Intersil ISL85005FRZ Internal or external compensation option Datasheet

DATASHEET
4.5V to 18V Input, 5A High Efficiency Synchronous
Buck Regulator
ISL85005, ISL85005A
Features
The ISL85005 and ISL85005A are monolithic, synchronous
buck regulators with integrated 5A, 18V high-side and low-side
FETs. These devices also provide an integrated bootstrap diode
for the high-side gate driver to reduce the external parts count.
These devices have a wide input voltage range to support
applications with input voltage from multi-cell batteries or
regulated 5V and 12V power rails.
• 4.5V to 18V input voltage range
• Internal 5A, 18V high-side and low-side MOSFET switches
• ±1%, 0.8V feedback voltage reference
• Integrated bootstrap diode with undervoltage detection
• Current mode control with internal slope compensation
• Internal or external compensation options
The ISL85005 and ISL85005A regulate the output voltage
with current mode control and have an internal oscillator. The
switching frequency of the ISL85005 is internally set as
500kHz, and can be synchronized to an external clock signal
with frequency ranges from 300kHz to 2MHz. The ISL85005A
has a fixed 500kHz switching frequency.
• Default internally set 500kHz switching frequency
• Synchronization capability to external clock (ISL85005)
• Diode Emulation Mode (DEM) and forced CCM (FCCM)
options (ISL85005)
• Adjustable soft-start time (ISL85005A)
• Output Power-Good (PG) indicator
• Input undervoltage lockout (UVLO), input and output
overvoltage protection
• High-side cycle-by-cycle current limit, low-side forward and
reverse overcurrent protection, and thermal shutdown
The ISL85005 has a fixed 2.3ms soft-start, while the
ISL85005A features programmable soft-start to limit inrush
current during startup. With SS pin floating, the soft-start time
of ISL85005A is also 2.3ms.
The ISL85005 can be configured in either forced Continuous
Conduction Mode (CCM) or Diode Emulation Mode (DEM). DEM
enables high efficiency at light-load conditions. The
ISL85005A always operates in forced CCM.
• Small 12-pin 3mmx4mm Dual Flat No-Lead (DFN) package
with EPAD for enhanced thermal performance
Applications
The ISL85005 and ISL85005A have built-in protections
including input UVLO protection, input and output overvoltage
protection, high-side cycle-by-cycle current limit, low-side
forward current limit and reverse current limit, and thermal
shutdown.
• Network and communication equipments
• Battery powered systems
• Multifunction printers
• Point-of-load regulators
Related Literature
• Standard 12V rail supplies
• For a full list of related documents, visit our website
- ISL85005, ISL85005A product pages
• Embedded computing systems
Typical Application
95
1
SYNC/
MODE
PG
2 PG
EN
3 EN
VIN 10
PGND
R2
C1
VIN
4.5V TO 18V
VDD 11
VIN
9
5 COMP
PHASE
8
6 AGND
PHASE
7
4 FB
R1
85
C4
BOOT 12
C3
C5
L1
C8
C6
VOUT
5A MAX
C9
EFFICIENCY (%)
GND = DEM; VCC = FCCM
MODE
90
ISL85005
80
75
70
12V TO 5V
65
12V TO 3.3V
60
12V TO 1.8V
55
50
0
1
2
3
4
5
OUTPUT CURRENT (A)
FIGURE 1. ISL85005 WITH INTERNAL COMPENSATION
November 28, 2016
FN8871.0
1
FIGURE 2. EFFICIENCY vs OUTPUT CURRENT
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 2016. 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.
ISL85005, ISL85005A
Table of Contents
Typical Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Functional Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Pin Configurations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Pin Descriptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Typical Application Schematics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Thermal Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Recommended Operating Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Typical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Typical Performance Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Detailed Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Operation Initialization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FCCM Control Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Light-Load Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Synchronization Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Enable, Soft-Start, and Disable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Voltage Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
15
15
15
16
16
Protection Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Forward Overcurrent Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reverse Overcurrent Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Overvoltage Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input Overvoltage Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Thermal Overload Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Derating Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
16
16
16
16
16
16
Application Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Boot Undervoltage Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Switching Regulator Output Capacitor Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Inductor Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input Capacitor Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Loop Compensation Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
17
17
18
18
19
Compensator Design Goal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
High DC Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Layout Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Revision History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
About Intersil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Package Outline Drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
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ISL85005, ISL85005A
Functional Block Diagram
1
SS (ISL85005A)
SOFT-START
BOOT
CONTROL
12
BOOT
UVP
SYNC/MODE (ISL85005)
1
VDD
UNDERVOLTAGE
VIN
LDO
EN
LOCKOUT
OSCILLATOR
11
9
10
CSA
2
PG
FAULT
0.8V
MONITOR
REFERENCE
+
SLOPE
COMP
CIRCUITS
+
-
3
EN
GATE DRIVE
CONTROL
CIRCUIT
+
+
THERMAL
SHUTDOWN
4
FB
600k
COMP
AGND
7
8
13
ZERO CROSS
DETECTOR
AND
NEGATIVE
CURRENT
LIMIT
GND DETECTION
6
VDD
PGND
EA
-
30pF
5
PHASE
POSITIVE
LS OCP
CIRCUIT
FIGURE 3. BLOCK DIAGRAM
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ISL85005, ISL85005A
Pin Configurations
ISL85005A
(12 LD 4x3 DFN)
TOP VIEW
ISL85005
(12 LD 4x3 DFN)
TOP VIEW
SYNC/MODE
1
12
BOOT
SS
1
12
BOOT
PG
2
11
VDD
PG
2
11
VDD
EN
3
10
VIN
EN
3
10
VIN
FB
4
9
VIN
FB
4
9
VIN
COMP
5
8
PHASE
COMP
5
8
PHASE
AGND
6
7
PHASE
AGND
6
7
PHASE
PGND
(EPAD)
PGND
(EPAD)
Pin Descriptions
PIN
NUMBER
PIN
NAME
1
(ISL85005)
SYNC/
MODE
Synchronization and mode selection input. Connect to VDD for Forced Continuous Conduction Mode (FCCM). Connect to AGND
for Diode Emulation Mode (DEM). Connect to an external function generator for synchronization with the positive edge trigger.
There is an internal 1MΩ pull-up resistor to VDD, which prevents an undefined logic state in cases where SYNC is floating.
1
(ISL85005A)
SS
Soft-start input. This pin provides a programmable soft-start. When the chip is enabled, the regulated 3.5µA pull-up current
source charges a capacitor connected from SS to ground. The output voltage of the converter follows the ramping voltage on
this pin. Without the external capacitor, the default soft-start is 2.3ms.
2
PG
Power-good, open-drain output. Connect 10kΩ to 100kΩ pull-up resistor between PG and VDD or between PG and a voltage not
exceeding 5.5V. PG transitions high about 1.5ms after the switching regulator’s output voltage reaches the regulation
threshold, which is 85% of the regulated output voltage typically.
