2.5A Regulator with Integrated High-Side MOSFET for
Synchronous Buck or Boost Buck Converter
ISL85403
The ISL85403 is an 36V, 2.5A synchronous buck or boost buck
controller with a high-side MOSFET and low-side driver integrated. In
buck mode, the ISL85403 supports a wide input range of 3V to 36V.
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 operation modes 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 be either 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 pre-regulator followed by a buck
controlled by the same IC, which greatly expands the operating
input voltage range down to 2.5V or lower (Refer to “Typical
Application Schematic III - Boost Buck Converter” on page 6).
The ISL85403 offers the most robust current protections. It uses
peak current mode control with cycle-by-cycle current limiting.
It is implemented with frequency foldback under current limit
condition; besides that, the hiccup overcurrent mode is also
implemented to guarantee reliable operations under harsh
short conditions.
The ISL85403 has comprehensive protections against various
faults including overvoltage and over-temperature protections,
etc.
Features
• Buck mode: input voltage range 3V to 36V (refer to “Input
Voltage” on page 15 for more details)
• Boost mode expands operating input voltage lower than
2.5V (refer to “Input Voltage” on page 15 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)
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
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 2014. 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.
March 12, 2014
FN8631.0
1
ISL85403
Table of Contents
Pin Configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Functional Pin Descriptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Typical Application Schematic I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Typical Application Schematic II - VCC Switch-Over to V
OUT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Typical Application Schematic III - Boost Buck Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
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 Switch-Over . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Boost Output Capacitor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Loop Compensation Design - Buck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PWM Comparator Gain Fm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Current Sampling Transfer Function He(S). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Stage Transfer Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
14
14
14
14
14
14
15
15
15
15
17
17
18
18
18
18
18
18
19
19
19
19
19
19
19
20
20
20
Loop Compensation Design for 2-Stage Boost Buck and Single-Stage Buck Boost. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Layout Suggestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Revision History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
About Intersil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Package Outline Drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
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March 12, 2014
ISL85403
Pin Configuration
ISL85403
(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
21
Thermal Pad
21
PAD
13
12
11
6
7
8
9
10
PHASE
Functional Pin Descriptions
PIN NAME
EN
FS
SS
FB
PIN #
1
2
3
4
DESCRIPTION
The controller is enabled when this pin is left floating or pulled HIGH. The IC is disabled when this pin is pulled LOW.
Range: 0V to 5.5V.
Connecting this pin to VCC, or GND, or leaving it open will force the IC to have 500kHz switching frequency. The oscillator switching
frequency can also be programmed by adjusting the resistor from this pin to GND.
Connect a capacitor from this pin to ground. This capacitor, along with an internal 5µA current source, sets the soft-start interval of
the converter. Also, this pin can be used to track a ramp on this pin.
This pin is 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. Loop compensation is achieved by connecting an RC network across COMP and FB. The FB pin is also monitored
for overvoltage events.
Output of the voltage feedback error amplifier.
Programmable current limit pin. With this pin connected to the VCC pin, or to GND, or left open, the current limiting threshold is set
to default of 3.6A; the current limiting threshold can be programmed with a resistor from this pin to GND.
Mode selection pin. Pull this pin to GND for forced PWM mode; to have it floating or connected to VCC will enable PFM mode when
the peak inductor current is below the default threshold of 700mA. The current boundary threshold between PFM and PWM can
also be programmed with a resistor at this pin to ground. Check for more details in the “PFM Mode Operation” on page 14.
PGOOD is an open drain output and pull-up pin with a resistor to VCC for proper function. PGOOD will be pulled low under the events
when the output is out of regulation (OV or UV) or EN pin is pulled low. PGOOD rising has a fixed 128 cycles delay.
COMP
ILIMIT
MODE
5
6
7
PGOOD
PHASE
EXT_BOOST
8
9, 10 These pins are the PHASE nodes that should be connected to the output inductor. These pins are connected to the source of the
high-side N-channel MOSFET.
11
This pin is used to set boost mode and monitor the battery voltage that is the input of the boost converter. After VCC POR, the
controller will detect the voltage on this pin; if voltage on this pin is below 200mV, the controller is set in
synchronous/non-synchronous buck mode and will latch in this state unless VCC is below POR falling threshold; if the voltage on
this pin after VCC POR is above 200mV, the controller is set in boost mode and latch in this state. In boost mode, the low-side driver
output PWM with same duty cycle with upper-side driver to drive the boost switch.
