1
Application Note 1759
3A/4A Low Quiescent Current High Efficiency
Synchronous Buck Regulator
Description
The ISL8023EVAL3Z, ISL8024EVAL3Z boards are intended for
use by individuals with requirements for point-of-load applications
sourcing from 2.7V to 5.5V. The ISL8023EVAL3Z, ISL8024EVAL3Z
simple smallest factor evaluation boards are used for a quick and
easy demonstration of the performance of the ISL8023, ISL8024
low quiescent high efficiency synchronous buck regulator.
The ISL8023 and ISL8024 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.
Key Features
• High efficiency synchronous buck regulator with up to 95%
efficiency
• 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
• Adjustable frequency from 500kHz to 4MHz - default at 1MHz
• External synchronization up to 4MHz
• Negative OC protection
References
ISL8023, ISL8024 Datasheet
Specifications
PART
NUMBER
VIN
RANGE
(V)
VOUT
RANGE
(V)
IOUT
(MAX)
(A)
fSW RANGE
(MHz)
PART SIZE
(2mm)
8023 2.7V to
5.5V
3 Programmable
0.5 to 4MHz 3x3
8024 4
NOTES:
1. The evaluation boards default configuration is VOUT = 1.8V,
fSW =1MHz (FS tied to V
IN)
2. VREF is 0.6V
Ordering Information
PART NUMBER DESCRIPTION
ISL8023EVAL3Z 3A low quiescent current high efficiency
synchronous buck regulator
ISL8024EVAL3Z 4A low quiescent current high efficiency
synchronous buck regulator
FIGURE 1. BLOCK DIAGRAM
VIN
VDD
PG
SYNC
PGND
FB
PGND
SGND
VOUT
GND
VIN
GND
ISL8023, ISL8024
EPAD
EN
FS
SS
COMP
VIN
PHASE
PHASE
PHASE
September 10, 2015
AN1759.1
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 1759
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September 10, 2015
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Recommended Equipment
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
• 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.
3. Connect the output load to VOUT, the plus terminal to VOUT, P3
and the negative return to PGND, P7.
4. Verify that the position is PWM for SW2.
5. Verify that the position is ON for SW1.
6. Turn on the power supply.
7. Verify the output voltage is 1.8V for VOUT.
Evaluating the Other Output Voltage
The ISL8023EVAL3Z, ISL8024EVAL3Z board 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.
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.
Frequency Control
The ISL8023, ISL8024 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 1MHz when FS is tied to VIN (R11 =0 and
R12 is open). By connecting R12 to GND, the switching frequency
could be changed from 500kHz (R12 = 426k) to 4MHz (R12 =
40k) according to Equation 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
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.
CSS must be less than 33nF to insure proper soft-start reset after
fault condition.
Switches Control
The ISL8023, ISL8024 evaluation boards contain SW1 and SW2 for
various controls of the ISL8023, ISL8024 circuitries. Table 1 details
this function.
R2R1
VFB
VOUT VFB–
----------------------------------
=(EQ. 1)
TABLE 1. SWITCH SETTINGS
SW1 ENABLE FUNCTION
1OFFDisable V
OUT
3ONEnable V
OUT
SW2 MODE FUNCTION
1 PWM Fixed PWM frequency at light load
3 PFM Force continuous mode
RTk 220 103
fOSC kHz
------------------------------ 14–= (EQ. 2)
CSS F 3.33 tSS s=(EQ. 3)
Application Note 1759
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September 10, 2015
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ISL8023EVAL3Z, ISL8024EVAL3Z Schematic
FIGURE 6. SCHEMATIC
OFF
ON
PFM
PWM
22UF
C5
P5
EN
21
D1
9
8
7
6
5
4
3
2
17
16
15
14
13
12
11
10
1
U1
R3
R14
C8
C7
CSS
R11 R12
1
4
3
2
J2
1
4
3
2
J1
C3
R10
21
R1
R4
R2
21
C4
C6
C2C1
1
3
2
SW2
L1
P6
1
3
P1
2
1
3
P4
P7
P3
1.0UH
PG
2N7002
200K
PHASE
VO
22UF
CH8
20
200K
22PF
22UF22UF
100K
VIN
OPEN
69.8K
SS
0.033UF
220PF
191K
0
VIN
EN
DNP
PG
SYNC
OPEN
VIN
VIN
200K
SW1
2
2K
VIN
R5
R7 R6
R9
R8
Q1
OPEN
200K
SYNC
P2
OPEN
A
EN
FS
SS
COMP PHASE
PHASE
PHASE
VIN
PGND
PGND
SGND
FB
VIN
VDD
SYNC
PG
EP
ISL8023/24
A
A
A
A
A
A
A
A
A
A
Application Note 1759
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September 10, 2015
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TABLE 2. BILL OF MATERIALS
MANUFACTURER PART QTY UNITS
REFERENCE
DESIGNATOR DESCRIPTION MANUFACTURER
ISL8023_24EVAL3ZREVAPCB 1 ea. PWB-PCB, ISL8023_24EVAL3Z, REVA, ROHS
C0603C0G500-220JNE 1 ea. C4 CAP, SMD, 0603, 22pF, 50V, 5%, C0G, ROHS VENKEL
GRM188R71H221KA01D 1 ea. C7 CAP, SMD, 0603, 220pF, 50V, 10%, X7R, ROHS MURATA
C0603X7R160-333KNE 1 ea. CSS CAP, SMD, 0603, 33000pF, 16V, 10%, X7R, ROHS VENKEL
0 ea. C3, C8 CAP, SMD, 0603, DNP-PLACE HOLDER, ROHS
GRM31CR60J226KE19L 2 ea. C2, C5 CAP, SMD, 1206, 22µF, 6.3V, 10%, X5R, ROHS MURATA
0 ea. C1, C6 CAP, SMD, 1206, DNP-PLACE HOLDER, ROHS
DR73-1R0-R 1 ea. L1 COIL-PWR INDUCTOR, SMD, 7.6mm, 1.0µH, 20%,
5.28A, ROHS, SHIELDED
COOPER ELECTRONIC
TECH.
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
ISL8023/24IRZ 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
GT11MSCBE 2 ea. SW1, SW2 SWITCH-TOGGLE, SMD, 6 PIN, SPDT, 2POS, ON-ON,
ROHS
ITT INDUSTRIES/C&K
DIVISION
0ea. P3
(3VH30/1JN5)
DO NOT POPULATE OR PURCHASE
Application Note 1759
11
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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FIGURE 12. BOTTOM LAYER COMPONENTS
ISL8023EVAL3Z, ISL8024EVAL3Z Board Layout (Continued)
