an1755

Application Note 1755
3A/4A Low Quiescent Current High Efficiency
Synchronous Buck Regulator
Description
Key Features
The ISL8023AEVAL3Z, ISL8024AEVAL3Z boards are intended for
use by individuals with requirements for point-of-load applications
sourcing from 2.7V to 5.5V. The ISL8023AEVAL3Z,
ISL8024AEVAL3Z simple smallest factor evaluation boards are
used for a quick and easy demonstration of the performance of
the ISL8023A, ISL8024A low quiescent high efficiency
synchronous buck regulator.
• High efficiency synchronous buck regulator with up to 95%
efficiency
The ISL8023A and ISL8024A are offered in a 3mmx3mm
16 Ld TQFN package with 1mm maximum height. The
complete area that the converter occupies can be as small as
0.22in2.
• Adjustable frequency from 500kHz to 4MHz - default at 2MHz
• 0.8% reference accuracy over temperature/load/line
• Start-up with prebiased output
• Internal soft-start - 1ms or adjustable
• Soft-stop output discharge during disabled
• External synchronization up to 4MHz
• Negative OC protection
Specifications
PART
NUMBER
8023A
8024A
VIN
RANGE
(V)
2.7V to
5.5V
VOUT
RANGE
(V)
References
IOUT
(MAX)
(A)
3
4
ISL8023, ISL8024 Datasheet
fSW RANGE
(MHz)
PART SIZE
(2mm)
Programmable
0.5 to 4MHz
3x3
Ordering Information
PART NUMBER
ISL8023AEVAL3Z
3A low quiescent current high efficiency
synchronous buck regulator
ISL8024AEVAL3Z
4A low quiescent current high efficiency
synchronous buck regulator
NOTES:
1. The evaluation boards default configuration is VOUT = 1.8V,
fSW = 2MHz (FS tied to VIN)
DESCRIPTION
2. VREF is 0.6V
ISL8023A, ISL8024A
VIN
PHASE
PHASE
PHASE
VIN
VOUT
VIN
GND
GND
PGND
VDD
PGND
EPAD
PG
SGND
COMP
SS
FS
FB
EN
SYNC
FIGURE 1. BLOCK DIAGRAM
September 10, 2015
AN1755.1
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Copyright Intersil Americas LLC. 2015. All Rights Reserved
Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries.
All other trademarks mentioned are the property of their respective owners.
Application Note 1755
Recommended Equipment
Frequency Control
The following materials are recommended to perform testing:
• 0V to 10V power supply with at least 10A source current
capability or 5V battery
• Electronic loads capable of sinking current up to 7A
• Digital Multimeters (DMMs)
• 100MHz quad-trace oscilloscope
The ISL8023A, ISL8024A has an FS pin that controls the frequency
of operation. Programmable frequency allows for optimization
between efficiency and external component size. Default
switching frequency is 2MHz when FS is tied to VIN (R11 = 0 and
R12 is open). By connecting R12 to GND, the switching frequency
could be changed from 1MHz (R12 = 206k) to 4MHz (R12 = 40k)
according to Equation 2:
220  10 3
R T  k  = ------------------------------ – 14
f OSC  kHz 
• Signal generator
Quick Setup Guide
1. Ensure that the circuit is correctly connected to the supply and
loads prior to applying any power.
2. Connect the bias supply to VIN, the plus terminal to VIN, P4
and the negative return to PGND, P5.
(EQ. 2)
When using R12 to adjust the operational frequency, this also
sets external compensation mode. Please refer to the ISL8023,
ISL8024 datasheet for more details.
Soft-start Control
4. Verify that the position is PWM for SW2.
Short CSS to SGND for internal soft-start (approximately 1ms).
Populate CSS to adjust the soft-start time. This capacitor, along
with an internal 1.6µA current source, sets the soft-start interval
of the converter, tSS.
5. Verify that the position is ON for SW1.
CSS  F  = 3.33  t SS  s 
3. Connect the output load to VOUT, the plus terminal to VOUT,
P3 and the negative return to PGND, P7.
