts the maximum output current based on the
following equation:
Where D is the duty cycle of the switching MOSFET.
V IN
∆I
I OMAX =  I LMT – --------L × --------
2  VO
Figure 19 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.
Where ∆IL is peak to peak inductor ripple current, and is set by:
V IN D
∆I L = --------- × ----L
fS
where fS is the switching frequency.
CLOCK
SHUTDOWN
& START-UP
CONTROL
SLOPE
COMPENSATION
Ifb
Iref
CURRENT
AMPLIFIER
PWM
LX
LOGIC
BUFFER
Ifb
FBB
GM
AMPLIFIER
Iref
VOLTAGE
AMPLIFIER
REFERENCE
GENERATOR
CINT
PGND
FIGURE 19. BLOCK DIAGRAM OF THE BOOST REGULATOR
9
FN7523.3
March 9, 2006
EL7585A
The following table gives typical values (margins are
considered 10%, 3%, 20%, 10%, and 15% on VIN, VO, L, fS,
and IOMAX:
TABLE 2.
VIN (V)
VO (V)
L (µH)
fS
(MHz)
3.3
9
6.8
1
1.040686
3.3
12
6.8
1
0.719853
3.3
15
6.8
1
0.527353
5
9
6.8
1
1.576797
5
12
6.8
1
1.090686
5
15
6.8
1
0.79902
IOMAX
Input Capacitor
An input capacitor is used to supply the peak charging
current to the converter. It is recommended that CIN be
larger than 10µF. The reflected ripple voltage will be smaller
with larger CIN. The voltage rating of input capacitor should
be larger than maximum input voltage.
Boost 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 to match the internal slope
compensation. The inductor must be able to handle the
following average and peak current:
IO
I LAVG = -----------1–D
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 them 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.
Compensation
The EL7585A can operate in either P mode or PI mode.
Connecting the CINT pin directly to VIN will enable P mode;
For better load regulation, use PI mode with a 4.7nF
capacitor in series with a 10K resistor between CINT and
ground. This value may be reduced to improve transient
performance, however, very low values will reduce loop
stability.
Boost feedback resistors
As the boost output voltage, AVDD, is reduced below 12V the
effective voltage feedback in the IC increases the ratio of
voltage to current feedback at the summing comparator
because R2 decreases relative to R1. To maintain stable
operation over the complete current range of the IC, the
voltage feedback to the FBB pin should be reduced
proportionally, as AVDD is reduced, by means of a series
resistor-capacitor network (R7 and C7) in parallel with R1,
with a pole frequency (fp) set to approximately 10kHz for C2
effective = 10µF and 4kHz for C2 (effective) = 30µF.
R7 = ((1/0.1 x R2) - 1/R1)^-1
C7 = 1/(2 x 3.142 x fp x R7)
∆I
I LPK = I LAVG + --------L
2
PI Mode CINT (C23) and RINT (R10)
The IC is designed to operate with a minimum C23 capacitor
of 4.7nF and a minimum C2 (effective) = 10µF.
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 rectifier
diode must meet the output current and peak inductor
current requirements.
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
10
Note that, for high voltage AVDD, the voltage coefficient of
ceramic capacitors (C2) reduces their effective capacitance
greatly; a 16V 10µF ceramic can drop to around 3µF at 15V.
To improve the transient load response of AVDD in PI mode,
a resistor may be added in series with the C23 capacitor. The
larger the resistor the lower the overshoot but at the expense
of stability of the converter loop - especially at high currents.
With L = 10µH, AVDD = 15V, C23 = 4.7nF, C2 (effective)
should have a capacitance of greater than 10µF. RINT (R7)
can have values up to 5kΩ for C2 (effective) up to 20µF and
up to 10K for C2 (effective) up to 30µF.
Larger values of RINT (R7) may be possible if maximum
AVDD load currents less than the current limit are used. To
ensure AVDD stability, the IC should be operated at the
maximum desired current and then the transient load
response of AVDD should be used to determine the
maximum value of RINT.
