Intersil EL7564CREZ-T13 Monolithic 4 amp dc/dc step-down regulator Datasheet

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May 9, 2005
Monolithic 4 Amp DC/DC Step-Down
Regulator
The EL7564 is specified for operation over the -40°C to
+85°C temperature range.
• Integrated synchronous MOSFETs and current mode
controller
• 4A continuous output current
• Up to 95% efficiency
• 4.5V to 5.5V input voltage
• Adjustable output from 1V to 3.8V
• Cycle-by-cycle current limit
• Precision reference
• ±0.5% load and line regulation
• Adjustable switching frequency to 1MHz
• Oscillator synchronization possible
• Internal soft start
• Over voltage protection
• Junction temperature indicator
• Over temperature protection
Typical Application Diagrams
• Under voltage lockout
EL7564
[20-PIN SO (0.300”)]
TOP VIEW
• Multiple supply start-up tracking
• Power good indicator
• 20-pin SO (0.300”) package
C5
0.1µF
C4
390pF
R4
1 VREF
EN 20
2 SGND
FB 19
3 COSC
PG 18
C3
4 VDD
0.22µF
VDRV 17
5 VTJ
VHI 16
C2
2.2nF
VIN
5V
FN7297.3
Features
The EL7564 is an integrated, full-featured synchronous stepdown regulator with output voltage adjustable from 1.0V to
3.8V. It is capable of delivering 4A continuous current at up
to 95% efficiency. The EL7564 operates at a constant
frequency pulse width modulation (PWM) mode, making
external synchronization possible. Patented on-chip
resistorless current sensing enables current mode control,
which provides cycle-by-cycle current limiting, over-current
protection, and excellent step load response. The EL7564
features power tracking, which makes the start-up
sequencing of multiple converters possible. A junction
temperature indicator conveniently monitors the silicon die
temperature, saving the designer time on the tedious
thermal characterization. The minimal external components
and full functionality make this EL7564 ideal for desktop and
portable applications.
22Ω
EL7564
I GN S
C1
330µF
6 PGND
LX 15
7 PGND
LX 14
8 VIN
PGND 13
9 STP
PGND 12
10 STN
PGND 11
• 28-pin HTSSOP package
• Pb-Free available (RoHS compliant)
Applications
• DSP, CPU core and IO supplies
C6
0.22µF
D1
• Logic/Bus supplies
VOUT
3.3V, 4A
L1
4.7µH
C7
330µF
C10
R2
2.37kΩ 100pF
• Portable equipment
• DC/DC converter modules
• GTL + Bus power supply
R1
1kΩ
Typical Application Diagrams continued on page 3
Manufactured Under U.S. Patent No. 5,7323,974
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-352-6832 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2003, 2005. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
EL7564
Ordering Information
PACKAGE
TAPE &
REEL
PKG. DWG.
#
EL7564CM
20-Pin SO (0.300”)
-
MDP0027
EL7564CM-T13
20-Pin SO (0.300”)
13”
MDP0027
EL7564CMZ
(See Note)
20-Pin SO (0.300”)
(Pb-free)
-
MDP0027
EL7564CMZ-T13
(See Note)
20-Pin SO (0.300”)
(Pb-free)
13”
MDP0027
EL7564CRE
28-Pin HTSSOP
-
MDP0048
EL7564CRE-T7
28-Pin HTSSOP
7”
MDP0048
EL7564CRE-T13
28-Pin HTSSOP
13”
MDP0048
EL7564CREZ
(See Note)
28-Pin HTSSOP
(Pb-free)
-
MDP0048
EL7564CREZ-T7
(See Note)
28-Pin HTSSOP
(Pb-free)
7”
MDP0048
EL7564CREZ-T13
(See Note)
28-Pin HTSSOP
(Pb-free)
13”
MDP0048
PART NUMBER
NOTE: Intersil Pb-free products employ special Pb-free material sets;
molding compounds/die attach materials and 100% matte tin plate
termination finish, which are RoHS compliant and compatible with
both SnPb and Pb-free soldering operations. Intersil Pb-free products
are MSL classified at Pb-free peak reflow temperatures that meet or
exceed the Pb-free requirements of IPC/JEDEC J STD-020.