3
EN
Enable input. The regulator is held off when the pin is pulled to ground. The device is enabled when the voltage on this pin rises
above 0.6V.
4
FB
Feedback input. The synchronous buck regulator employs a current mode control loop. FB is the negative input to the voltage
loop error amplifier. The output voltage is set by an external resistor divider connected to FB. The output voltage can be set to
any voltage between the power rail (reduced by converter losses) and the 0.8V reference.
5
COMP
Compensation node. This pin is connected to the output of the error amplifier, and is used to compensate the loop. Internal
compensation is used to meet most applications. Connect COMP to AGND to select internal compensation. Connect a
compensation network between COMP and FB to use external compensation.
6
AGND
The AGND terminal. Provides the return path for the core analog control circuitry within the device. Connect AGND to the board
ground plane. AGND and PGND are connected internally within the device. Do not operate the device with AGND and PGND
connected to dissimilar voltages.
Phase switch output node. Connect to the external output inductor.
DESCRIPTION
7, 8
PHASE
9, 10
VIN
Voltage supply input. The main power input for the IC. Connect to a suitable voltage supply. Place a ceramic capacitor from VIN
to PGND, close to the IC for decoupling.
11
VDD
Low dropout linear regulator decoupling pin. VDD is the internally generated 5V supply voltage and is derived from VIN. The
VDD is used to power all the internal core analog control blocks and drivers. Connect a 1µF capacitor from VDD to the board
ground plane. If VIN is between 3V to 5.5V, then connect VDD directly to VIN to improve efficiency.
12
BOOT
Bootstrap input. Floating bootstrap supply pin for the upper power MOSFET gate driver. Connect a 0.1µF capacitor between
BOOT and PHASE.
(EPAD)
PGND
Power ground terminal. Provides thermal relief for the package and is connected to the source of the low-side output MOSFET.
Connect PGND to the board ground plane using as many vias as possible. AGND and PGND are connected internally within the
device. Do not operate the device with AGND and PGND connected to dissimilar voltages.
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ISL85005, ISL85005A
Ordering Information
PART NUMBER
(Notes 1, 2, 3, 4)
PART
MARKING
TEMP. RANGE
(°C)
OPTION
FREQUENCY
(kHz)
PACKAGE
(RoHS COMPLIANT)
PKG.
DWG. #
ISL85005FRZ
005F
-40 to +125
SYNC
500
12 Ld DFN
L12.3x4
ISL85005AFRZ
005A
-40 to +125
SOFT-START
500
12 Ld DFN
L12.3x4
ISL85005AEVAL1Z
Evaluation Board
ISL85005EVAL1Z
Evaluation Board
NOTES:
1. Add “-T” suffix for 6k unit, “-TK” suffix for 1k unit, or “-T7A” suffix for 250 unit Tape and Reel options. 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), see product information page for ISL85005, ISL85005A. For more information on MSL, see tech brief TB363.
4. The ISL85005 is provided with a frequency synchronization input. The ISL85005A is a version of the part with programmable soft-start.
TABLE 1. KEY DIFFERENCES BETWEEN FAMILY OF PARTS
INTERNAL/EXTERNAL
COMPENSATION
EXTERNAL FREQUENCY
SYNC
PROGRAMMABLE
SOFT-START
SWITCHING
FREQUENCY (kHz)
CURRENT
RATING
ISL85003
Yes
Yes
No
500
3A
ISL85003A
Yes
No
Yes
500
3A
ISL85005
Yes
Yes
No
500
5A
ISL85005A
Yes
No
Yes
500
5A
PART NUMBER
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ISL85005, ISL85005A
Typical Application Schematics
ISL85005
GND = DEM; VCC = FCCM
MODE
1 SYNC/
MODE
2 PG
PG
EN
BOOT 12
3 EN
R1
C1
VIN
4.5V TO 18V
VIN 10
PGND
VIN 9
4 FB
R2
C4
VDD 11
5 COMP
PHASE 8
6 AGND
PHASE 7
C3
C6
C5
VOUT
5A MAX
L1
C8
C9
FIGURE 4. ISL85005 VIN RANGE FROM 4.5V TO 18V WITH INTERNAL COMPENSATION
ISL85005A
CSS
1 SS
BOOT 12
PG
2 PG
VDD 11
EN
3 EN
4 FB
R1
R2
C1
PGND
C4
VIN
4.5V TO 18V
VIN 10
VIN 9
5 COMP
PHASE 8
6 AGND
PHASE 7
C3
C6
C5
VOUT
5A MAX
L1
C8
C9
FIGURE 5. ISL85005A VIN RANGE FROM 4.5V TO 18V, WITH INTERNAL COMPENSATION WITH PROGRAMMABLE SOFT-START
TABLE 2. COMPONENTS SELECTION (REFER TO Figures 1 AND 2)
VOUT
1.2V
1.8V
2.5V
3.3V
5V
C5, C6
1OµF
1OµF
1OµF
1OµF
1OµF
C8, C9
47µF
47µF
47µF
47µF
47µF
C1
15pF
15pF
15pF
15pF
15pF
L1
3.3µH
3.3µH
3.3µH
3.3µH
3.3µH
R1
499kΩ
499kΩ
499kΩ
499kΩ
499kΩ
R2
998kΩ
392kΩ
232kΩ
157kΩ
95.3kΩ
NOTE: VIN = 12V, IOUT = 5A; The components selection table is a suggestion for typical application using internal compensation mode. For application
that requires high output capacitance greater than 200µF, R1 should be adjusted to maintain loop response bandwidth about 40kHz. See “Loop
Compensation Design” on page 19 for more detail.
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Absolute Maximum Ratings
Thermal Information
VIN, EN to AGND and PGND. . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to + 24V
PHASE to AGND and PGND . . . . . . . . . . . . . . . . . . . . . . . -0.7V to +24V (DC)
PHASE to AGND and PGND . . . . . . . . . . . . . . . . . . . . . . . -2V to +24V (40ns)
FB to AGND and PGND. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to + 7V
BOOT to PHASE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to + 7V
VDD, COMP, SYNC, PG to AGND and PGND . . . . . . . . . . . . . . . -0.3V to + 7V
Junction Temperature Range at 0A . . . . . . . . . . . . . . . . . .-55°C to +150°C
ESD Rating
Human Body Model (Tested per JESD22-A114F) . . . . . . . . . . . . . . .2.5kV
Machine Model (Tested per JESD22-A115-C) . . . . . . . . . . . . . . . . . 150V
Charged Device Model (Tested per JESD22-C101-E) . . . . . . . . . . . . . 1kV
Latch-Up (Tested per JESD-78D; Class 2, Level A) . . . . . . . . . . . . . . 100mA
Thermal Resistance
JA (°C/W) JC (°C/W)
DFN Package (Notes 5, 6) . . . . . . . . . . . . . .