FN7523.3
March 9, 2006
EL7585A
Operation of the DELB Output Function
An open drain DELB output is provided to allow the boost
output voltage, developed at C2 (see application diagram),
to be delayed via an external switch (Q4) to a time after the
VBOOST supply and negative VOFF charge pump supply
have achieved regulation during the start-up sequence
shown in Figure 28. This then allows the AVDD and VON
supplies to start-up from 0V instead of the normal offset
voltage of VIN-VDIODE (D1) if Q4 were not present.
When DELB is activated by the start-up sequencer, it sinks
50µA allowing a controlled turn-on of Q4 and charge-up of
C9. C16 can be used to control the turn-on time of Q4 to
reduce inrush current into C9. The potential divider formed
by R9 and R8 can be used to limit the VGS voltage of Q4 if
required by the voltage rating of this device. When the
voltage at DELB falls to less than 0.6V, the sink current is
increased to ~1.2mA to firmly pull DELB to 0V.
The voltage at DELB is monitored by the fault protection
circuit so that if the initial 50µA sink current fails to pull DELB
below ~0.6V after the start-up sequencing has completed,
then a fault condition will be detected and a fault time-out
ramp will be initiated on the CDEL capacitor (C7).
Operation of the PG Output Function
The PG output consists of an internal pull-up PMOS device
to VIN, to turn-off the external Q1 protection switch and a
current limited pull-down NMOS device which sinks ~15µA
allowing a controlled turn-on of Q1 gate capacitance. CO is
used to control how fast Q1 turns-on - limiting inrush current
into C1. When the voltage at the PG pin falls to less than
0.6V, the PG sink current is increased to ~1.2mA to firmly
pull the pin to 0V.
The voltage at PG is monitored by the fault protection circuit
so that if the initial 15µA sink current fails to pull PG below
~0.6V after the start-up sequencing has completed, then a
fault condition will be detected and a fault time-out ramp will
be initiated on the CDEL capacitor (C7).
Cascaded MOSFET Application
A 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 20. The voltage rating of the external
MOSFET should be greater than VBOOST.
VIN
VBOOST
LX
FB
EL7585A
FIGURE 20. CASCADED MOSFET TOPOLOGY FOR HIGH
OUTPUT VOLTAGE APPLICATIONS
Linear-Regulator Controllers (VON, VLOGIC, and
VOFF)
The EL7585A includes three independent linear-regulator
controllers, in which two are positive output voltage (VON
and VLOGIC), and one is negative. The VON, VOFF, and
VLOGIC linear-regulator controller functional diagrams,
applications circuits are shown in Figures 21, 22, and 23
respectively.
Calculation of the Linear Regulator Base-Emitter
Resistors (RBL, RBP and RBN)
For the pass transistor of the linear regulator, low frequency
gain (Hfe) and unity gain freq. (fT) are usually specified in the
datasheet. The pass transistor adds a pole to the loop
transfer function at fp=fT/Hfe. Therefore, in order to maintain
phase margin at low frequency, the best choice for a pass
device is often a high frequency low gain switching
transistor. Further improvement can be obtained by adding a
base-emitter resistor RBE (RBP, RBL, RBN in the Functional
Block Diagram), which increase the pole frequency to:
fp=fT*(1+ Hfe *re/RBE)/Hfe, where re=KT/qIc. So choose the
lowest value RBE in the design as long as there is still
enough base current (IB) to support the maximum output
current (IC).
We will take as an example the VLOGIC linear regulator. If a
Fairchild FMMT549 PNP transistor is used as the external
pass transistor, Q5 in the application diagram, then for a
maximum VLOGIC operating requirement of 500mA the data
sheet indicates Hfe_min = 100.
The base-emitter saturation voltage is: Vbe_max = 1.25V
(note this is normally a Vbe ~ 0.7V, however, for the Q5
transistor an internal Darlington arrangement is used to
increase it's current gain, giving a 'base-emitter' voltage of
2 x VBE).
(Note that using a high current Darlington PNP transistor for
Q5 requires that VIN > VLOGIC + 2V. Should a lower input
voltage be required, then an ordinary high gain PNP
transistor should be selected for Q5 so as to allow a lower
collector-emitter saturation voltage).
