DATASHEET
ISL85403
2.5A Regulator with Integrated High-side MOSFET for Synchronous Buck or
Boost Buck Converter
The
ISL85403
is a 40V, 2.5A synchronous buck or boost buck
controller with an integrated high-side MOSFET and low-side
driver. In Buck mode, the ISL85403 supports a wide input
range of 3V to 40V. In Boost-Buck mode, the input range can
be extended down to 2.5V and output regulation can be
maintained when V
IN
drops below V
OUT
, enabling sensitive
electronics to remain on in low input voltage conditions.
The ISL85403 has a flexible selection of Forced PWM mode
and PFM mode. In PFM mode, the quiescent input current is as
low as 180µA (AUXVCC connected to V
OUT
). The load boundary
between PFM and PWM can be programmed to cover wide
applications.
The low-side driver can either be used to drive an external
low-side MOSFET for a synchronous buck or left unused for a
standard non-synchronous buck. The low-side driver can also
be used to drive a boost converter as a preregulator followed
by a buck controlled by the same IC, which greatly expands the
operating input voltage range down to 2.5V or lower (See
Figure 5).
ISL85403 offers robust current protection. It uses peak current
mode control with cycle-by-cycle current limiting. It is
implemented with frequency foldback under current limit
condition; also, the hiccup overcurrent mode ensures reliable
operations under harsh short conditions.
The ISL85403 has comprehensive protections against various
faults including overvoltage and over-temperature protections.
FN8631
Rev.4.00
Sep 28, 2020
Features
• Buck mode: input voltage range 3V to 40V (See
“Input
Voltage”
for more details)
• Boost mode expands operating input voltage lower than
2.5V (See
“Input Voltage”
for more details)
• Selectable Forced PWM mode or PFM mode
• 300µA IC quiescent current (PFM, no load); 180µA input
quiescent current (PFM, no load, V
OUT
tied to AUXVCC)
• Less than 5µA (MAX) shutdown input current (IC disabled)
• Operational topologies
- Synchronous buck
- Non-synchronous buck
- Two-stage boost buck
- Non-inverting single inductor buck boost
• Programmable frequency from 200kHz to 2.2MHz and
frequency synchronization capability
•
±
1% tight voltage regulation accuracy
• Reliable overcurrent protection
- Temperature compensated current sense
- Cycle-by-cycle current limiting with frequency foldback
- Hiccup mode for worst case short condition
• 20 Ld 4x4 QFN package
• Pb-free (RoHS compliant)
Related Literature
For a full list of related documents, visit our website:
•
ISL85403
device page
Applications
• General purpose
• 24V bus power
• Battery power
• Point-of-load
• Embedded processor and I/O supplies
100
PGOOD
EN
MODE
SYNC
AUXVCC
VCC
ILIMIT
SS
EXT_BOOST
FS
SGND
95
VIN
VIN
6V V
IN
12V V
IN
36V V
IN
24V V
IN
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
0.1m
1m
10m
100m
1.0
2.5
BOOT
ISL85403
ISL85403
PHASE
LGATE
PGND
FB
COMP
V OUT
LOAD CURRENT (A)
FIGURE 1. TYPICAL APPLICATION
FIGURE 2. EFFICIENCY, SYNCHRONOUS BUCK, PFM MODE,
V
OUT
5V, T
A
= +25°C
FN8631 Rev.4.00
Sep 28, 2020
Page 1 of 24
ISL85403
Table of Contents
Typical Application Schematics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Pin Configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Functional Pin Descriptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Thermal Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Recommended Operating Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Typical Performance Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Soft-Start. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PWM Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PFM Mode Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Synchronous and Non-Synchronous Buck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
AUXVCC Switchover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2-Stage Boost Buck Converter Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Oscillator and Synchronization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PGOOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fault Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Overcurrent Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Overvoltage Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Thermal Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Component Selections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Capacitors - Buck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input Capacitors - Buck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Inductor - Buck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Side Power MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Voltage Feedback Resistor Divider. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Boost Inductor (2-Stage Boost Buck) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Boost Output Capacitor (2-Stage Boost Buck) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Loop Compensation Design - Buck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PWM Comparator Gain Fm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Current Sampling Transfer Function He(S). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Stage Transfer Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