41
3
Maximum Storage Temperature Range . . . . . . . . . . . . . .-65°C to +150°C
Junction Temperature Range . . . . . . . . . . . . . . . . . . . . . . .-40°C to +125°C
Pb-Free Reflow Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . see TB493
Recommended Operating Conditions
VIN Supply Voltage Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5V to 18V
Load Current Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0A to 5A
CAUTION: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to such conditions may adversely impact product
reliability and result in failures not covered by warranty.
NOTES:
5. JA is measured in free air with the component mounted on a high-effective thermal conductivity test board with “direct attach” features. See Tech
Brief TB379.
6. For JC, the “case temp” location is the center of the exposed metal pad on the package underside.
Electrical Specifications All parameter limits are established over the recommended operating conditions with TJ = -40°C to +125°C,
and with VIN = 12V unless otherwise noted. Typical values are at TA = +25°C. Boldface limits apply across the operating junction temperature range,
-40°C to +125°C.
PARAMETER
SYMBOL
TEST CONDITIONS
MIN
(Note 7)
MAX
(Note 7)
UNIT
18
V
3.2
4.5
mA
TYP
SUPPLY VOLTAGE
VIN Voltage Range
VIN
VIN Quiescent Supply Current
IQ
SYNC = Low, EN > 1V, FB = 0.85V, not switching
VIN Shutdown Supply Current
ISD
EN = AGND
6
11
µA
Rising edge
4.20
4.35
V
4.5
UNDERVOLTAGE LOCKOUT
VIN UVLO Threshold
Falling edge
3.5
3.8
VIN = 6V to 18V, IVDD = 0mA to 30mA
4.30
5.00
V
INTERNAL VDD LDO
VDD Output Voltage
VDD Output Current Limit
5.50
50
V
mA
OSCILLATOR
Nominal Switching Frequency
fSW
Minimum On-Time
tON
Minimum Off-Time
Synchronization Range
400
500
600
kHz
IOUT = 0mA (Note 8)
120
140
ns
tOFF
(Note 8)
140
180
ns
SYNC
ISL85005
300
2000
kHz
SYNC High-Time
tHI
ISL85005
100
ns
SYNC Low-Time
tLO
ISL85005
100
ns
SYNC Logic Input Low
ISL85005
0.50
SYNC Logic Input High
ISL85005
1.20
VIN = 4.5V to 18V
0.792
V
V
ERROR AMPLIFIER
FB Regulation Voltage
VFB
FB Leakage Current
VFB = 0.8V (Note 8)
Open-Loop Bandwidth
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BW
7
0.800
0.808
V
0.3
10.0
nA
5.5
MHz
FN8871.0
November 28, 2016
ISL85005, ISL85005A
Electrical Specifications All parameter limits are established over the recommended operating conditions with TJ = -40°C to +125°C,
and with VIN = 12V unless otherwise noted. Typical values are at TA = +25°C. Boldface limits apply across the operating junction temperature range,
-40°C to +125°C. (Continued)
PARAMETER
SYMBOL
TEST CONDITIONS
MIN
(Note 7)
Gain
Output Drive
VCOMP = 1.5V
Current Sense Gain
RT
Slope Compensation
Se
fSW = 500kHz
TYP
MAX
(Note 7)
UNIT
70
dB
±110
µA
0.15
Ω
550
mV/µs
ENABLE INPUT
EN Input Threshold
Rising edge
0.5
0.6
0.7
V
Hysteresis
60
100
140
mV
Default Soft-Start Time
ISL85005, ISL85005A with SS pin floating
1.0
2.3
3.6
ms
SS Internal Soft-Start Charging Current
ISL85005A
2.5
3.5
4.5
µA
SOFT-START FUNCTION
POWER-GOOD OPEN-DRAIN OUTPUT
Output Low Voltage
IPG = 5mA sinking
0.25
V
PG Pin Leakage Current
VPG = VDD
0.01
µA
PG Lower Threshold
Percentage of output regulation
80
85
90
%
PG Upper Threshold
Percentage of output regulation
110
115
120
%
PG Thresholds Hysteresis
Delay Time
3
%
Rising edge
1.5
ms
Falling edge
18
µs
FAULT PROTECTION
High-Side MOSFET Forward Current Limit
Threshold
IPOCP
Low-Side MOSFET Reverse Current Limit
Threshold
INOCP
6
7.8
9.5
A
Current forced into PHASE node, high-side MOSFET is off,
SYNC = High
-3.3
A
Low-Side MOSFET Forward Current Limit
Threshold
Current in low-side MOSFET at end of low-side cycle.
8.6
A
VIN Overvoltage Threshold
VIN rising
20
V
19
Hysteresis
1
V
TSD
Temperature rising
165
°C
THYS
Hysteresis
10
°C
High-Side MOSFET On-Resistance
RHDS
IPHASE = 100mA
57
95
mΩ
Low-Side MOSFET On-Resistance
RLDS
IPHASE = 100mA
40
75
mΩ
EN = AGND
10
kΩ
ISL85005
150
mA
Thermal Shutdown Threshold
POWER MOSFET
PHASE Pull-Down Resistor
DIODE EMULATION
Zero-Cross Detection Threshold
NOTE:
7. Compliance to datasheet limits is assured by one or more methods: production test, characterization, and/or design.
8. Compliance to limits is assured by characterization and design.
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FN8871.0
November 28, 2016
ISL85005, ISL85005A
10
10
9
9
QUIESCENT CURRENT (mA)
SHUTDOWN CURRENT (µA)
Typical Characteristics VIN = 12V, TA = +25°C, unless otherwise noted.