In boost mode, this pin is used to monitor input voltage through a resistor divider. By setting the resistor divider, the high threshold
and hysteresis can be programmed. When voltage on this pin is above 0.8V, the PWM output (LGATE) for the boost converter is
disabled, and when voltage on this pin is below 0.8V minus the hysteresis, the boost PWM is enabled.
In boost mode operation, PFM is disabled when boost PWM is enabled. Check the “2-Stage Boost Buck Converter Operation” on
page 15 for more details.
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PGOOD
PHASE
MODE
ILIMIT
FN8631.0
March 12, 2014
ISL85403
Functional Pin Descriptions
PIN NAME
SYNC
PIN #
12
(Continued)
DESCRIPTION
This pin can be used to synchronize two or more ISL85403 controllers. Multiple ISL85403s can be synchronized with their SYNC
pins connected together. 180° phase shift is automatically generated between the master and slave ICs.
The internal oscillator can also lock to an external frequency source applied on this pin with square pulse waveform (with frequency
10% higher than the IC’s local frequency, and pulse width higher than 150ns). Range: 0V to 5.5V.
This pin should be left floating if not used.
In synchronous buck mode, this pin is used to drive the lower side MOSFET to improve efficiency. A 5.1k or smaller value resistor
has to be added to connect LGATE to ground to avoid falsely turn-on of LGATE caused by coupling noise.
In non-synchronous buck when a diode is used as the bottom side power device, this pin should be connected to VCC through a
resistor (less than 5k) before IC start-up to have the low-side driver (LGATE) disabled.
In boost mode, it can be used to drive the boost power MOSFET. The boost control PWM is same with the buck control PWM.
This pin is used as the ground connection of the power flow including driver. Connect it to large ground plane.
This pin provides bias voltage to the high-side MOSFET driver. A bootstrap circuit is used to create a voltage suitable to drive the
internal N-channel MOSFET. The boot charge circuitries are integrated inside of the IC. No external boot diode is needed. A 1µF
ceramic capacitor is recommended to be used between BOOT and PHASE pin.
LGATE
13
PGND
BOOT
14
15
VIN
16, 17 Connect the input rail to these pins that are connected to the drain of the integrated high-side MOSFET as well as the source for the
internal linear regulator that provides the bias of the IC. Range: 3V to 36V.
With the part switching, the operating input voltage applied to the VIN pins must be under 36V. This recommendation allows for
short voltage ringing spikes (within a couple of ns time range) due to switching while not exceeding “Absolute Maximum Ratings”
on page 7.
18
19
20
This pin provides the return path for the control and monitor portions of the IC. Connect it to a quiet ground plane.
This pin is the output of the internal linear regulator that supplies the bias for the IC including the driver. A minimum 4.7µF
decoupling ceramic capacitor is recommended between VCC to ground.
This pin is the input of the auxiliary internal linear regulator, which can be supplied by the regulator output after power-up. With
such configuration, the power dissipation inside of the IC is reduced. The input range for this LDO is 3V to 20V.
In boost mode operation, this pin works as boost output overvoltage detection pin. It detects the boost output through a resistor
divider. When voltage on this pin is above 0.8V, the boost PWM is disabled; and when voltage on this pin is below 0.8V minus the
hysteresis, the boost PWM is enabled.
Range: 0V to 20V.
Bottom thermal pad. It is not connected to any electrical potential of the IC. In layout it must be connected to PCB ground copper
plane with area as large as possible to effectively reduce the thermal impedance.
SGND
VCC
AUXVCC
PAD
21
Ordering Information
PART NUMBER
(Notes 1, 2, 3)
ISL85403FRZ
ISL85403DEMO1Z
NOTES:
1. 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 product information page for
ISL85403.
For more information on MSL please see techbrief
TB363.
PART
MARKING
85 403FRZ
TEMP.
RANGE (°C)
-40 to +105
PACKAGE
(PB-Free)
20 Ld 4x4 QFN
PKG. DWG. #
L20.4x4C
Compact size demo board for SYNC buck
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FN8631.0
March 12, 2014
Block Diagram
VCC
AUXVCC
PGOOD
VIN (x2)
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VIN
CURRENT
MONITOR
BIAS LDO
AUXILARY LDO
5
ILIMIT
SGND
POWER-ON
RESET
VCC
EN
EXT_BOOST
OCP, OVP, OTP
PFM LOGIC
BOOST MODE CONTROL
BOOT
ISL85403
MODE
PFM/FPWM
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
FN8631.0
March 12, 2014
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