11
FN7523.3
March 9, 2006
EL7585A
For the EL7585A, the minimum drive current is:
I_DRVL_min = 8mA
VIN OR VPROT
(3V TO 6V)
The minimum base-emitter resistor, RBL, can now be
calculated as:
LDO_LOG
0.9V
PG_LDOL
RBL_min = VBE_max/(I_DRVL_min - Ic/Hfe_min) =
1.25V/(8mA - 500mA/100) = 417Ω
RBL
500Ω
+
-
Q5
VLOGIC
(1.3V TO 3.6V)
DRVL
This is the minimum value that can be used - so, we now
choose a convenient value greater than this minimum value;
say 500Ω. Larger values may be used to reduce quiescent
current, however, regulation may be adversely affected, by
supply noise if RBL is made too high in value.
VBOOST
LX
RL1
CLOG
10µF
FBL
+
GML
RL2
20kΩ
1: N1
0.1µF
LDO_ON
0.9V
PG_LDOP
FIGURE 23. VLOGIC FUNCTIONAL BLOCK DIAGRAM
CP (TO 36V)
36V
ESD
CLAMP
+
-
RBP
7kΩ
0.1µF
Q3
VON (TO 35V)
DRVP
RP1
FBP
CON
RP2
20kΩ
+
GMP
1: Np
FIGURE 21. VON FUNCTIONAL BLOCK DIAGRAM
LX
0.1µF
CP (TO -26V)
LDO_OFF
PG_LDON
0.4V
VREF
+
FBN
1: Nn
0.1µF
RN2
20kΩ
RN1
VOFF (TO -20V)
+
GMN
DRVN
36V
ESD
CLAMP
RBN
3kΩ
Q2
COFF
FIGURE 22. VOFF FUNCTIONAL BLOCK DIAGRAM
12
The VON power supply is used to power the positive supply
of the row driver in the LCD panel. The DC-DC consists of an
external diode-capacitor charge pump powered from the
inductor (LX) of the boost converter, followed by a low
dropout linear regulator (LDO_ON). The LDO_ON regulator
uses an external PNP transistor as the pass element. The
onboard LDO controller is a wide band (>10MHz)
transconductance amplifier capable of 4mA drive current,
which is sufficient for up to 40mA or more output current
under the low dropout condition (forced beta of 10). Typical
VON voltage supported by EL7585A ranges from +15V to
+36V. A fault comparator is also included for monitoring the
output voltage. The under-voltage threshold is set at 25%
below the 1.2V reference.
The VOFF power supply is used to power the negative
supply of the row driver in the LCD panel. The DC-DC
consists of an external diode-capacitor charge pump
powered from the inductor (LX) of the boost converter,
followed by a low dropout linear regulator (LDO_OFF). The
LDO_OFF regulator uses an external NPN transistor as the
pass element. The onboard LDO controller is a wide band
(>10MHz) transconductance amplifier capable of 4mA drive
current, which is sufficient for up to 40mA or more output
current under the low dropout condition (forced beta of 10).
Typical VOFF voltage supported by EL7585A ranges from
-5V to -20V. A fault comparator is also included for
monitoring the output voltage. The undervoltage threshold is
set at 200mV above the 0.2V reference level.
The VLOGIC power supply is used to power the logic circuitry
within the LCD panel. The DC-DC may be powered directly
from the low voltage input, 3.3V or 5.0V, or it may be
powered through the fault protection switch. The
LDO_LOGIC regulator uses an external PNP transistor as
the pass element. The onboard LDO controller is a wide
band (>10MHz) transconductance amplifier capable of
16mA drive current, which is sufficient for up to 160mA or
FN7523.3
March 9, 2006
EL7585A
more output current under the low dropout condition (forced
beta of 10). Typical VLOGIC voltage supported by EL7585A
ranges from +1.3V to VDD-0.2V. A fault comparator is also
included for monitoring the output voltage. The undervoltage
threshold is set at 25% below the 1.2V reference.
