DATASHEET
ISL85415
Wide V
IN
500mA Synchronous Buck Regulator
The ISL85415 is a 500mA Synchronous buck regulator with an
input range of 3V to 36V. It provides an easy to use, high
efficiency low BOM count solution for a variety of applications.
The ISL85415 integrates both high-side and low-side NMOS
FET's and features a PFM mode for improved efficiency at light
loads. This feature can be disabled if forced PWM mode is
desired. The part switches at a default frequency of 500kHz
but may also be programmed using an external resistor from
300kHz to 2MHz. The ISL85415 has the ability to utilize
internal or external compensation. By integrating both NMOS
devices and providing internal configuration options, minimal
external components are required, reducing BOM count and
complexity of design.
With the wide V
IN
range and reduced BOM the part provides an
easy to implement design solution for a variety of applications
while giving superior performance. It will provide a very robust
design for high voltage Industrial applications as well as an
efficient solution for battery powered applications.
The part is available in a small Pb free 4mmx3mm DFN plastic
package with an operation temperature range of -40°C to
+125°C
FN8373
Rev 4.00
October 30, 2014
Features
• Wide input voltage range 3V to 36V
• Synchronous Operation for high efficiency
• No compensation required
• Integrated High-side and Low-side NMOS devices
• Selectable PFM or forced PWM mode at light loads
• Internal fixed (500kHz) or adjustable Switching frequency
300kHz to 2MHz
• Continuous output current up to 500mA
• Internal or external soft-start
• Minimal external components required
• Power-good and enable functions available.
Applications
• Industrial control
• Medical devices
• Portable instrumentation
• Distributed Power supplies
•
Cloud Infrastructure
Related Literature
•
AN1859,
“ISL85415EVAL1Z Wide V
IN
500mA Synchronous
Buck Regulator”
•
AN1860
ISL85415DEMO1Z Wide V
IN
500mA Synchronous
Buck Regulator
100
95
90
EFFICIENCY (%)
1
2
SS
FS
12
11
R
2
10
FB
GND
VIN
PHASE
VCC
9
C
VCC
1µF
R
3
C
FB
V
IN
= 15V
V
IN
= 12V
V
IN
= 5V
85
80
75
70
65
60
V
IN
= 24V
V
IN
= 33V
SYNC
BOOT
COMP
3
C
BOOT
100nF
C
VIN
10µF
V
OUT
C
OUT
10µF
L1
22µH
5
6
4
PG
EN
PGND
55
INTERNAL DEFAULT PARAMETER SELECTION
50
0
0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
OUTPUT LOAD (A)
FIGURE 1. TYPICAL APPLICATION
FIGURE 2. EFFICIENCY vs LOAD, PFM, V
OUT
= 3.3V
FN8373 Rev 4.00
October 30, 2014
Page 1 of 24
ISL85415
Table of Contents
Typical Application Schematics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Functional Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Thermal Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Recommended Operating Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Efficiency Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Efficiency Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Typical Performance Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Detailed Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power-On Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Soft Start. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power-Good . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PWM Control Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Light Load Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Voltage Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Protection Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Overcurrent Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Negative Current Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Over-Temperature Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Boot Undervoltage Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Application Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Simplifying the Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Synchronization Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Inductor Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Buck Regulator Output Capacitor Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Loop Compensation Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Layout Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
17
17
17
17
17
18
18
18
18
19
19
19
19
19
19
19
19
20
22
Revision History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
About Intersil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Package Outline Drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
FN8373 Rev 4.00
October 30, 2014
Page 2 of 24
ISL85415
Pin Configuration
ISL85415
(12 LD 3x4 DFN)
TOP VIEW
SS 1
SYNC 2
BOOT 3
VIN 4
PHASE 5
PGND 6
GND
12 FS
11 COMP
10 FB
9
8
7
VCC
PG
EN
Pin Descriptions
PIN NUMBER
1
SYMBOL
SS
PIN DESCRIPTION
The SS pin controls the soft-start ramp time of the output. A single capacitor from the SS pin to ground
determines the output ramp rate. See
“Soft Start” on page 17
for soft-start details. If the SS pin is tied to
VCC, an internal soft-start of 2ms will be used.
Synchronization and light load operational mode selection input. Connect to logic high or VCC for PWM
mode. Connect to logic low or ground for PFM mode. Logic ground enables the IC to automatically choose
PFM or PWM operation. Connect to an external clock source for synchronization with positive edge trigger.
Sync source must be higher than the programmed IC frequency. There is an internal 5MΩ pull-down resistor
to prevent an undefined logic state if SYNC is left floating.
Floating bootstrap supply pin for the power MOSFET gate driver. The bootstrap capacitor provides the
necessary charge to turn on the internal N-Channel MOSFET. Connect an external 100nF capacitor from this
pin to PHASE.
The input supply for the power stage of the regulator and the source for the internal linear bias regulator.
Place a minimum of 4.7µF ceramic capacitance from VIN to GND and close to the IC for decoupling.
Switch node output. It connects the switching FET’s with the external output inductor.