(EQ. 3)
6. Turn on the power supply.
CSS must be less than 33nF to insure proper soft-start reset after
fault condition.
7. Verify the output voltage is 1.8V for VOUT.
Evaluating the Other Output Voltage
The ISL8023AEVAL3Z, ISL8024AEVAL3Z kit output is preset to
1.8V for VOUT, however, output voltages can be adjusted from
0.6V to 5V. The output voltage programming resistor, R1, will
depend on the desired output voltage of the regulator. The value
for the feedback resistor is typically between 0Ω and 200kΩ as
shown in Equation 1.
VFB
R 2 = R 1  ------------------------------------
 VOUT – VFB
(EQ. 1)
If the output voltage desired is 0.6V, then R2 is left unpopulated
and R1 is shorted. For faster response performance, add 10pF to
47pF in parallel to R1. Check bode plot to insure optimum
performance.
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2
Switches Control
The ISL8023A, ISL8024A evaluation boards contain SW1 and SW2
for various controls of the ISL8023A, ISL8024A circuitries. Table 1
details this function.
TABLE 1. SWITCH SETTINGS
SW1
ENABLE
FUNCTION
1
OFF
Disable VOUT
3
ON
Enable VOUT
SW2
MODE
1
PWM
Fixed PWM frequency at light load
3
PFM
Force continuous mode
FUNCTION
AN1755.1
September 10, 2015
Application Note 1755
ISL8023AEVAL3Z and ISL8024AEVAL3Z Evaluation Boards
FIGURE 2. ISL8023AEVAL3Z TOP
FIGURE 3. ISL8023AEVAL3Z BOTTOM
FIGURE 4. ISL8024AEVAL3Z TOP
FIGURE 5. ISL8024AEVAL3Z BOTTOM
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Application Note 1755
ISL8023AEVAL3Z, ISL8024AEVAL3Z Schematic
1
2
16
15
14
13
VIN
0
C1
22UF
PHASE
1
2
3
4
C2
22UF
C3
OPEN
VIN
VDD
PG
SYNC
17
PG
SYNC
EP
3
22UF
U1
ISL8023/24
C6
22UF
R3
12
11
10
9
PGND
PGND
SGND
FB
P3
20
A
C4
R2
100K
22PF
1
P7
2
A
R1
2
200K
CH8
1
A
EN
5
6
7
8
P5
VO
C5
VIN
PHASE
PHASE
PHASE
R10
L1
0.47uH
1.0UH
A
EN
FS
SS
COMP
P4
1
2
J2 4
3
J1 4
A
R11
VIN
DNP
SS
R12
191K
C7
220PF
CSS
0.033UF
C8
OPEN
R14
69.8K
A
A
A
VIN
VIN
R5
2K
32
P6
Q1
1
2
EN
D1
2N7002
3
SW1
1
R6
200K
ON
OFF
SYNC
2
3
SW2
P2
1
PWM
PFM
R9
OPEN
R8
OPEN
2
P1
R7
200K
1
R4
200K
PG
VIN
A
A
A
FIGURE 6. SCHEMATIC
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Application Note 1755
TABLE 2. BILL OF MATERIALS
MANUFACTURER PART
QTY
UNITS
ISL8023_24AEVAL3ZREVAPCB
1
ea.
C0603C0G500-220JNE
1
ea.
GRM188R71H221KA01D
1
C0603X7R160-333KNE
REFERENCE
DESIGNATOR
DESCRIPTION
MANUFACTURER
PWB-PCB, ISL8023_24EVAL3Z, REVA, ROHS
Generic
C4
CAP, SMD, 0603, 22pF, 50V, 5%, C0G, ROHS
VENKEL
ea.
C7
CAP, SMD, 0603, 220pF, 50V, 10%, X7R, ROHS
MURATA
1
ea.
CSS
CAP, SMD, 0603, 33000pF, 16V, 10%, X7R, ROHS
VENKEL
0
ea.