CHARGE PUMP
VIN
OUTPUT
OR AVDD
7kΩ
DRVP
Set-Up Output Voltage
Refer to the Typical Application Diagram, the output voltages
of VON, VOFF, and VLOGIC are determined by the following
equations:
NPN
CASCODE
TRANSISTOR
Q3
VON
EL7585A
R 12

V ON = V REF ×  1 + ---------
R 11

FBP
R 22
V OFF = V REFN + ---------- × ( V REFN – V REF )
R
21
R 42

V LOGIC = V REF ×  1 + ---------
R 41

FIGURE 24. CASCODE NPN TRANSISTOR CONFIGURATION
FOR HIGH CHARGE PUMP OUTPUT VOLTAGE
(>36V)
Where VREF = 1.2V, VREFN = 0.2V.
LX
0.1µF
Resistor networks in the order of 250kΩ, 120kΩ and 10kΩ
are recommended for VON, VOFF and VLOGIC, respectively.
Charge Pump
7kΩ
To generate an output voltage higher than VBOOST, single or
multiple stages of charge pumps are needed. The number of
stage is determined by the input and output voltage. For
positive charge pump stages:
V OUT + V CE – V INPUT
N POSITIVE ≥ -------------------------------------------------------------V INPUT – 2 × V F
AVDD
0.1µF
DRVP
Q3
0.1µF
0.1µF
VON
0.47µF
EL7585A
(>36V)
0.1µF
0.22µF
FBP
where VCE is the dropout voltage of the pass component of
the linear regulator. It ranges from 0.3V to 1V depending on
the transistor. VF is the forward-voltage of the charge pump
rectifier diode.
The number of negative charge pump stages is given by:
V OUTPUT + V CE
N NEGATIVE ≥ ------------------------------------------------V INPUT – 2 × V F
To achieve high efficiency and low material cost, the lowest
number of charge pump stages which can meet the above
requirements, is always preferred.
High Charge Pump Output Voltage (>36V)
Applications
In the applications where the charge pump output voltage is
over 36V, an external npn transistor need to be inserted into
between DRVP pin and base of pass transistor Q3 as shown
in Figure 24; or the linear regulator can control only one
stage charge pump and regulate the final charge pump
output as shown in Figure 25.
13
FIGURE 25. THE LINEAR REGULATOR CONTROLS ONE
STAGE OF CHARGE PUMP
Discontinuous/Continuous Boost Operation and
its Effect on the Charge Pumps
The EL7585A VON and VOFF architecture uses LX switching
edges to drive diode charge pumps from which LDO
regulators generate the VON and VOFF supplies. It can be
appreciated that should a regular supply of LX switching
edges be interrupted, for example during discontinuous
operation at light AVDD boost load currents, then this may
affect the performance of VON and VOFF regulation depending on their exact loading conditions at the time.
To optimize VON/VOFF regulation, the boundary of
discontinuous/continuous operation of the boost converter
can be adjusted, by suitable choice of inductor given VIN,
VOUT, switching frequency and the AVDD current loading, to
be in continuous operation.
FN7523.3
March 9, 2006
EL7585A
The following equation gives the boundary between
discontinuous and continuous boost operation. For
continuous operation (LX switching every clock cycle) we
require that:
I(AVDD_load) > D*(1-D)*VIN/(2*L*FOSC)
where the duty cycle, D = (AVDD - VIN)/AVDD
For example, with VIN = 5V, FOSC = 1.0MHz and AVDD =
12V we find continuous operation of the boost converter can
be guaranteed for:
L = 10µH and I(AVDD) > 61mA
L = 6.8µH and I(AVDD) > 89mA
L = 3.3µH and I(AVDD) > 184mA
Charge Pump Output Capacitors
Ceramic capacitors with low ESR are recommended. With
ceramic capacitors, the output ripple voltage is dominated by
the capacitance value. The capacitance value can be
chosen by the following equation:
I OUT
C OUT ≥ -----------------------------------------------------2 × V RIPPLE × f OSC
where fOSC is the switching frequency.
Start-Up Sequence
Figure 26 shows a detailed start-up sequence waveform. For
a successful power-up, there should be six peaks at VCDLY.
When a fault is detected, the device will latch off until either
EN is toggled or the input supply is recycled.
When the input voltage (VDD) exceeds 2.5V, VREF and
VLOGIC turn on. At the same time, if EN is tied to VDD, an
internal current source starts to charge CDLY to an upper
threshold using a fast ramp followed by a slow ramp. If EN is
low at this point, the CDLY ramp will be delayed until EN
goes high.