8
7
6
5
4
3
2
1
8
7
6
5
4
3
2
1
0
0
-40
-25
-10
5
20
35
50
65
80
95
-40
110 125
-25
-10
0.83
0.9
0.82
0.8
EN THRESHOLD (V)
FB REFERENCE VOLTAGE (V)
20
35
50
65
80
95
110 125
FIGURE 7. VIN QUIESCENT CURRENT vs JUNCTION TEMPERATURE
FIGURE 6. VIN SHUTDOWN CURRENT vs JUNCTION TEMPERATURE
0.81
0.80
0.79
0.78
EN RISING
EN FALLING
0.7
0.6
0.5
0.4
0.3
0.2
0.77
-40
-25
-10
5
20
35
50
65
80
95
-40
110 125
-25
-10
JUNCTION TEMPERATURE (oC)
5
20
35
50
65
80
95
110 125
JUNCTION TEMPERATURE (oC)
FIGURE 8. FEEDBACK VOLTAGE vs JUNCTION TEMPERATURE
FIGURE 9. ENABLE THRESHOLDS vs JUNCTION TEMPERATURE
4.5
560
UVLO START SWITCHING
SWITCHING FREQUENCY (kHz)
VIN UVLO THRESHOLD (V)
5
JUNCTION TEMPERATURE (oC)
JUNCTION TEMPERATURE (oC)
UVLO STOP SWITCHING
4.3
4.1
3.9
3.7
3.5
3.3
-40
-25
-10
5
20
35
50
65
80
95
110 125
JUNCTION TEMPERATURE (oC)
FIGURE 10. VIN UVLO THRESHOLD vs JUNCTION TEMPERATURE
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540
520
500
480
460
440
420
400
-40
-25
-10
5
20
35
50
65
80
95
110 125
JUNCTION TEMPERATURE (oC)
FIGURE 11. SWITCHING FREQUENCY vs JUNCTION TEMPERATURE
FN8871.0
November 28, 2016
ISL85005, ISL85005A
Typical Characteristics VIN = 12V, TA = +25°C, unless otherwise noted. (Continued)
2.4
26
PG RISING EDGE DELAY (ms)
PG FALLING EDGE DELAY (µs)
28
24
22
20
18
16
14
12
2.0
1.6
1.2
0.8
10
-40
-25
-10
5
20
35
50
65
80
95
0.4
110 125
-40
-25
-10
JUNCTION TEMPERATURE (oC)
12
35
50
65
80
95
110 125
0
REVERSE OCP THRESHOLD (A)
FORWARD OCP THRESHOLD (A)
20
FIGURE 13. PG DELAY (RISING) vs JUNCTION TEMPERATURE
FIGURE 12. PG DELAY (FALLING) vs JUNCTION TEMPERATURE
11
10
9
8
7
6
HIGH SIDE MOSFET
5
LOW SIDE MOSFET
-1
-2
-3
-4
-5
-6
4
-40
-25
-10
5
20
35
50
65
80
95
110 125
-40
-25
-10
JUNCTION TEMPERATURE (oC)
5
20
35
50
65
80
95
110 125
JUNCTION TEMPERATURE (oC)
FIGURE 14. FORWARD OCP THRESHOLD vs JUNCTION TEMPERATURE
FIGURE 15. LOW-SIDE REVERSE OCP THRESHOLD vs JUNCTION
TEMPERATURE
80
80
LOW-SIDE ON-RESISTANCE (mΩ)
HIGH-SIDE ON-RESISTANCE (mΩ)
5
JUNCTION TEMPERATURE (oC)
70
60
50
40
30
20
10
0
70
60
50
40
30
20
10
0
-40
-25
-10
5
20
35
50
65
80
95
110 125
JUNCTION TEMPERATURE (oC)
FIGURE 16. HIGH-SIDE rDS(ON) vs JUNCTION TEMPERATURE
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10
-40
-25
-10
5
20
35
50
65
80
95
110 125
JUNCTION TEMPERATURE (oC)
FIGURE 17. LOW-SIDE rDS(ON) vs JUNCTION TEMPERATURE
FN8871.0
November 28, 2016
ISL85005, ISL85005A
Typical Performance Curves Circuit of Figure 1. VIN = 12V, VOUT = 5V, L = 3.3µH, fSW = 500kHz, TA = +25°C, unless
100
100
95
95
90
90
85
85
EFFICIENCY (%)
EFFICIENCY (%)
otherwise noted.
80
75
70
65
80
75
70
65
60
VIN = 12V, DEM
60
55
VIN = 12V, FORCED CCM
55
VIN = 12 V, DEM
VIN = 5V , DEM
50
50
0
1
2
3
4
0
5
1
100
95
95
90
90
85
EFFICIENCY (%)
EFFICIENCY (%)
100
80
75
70
VIN = 12V, FORCED CCM
75
70
65
VIN = 12V, DEM
55
VIN = 5V, DEM
50
50
1
2
5
80
60
VIN = 5V, FORCED CCM
0
4
85
55
60
3
4
0
5
1
2
3
4
5
OUTPUT CURREN T (A)
OUTPUT CURRENT (A)
FIGURE 20. EFFICIENCY vs LOAD, VOUT = 3.3V, FORCED CCM
FIGURE 21. EFFICIENCY vs LOAD, VOUT = 2.5V, DEM
100
100
95
95
90
90
85
85
EFFICIENCY (%)
EFFICIENCY (%)
3
FIGURE 19. EFFICIENCY vs LOAD, VOUT = 3.3V, DEM
FIGURE 18. EFFICIENCY vs LOAD, VOUT = 5V
65
2
OUTPUT CURREN T (A)
OUTPUT CURRENT (A)
80
75
70
65
80
75
70
65
60
V IN = 12V, FORCED CCM
60
VIN = 12V, DEM
55
V IN = 5V, FORCED CCM
55
VIN = 5V, DEM
50
50
0
1
2
3
4
5
OUTPUT CURRENT (A)
FIGURE 22. EFFICIENCY vs LOAD, VOUT = 2.5V, FORCED CCM
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0
1
2
3
4
5
OUTPUT CURREN T (A)
FIGURE 23. EFFICIENCY vs LOAD, VOUT = 1.8V, DEM
FN8871.0
November 28, 2016
ISL85005, ISL85005A
Typical Performance Curves Circuit of Figure 1. VIN = 12V, VOUT = 5V, L = 3.3µH, fSW = 500kHz, TA = +25°C, unless
100
100
95
95
90
90
85
85
EFFICIENCY (%)
EFFICIENCY (%)
otherwise noted. (Continued)
80
75
70
65
80
75
70
65
60
VIN = 12V, FORCED CCM
60
VIN = 12V, DEM
55
VIN = 5V, FORCED CCM
55
VIN = 5V, DEM
50
50
0
1
2
3
4
5
0
1
OUTPUT CURRENT (A)
2
3
4
5
OUTPUT CURREN T (A)
FIGURE 24. EFFICIENCY vs LOAD, VOUT = 1.8V, FORCED CCM
FIGURE 25. EFFICIENCY vs LOAD, VOUT = 1.2V, DEM
100
95
VOUT (2V/DIV)
EFFICIENCY (%)
90
85
80
75
70
65
60
VIN = 12V, FORCED CCM
55
VIN = 5V, FORCED CCM
IL (2A/DIV)
EN (10V/DIV)
50
0
1
2
3
4
5
1ms/DIV
OU TPUT CURRENT (A)
FIGURE 26. EFFICIENCY vs LOAD, VOUT = 1.2V, FORCED CCM
FIGURE 27. START-UP WITH EN, NO LOAD
VOUT (2V/DIV)
VOUT (2V/DIV)
IL (2A/DIV)
IL (2A/DIV)
VIN (5V/DIV)
EN (10V/DIV)
1ms/DIV
1ms/DIV
FIGURE 28. START-UP WITH EN, IOUT = 5A
FIGURE 29. START-UP WITH VIN, NO LOAD
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FN8871.0
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ISL85005, ISL85005A
Typical Performance Curves Circuit of Figure 1. VIN = 12V, VOUT = 5V, L = 3.3µH, fSW = 500kHz, TA = +25°C, unless
otherwise noted. (Continued)
VOUT (2V/DIV)
VOUT (2V/DIV)
IL (2A/DIV)
IL (2A/DIV)
EN (10V/DIV)
VIN (5V/DIV)
1ms/DIV
50ms/DIV
FIGURE 30. START-UP WITH VIN, IOUT = 5A
FIGURE 31. SHUTDOWN WITH EN, IOUT = 10mA
VOUT (2V/DIV)
VOUT (2V/DIV)
IL (2A/DIV)
IL (2A/DIV)
EN (10V/DIV)
VIN (10V/DIV)
200µs/DIV
50ms/DIV
FIGURE 32. SHUTDOWN WITH EN, IOUT = 5A
FIGURE 33. SHUTDOWN WITH VIN, IOUT = 10mA
IL (500mA/DIV)
VOUT (2V/DIV)
IL (2A/DIV)
VIN (10V/DIV)
PHASE (5V/DIV)
200µs/DIV
1µs/DIV
FIGURE 34. SHUTDOWN WITH VIN, IOUT = 5A
FIGURE 35. STEADY STATE OPERATION IN DCM, IOUT = 0.2A
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FN8871.0