2
FN7297.3
May 9, 2005
EL7564
Absolute Maximum Ratings (TA = 25°C)
Supply Voltage between VIN or VDD and GND . . . . . . . . . . . . +6.5V
VLX Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIN +0.3V
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . GND -0.3V, VDD +0.3V
VHI Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . GND -0.3V, VLX +6.5V
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
Operating Ambient Temperature . . . . . . . . . . . . . . . .-40°C to +85°C
Operating Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . +135°
CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typical values are for information purposes only. Unless otherwise noted, all tests
are at the specified temperature and are pulsed tests, therefore: TJ = TC = TA
DC Electrical Specifications
PARAMETER
VDD = VIN = 5V, TA = TJ = 25°C, COSC = 1.2nF, Unless Otherwise Specified.
DESCRIPTION
CONDITIONS
MIN
TYP
MAX
UNIT
1.24
1.26
1.28
V
VREF
Reference Accuracy
VREFTC
Reference Temperature Coefficient
VREFLOAD
Reference Load Regulation
VRAMP
Oscillator Ramp Amplitude
IOSC_CHG
Oscillator Charge Current
0.1V < VOSC < 1.25V
IOSC_DIS
Oscillator Discharge Current
0.1V < VOSC < 1.25V
IVDD+VDRV
VDD+VDRV Supply Current
VEN = 4V, FOSC = 120kHz
IVDD_OFF
VDD Standby Current
EN = 0
VDD_OFF
VDD for Shutdown
VDD_ON
VDD for Startup
TOT
Over Temperature Threshold
135
°C
THYS
Over Temperature Hysteresis
20
°C
ILEAK
Internal FET Leakage Current
ILMAX
Peak Current Limit
RDSON
FET On Resistance
RDSONTC
RDSON Tempco
ISTP
Auxiliary Supply Tracking Positive
Input Pull Down Current
VSTP = VIN / 2
ISTN
Auxiliary Supply Tracking Negative
Input Pull Up Current
VSTN = VIN / 2
VPGP
Positive Power Good Threshold
With respect to target output voltage
VPGN
Negative Power Good Threshold
With respect to target output voltage
VPG_HI
Power Good Drive High
IPG = +1mA
IPG = -1mA
50
0 < IREF < 50µA
ppm/°C
-1
%
1.15
V
200
µA
8
2
mA
3.5
5
mA
1
1.5
mA
3.9
V
3.5
4
4.35
EN = 0, LX = 5V (low FET), LX = 0V (high FET)
10
µA
60
mΩ
5
Wafer level test only
A
30
-4
V
0.2
mΩ/°C
2.5
µA
2.5
4
µA
6
14
%
-14
-6
%
4
V
VPG_LO
Power Good Drive Low
VOVP
Over Voltage Protection
0.5
VFB
Output Initial Accuracy (EL7564CM) ILOAD = 0A
0.960
0.975
0.99
V
Output Initial Accuracy
(EL7564CRE)
0.977
0.992
1.007
V
10
V
%
VFB_LINE
Output Line Regulation
VIN = 5V, ∆VIN = 10%, ILOAD = 0A
0.5
%
VFB_LOAD
Output Load Regulation
0.5A < ILOAD < 4A
0.5
%
VFB_TC
Output Temperature Stability
-40°C < TA < 85°C, ILOAD = 2A
±1
IFB
Feedback Input Pull Up Current
VFB = 0V
100
200
nA
VEN_HI
EN Input High Level
3.2
4
V
VEN_LO
EN Input Low Level
IEN
Enable Pull Up Current
3
1
VEN = 0
-4
%
V
-2.5
µA
FN7297.3
May 9, 2005
EL7564
Closed-Loop AC Electrical Specifications
PARAMETER
VS = VIN = 5V, TA = TJ = 25°C, COSC = 1.2nF, Unless Otherwise Specified.
