INTERSIL EL7531_06

EL7531
®
Data Sheet
July 13, 2006
Monolithic 1A Step-Down Regulator with
Low Quiescent Current
The EL7531 is a synchronous, integrated FET 1A step-down
regulator with internal compensation. It operates with an input
voltage range from 2.5V to 5.5V, which accommodates
supplies of 3.3V, 5V, or a Li-Ion battery source. The output can
be externally set from 0.8V to VIN with a resistive divider.
The EL7531 features automatic PFM/PWM mode control, or
PWM mode only. The PWM frequency is typically 1.4MHz
and can be synchronized up to 12MHz. The typical no load
quiescent current is only 120µA. Additional features include
a Power-Good output, <1µA shut-down current, short-circuit
protection, and over-temperature protection.
FN7428.9
Features
• Less than 0.15 in2 (0.97 cm2) footprint for the complete 1A
converter
• Components on one side of PCB
• Max height 1.1mm MSOP10
• Power-Good (PG) output
• Internally-compensated voltage mode controller
• Up to 94% efficiency
• <1µA shut-down current
• 120µA quiescent current
• Overcurrent and over-temperature protection
The EL7531 is available in the 10 Ld MSOP package,
making the entire converter occupy less than 0.15 in2 of
PCB area with components on one side only. The 10 Ld
MSOP package is specified for operation over the full -40°C
to +85°C temperature range.
• Pb-Free plus anneal available (RoHS compliant)
Applications
• PDA and pocket PC computers
Ordering Information
PART
PART NUMBER MARKING
• External synchronizable up to 12MHz
TAPE &
REEL
PACKAGE
PKG.
DWG. #
EL7531IY
BEAAA
-
10 Ld MSOP
MDP0043
EL7531IY-T7
BEAAA
7”
10 Ld MSOP
MDP0043
EL7531IY-T13
BEAAA
13”
10 Ld MSOP
MDP0043
EL7531IYZ
(Note)
BHAAA
-
10 Ld MSOP
(Pb-free)
MDP0043
EL7531IYZ-T7
(Note)
BHAAA
7”
10 Ld MSOP
(Pb-free)
MDP0043
EL7531IYZ-T13
(Note)
BHAAA
10 Ld MSOP
(Pb-free)
MDP0043
13”
• Bar code readers
• Cellular phones
• Portable test equipment
• Li-Ion battery powered devices
• Small form factor (SFP) modules
Typical Application Diagram
EL7531
TOP VIEW
VS
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.
(2.5V to 5.5V)
VIN
R3 100Ω
C2
10µF
LX
EL7531
R5 100kΩ
R1*
124kΩ
PG
Pinout
EN
EL7531 (10 LD MSOP)
TOP VIEW
1 SGND
FB 10
2 PGND
VO 9
3 LX
PG 8
4 VIN
EN 7
5 VDD
R4 100kΩ
R6
100kΩ
1.8µH
C1
10µF
VDD
C3
0.1µF
VO
L1
FB
SYNC
PGND
SGND
R2*
100kΩ
VO
C4
470pF
(1.8V @ 1A)
* VO = 0.8V * (1 + R1 / R2)
SYNC 6
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright © Intersil Americas Inc. 2004, 2005, 2006. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
EL7531
Absolute Maximum Ratings (TA = 25°C)
VIN, VDD, PG to SGND . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6.5V
LX to PGND . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to (VIN + +0.3V)
SYNC, EN, VO, FB to SGND . . . . . . . . . . . . . -0.3V to (VIN + +0.3V)
PGND to SGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +0.3V
Peak Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2A
Operating Ambient Temperature . . . . . . . . . . . . . . . .-40°C to +85°C
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
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.
IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typ 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 = VIN = VEN = 3.3V, C1 = C2 = 10µF, L = 1.8µH, VO = 1.8V (as shown in Typical Application Diagram),
unless otherwise specified.