November 28, 2016
ISL85005, ISL85005A
Typical Performance Curves Circuit of Figure 1. VIN = 12V, VOUT = 5V, L = 3.3µH, fSW = 500kHz, TA = +25°C, unless
otherwise noted. (Continued)
IL (500mA/DIV)
VOUT (100mV/DIV),
AC COUPLING
IOUT (1A/DIV)
PHASE (5V/DIV)
1µs/DIV
50µs/DIV
FIGURE 36. STEADY STATE IN FORCED CCM, IOUT = 0.2A
FIGURE 37. LOAD TRANSIENT, 0A → 2.5A → 0A, 2.5A/µs
VOUT (200mV/DIV),
AC COUPLING
VOUT (2V/DIV)
IL (2A/DIV)
IOUT (2A/DIV)
50µs/DIV
1ms/DIV
FIGURE 38. LOAD TRANSIENT, 0A → 5A → 0A, 2.5A/µs
FIGURE 39. HIGH-SIDE FORWARD OVER CURRENT PROTECTION
IL (2A/DIV)
IL (2A/DIV)
PHASE (5V/DIV)
PHASE (10V/DIV)
20µs/DIV
FIGURE 40. OUTPUT SHORT-CIRCUIT BEHAVIOR
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1µs/DIV
FIGURE 41. LOW-SIDE MOSFET REVERSE OVER CURRENT
PROTECTION
FN8871.0
November 28, 2016
ISL85005, ISL85005A
Detailed Description
The ISL85005 and ISL85005A combine a synchronous buck
controller with a pair of integrated switching MOSFETs. The buck
controller drives the internal high-side and low-side N-channel
MOSFETs to deliver load currents up to 5A. The buck regulator
can operate from an unregulated DC source, such as a battery,
with a voltage ranging from +4.5V to +18V. An internal 5V LDO
voltage regulator is used to bias the controller. The converter
output voltage is programmed using an external resistor divider
and will generate regulated voltages down to 0.8V. These
features make the regulator suited for a wide range of
applications.
The controller uses a current mode loop, which simplifies the
loop compensation and permits fixed frequency operation over a
wide range of input and output voltages. The internal feedback
loop compensation option allows for a lower number of external
components. The regulator switches at a default of 500kHz or it
can be synchronized from 300kHz to 2MHz on the ISL85005.
The buck regulator is equipped with a lossless current limit
scheme. The current in the output stage is derived from
temperature compensated measurements of the drain-to-source
voltage of the internal power MOSFETs. The current limit
threshold is internally set at 7.8A.
Operation Initialization
Pull EN above 0.6V (typical) to start operation. The power-on
reset circuitry will prevent operation if the input voltage is below
4.2V. Once the power-on reset requirement is met, the controller
will soft-start with a 2.3ms ramp on the ISL85005 or at a rate
determined by the value of a capacitor connected between SS
and AGND on the ISL85005A.
FCCM Control Scheme
The regulator employs a current mode pulse-width modulation
control scheme for fast transient response and pulse-by-pulse
current limiting. The current loop consists of the oscillator, the
PWM comparator, current-sensing circuit, and a slope
compensation circuit. The gain of the current-sensing circuit is
typically 150mV/A and the slope compensation is 1.1V/T. The
reference for the current loop is in turn provided by the output of
an Error Amplifier (EA), which compares the feedback signal at
the FB pin to the integrated 0.8V reference. Therefore, the output
voltage is regulated by using the error amplifier to control the
reference for the current loop.
The error amplifier is an operational amplifier that converts the
voltage error signal to a voltage output. The voltage loop is
internally compensated with the 30pF and 600kΩ RC network
that can support most applications.
PWM operation is initialized by the clock from the oscillator. The
upper MOSFET is turned on at the beginning of a cycle and the
current in the MOSFET starts to ramp up. When the sum of the
current amplifier CSA signal and the slope compensation reaches
the control reference of the current loop, the PWM comparator
sends a signal to the logic to turn off the upper MOSFET and turn
on the lower MOSFET. The lower MOSFET stays on until the end of
the cycle. Figure 42 shows the typical operating waveforms during
Continuous Conduction Mode (CCM) operation. The dotted lines
illustrate the sum of the compensation ramp and the
current-sense amplifier’s output.
VEAMP
VCSA
DUTY
CYCLE
IL
VOUT
FIGURE 42. CCM OPERATION WAVEFORMS
Light-Load Operation
The ISL85005 monitors both the current in the low-side MOSFET
and the voltage of the FB node for regulation. Pulling the
SYNC/MODE pin low allows the ISL85005 to enter discontinuous
operation when lightly loaded by operating the low-side MOSFET
in Diode Emulation Mode (DEM). In this mode, reverse current is
not allowed in the inductor, and the output falls naturally to the
regulation voltage before the high-side MOSFET is switched for
the next cycle. The boundary is set by Equation 1:
V OUT  1 – D 
I OUT = ----------------------------------2Lf SW
(EQ. 1)
where D = duty cycle, fSW = switching frequency, L = inductor
value, IOUT = output loading current, VOUT = output voltage.
Synchronization Control
The ISL85005 can be synchronized from 300kHz to 2MHz by an
external signal applied to the SYNC pin. The rising edge on the SYNC
triggers the rising edge of the PHASE pulse. Make sure that the
on-time of the SYNC pulse is greater than 100ns. Although the
maximum synchronized frequency can be as high as 2MHz, the
ISL85005 is a current mode regulator that requires a minimum
of 140ns on-time to regulate properly. As an example, the
maximum recommended synchronized frequency will be about
600kHz with 12VIN and 1VOUT.