The first four ramps on CDLY (two up, two down) are used to
initialize the fault protection switch and to check whether
there is a fault condition on CDLY or VREF. If a fault is
detected, the outputs and the input protection will turn off,
but VREF will stay on. If no fault is found, CCDLY continues
ramping up and down.
During the second ramp, the device checks the status of
VREF and over temperature. At the peak of the second ramp,
PG output goes low and enables the input protection PMOS
Q1. Q1 is a controlled FET used to prevent in-rush current into
VBOOST before VBOOST is enabled internally. Its rate of turn
on is controlled by Co. When a fault is detected, M1 will turn
off and disconnect the inductor from VIN.
With the input protection FET on, NODE1 (See Typical
Application Diagram) will rise to ~VIN. Initially the boost is not
enabled so VBOOST rises to VIN-VDIODE through the output
diode. Hence, there is a step at VBOOST during this part of the
14
start-up sequence. If this step is not desirable, an external
PMOS FET can be used to delay the output until the boost is
enabled internally. The delayed output appears at AVDD.
For EL7585A, VBOOST soft-start at the beginning of the third
ramp. The soft-start ramp depends on the value of the CDLY
capacitor. For CDLY of 220nF, the soft-start time is ~2ms.
VOFF turns on at the start of the fourth peak. At the fifth
peak, the open drain o/p DELB goes low to turn on the
external PMOS Q4 to generate a delayed VBOOST output.
VON is enabled at the beginning of the sixth ramp. AVDD,
PG, VOFF, DELB and VON are checked at end of this ramp.
Fault Protection
During the startup sequence, prior to BOOST soft-start,
VREF is checked to be within ±20% of its final value and the
device temperature is checked. If either of these are not
within the expected range, the part is disabled until the
power is recycled or EN is toggled.
If CDELAY is shorted low, then the sequence will not start,
while if CDELAY is shorted H, the first down ramp will not
occur and the sequence will not complete.
Once the start-up sequence is completed, the chip
continuously monitors CDLY, DELB, FBP, FBL, FBN, VREF,
FBB and PG and checks for faults. During this time, the
voltage on the CDLY capacitor remains at 1.15V until either a
fault is detected, or the EN pin is pulled low.
A fault on CDELAY, VREF or temperature will shut down the
chip immediately. If a fault on any other output is detected,
CDELAY will ramp up linearly with a 5µA (typical) current to
the upper fault threshold (typically 2.4V), at which point the
chip is disabled until the power is recycled or EN is toggled.
If the fault condition is removed prior to the end of the ramp,
the voltage on the CDLY capacitor returns to 1.15V.
Typical fault thresholds for FBP, FBL, FBN and FBB are
included in the tables. PG and DELB fault thresholds are
typically 0.6V.
CINT has an internal current-limited clamp to keep the
voltage within its normal range. If CINT is shorted low, the
boost regulator will attempt to regulate to 0V. If CINT is
shorted H, the regulator switches to P mode.
If any of the regulated outputs (VBOOST, VON, VOFF or
VLOGIC) are driven above their target levels the drive
circuitry will switch off until the output returns to its expected
value.
If VBOOST is excessively loaded, the current limit will
prevent damage to the chip. While in current limit, the part
acts like a current source and the regulated output will drop.
If the output drops below the fault threshold, a ramp will be
initiated on CDELAY and, provided that the fault is sustained,
the chip will be disabled on completion of the ramp.
FN7523.3
March 9, 2006
EL7585A
In some circumstances, (depending on ambient temperature
and thermal design of the board), continuous operation at
current limit may result in the over-temperature threshold
being exceeded, which will cause the part to disable
immediately.
All I/O also have ESD protection, which in many cases will
also provide overvoltage protection, relative to either ground
or VDD. However, these will not generally operate unless
abs max ratings are exceeded.
Component Selection for Start-Up Sequencing and
Fault Protection
Fault Sequencing
The EL7585A has an advanced fault detection system which
protects the IC from both adjacent pin shorts during
operation and shorts on the output supplies.