DESCRIPTION
CONDITIONS
MIN
TYP
MAX
UNIT
790
800
810
mV
DC CHARACTERISTICS
VFB
Feedback Input Voltage
PWM mode
∆VOUT/VOUT
VFB vs Temperature
Junction temperature = -40°C to +85°C
(see Figure 7)
0.3
%
∆VOUT/VOUT
Line Regulation
VIN = 3.3V to 5V, IO = 1A (see Figure 7)
0.1
%
∆VOUT/VOUT
Load Regulation
IO = 0A to 1A, VIN = 3.3V (see Figure 7)
0.4
%
IFB
Feedback Input Current
100
nA
2.5
5.5
V
VIN, VDD
Input Voltage
VIN,OFF
Minimum Voltage for Shutdown
VIN falling
2
2.2
V
VIN,ON
Maximum Voltage for Startup
VIN rising
2.2
2.4
V
IS
Input Supply Quiescent Current
Active - PFM Mode
VSYNC = 0V
120
145
µA
Active - PWM Mode
VSYNC = 3.3V
6.5
7.5
mA
Supply Current
PWM, VIN = VDD = 5V
400
500
µA
EN = 0, VIN = VDD = 5V
0.1
1
µA
RDS(ON)-PMOS PMOS FET Resistance
VDD = 5V, wafer test only
70
100
mΩ
RDS(ON)-NMOS NMOS FET Resistance
VDD = 5V, wafer test only
45
75
mΩ
IDD
ILMAX
Current Limit
1.5
A
TOT,OFF
Over-temperature Threshold
T rising
145
°C
TOT,ON
Over-temperature Hysteresis
T falling
130
°C
EN, SYNC Current
VEN, VRSI = 0V and 3.3V
-1
VEN1, VSYNC1
EN, SYNC Rising Threshold
VDD = 3.3V
2.4
1.8
VEN2, VSYNC2
EN, SYNC Falling Threshold
VDD = 3.3V
9
1.4
Minimum VFB for PG, WRT Targeted
VFB Value
VFB rising
PG Voltage Drop
ISINK = 3.3mA
IEN, ISYNC
VPG
VOLPG
VFB falling
1
µA
V
0.8
V
95
%
86
%
35
70
mV
1.4
1.6
MHz
AC CHARACTERISTICS
FPWM
PWM Switching Frequency
tSYNC
Minimum SYNC Pulse Width
tSS
Soft-start Time
1.25
Guaranteed by design
25
ns
650
2
µs
FN7428.9
July 13, 2006
EL7531
Pin Descriptions
PIN NUMBER
PIN NAME
PIN FUNCTION
1
SGND
Negative supply for the controller stage
2
PGND
Negative supply for the power stage
3
LX
Inductor drive pin; high current digital output with average voltage equal to the regulator output voltage
4
VIN
Positive supply for the power stage
5
VDD
Power supply for the controller stage
6
SYNC
7
EN
Enable
8
PG
Power-Good open drain output
9
VO
Output voltage sense
10
FB
Voltage feedback input; connected to an external resistor divider between VO and SGND for variable
output
SYNC input pin; when connected to HI, regulator runs at forced PWM mode; when connected to Low, auto
PFM/PWM mode; when connected to external sync signal, at external PWM frequency up to 12MHz
Block Diagram
100Ω
0.1µF
C4
VDD
INDUCTOR SHORT
VO
+
CURRENT
SENSE
10pF
124K
470pF
FB
5M
+
PWM
COMPENSATION
100K
SYNC
SYNC
RAMP
GENERATOR
EN
EN
SOFTSTART
10µF
3.3V
CLOCK
+
–
BANDGAP
REFERENCE
+
PWM
COMPARATOR
PFM
ON-TIME
CONTROL
+
PWM
COMPARATOR
UNDERVOLTAGE
LOCKOUT
TEMPERATURE
SENSE
SGND
VIN
P-DRIVER
LX
CONTROL
LOGIC
1.8V
0 TO 1A
10µF
N-DRIVER
+
SYNCHRONOUS
RECTIFIER
1.8µH
PGND
100K
PG
PG
POWER
GOOD
3
FN7428.9
July 13, 2006
EL7531
Performance Curves and Waveforms
All waveforms are taken at VIN = 3.3V, VO = 1.8V, IO = 1A with component values shown on page 1 at room ambient temperature, unless otherwise
noted.