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FN8871.0
November 28, 2016
ISL85005, ISL85005A
Enable, Soft-Start, and Disable
Forward Overcurrent Protection
Chip operation begins after VIN exceeds its rising POR trip point
(nominal 4.2V). If EN is held low externally, nothing happens until
this pin is released. Once the voltage on the EN pin is above 0.6V,
the LDO powers up and soft-start control begins. The default
soft-start time is 2.3ms.
The current flowing through the internal high-side MOSFET is
monitored during the on-time and compared to a typical 7.8A
overcurrent limit threshold. If the current exceeds the overcurrent
limit threshold, the high-side MOSFET is immediately turned off
and will not turn on again until the next switching cycle. The
current through the low-side switching MOSFET is sampled
during off time. If the low-side MOSFET current exceeds 8.6A at
the end of the low-side cycle, then the high-side MOSFET will skip
the next cycle, allowing the inductor current to decay to a safe
level before resuming switching.
On the ISL85005A, let SS float to select the internal soft-start
time with a default of 2.3ms. The soft-start time is extended by
connecting an external capacitor between SS and AGND. A 3.5µA
current source charges up the capacitor. The soft-start capacitor
is charged until the voltage on the SS pin reaches a 2.0V clamp
level. However, the output voltage reaches its regulation value
when the voltage on the SS pin reaches approximately 0.9V. The
capacitor, along with an internal 3.5µA current source, sets the
soft-start interval of the converter, tSS, according to Equation 2:
C SS  nF  = 3.5  t SS  mS  – 1.6nF
(EQ. 2)
Output Voltage Selection
The regulator output voltage is programmed using an external
resistor divider that scales the feedback relative to the internal
reference voltage. The scaled voltage is fed back to the inverting
input of the error amplifier (see Figure 43).
The output voltage programming resistor, R2, will depend on the
value chosen for the feedback resistor, R1, and the desired
regulator output voltage, VOUT (see Equation 2). The R1 value will
determine the gain of the feedback loop. See “Loop
Compensation Design” on page 19 for more details. The value for
the feedback resistor is typically between 10kΩ and 400kΩ.
R 1  0.8V
R 2 = ---------------------------------V OUT – 0.8V
(EQ. 3)
If the output voltage desired is 0.8V, then R2 is left unpopulated.
R1 is still required to set the low frequency pole of the modulator
compensation.
VOUT
R1
+
-
EA
R2
0.8V
REFERENCE
FIGURE 43. EXTERNAL RESISTOR DIVIDER
Protection Features
The regulator limits current in all on-chip power devices.
Overcurrent limits are applied to the two output switching
MOSFETs as well as to the LDO linear regulator that feeds VDD.
Input and output overvoltage protection circuitry on the switching
regulator provides a second layer of protection.
Reverse Overcurrent Protection
Similar to the overcurrent, the negative current protection is
realized by monitoring the current across the low-side MOSFET, as
shown in Figure 41 on page 14. When the inductor current
reaches -3.3A, the synchronous rectifier is turned off. This limits
the ability of the regulator to actively pull down the output voltage
and prevents large reverse currents that may fall outside the range
of the high-side current-sense amplifier.
Output Overvoltage Protection
The output overvoltage protection is triggered when the output
voltage exceeds 115% of the nominal voltage setting point. In
this condition, high-side and low-side MOSFETs are turned off
until the output drops to within the regulation band. Once the
output is in regulation, the controller will restart under internal
SS control.
Input Overvoltage Protection
The input overvoltage protection system prevents operation of the
switching regulator whenever the input voltage is higher than 20V.
The high-side and low-side MOSFETs are turned off and the
converter will restart under internal SS control when the input
voltage returns to normal.
Thermal Overload Protection
Thermal overload protection limits the maximum die
temperature, and thus the total power dissipation in the
regulator. A sensor on the chip monitors the junction
temperature. A signal is sent to the fault monitor circuits
whenever the junction temperature (TJ) exceeds +165°C, and
this causes the switching regulator and LDO to shut down.
The switching regulator turns on again and soft-starts after the
IC’s junction temperature cools by 10°C. The switching regulator
exhibits Hiccup mode operation during continuous thermal
overload conditions. For continuous operation, do not exceed the
+125°C junction temperature rating.
Power Derating Characteristics
To prevent the regulator from exceeding the maximum junction
temperature, some thermal analysis is required. The
temperature rise is given by Equation 4:
T RISE =  PD    JA 
(EQ. 4)
where PD is the power dissipated by the regulator and JA is the
thermal resistance from the junction of the die to the ambient
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November 28, 2016
ISL85005, ISL85005A
temperature. The junction temperature, TJ, is given by
Equation 5:
(EQ. 5)
T J =  T A + T RISE 
where TA is the ambient temperature. For the DFN package, the
JA is 49 (°C/W).
The actual junction temperature should not exceed the absolute
maximum junction temperature of +125°C when considering
the thermal design.
The shape of the output voltage waveform during a load transient
that represents the worst case loading conditions will ultimately
determine the number of output capacitors and their type. When
this load transient is applied to the converter, most of the energy
required by the load is initially delivered from the output capacitors.
This is due to the finite amount of time required for the inductor
current to slew up to the level of the output current required by the
load. This phenomenon results in a temporary dip in the output
voltage. At the very edge of the transient, the Equivalent Series
Inductance (ESL) of each capacitor induces a spike that adds on top
of the existing voltage drop due to the ESR.
T
Application Guidelines
Boot Undervoltage Detection
The internal driver of the high-side FET is equipped with a boot
Undervoltage (UV) detection circuit. In the event the voltage
difference between BOOT and PHASE falls below 2.5V, the UV
detection circuit allows the low-side MOSFET on for 300ns to
recharge the bootstrap capacitor.
While ISL85005 and ISL85005A include an internal bootstrap
diode, efficiency can be improved by using an external supply
voltage and bootstrap Schottky diode. The external diode is then
sourced from a fixed external 5V supply or from the output of the
switching regulator if this is at 5V. The bootstrap diode can be a
low cost type, such as the BAT54.
BOOT
During the removal of the same output load, the energy stored in the
inductor is dumped into the output capacitors. This energy dumping
creates a temporary hump in the output voltage. This hump, as with
the sag, can be attributed to the total amount of capacitance on the
output. Figure 45 shows a typical response to a load transient.
VHUMP
VOUT
VESR
PHASE
ISL85005
ISL85005A
After the initial spike, attributable to the ESR and ESL of the
capacitors, the output voltage experiences sag. This sag is a direct
consequence of the amount of capacitance on the output.
VSAG
C4
0.1µF
BAT54
VESL
IOUT
Itran
5VOUT or 5V SOURCE
FIGURE 44. EXTERNAL BOOTSTRAP DIODE
Switching Regulator Output Capacitor
Selection
An output capacitor is required to filter the inductor current and
supply the load transient current. The filtering requirements are a
function of the switching frequency, the ripple current, and the
required output ripple. The load transient requirements are a
function of the slew rate (di/dt) and the magnitude of the transient
load current. These requirements are generally met with a mix of
capacitor types and careful layout.