DESCRIPTION
CONDITIONS
MIN
TYP
MAX
UNIT
105
117
130
kHz
FOSC
Oscillator Initial Accuracy
tSYNC
Minimum Oscillator Sync Width
25
ns
MSS
Soft Start Slope
0.5
V/ms
tBRM
FET Break Before Make Delay
15
ns
tLEB
High Side FET Minimum On Time
150
ns
DMAX
Maximum Duty Cycle
95
%
Typical Application Diagrams
(Continued)
EL7654
(28-PIN HTSSOP)
TOP VIEW
C5
0.1µF
C4
390pF
R4
22Ω
C2
2.2nF
VIN
5V
330µF
4
1 VREF
EN 28
2 SGND
FB 27
3 COSC
PG 26
C3
4 VDD
0.22µF
VDRV 25
5 VTJ
VHI 24
6 PGND
LX 23
7 PGND
LX 22
8 PGND
LX 21
9 PGND
LX 20
10 VIN
LX 19
11 VIN
LX 18
12 NC
NC 17
13 STP
PGND 16
14 STN
PGND 15
C6
0.22µF
D1
VOUT
3.3V, 4A
L1
4.7µH
C7
330µF
R2
2.37kΩ
C10
100pF
R1
1kΩ
FN7297.3
May 9, 2005
EL7564
Pin Descriptions
20-PIN SO
(0.300”)
28-PIN
HTSSOP
PIN NAME
1
1
VREF
Bandgap reference bypass capacitor; typically 0.1µF to SGND
2
2
SGND
Control circuit negative supply or signal ground
3
3
COSC
Oscillator timing capacitor (see performance curves)
4
4
VDD
Control circuit positive supply; normally connected to VIN through an RC filter
5
5
VTJ
Junction temperature monitor; connected with 2.2nF to 3.3nF to SGND
6, 7
6, 7, 8, 9
PGND
8
10, 11
VIN
Power supply input of the regulator; connected to the drain of the high-side NMOS power FET
9
13
STP
Auxiliary supply tracking positive input; tied to regulator output to synchronize start up with a
second supply; leave open for stand alone operation; 2µA internal pull down current
10
14
STN
Auxiliary supply tracking negative input; connect to output of a second supply to synchronize
start up; leave open for stand alone operation; 2µA internal pull up current
11, 12, 13
15, 16
PGND
Ground return of the regulator; connected to the source of the low-side synchronous NMOS
power FET
14, 15
18, 19, 20, 21,
22, 23
LX
Inductor drive pin; high current output whose average voltage equals the regulator output
voltage
16
24
VHI
Positive supply of high-side driver; boot strapped from VDRV to LX with an external 0.22µF
capacitor
17
25
VDRV
18
26
PG
Power good window comparator output; logic 1 when regulator output is within ±10% of target
output voltage
19
27
FB
Voltage feedback input; connected to external resistor divider between VOUT and SGND; a
125nA pull-up current forces VOUT to SGND in the event that FB is floating
20
28
EN
Chip enable, active high; a 2µA internal pull up current enables the device if the pin is left open;
a capacitor can be added at this pin to delay the start of converter
PIN FUNCTION
Ground return of the regulator; connected to the source of the low-side synchronous NMOS
power FET
Positive supply of low-side driver and input voltage for high side boot strap
Typical Performance Curves
100
VIN=5V
100
95
90
EFFICIENCY (%)
EFFICIENCY (%)
VO=3.3V
95
VO=3.3V
90
85
VO=2.8V
80
VO=1.8V
75
75
65
65
0.5
1
1.5
2
2.5
3
LOAD CURRENT IO (A)
FIGURE 1. EL7564CM EFFICIENCY
5
3.5
4
VO=1.8V
80
70
0
VO=2.5V
85
70
60
VIN=5V
60
0.1
0.6
1.1
1.6
2.1
2.6
3.1
3.6
4.1
IO (A)
FIGURE 2. EL7564CRE EFFICIENCY
FN7297.3
May 9, 2005
EL7564
Typical Performance Curves (Continued)
VIN=5V
2
1.8
1.6
VO=3.3V
1.4
VO=2.8V
1.2
VO=1.8V
0.8
VO=3.3V
1.2
PLOSS (W)
POWER LOSS (W)
1.6
1
0.8
VO=1.8V
0.6
0.4
0.4
0.2
0
0
0
0.5
1
1.5
2
2.5
3
3.5
4
0
0.5
1
1.5
OUTPUT CURRENT IO (A)
2
2.5
3
3.5
4
IO (A)
FIGURE 3. EL7564CM TOTAL CONVERTER POWER LOSS
FIGURE 4. EL7564CRE TOTAL CONVERTER POWER LOSS