100
100
VO = 3.3V
95
85
80
75
VO = 1.8V
VO = 1.5V
70
VO = 1.0V
65
VO = 0.8V
60
VO = 1.2V
40
VO = 1.0V
30
20
10
VIN = 5V
0.100
VO = 1.5V
50
45
0.010
VO = 1.8V
60
50
40
0.001
VO = 2.5V
70
VO = 1.2V
55
VO = 3.3V
80
EFFICIENCY (%)
EFFICIENCY (%)
90
VO = 2.5V
90
VO = 0.8V
VIN = 5V
0
0.001
1.000
0.010
IO (A)
FIGURE 1. EFFICIENCY vs IO (PFM/PWM MODE)
100
VO = 2.5V
VO = 1.8V
85
80
VO = 1.5V
75
VO = 1.2V
VO = 1.0V
70
65
VO = 2.5V
90
EFFICIENCY (%)
EFFICIENCY (%)
90
VO = 0.8V
60
55
80
VO = 1.8V
70
VO = 1.5V
VO = 1.2V
60
50
VO = 1.0V
40
30
20
50
VO = 0.8V
10
45
VIN = 3.3V
40
0.001
0.010
0.100
VIN = 3.3V
0
0.001
1.000
0.010
0.100
1.000
IO (A)
IO (A)
FIGURE 3. EFFICIENCY vs IO (PFM/PWM MODE)
FIGURE 4. EFFICIENCY vs IO (PWM MODE)
1.44
0.1%
VIN = 3.3V IO = 1A
VIN = 5V IO = 1A
VIN = 5V IO = 0A
0.0%
VO CHANGES
1.42
FS (MHz)
1.000
FIGURE 2. EFFICIENCY vs IO (PWM MODE)
100
95
0.100
IO (A)
1.4
VIN = 3.3V IO = 0A
1.38
1.36
1.34
1.32
-50
-0.1%
VIN = 3.3V
-0.2%
VIN = 5V
-0.3%
-0.4%
-0.5%
0
50
100
150
TA (°C)
FIGURE 5. FS vs JUNCTION TEMPERATURE (PWM MODE)
4
0
0.2
0.4
0.6
0.8
1
IO (A)
FIGURE 6. LOAD REGULATIONS (PWM MODE)
FN7428.9
July 13, 2006
EL7531
Performance Curves and Waveforms
(Continued)
All waveforms are taken at VIN = 3.3V, VO = 1.8V, IO = 1A with component values shown on page 1 at room ambient temperature, unless otherwise
noted.
0.1%
12
0.0%
VIN = 5V IO = 0A
8
-0.2%
-0.3%
IS (mA)
VO CHANGES
10
VIN = 3.3V IO = 0A
-0.1%
VIN = 3.3V IO = 1A
-0.4%
6
4
-0.5%
-0.6%
VIN = 5V IO = 1A
-0.7%
-50
0
2
50
100
0
150
2.5
3
3.5
TJ (°C)
FIGURE 7. PWM MODE LOAD/LINE REGULATIONS vs
JUNCTION TEMPERATURE
100
VO = 3.3V
VO = 1.8V
120
EFFICIENCY (%)
IS (µA)
90
5
1.4MHz
80
110
100
4.5
FIGURE 8. NO LOAD QUIESCENT CURRENT (PWM MODE)
140
130
4
VS (V)
VO = 1.5V
VO = 1.2V VO = 1.0V
VO = 0.8V
80
70
5MHz
60
12MHz
40
20
60
50
2.0
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
0
200
400
VS (V)
600
800
1K
1.2K
IO (mA)
FIGURE 9. NO LOAD QUIESCENT CURRENT (PFM MODE)
FIGURE 10. EFFICIENCY vs IO (PWM MODE)
1
0.5
12MHz
0.3
VO CHANGES (%)
VO CHANGES (%)
0.6
1.4MHz
0.2
5MHz
0
-0.2
-0.6
12MHz
0.1
1.4MHz
-0.1
5MHz
-0.3
0
200
400
600
800
1K
1.2K
IO (mA)
FIGURE 11. LOAD REGULATION (PWM MODE)
5
-0.5
2.5
3
3.5
4
4.5
5
5.5
VIN (V)
FIGURE 12. LINE REGULATION @ 500mA (PWM MODE)
FN7428.9
July 13, 2006
EL7531
Performance Curves and Waveforms
(Continued)
All waveforms are taken at VIN = 3.3V, VO = 1.8V, IO = 1A with component values shown on page 1 at room ambient temperature, unless otherwise
noted.