High-frequency ceramic capacitors initially supply the transient and
slow the current load rate seen by the bulk capacitors. The bulk filter
capacitor values are generally determined by the Equivalent Series
Resistance (ESR) and voltage rating requirements rather than actual
capacitance requirements.
The high-frequency decoupling capacitors should be placed as close
to the power pins of the load as physically possible. Be careful not to
add inductance in the circuit board wiring that could cancel the
usefulness of these low inductance components. Consult with the
manufacturer of the load on specific decoupling requirements.
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FIGURE 45. TYPICAL TRANSIENT RESPONSE
The amplitudes of the different types of voltage excursions can
be approximated using Equations 6, 7, 8, and 9.
V ESR = ESR  I tran
(EQ. 6)
dI tran
V ESL = ESL  --------------dt
(EQ. 7)
2
L OUT  I tran
V SAG = ----------------------------------------------------------C OUT   V IN – V OUT 
(EQ. 8)
2
L OUT  I tran
V HUMP = -------------------------------------C OUT  V OUT
(EQ. 9)
where Itran = Output load current transient and COUT = Total
output capacitance.
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In a typical converter design, the ESR of the output capacitor bank
dominates the transient response. The ESR and the ESL are
typically the major contributing factors in determining the output
capacitance. The number of output capacitors can be determined
by using Equation 10, which relates the ESR and ESL of the
capacitors to the transient load step and the voltage limit (VO):
ESL  I tran
------------------------------ + ESR  I tran
dt
Number of Caps = -------------------------------------------------------------------V O
(EQ. 10)
If VSAG or VHUMP are found to be too large for the output
voltage limits, then the amount of capacitance may need to be
increased. In this situation, a trade-off between output
inductance and output capacitance may be necessary.
The ESL of the capacitors, which is an important parameter in
the above equations, is not usually listed in the specification.
Practically, it can be approximated using Equation 11 if an
Impedance vs Frequency curve is given for a specific capacitor:
1
ESL = ---------------------------------------2
C  2    f res 
(EQ. 11)
where fres is the resonant frequency where the lowest
impedance is achieved.
The ESL of the capacitors becomes a concern when designing
circuits that supply power to loads with high rates of change in
the current.
Output Inductor Selection
The output inductor is selected to meet the output voltage ripple
requirements and minimize the converter’s response time to the
load transient. The inductor value determines the converter’s
ripple current and the output ripple voltage is a function of the
ripple current. The ripple voltage and current are approximated
by Equations 12 and 13:
 V IN – V OUT  V OUT
I = ------------------------------------  ---------------Fs  L
V IN
(EQ. 12)
VOUT = I x ESR
(EQ. 13)
The response time to a transient is different for the application of
load and the removal of load. Equations 14 and 15 give the
approximate response time interval for application and removal
of a transient load:
L x Itran
tRISE =
tFALL =
VIN - VOUT
L x Itran
VOUT
(EQ. 14)
(EQ. 15)
where Itran is the transient load current step, tRISE is the
response time to the application of load, and tFALL is the
response time to the removal of load. The worst case response
time can be either at the application or removal of load. Be sure
to check both of these equations at the minimum and maximum
output levels for the worst case response time.
Input Capacitor Selection
Use a mix of input bypass capacitors to control the input voltage
ripple. Use ceramic capacitors for high frequency decoupling and
bulk capacitors to supply the current needed each time the
switching MOSFET turns on. Place the ceramic capacitors
physically close to the MOSFET VIN pins (switching MOSFET
drain) and PGND.
The important parameters for the bulk input capacitance are the
voltage rating and the RMS current rating. For reliable operation,
select bulk capacitors with voltage and current ratings above the
maximum input voltage and largest RMS current required by the
circuit. Their voltage rating should be at least 1.25 times greater
than the maximum input voltage, while a voltage rating of 1.5
times is a conservative guideline. For most cases, the RMS
current rating requirement for the input capacitor of a buck
regulator is approximately 1/2 the DC load current.
The maximum RMS current required by the regulator may be
more closely approximated through Equation 16:
I RMS
 MAX 
=
V OUT 
V IN – V OUT V OUT 2
2
1
--------------  I OUT
+ ------   -----------------------------  -------------- 


V IN
V IN  
L  fs
12
 MAX 
(EQ. 16)
Increasing the value of inductance reduces the ripple current and
voltage. However, the large inductance values reduce the
converter’s response time to a load transient. Furthermore, the
ripple current is an important signed-in current mode control.
Therefore, set the ripple inductor current to approximately 30%
of the maximum output current for optimized performance.
One of the parameters limiting the converter’s response to a load
transient is the time required to change the inductor current.
Given a sufficiently fast control loop design, the regulator will
provide either 0% or 100% duty cycle in response to a load
transient. The response time is the time required to slew the
inductor current from an initial current value to the transient
current level. During this interval, the difference between the
inductor current and the transient current level must be supplied
by the output capacitor. Minimizing the response time can
minimize the output capacitance required.
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18
For a through-hole design, several electrolytic capacitors may be
needed, especially at temperatures less than -25°C. The
electrolytic's ESR can increase ten times higher than at room
temperature and cause input line oscillation. In this case, a more
thermally stable capacitor such as X7R ceramic should be used.
For surface mount designs, solid tantalum capacitors can be
used, but caution must be exercised with regard to the capacitor
surge current rating. Some capacitor series available from
reputable manufacturers are surge current tested.
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Compensator Design Goal
Loop Compensation Design
When COMP is not connected to GND, the COMP pin is active for
external loop compensation. In an application with extreme
temperatures, such as less than -10°C or greater than +85°C,
external compensation mode should be used. The regulator uses
constant frequency peak current mode control architecture to
achieve a fast loop transient response. An accurate current
sensing pilot device in parallel with the upper MOSFET is used for
peak current control signal and overcurrent protection. The
inductor is not considered as a state variable since its peak
current is constant, and the system becomes a single order
system. It is much easier to design a Type II compensator to
stabilize the loop than to implement voltage mode control. Peak
current mode control has an inherent input voltage feed-forward
function to achieve good line regulation. Figure 46 shows the
small signal model of the synchronous buck regulator.
+
^
iin
^
iL
RLP
LP
V d^
ILd^ 1:D IN
^
VIN
+
GAIN (VLOOP (S(fi))
RT
Rc
Ro
• Gain margin: >10dB
• Phase margin: >40°
The compensator design procedure is as follows:
The loop gain at crossover frequency of fc has a unity gain.
Therefore, the compensator resistance, R6, is determined by
Equation 18.
R 6 = 2f c C o R t R 1  f c  C o R 1
Vo Co
Ro Co
C 6 = --------------- = ------------------10R 6 10I o R 6
Ti (S)
d^
Choose Loop bandwidth fc of approximately 50kHz or 1/10 of
the switching frequency.