VO=3.3V
1.5
VO=3.3V
1
VIN=5.5V
3.315
VIN=4.5V
0.5
VO (V) (%)
OUTPUT VOLTAGE (V)
3.325
3.305
VIN=5V
3.295
VIN=5V
0
VIN=5.5V
-0.5
3.285
-1
VIN=4.5V
3.275
0.5
-1.5
1
1.5
2
2.5
3
3.5
0
4
1
2
FIGURE 5. EL7564CM LOAD REGULATION
4
FIGURE 6. EL7564CRE LOAD REGULATION
CONDITION:
EL7564RE THERMAL PAD SOLDERED TO 2-LAYER
PCB WITH 0.039” THICKNESS AND 1 OZ. COPPER
ON BOTH SIDES
TEST CONDITION:
CHIP IN THE CENTER OF COPPER AREA
50
50
46
45
WITH NO AIRFLOW
θJA (°C/W)
THERMAL RESISTANCE (°C/W)
3
IO (A)
LOAD CURRENT IO (A)
42
38
40
35
WITH 100 LFPM AIRFLOW
34
30
1 OZ. COPPER PCB USED
25
30
1
1.5
2.5
2
3
3.5
PCB COPPER HEAT-SINKING AREA (in2)
FIGURE 7. EL7564CM θJA vs COPPER AREA
6
4
1
1.5
2
2.5
3
3.5
4
PCB AREA (in2)
FIGURE 8. EL7564CRE THERMAL RESISTANCE vs PCB
AREA - NO AIRFLOW
FN7297.3
May 9, 2005
EL7564
360
1000
350
900
340
800
IO=4A
700
330
FS (kHz)
OSCILLATOR FREQUENCY (kHz)
Typical Performance Curves (Continued)
320
310
IO=0A
600
500
400
300
300
290
200
280
-40
0
-20
20
40
60
100
100
80
200
300
400
500
600
700
800
900 1000
COSC (pF)
TEMPERATURE (°C)
FIGURE 9. OSCILLATOR FREQUENCY vs TEMPERATURE
FIGURE 10. SWITCHING FREQUENCY vs COSC
8
1.5
VIN=5.5V
6
1.3
VIN=5V
VTJ
ILMT (A)
7
VIN=4.5V
5
1.1
4
3
-40
0.9
-20
0
40
20
60
100
80
120
0
TJ (°C)
25
50
75
100
125
150
JUNCTION TEMPERATURE (°C)
FIGURE 11. CURRENT LIMIT vs TJ
FIGURE 12. VTJ vs JUNCTION TEMPERATURE
VIN=5V, VO=3.3V, IO=4A
1.27
1.268
∆VIN
VREF (V)
1.266
VLX
1.264
iL
1.262
∆VO
1.26
1.258
1.256
-50
-10
30
70
110
150
DIE TEMPERATURE (°C)
FIGURE 13. VREF vs DIE TEMPERATURE
7
FIGURE 14. SWITCHING WAVEFORMS
FN7297.3
May 9, 2005
EL7564
Typical Performance Curves (Continued)
VIN=5V, VO=3.3V, IO=0.2A-4A
VIN=5V, VO=3.3V, IO=2A
IO
∆VO
VIN
VO
FIGURE 15. TRANSIENT RESPONSE
FIGURE 16. POWER-UP
VIN=5V, VO=3.3V, IO=4A
VIN=5V, VO=3.3V, IO=2A
VIN
EN
VO
VO
FIGURE 17. POWER-DOWN
FIGURE 18. RELEASING EN
VIN=5V, VO=3.3V, IO=4A
VIN=5V
EN
IO
VO
VO
FIGURE 19. SHUT-DOWN
8
FIGURE 20. SHORT-CIRCUIT PROTECTION
FN7297.3
May 9, 2005
EL7564
Typical Performance Curves (Continued)
JEDEC JESD51-7 HIGH EFFECTIVE THERMAL
CONDUCTIVITY TEST BOARD. HTSSOP EXPOSED
DIEPAD SOLDERED TO PCB PER JESD51-5
1
0.9
1
0.5
0
0.6
A
1.5
0.7
8
P2 W
SO °C/
T S 10
=1
8
P2
O
W
C/
0°
=3
A
2
θJ
SS
θJ
2.5
909mW
0.8
H
POWER DISSIPATION (W)
3 3.333W
HT
POWER DISSIPATION (W)
3.5
JEDEC JESD51-3 LOW EFFECTIVE THERMAL
CONDUCTIVITY TEST BOARD
0.5
0.4
0.3
0.2
0.1
0
25
75 85 100
50
125
0
150
0
25
50
75 85 100
125
150
AMBIENT TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
FIGURE 21. PACKAGE POWER DISSIPATION vs AMBIENT
TEMPERATURE
FIGURE 22. PACKAGE POWER DISSIPATION vs AMBIENT
TEMPERATURE
Block Diagram
0.1µF
VTJ
JUNCTION
TEMPERATURE
390pF
VREF
COSC
VOLTAGE
REFERENCE
OSCILLATOR
VDRV
2.2nF
VHI
CONTROLLER
SUPPLY
22Ω
VIN
VDD
0.22µF
POWER
0.22µF
PWM
CONTROLLER
FET
DRIVERS
VOUT
POWER
330µF
FET
PGND
EN
STP
POWER
TRACKING
D1
4.7µH
2370Ω
100pF
1kΩ
CURRENT
SENSE
STN
VREF
-
PG
+
SGND
9
FB
FN7297.3
May 9, 2005
EL7564
Applications Information
Circuit Description
General
The EL7564 is a fixed frequency, current mode controlled
DC/DC converter with integrated N-channel power
MOSFETs and a high precision reference. The device
incorporates all the active circuitry required to implement a
cost effective, user-programmable 4A synchronous stepdown regulator suitable for use in DSP core power supplies.