C3, C8
CAP, SMD, 0603, DNP-PLACE HOLDER, ROHS
2
ea.
C2, C5
CAP, SMD, 1206, 22µF, 6.3V, 10%, X5R, ROHS
0
ea.
C1, C6
CAP, SMD, 1206, DNP-PLACE HOLDER, ROHS
FDVE0630-R47M
1
ea.
L1
COIL-PWR INDUCTOR, SMD, 7.4x6.7, 0.47µH, 20%,
14, 1A, ROHS
TOKO
131-4353-00
2
ea.
J1, J2
CONN-SCOPE PROBE TEST PT, COMPACT, PCB MNT,
ROHS
TEKTRONIX
1514-2
4
ea.
P4, P5,
P7, P8
CONN-TURRET, TERMINAL POST, TH, ROHS
KEYSTONE
5002
3
ea.
P1, P2,
P6
CONN-MINI TEST POINT, VERTICAL, WHITE, ROHS
KEYSTONE
LTST-C170CKT
1
ea.
D1
LED-GaAs RED, SMD, 2X1.25mm, 100mW, 40mA,
10mcd, ROHS
LITEON/VISHAY
ISL8023/24AIRZ
1
ea.
U1
IC-3A/4A BUCK REGULATOR, 16P, QFN, 3X3, ROHS
INTERSIL
2N7002-7-F
1
ea.
Q1
TRANSISTOR, N-CHANNEL, 3 LD, SOT-23, 60V,
115mA, ROHS
DIODES, INC.
0
ea.
R11
RESISTOR, SMD, 0603, 0.1%, MF,
DNP-PLACE HOLDER
ERJ-3EKF20R0V
1
ea.
R3
RES, SMD, 0603, 20Ω, 1/10W, 1%, TF, ROHS
PANASONIC
CR0603-10W-000T
1
ea.
R10
RES, SMD, 0603, 0Ω,1/10W, TF, ROHS
VENKEL
CR0603-10W-1003FT
2
ea.
R2, R14
RES, SMD, 0603, 100k, 1/10W, 1%, TF, ROHS
VENKEL
CR-0603-10W-1913FT
1
ea.
R12
RES, SMD, 0603, 191k, 1/10W, 1%, TF, ROHS
VENKEL
CR0603-10W-2003FT
4
ea.
R1, R4,
R6, R7
RES, SMD, 0603, 200k, 1/10W, 1%, TF, ROHS
VENKEL
0
ea.
R5, R8,
R9
RES, SMD, 0603, DNP-PLACE HOLDER, ROHS
2
ea.
SW1, SW2
0
ea.
P3
(3VH30/1JN5)
GRM31CR60J226KE19L
GT11MSCBE
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SWITCH-TOGGLE, SMD, 6 PIN, SPDT, 2POS, ON-ON,
ROHS
MURATA
ITT INDUSTRIES/C&K
DIVISION
DO NOT POPULATE OR PURCHASE
AN1755.1
September 10, 2015
Application Note 1755
ISL8023AEVAL3Z, ISL8024AEVAL3Z Board Layout
FIGURE 7. TOP LAYER COMPONENTS
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Application Note 1755
ISL8023AEVAL3Z, ISL8024AEVAL3Z Board Layout (Continued)
FIGURE 8. TOP LAYER ETCH
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Application Note 1755
ISL8023AEVAL3Z, ISL8024AEVAL3Z Board Layout (Continued)
FIGURE 9. SECOND LAYER ETCH
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Application Note 1755
ISL8023AEVAL3Z, ISL8024AEVAL3Z Board Layout (Continued)
FIGURE 10. THIRD LAYER ETCH
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Application Note 1755
ISL8023AEVAL3Z, ISL8024AEVAL3Z Board Layout (Continued)
FIGURE 11. BOTTOM LAYER ETCH
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Application Note 1755
ISL8023AEVAL3Z, ISL8024AEVAL3Z Board Layout (Continued)
FIGURE 12. BOTTOM LAYER COMPONENTS
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 the document is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
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