VIN
(2V/DIV)
EN
IIN
(0.5A/DIV)
IIN
(0.5A/DIV)
VO
(2V/DIV)
VO
(2V/DIV)
PG
PG
500µs/DIV
200µs/DIV
FIGURE 13. START-UP AT IO = 1A
FIGURE 14. ENABLE AND SHUT-DOWN
LX
(2V/DIV)
LX
(2V/DIV)
IL
(0.5A/DIV)
IL
(0.5A/DIV)
∆VO
(10mV/DIV)
∆VO
(50mV/DIV)
0.5µs/DIV
2µs/DIV
FIGURE 15. PFM STEADY-STATE OPERATION WAVEFORM
(IO = 100mA)
SYNC
(2V/DIV)
SYNC
(2V/DIV)
LX
(2V/DIV)
IL
(0.5A/DIV)
LX
(2V/DIV)
IL
(0.5A/DIV)
0.2µs/DIV
FIGURE 17. EXTERNAL SYNCHRONIZATION TO 2MHz
6
FIGURE 16. PWM STEADY-STATE OPERATION (IO = 1A)
20ns/DIV
FIGURE 18. EXTERNAL SYNCHRONIZATION TO 12MHz
FN7428.9
July 13, 2006
EL7531
Performance Curves and Waveforms
(Continued)
All waveforms are taken at VIN = 3.3V, VO = 1.8V, IO = 1A with component values shown on page 1 at room ambient temperature, unless otherwise
noted.
IO
(0.5A/DIV)
IO
(0.5A/DIV)
∆VO
(100mV/DIV)
∆VO
(100mV/DIV)
50µs/DIV
100µs/DIV
FIGURE 19. LOAD TRANSIENT RESPONSE (22mA to 1A)
FIGURE 20. PWM LOAD TRANSIENT RESPONSE (0A TO 1A)
IO=150mA
SYNC
(2V/DIV)
IO
(0.5A/DIV)
∆VO
(100mV/DIV)
LX
(2V/DIV)
2µs/DIV
50µs/DIV
FIGURE 21. PWM LOAD TRANSIENT RESPONSE
(0.25A TO 0.75A)
FIGURE 22. PFM-PWM TRANSITION TIME
3
IO=50mA
SYNC
(2V/DIV)
LX
(2V/DIV)
VO CHANGES (%)
2
1
0
-1
PFM
PWM
-2
-3
0
200
400
600
800
1000
1200
IOUT (mA)
2µs/DIV
FIGURE 23. PFM-PWM TRANSITION TIME
7
FIGURE 24. PFM-PWM LOAD REGULATION
FN7428.9
July 13, 2006
EL7531
Performance Curves and Waveforms
(Continued)
All waveforms are taken at VIN = 3.3V, VO = 1.8V, IO = 1A with component values shown on page 1 at room ambient temperature, unless otherwise
noted.
JEDEC JESD51-7 HIGH EFFECTIVE THERMAL
CONDUCTIVITY TEST BOARD
JEDEC JESD51-3 LOW EFFECTIVE THERMAL
CONDUCTIVITY TEST BOARD
1
870mW
0.9
486mW
0.5
0.4
M
θ
JA
=
0.3
POWER DISSIPATION (W)
POWER DISSIPATION (W)
0.6
SO
P1
20
0
6°
C/
W
0.2
0.1
0.8
0.7
θ
JA
=
0.6
0.5
M
SO
P1
11
0
5°
C/
W
0.4
0.3
0.2
0.1
0
0
0
25
50
75 85
100
125
AMBIENT TEMPERATURE (°C)
FIGURE 25. PACKAGE POWER DISSIPATION vs AMBIENT
TEMPERATURE
8
0
25
50
75 85
100
125
AMBIENT TEMPERATURE (°C)
FIGURE 26. PACKAGE POWER DISSIPATION vs AMBIENT
TEMPERATURE
FN7428.9
July 13, 2006
EL7531
Applications Information
Product Description
The EL7531 is a synchronous, integrated FET 1A step-down
regulator which operates from an input of 2.5V to 5.5V. The
output voltage is user-adjustable with a pair of external
resistors.
When the load is very light, the regulator automatically
operates in the PFM mode, thus achieving high efficiency at
light load (>70% for 1mA load). When the load increases to
typically 250mA, the regulator automatically switches over to
a voltage-mode PWM operating at nominal 1.4MHz
switching frequency. The efficiency is up to 94%.
It can also operate in a fixed PWM mode or be synchronized
to an external clock up to 12MHz for improved EMI
performance.
PFM Operation
The heart of the EL7531 regulator is the automatic
PFM/PWM controller.