By combining fused-lead packaging technology with an
efficient synchronous switching architecture, high power
output (13W) can be realized without the use of discrete
external heat sinks.
Theory of Operation
The EL7564 is composed of seven major blocks:
1. PWM Controller
2. NMOS Power FETs and Drive Circuitry
3. Bandgap Reference
4. Oscillator
5. Temperature Sensor
6. Power Good and Power On Reset
7. Auxiliary Supply Tracking
PWM Controller
The EL7564 regulates output voltage through the use of
current-mode controlled pulse width modulation. The three
main elements in a PWM controller are the feedback loop
and reference, a pulse width modulator whose duty cycle is
controlled by the feedback error signal, and a filter which
averages the logic level modulator output. In a step-down
(buck) converter, the feedback loop forces the timeaveraged output of the modulator to equal the desired output
voltage. Unlike pure voltage-mode control systems, currentmode control utilizes dual feedback loops to provide both
output voltage and inductor current information to the
controller. The voltage loop minimizes DC and transient
errors in the output voltage by adjusting the PWM duty-cycle
in response to changes in line or load conditions. Since the
output voltage is equal to the time-averaged of the modulator
output, the relatively large LC time constant found in power
supply applications generally results in low bandwidth and
poor transient response. By directly monitoring changes in
inductor current via a series sense resistor the controller's
response time is not entirely limited by the output LC filter
and can react more quickly to changes in line and load
conditions. This feed-forward characteristic also simplifies
AC loop compensation since it adds a zero to the overall
loop response. Through proper selection of the currentfeedback to voltage-feedback ratio the overall loop response
will approach a one-pole system. The resulting system offers
several advantages over traditional voltage control systems,
10
including simpler loop compensation, pulse by pulse current
limiting, rapid response to line variation and good load step
response.
The heart of the controller is an input direct summing
comparator which sum voltage feedback, current feedback,
slope compensation ramp and power tracking signals
together. Slope compensation is required to prevent system
instability that occurs in current-mode topologies operating
at duty-cycles greater than 50% and is also used to define
the open-loop gain of the overall system. The slope
compensation is fixed internally and optimized for 500mA
inductor ripple current. The power tracking will not contribute
any input to the comparator steady-state operation. Current
feedback is measured by the patented sensing scheme that
senses the inductor current flowing through the high-side
switch whenever it is conducting. At the beginning of each
oscillator period the high-side NMOS switch is turned on.
The comparator inputs are gated off for a minimum period of
time of about 150ns (LEB) after the high-side switch is
turned on to allow the system to settle. The Leading Edge
Blanking (LEB) period prevents the detection of erroneous
voltages at the comparator inputs due to switching noise. If
the inductor current exceeds the maximum current limit
(ILMAX) a secondary over-current comparator will terminate
the high-side switch on time. If ILMAX has not been reached,
the feedback voltage FB derived from the regulator output
voltage VOUT is then compared to the internal feedback
reference voltage. The resultant error voltage is summed
with the current feedback and slope compensation ramp.
The high-side switch remains on until all four comparator
inputs have summed to zero, at which time the high-side
switch is turned off and the low-side switch is turned on.