(EQ. 18)
Note that Co is the actual capacitance seen by the regulator,
which may include ceramic high frequency decoupling and bulk
output capacitors. Ceramic may have to be derated by
approximately 40% depending on dielectric, voltage stress, and
temperature. Compensator capacitor C6 is then given by
Equations 19 and 20.
vo^
Co
High DC Gain
K
(EQ. 19)
Fm
+
Rc Co 1
-,----------------]
C 7 = max [-------------10R 6 f s R 6
Tv(S)
He(S)
^
Vcomp
-Av(S)
FIGURE 46. SMALL SIGNAL MODEL OF SYNCHRONOUS BUCK
REGULATOR
R6
R1
C3
Put compensator zero, CZ2 from 1/2fc to fc.
-
(EQ. 21)
For internal compensation mode, R6 is equal 600kΩ and C6 is
30pF. Equation 18 can be rearranged to solve for R1.
C6
VCOMP
VFB
R2
An optional zero can boost the phase margin. CZ2 is a zero due
to R1 and C3.
1
C 3 = -------------------2f c R 1
C7
VO
(EQ. 20)
+
VREF
FIGURE 47. TYPE II COMPENSATOR
Figure 47 shows the Type II compensator. Its transfer function is
expressed, as shown in Equation 17:
S 
S
 1 + ------------ 1 + -------------

 cz1 
 cz2
v̂ comp
1
A v  S  = ----------------- = -------------------------------------- -------------------------------------------------------------- C6 + C7   R1 
S
S
v̂ o
S 1 + -------------  1 + -------------

 cp2
 cp1 
(EQ. 17)
where:
C6 + C7
1
1
 cz1 = --------------- ,  cz2 = ---------------  cp1 = -----------------------  cp2  350kHz
R6 C6 C7
R6 C6
R1 C3
Layout Considerations
The layout is very important in a high frequency switching
converter design. With power devices switching efficiently at
500kHz, the resulting current transitions from one device to
another cause voltage spikes across the interconnecting
impedances and parasitic circuit elements. These voltage spikes
can degrade efficiency, radiate noise into the circuit, and lead to
device overvoltage stress. Careful component layout and printed
circuit board design minimizes these voltage spikes.
As an example, consider the turn-off transition of the upper
MOSFET. Prior to turn-off, the MOSFET is carrying the full load
current. During turn-off, current stops flowing in the MOSFET and
is picked up by the internal body diode. Any parasitic inductance
in the switched current path generates a large voltage spike
during the switching interval. Careful component selection, tight
layout of the critical components, and short, wide traces
minimize the magnitude of voltage spikes.
There are two sets of critical components in the regulator
switching converter. The switching components are the most
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ISL85005, ISL85005A
critical because they switch large amounts of energy and,
therefore, tend to generate large amounts of noise. Next are the
small signal components, which connect to sensitive nodes or
supply critical bypass current and signal coupling.
close as possible to the FB pin with vias tied straight to the
ground plane. Figure 49 shows a recommended layout example.
A multi-layer printed circuit board is recommended. Figure 48
shows the connections of the critical components in the
converter. Note that capacitors CIN and COUT could each
represent numerous physical capacitors. Dedicate one solid
layer, usually a middle layer of the PC board, for a ground plane
and make all critical component ground connections with vias to
this layer. Dedicate another solid layer as a power plane and
break this plane into smaller islands of common voltage levels.
Keep the metal runs from the PHASE terminals to the output
inductor short. The power plane should support the input power
and output power nodes. Use copper-filled polygons on the top
and bottom circuit layers for the phase nodes. Use the remaining
printed circuit layers for small signal wiring.
In order to dissipate heat generated by the internal LDO and
MOSFETs, the ground pad should be connected to the internal
ground plane through at least five vias. This allows the heat to
move away from the IC and also ties the pad to the ground plane
through a low impedance path.
FIGURE 49. RECOMMEND LAYOUT (TOP LAYER)
The switching components should be placed close to the
regulator first. Minimize the length of the connections between
the input capacitors, CIN, and the power switches by placing
them nearby. Position both the ceramic and bulk input capacitors
as close to the upper MOSFET drain as possible.
VIN
VIN
CIN
ISL85005
ISL85005A
L
VOUT1
COUT1
PGND
COMP
C6
LOAD
PHASE
C7
R6
R1
FB
R2
PGND PAD
C3
KEY
ISLAND ON CIRCUIT AND/OR POWER PLANE LAYER
VIA CONNECTION TO GROUND PLANE
FIGURE 48. PRINTED CIRCUIT BOARD POWER PLANES AND ISLANDS
The critical small signal components include any bypass
capacitors, feedback components, and compensation
components. Place the compensation components close to the
FB and COMP pins. The feedback resistors should be located as
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Revision History
The revision history provided is for informational purposes only and is believed to be accurate, however, not
warranted. Please visit our website to make sure you have the latest revision.
DATE
REVISION
November 28, 2016
FN8871.0
CHANGE
Initial Release
About Intersil
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information page found at www.intersil.com.
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FN8871.0
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ISL85005, ISL85005A
Package Outline Drawing
For the most recent package outline drawing, see L12.3x4.
L12.3x4
12 LEAD DUAL FLAT NO-LEAD PLASTIC PACKAGE
Rev 1, 3/15
3.00
B
6
PIN 1
INDEX AREA
1
12
4.00
(4X)
6
PIN #1
INDEX AREA
SEE DETAIL "X"
A
3.30 ±0.10
0.10
2X 2.50
6
7
12X 0.25 ±0.05
0.10 M C A B
TOP VIEW
0.90 MAX
4
C
SIDE VIEW
1.70
±0.10
10X 0.50
12X 0.40 ± 0.05
BOTTOM VIEW
(12X 0.60)
( 12 X 0.25)
( 3.30 )
( 2.50)
0.10 C
(10x 0.50)
C
0 . 203 REF
SEATING PLANE
(1.70)
0.08 C
0 . 00 MIN.
0 . 05 MAX.
( 2.80 )
TYPICAL RECOMMENDED LAND PATTERN
DETAIL "X"
NOTES:
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22
1.
Dimensions are in millimeters.
Dimensions in ( ) for Reference Only.
2.
Dimensioning and tolerancing conform to ASME Y14.5m-1994.
3.
Unless otherwise specified, tolerance : Decimal ± 0.05
4.
Dimension applies to the metallized terminal and is measured
between 0.15mm and 0.30mm from the terminal tip.
5.
Tiebar shown (if present) is a non-functional feature and may be
located on any of the 4 sides (or ends).
6.
The configuration of the pin #1 identifier is optional, but must be
located within the zone indicated. The pin #1 identifier may be
either a mold or mark feature.
7.
Reference document JEDEC MO-229.
FN8871.0
November 28, 2016