A high quality layout/design of the PCB, in respect of
grounding quality and decoupling is necessary to avoid
falsely triggering the fault detection scheme - especially
during start-up. The user is directed to the layout guidelines
and component selection sections to avoid problems during
initial evaluation and prototype PCB generation.
The CREF capacitor is typically set at 220nF and is required
to stabilize the VREF output. The range of CREF is from
22nF to 1µF and should not be more than five times the
capacitor on CDEL to ensure correct start-up operation.
The CDEL capacitor is typically 220nF and has a usable
range from 47nF minimum to several microfarads - only
limited by the leakage in the capacitor reaching µA levels.
CDEL should be at least 1/5 of the value of CREF (See
above). Note with 220nF on CDEL the fault time-out will be
typically 50ms and the use of a larger/smaller value will vary
this time proportionally (e.g. 1µF will give a fault time-out
period of typically 230ms).
15
FN7523.3
March 9, 2006
CHIP DISABLED
FAULT DETECTED
VON SOFT-START
DELB ON
VOFF ON
AVDD SOFT-START
PG ON
VREF, VLOGIC ON
EL7585A
VCDLY
VIN
EN
VREF
VBOOST
tON
tOS
VLOGIC
VOFF
tDEL1
DELAYED
VBOOST
tDEL2
START-UP SEQUENCE
TIMED BY CDLY
FAULT
PRESENT
tDEL3
NORMAL
OPERATION
VON
FIGURE 26. START-UP SEQUENCE
16
FN7523.3
March 9, 2006
EL7585A
Over-Temperature Protection
An internal temperature sensor continuously monitors the
die temperature. In the event that the die temperature
exceeds the thermal trip point of 140°C, the device will shut
down.
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 VREF and VDD bypass capacitors close to the pins.
3. Minimize the length of traces carrying fast signals and
high current.
4. All feedback networks should sense the output voltage
directly from the point of load, and be as far away from LX
node as possible.
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 feedback resistor networks (R1, R11,
R41) and the VREF capacitor, C22, the CDELAY capacitor
C7 and the integrator capacitor C23.
9. Minimize feedback input track lengths to avoid switching
noise pick-up.
A two-layer demo board is available to illustrate the proper
layout implementation. A four-layer demo board can be used
to further optimize the layout recommendations.
5. The power ground (PGND) and signal ground (SGND)
pins should be connected at only one point near the main
decoupling capacitors.
Demo Board Layout
FIGURE 27. TOP LAYER
17
FIGURE 28. BOTTOM LAYER
FN7523.3
March 9, 2006
EL7585A
Typical Application Diagram
LX
VIN
C0
C1
1nF
10µF
x2
PG
CDELAY
C10
D1
6.8µH
C7
46.5kΩ
LX
R2
R1
5kΩ
FBB
AVDD
(12V)
Q4
R9
C2
10µF
1MΩ
X2
R7 OPEN
C9
C16
0.1µF
22nF
R8
C7 OPEN
10kΩ
0.22µF
4.7µF
C41
NODE 1
10Ω
C6
4.7µF
R7
10kΩ
VDD
0.1µF VREF
C22
CINT
R41
CP
1nF
DRVP
C14
0.1µF
Q3
R12
C11
0.1µF
C13
0.1µF
7kΩ
VREF
FBP
5.4kΩ
10kΩ
LX
4.7nF
R13
DRVL
R42
R10 C
23
EN
0.1µF
500Ω
Q5
DELB
R6
R43
VLOGIC
(2.5V) C
31
4.7µF
L1
NODE 1
Q1
C12
D12
0.1µF
D11
230kΩ
R11
C15
20kΩ
0.47µF
FBL
VON
(15V)
C24
LX
0.1µF
R23
5kΩ
C25
3kΩ
DRVN
FBN
SGND
PGND
0.1µF D21
Q2
R22
104K
R21
C20
20K
4.7µF
VOFF
(-5V)
VREF
NOTE: The SGND should be connected to the exposed die plate and connected to the PGND at one point only.
18
FN7523.3
March 9, 2006
EL7585A
QFN 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
19
FN7523.3
March 9, 2006