If the SYNC pin is connected to ground, the regulator
operates automatically in either the PFM or PWM mode,
depending on load. When the SYNC pin is connected to VIN,
the regulator operates in the fixed PWM mode. When the pin
is connected to an external clock ranging from 1.6MHz to
12MHz, the regulator is in the fixed PWM mode and
synchronized to the external clock frequency.
In the automatic PFM/PWM operation, when the load is light,
the regulator operates in the PFM mode to achieve high
efficiency. The top P channel MOSFET is turned on first. The
inductor current increases linearly to a preset value before it
is turned off. Then the bottom N channel MOSFET turns on,
and the inductor current linearly decreases to zero current.
The N channel MOSFET is then turned off, and an antiringing MOSFET is turned on to clamp the VLX pin to VO.
The inductor current looks like triangular pulses. The
frequency of the pulses is mainly a function of output current.
The higher the load, the higher the frequency of the pulses
until the inductor current becomes continuous. At this point,
the controller automatically changes to PWM operation.
When the controller transitions to PWM mode, there can be
a perturbation to the output voltage. This perturbation is due
to the inherent behavior of switching converters when
transitioning between two control loops. To reduce this
effect, it is recommended to use the phase-lead capacitor
(C4) shown in the Typical Application Diagram on page 1.
This capacitor allows the PWM loop to respond more quickly
to this type of perturbation. To properly size C4, refer to the
Component Selection section.
9
PWM Operation
The regulator operates the same way in the forced PWM or
synchronized PWM mode. In this mode, the inductor current
is always continuous and does not stay at zero.
In this mode, the P channel MOSFET and N channel
MOSFET always operate complementary. When the
PMOSFET is on and the NMOSFET off, the inductor current
increases linearly. The input energy is transferred to the
output and also stored in the inductor. When the P channel
MOSFET is off and the N channel MOSFET on, the inductor
current decreases linearly, and energy is transferred from
the inductor to the output. Hence, the average current
through the inductor is the output current. Since the inductor
and the output capacitor act as a low pass filter, the duty
cycle ratio is approximately equal to VO divided by VIN.
The output LC filter has a second order effect. To maintain
the stability of the converter, the overall controller must be
compensated. This is done with the fixed internally
compensated error amplifier and the PWM compensator.
Because the compensations are fixed, the values of input
and output capacitors are 10µF to 22µF ceramic and
inductor is 1.5µH to 2.2µH.
Forced PWM Mode/SYNC Input
Pulling the SYNC pin HI (>2.5V) forces the converter into
PWM mode in the next switching cycle regardless of output
current. The duration of the transition varies depending on
the output current. Figures 22 and 23 (under two different
loading conditions) show the device goes from PFM to PWM
mode.
Note: In forced PWM mode, the IC will continue to start-up in
PFM mode to support pre-biased load applications.
Start-Up and Shut-Down
When the EN pin is tied to VIN, and VIN reaches
approximately 2.4V, the regulator begins to switch. The
inductor current limit is gradually increased to ensure proper
soft-start operation.
When the EN pin is connected to a logic low, the EL7531 is
in the shut-down mode. All the control circuitry and both
MOSFETs are off, and VOUT falls to zero. In this mode, the
total input current is less than 1µA.
When the EN reaches logic HI, the regulator repeats the
start-up procedure, including the soft-start function.
Current Limit and Short-Circuit Protection
The current limit is set at about 2A for the PMOS. When a
short-circuit occurs in the load, the preset current limit
restricts the amount of current available to the output, which
causes the output voltage to drop below the preset voltage.
In the meantime, the excessive current heats up the
regulator until it reaches the thermal shut-down point.
FN7428.9
July 13, 2006
EL7531
Thermal Shut-Down
Once the junction reaches about 145°C, the regulator shuts
down. Both the P channel and the N channel MOSFETs turn
off. The output voltage will drop to zero. With the output
MOSFETs turned off, the regulator will soon cool down.
Once the junction temperature drops to about 130°C, the
regulator will restart again in the same manner as EN pin
connects to logic HI.
Thermal Performance
The EL7531 is available in a fused-lead MSOP10 package.
Compared with regular MSOP10 package, the fused- lead
package provides lower thermal resistance. The θJA is
100°C/W on a 4-layer board and 125°C/W on 2-layer board.
Maximizing the copper area around the pins will further
improve the thermal performance.