Power ground connection. Connect directly to the system GND plane.
Regulator enable input. The regulator and bias LDO are held off when the pin is pulled to ground. When the
voltage on this pin rises above 1V, the chip is enabled. Connect this pin to VIN for automatic start-up. Do
NOT connect EN pin to VCC since the LDO is controlled by EN voltage.
Open-drain power-good output that is pulled to ground when the output voltage is below regulation limits or
during the soft-start interval. There is an internal 5MΩ internal pull-up resistor.
Output of the internal 5V linear bias regulator. Decouple to PGND with a 1µF ceramic capacitor at the pin.
Feedback pin for the regulator. FB is the inverting input to the voltage loop error amplifier. COMP is the
output of the error amplifier. The output voltage is set by an external resistor divider connected to FB. In
addition, the PWM regulator’s power-good and UVLO circuits use FB to monitor the regulator output voltage.
COMP is the output of the error amplifier. When it is tied to VCC, internal compensation is used. When only
an RC network is connected from COMP to GND, external compensation is used. See
“Loop Compensation
Design” on page 20
for more details.
Frequency selection pin. Tie to VCC for 500kHz switching frequency. Connect a resistor to GND for
adjustable frequency from 300kHz to 2MHz.
Signal ground connections. Connect to application board GND plane with at least 5 vias. All voltage levels
are measured with respect to this pin. The EPAD MUST NOT float.
2
SYNC
3
BOOT
4
5
6
7
VIN
PHASE
PGND
EN
8
9
10
PG
VCC
FB
11
COMP
12
EPAD
FS
GND
FN8373 Rev 4.00
October 30, 2014
Page 3 of 24
ISL85415
Typical Application Schematics
1
2
SS
FS
12
11
R
2
10
C
FB
SYNC
BOOT
GND
VIN
PHASE
COMP
3
C
BOOT
100nF
C
VIN
10µF
V
OUT
C
OUT
10µF
L1
22µH
4
5
6
FB
9
VCC
C
VCC
1µF
R
3
PG
EN
PGND
FIGURE 3. INTERNAL DEFAULT PARAMETER SELECTION
1
C
SS
2
SS
FS
12
R
FS
SYNC
3
C
BOOT
100nF
C
VIN
10µF
V
OUT
C
OUT
10µF
L1
22µH
4
5
6
BOOT
GND
VIN
PHASE
COMP
11
R
2
10
C
FB
FB
9
VCC
C
VCC
1µF
R
3
PG
EN
R
COMP
C
COMP
PGND
FIGURE 4. USER PROGRAMMABLE PARAMETER SELECTION
TABLE 1. EXTERNAL COMPONENT SELECTION
V
OUT
(V)
12
5
3.3
2.5
1.8
L
1
(µH)
45
22
22
22
22
C
OUT
(µF)
10
2 x 22
2 x 22
2 x 22
22
R
2
(kΩ)
90.9
90.9
90.9
90.9
100
R
3
(kΩ)
4.75
12.4
20
28.7
50
C
FB
(pF)
22
100
100
100
22
R
FS
(kΩ)
115
120
120
120
120
R
COMP
(kΩ)
100
100
100
100
50
C
COMP
(pF)
470
470
470
470
470
FN8373 Rev 4.00
October 30, 2014
Page 4 of 24
ISL85415
Functional Block Diagram
EN
PG
SS
VIN
5M
VCC
BIAS
LDO
BOOT
PWM
GATE
DRIVE
AND
PWM DEADTIME
FB
POWER
GOOD
LOGIC
EN/SOFT
START
FB
600mV VREF
FS
FAULT
LOGIC
600MV/AMP
CURRENT SENSE
OSCILLATOR
PFM
CURRENT
SET
PWM/PFM
SELECT LOGIC
FB
s Q
R Q
PHASE
SYNC
5M
ZERO CURRENT
DETECTION
450MV/T SLOPE
COMPENSATION
(PWM ONLY)
PGND
g
m
INTERNAL = 50µs
EXTERNAL = 230µs
150k
54pF
INTERNAL
COMPENSATION
PACKAGE
PADDLE
Ordering Information
PART NUMBER
(Notes
1, 2, 3)
ISL85415FRZ
ISL85415EVAL1Z
NOTES:
1. Add “T” suffix for Tape and Reel. Please refer to
TB347
for details on reel specifications.
2. These Intersil Pb-free plastic packaged products employ special Pb-free material sets, molding compounds/die attach materials, and 100% matte
tin plate plus anneal (e3 termination finish, which is 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.
3. For Moisture Sensitivity Level (MSL), please see device information page for
ISL85415.
For more information on MSL please see techbrief
TB363.
5415
Evaluation Board
PART
MARKING
TEMP. RANGE
(°C)
-40 to +125
PACKAGE
(Pb-Free)
12 Ld DFN
PKG.
DWG. #
L12.4x3
FN8373 Rev 4.00
October 30, 2014
COMP
GND
Page 5 of 24
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