14
14
14
14
14
15
15
15
15
16
17
18
18
18
18
18
18
18
19
19
19
19
19
19
20
20
20
20
Loop Compensation Design for 2-Stage Boost Buck and Single-Stage Buck Boost. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Layout Suggestions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Revision History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Package Outline Drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
FN8631 Rev.4.00
Sep 28, 2020
Page 2 of 24
ISL85403
Typical Application Schematics
I
PGOOD
EN
MODE
SYNC
AUXVCC
VCC
ILIMIT
SS
EXT_BOOST
FS
SGND
ISL85403
VIN
VIN
PGOOD
EN
MODE
SYNC
AUXVCC
V OUT
VCC
ILIMIT
ISL85403
VIN
VIN
BOOT
BOOT
V OUT
PHASE
LGATE
PGND
FB
COMP
PHASE
LGATE
PGND
FB
COMP
SS
EXT_BOOST
FS
SGND
(a) SYNCHRONOUS BUCK
(b) NON-SYNCHRONOUS BUCK
FIGURE 3. TYPICAL APPLICATION SCHEMATIC I
PGOOD
EN
MODE
SYNC
AUXVCC
VCC
ILIMIT
SS
EXT_BOOST
FS
SGND
ISL85403
VIN
VIN
PGOOD
EN
MODE
SYNC
AUXVCC
V OUT
VCC
ILIMIT
SS
EXT_BOOST
FS
SGND
ISL85403
VIN
VIN
BOOT
BOOT
V OUT
PHASE
LGATE
PGND
FB
COMP
PHASE
LGATE
PGND
FB
COMP
(a) SYNCHRONOUS BUCK
(b) NON-SYNCHRONOUS BUCK
FIGURE 4. TYPICAL APPLICATION SCHEMATIC II - VCC SWITCHOVER TO V
OUT
Battery
R1
R2
+
+
1M
PGOOD
EN
SYNC
VCC
ILIMIT
ISL85403
EXT_BOOST
AUXVCC
VIN
BOOT
PHASE
VIN
130k
VCC
PGOOD
EN
MODE
SYNC
VCC
ILIMIT
SS
FS
SGND
EXT_BOOST
LGATE
AUXVCC
VIN
ISL85403
BOOT
PHASE
R3
R4
V OUT
V OUT
SS
PGND
FS
LGATE
COMP
FB
PGND
COMP
FB
SGND
(a) 2-STAGE BOOST BUCK
(b) NON-INVERTING SINGLE INDUCTOR BUCK BOOST
FIGURE 5. TYPICAL APPLICATION SCHEMATIC III - BOOST BUCK CONVERTER
FN8631 Rev.4.00
Sep 28, 2020
Page 3 of 24
Block Diagram
VCC
AUXVCC
PGOOD
VIN (x2)
FN8631 Rev.4.00
Sep 28, 2020
Page 4 of 24
ISL85403
VIN
CURRENT
MONITOR
BIAS LDO
AUXILARY LDO
ILIMIT
SGND
POWER-ON
RESET
VCC
EN
EXT_BOOST
MODE
PFM/FPWM
OCP, OVP, OTP
PFM LOGIC
BOOST MODE CONTROL
BOOT
PHASE (x2)
GATE DRIVE
SYNC
VOLTAGE
MONITOR
OSCILLATOR
SLOPE
COMPENSATION
LGATE
FS
+
SOFT-START
LOGIC
+
BOOT REFRESH
VCC
5 µA
0.8V
REFERENCE
EA
COMPARATOR
SS
FB
COMP
PGND
FIGURE 6. BLOCK DIAGRAM
ISL85403
Ordering Information
PART NUMBER
(Notes
2, 3)
ISL85403FRZ
ISL85403FRZ-T
ISL85403FRZ-T7A
ISL85403FRZ-TK
ISL85403DEMO1Z
ISL85403EVAL1Z
ISL85403EVAL2Z
NOTES:
1. See
TB347
for details about reel specifications.
2. These 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). 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), see the
ISL85403
device page. For more information about MSL see
TB363.
PART
MARKING
85 403FRZ
85 403FRZ
85 403FRZ
85 403FRZ
TEMP.
RANGE (°C)
-40 to +105
-40 to +105
-40 to +105
-40 to +105
Tape and Reel
(Units) (Note
1)
-
6k
250
1k
PACKAGE
(RoHS Compliant)
20 Ld 4x4 QFN
20 Ld 4x4 QFN
20 Ld 4x4 QFN
20 Ld 4x4 QFN
PKG. DWG. #
L20.4x4C
L20.4x4C
L20.4x4C
L20.4x4C
Compact size demo board for SYNC buck
Evaluation Board
Evaluation Board for non-inverting buck-boost configuration
Pin Configuration
20 LD QFN
TOP VIEW
AUXVCC
SGND
VCC
20
19
18
17
16
VIN
VIN
EN
FS
SS
FB
COMP
1
2
3
4
5
15
14
BOOT
PGND
LGATE
SYNC
EXT_BOOST
PAD
Thermal Pad
21
13
12
11
6
7
8
9
10
PHASE
Functional Pin Descriptions
PIN NAME
EN
FS
SS
FB
PIN #
1
2
3
4
DESCRIPTION
Enable the IC by leaving the EN pin floating or pulling it HIGH. Disable the IC by pulling this pin LOW.
Range: 0V to 5.5V.
Force the IC to have a 500kHz switching frequency by connecting the FS pin to VCC or GND, or by leaving the FS pin open. Program
the oscillator switching frequency by adjusting the resistor from this pin to GND.
Connect a capacitor from this pin to ground. The capacitor, along with an internal 5µA current source, sets the converter's soft-start
interval. Also, this pin can be used to track a ramp on this pin.
The inverting input of the voltage feedback error amplifier. With a properly selected resistor divider connected from V
OUT
to FB, the
output voltage can be set to any voltage between the power rail (reduced by maximum duty cycle and voltage drop) and the 0.8V
reference. Connect an R-C network across COMP and FB for loop compensation. The FB pin is also monitored for overvoltage events.
Output of the voltage feedback error amplifier.
COMP
5
FN8631 Rev.4.00
Sep 28, 2020
PGOOD
PHASE
MODE
ILIMIT
Page 5 of 24
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