However, the maximum on-duty ratio of the high-side switch
is limited to 95%. In order to eliminate cross-conduction of
the high-side and low-side switches a 15ns break-beforemake delay is incorporated in the switch drive circuitry. The
output enable (EN) input allows the regulator output to be
disabled by an external logic control signal.
Output Voltage Setting
In general, EL7564CM:
R 

V OUT = 0.975V ×  1 + ------2-
R 1

and EL7564CRE:
R 

V OUT = 0.992V ×  1 + ------2-
R 1

A 100nA pull-up current from FB to VDD forces VOUT to
GND in the event that FB is floating.
FN7297.3
May 9, 2005
EL7564
NMOS Power FETs and Drive Circuitry
When external synchronization is required, always choose
COSC such that the free-running frequency is at least 20%
lower than that of the sync source to accommodate
component and temperature variations. Figure 21 shows a
typical connection.
The EL7564 integrates low on-resistance (30mΩ) NMOS
FETs to achieve high efficiency at 4A. In order to use an
NMOS switch for the high-side drive it is necessary to drive
the gate voltage above the source voltage (LX). This is
accomplished by bootstrapping the VHI pin above the LX
voltage with an external capacitor CVHI and internal switch
and diode. When the low-side switch is turned on and the
LX voltage is close to GND potential, capacitor CVHI is
charged through an internal switch to VDRV, typically 5V. At
the beginning of the next cycle the high-side switch turns
on and the LX pins begin to rise from GND to VIN potential.
As the LX pin rises the positive plate of capacitor CVHI
follows and eventually reaches a value of VDRV + VIN,
typically 10V, for VDRV = VIN = 5V. This voltage is then
level shifted and used to drive the gate of the high-side
FET, via the VHI pin. A value of 0.22µF for CVHI is
recommended.
Junction Temperature Sensor
An internal temperature sensor continuously monitors die
temperature. In the event that the die temperature exceeds
the thermal trip-point, the system is in a fault state and will
be shut down. The upper and low trip-points are set to 135°C
and 115°C respectively.
The VTJ pin is an accurate indication of the internal silicon
junction temperature (see performance curve.) The junction
temperature TJ (°C) can be determined from the following
relation:
– VTJ
T J = 75 + 1.2
------------------------0.00384
Reference
Where VTJ is the voltage at the VTJ pin in volts.
A 1.5% temperature compensated bandgap reference is
integrated in the EL7564. The external VREF capacitor acts
as the dominant pole of the amplifier and can be increased
in size to maximize transient noise rejection. A value of
0.1µF is recommended.
Power Good and Power On Reset
During power up the output regulator will be disabled until
VIN reaches a value of approximately 4V. About 500mV
hysteresis is present to eliminate noise-induced oscillations.
Under-voltage and over-voltage conditions on the regulator
output are detected through an internal window comparator.
A logic high on the PG output indicates that the regulated
output voltage is within about +10% of the nominal selected
Oscillator
The system clock is generated by an internal relaxation
oscillator with a maximum duty-cycle of approximately 95%.
Operating frequency can be adjusted through COSC.
100pF
BAT54S
EXTERNAL
OSCILLATOR
390pF
1
20
2
19
3
18
5
16
6
EL7564
15
7
14
8
13
9
12
10
11
FIGURE 23. OSCILLATOR SYNCHRONIZATION
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EL7564
Power Tracking
1. Linear Tracking
The power tracking pins STP and STN are the inputs to a
comparator, whose HI output forces the PWM controller to
skip switching cycles.
In this application, it is always the case that the lower voltage
supply VC tracks the higher output supply VP. Please see
Figure 22 below.
1
20
2
19
6
15
7
EL7564
8
VC
14
13
9
+
-
10
11
1
20
2
19
6
15
7
EL7564
8
VP
12
VOUT
VC
TIME
VP
14
13
9
+
-
10
12
11
FIGURE 24. LINEAR POWER TRACKING
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May 9, 2005
EL7564
2. Offset Tracking
The intended start-up sequence is shown in Figure 23a. In
this configuration, VC will not start until VP reaches a preset
value of:
RB
--------------------- × V IN
RA + RB
1
20
2
19
6
15
VIN
7
RA
8
9
RB
10
EL7564
14
13
STP
+
STN -
11
20
2
19
6
15
EL7564
8
9
10
VP
12
1
7
VC
VOUT
VC
TIME
VP
14
13
STP
+
STN -
12
11
FIGURE 25. OFFSET POWER TRACKING
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EL7564
3. External Soft Start
The second way of offset tracking is to use the EN and
Power Good pins, as shown in Figure 24. In this
configuration, VP does not have to be larger than VC.