Power Good Output
The PG (pin 8) output is used to indicate when the output
voltage is properly regulating at the desired set point. It is an
open-drain output that should be tied to VIN or VCC through
a 100kΩ resistor. If no faults are detected, EN is high, and
the output voltage is within ~5% of regulation, the PG pin will
be allowed to go high. Otherwise, the open-drain NMOS will
pull PG low.
Output Voltage Selection
Users can set the output voltage of the variable version with
a resister divider, which can be chosen based on the
following formula:
R ⎞
⎛
V O = 0.8 × ⎜ 1 + ------2-⎟
R 1⎠
⎝
The inductor must be able to handle IO for the RMS load
current, and to assure that the inductor is reliable, it must
handle the 2A surge current that can occur during a current
limit condition.
In addition to decoupling capacitors and inductor value, it is
important to properly size the phase-lead capacitor C4
(Refer to the Typical Application Diagram). The phase-lead
capacitor creates additional phase margin in the control loop
by generating a zero and a pole in the transfer function. As a
general rule of thumb, C4 should be sized to start the phaselead at a frequency of ~2.5kHz. The zero will always appear
at lower frequency than the pole and follow the equation
below:
1
f Z = ---------------------2πR 2 C 4
Over a normal range of R2 (~10-100k), C4 will range from
~470-4700pF. The pole frequency cannot be set once the
zero frequency is chosen as it is dictated by the ratio of R1
and R2, which is solely determined by the desired output set
point. The equation below shows the pole frequency
relationship:
1
f P = --------------------------------------2π ( R 1 R 2 )C 4
Layout Considerations
The layout is very important for the converter to function
properly. The following PC layout guidelines should be
followed:
1. Separate the Power Ground ( ) and Signal Ground
(
); connect them only at one point right at the pins
Component Selection
Because of the fixed internal compensation, the component
choice is relatively narrow. For a regulator with fixed output
voltage, only two capacitors and one inductor are required.
We recommend 10µf to 22µF multi-layer ceramic capacitors
with X5R or X7R rating for both the input and output
capacitors, and 1.5 to 2.2µH for the inductor.
The RMS current present at the input capacitor is decided by
the following formula:
V O × ( V IN – V O )
I INRMS = ----------------------------------------------- × I O
V IN
2. Place the input capacitor as close to VIN and PGND pins
as possible
3. Make the following PC traces as small as possible:
4. from LX pin to L
5. from CO to PGND
6. If used, connect the trace from the FB pin to R1 and R2
as close as possible
7. Maximize the copper area around the PGND pin
8. Place several via holes under the chip to additional
ground plane to improve heat dissipation
The demo board is a good example of layout based on this
outline. Please refer to the EL7531 Application Brief.
This is about half of the output current IO for all the VO. This
input capacitor must be able to handle this current.
The inductor peak-to-peak ripple current is given as:
( V IN – V O ) × V O
∆I IL = ------------------------------------------L × V IN × f S
L is the inductance
fS the switching frequency (nominally 1.4MHz)
10
FN7428.9
July 13, 2006
EL7531
Mini SO Package Family (MSOP)
0.25 M C A B
D
MINI SO PACKAGE FAMILY
(N/2)+1
N
E
MDP0043
A
E1
PIN #1
I.D.
1
B
(N/2)
e
H
C
SEATING
PLANE
SYMBOL
MSOP8
MSOP10
TOLERANCE
NOTES
A
1.10
1.10
Max.
-
A1
0.10
0.10
±0.05
-
A2
0.86
0.86
±0.09
-
b
0.33
0.23
+0.07/-0.08
-
c
0.18
0.18
±0.05
-
D
3.00
3.00
±0.10
1, 3
E
4.90
4.90
±0.15
-
E1
3.00
3.00
±0.10
2, 3
e
0.65
0.50
Basic
-
L
0.55
0.55
±0.15
-
L1
0.95
0.95
Basic
-
N
8
10
Reference
Rev. C 6/99
0.10 C
N LEADS
0.08 M C A B
b
NOTES:
1. Plastic or metal protrusions of 0.15mm maximum per side are not
included.
2. Plastic interlead protrusions of 0.25mm maximum per side are
not included.
L1
3. Dimensions “D” and “E1” are measured at Datum Plane “H”.
A
4. Dimensioning and tolerancing per ASME Y14.5M-1994.
c
SEE DETAIL "X"
A2
GAUGE
PLANE
L
A1
0.25
3° ±3°
DETAIL X
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11
FN7428.9
July 13, 2006