An external soft start can be combined with auxiliary supply
tracking to provide desired soft start other than internally
preset soft start (Figure 25). The appropriate start-up time is:
VO
t s = R × C × --------V IN
1
EN 20
2
19
3
PG 18
5
16
6
EL7564
15
7
14
8
13
9
12
10
11
VC
VP
VC
1
EN 20
2
19
3
PG 18
5
16
6
EL7564
TIME
15
7
14
8
13
9
12
10
11
VP
FIGURE 26. OFFSET TRACKING
VIN
1
20
2
19
6
15
7
R
EL7564
8
9
10
VOUT
14
13
STP
STN
+
-
12
11
C
FIGURE 27. EXTERNAL SOFT START
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EL7564
4. Start-up Delay
A capacitor can be added to the EN pin to delay the
converter start-up (Figure 26) by utilizing the pull-up current.
The delay time is approximately:
t d ( ms ) = 1200 × C ( µF )
1
20
2
19
6
15
Since the thermal performance of the IC is heavily
dependent on the board layout, the system designer should
exercise care during the design phase to ensure that the IC
will operate under the worst-case environmental conditions.
C
7
EL7564
8
9
10
VOUT
14
Layout Considerations
VIN
13
STP
+
STN -
The EL7564CRE utilizes the 28-pin HTSSOP package. The
majority of heat is dissipated through the heat pad exposed
at the bottom of the package. Therefore, the heat pad needs
to be soldered to the PCB. The thermal resistance for this
package is as low as 29°C/W, better than that of SO20.
Typical performance is shown in the curves section. The
actual junction temperature can be measured at VTJ pin.
12
VO
td
11
TIME
FIGURE 28. START-UP DELAY
Thermal Management
The EL7564CM utilizes “fused lead” packaging technology in
conjunction with the system board layout to achieve a lower
thermal resistance than typically found in standard SO20
packages. By fusing (or connecting) multiple external leads
to the die substrate within the package, a very conductive
heat path is created to the outside of the package. This
conductive heat path MUST then be connected to a heat
sinking area on the PCB in order to dissipate heat out and
away from the device. The conductive paths for the
EL7564CM package are the fused leads: # 6, 7, 11, 12, and
13. If a sufficient amount of PCB metal area is connected to
the fused package leads, a junction-to-ambient resistance of
43°C/W can be achieved (compared to 85°C/W for a
standard SO20 package). The general relationship between
PCB heat-sinking metal area and the thermal resistance for
this package is shown in the Performance Curves section of
this data sheet. It can be readily seen that the thermal
resistance for this package approaches an asymptotic value
of approximately 43°C/W without any airflow, and 33°C/W
with 100 LFPM airflow. Additional information can be found
in Application Note #8 (Measuring the Thermal Resistance
of Power Surface-Mount Packages). For a thermal shutdown
die junction temperature of 135°C, and power dissipation of
1.5W, the ambient temperature can be as high as 70°C
without airflow. With 100 LFPM airflow, the ambient
temperature can be extended to 85°C.
15
The layout is very important for the converter to function
properly. Power Ground ( ) and Signal Ground ( ) should
be separated to ensure that the high pulse current in the
Power Ground never interferes with the sensitive signals
connected to Signal Ground. They should only be connected
at one point (normally at the negative side of either the input
or output capacitor.)
The trace connected to the FB pin is the most sensitive
trace. It needs to be as short as possible and in a “quiet”
place, preferably with the PGND or SGND traces
surrounding it.
In addition, the bypass capacitor connected to the VDD pin
needs to be as close to the pin as possible.
The heat of the chip is mainly dissipated through the PGND
pins for the CM package, and through the heat pad at the
bottom for the CRE package. Maximizing the copper area
around these PGND pins or the heat pad is preferable. In
addition, a solid ground plane is always helpful for the EMI
performance.
The demo board is a good example of layout based on these
principles. Please refer to the EL7564 Application Brief for
the layout.
FN7297.3
May 9, 2005
EL7564
Package Outline Drawing - 20-Pin SO (0.300”) Package
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>
16
FN7297.3
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EL7564
Package Outline Drawing (28-Pin HTSSOP Package)
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
17
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