Intersil ISL8002 Compact synchronous buck regulator Datasheet

Compact Synchronous Buck Regulators
ISL8002, ISL8002A, ISL80019, ISL80019A
ISL8002, ISL8002A, ISL80019 and ISL80019A are highly
Features
efficient, monolithic, synchronous step-down DC/DC converters
• VIN range 2.7V to 5.5V
that can deliver up to 2A of continuous output current from a 2.7V
to 5.5V input supply. They use peak current mode control
architecture to allow very low duty cycle operation. They operate
at either 1MHz or 2MHz switching frequency, thereby providing
superior transient response and allowing for the use of small
inductors. They also have excellent stability and provide both
internal and external compensation options.
• VOUT range is 0.6V to VIN
• IOUT maximum is 1.5A or 2A (see Table 1 on page 3)
• Switching frequency is 1MHz or 2MHz (see Table 1 on
page 3)
• Internal or external compensation option
ISL8002, ISL8002A, ISL80019 and ISL80019A integrate very low
rDS(ON) MOSFETs in order to maximize efficiency. In addition,
since the high side MOSFET is a PMOS, the need for a Boot
capacitor is eliminated, thereby reducing external component
count. They can operate at 100% duty cycle (at 1MHz) with a
dropout of 200mV at 2A output current.
• Selectable PFM or PWM operation option
• Overcurrent and short circuit protection
• Over-temperature/thermal protection
• VIN Undervoltage Lockout and VOUT Overvoltage Protection
• Up to 95% peak efficiency
These devices can be configured for either PFM (discontinuous
conduction) or PWM (continuous conduction) operation at light
load. PFM provides high efficiency by reducing switching losses at
light loads and PWM reduces noise susceptibility and RF
interference.
Applications
• General purpose point of load DC/DC
• Set-top boxes and cable modems
These devices are offered in a space saving 8 pin 2mmx2mm
TDFN lead free package with exposed pad for improved thermal
performance. The complete converter occupies less than
0.10in2 area.
• FPGA power
• DVD, HDD drives, LCD panels, TV
Related Literature
• See AN1803, “1.5A/2A Low Quiescent Current High
Efficiency Synchronous Buck Regulator”
VIN
GND
EN
PG
C1
22μF
2
3
4
PHASE 8
VIN
PGND
EN
FB
MODE
PG
COMP
PAD
L1
1.2μH
100
+1.8V/2A
C5
22μF
VOUT
C6
22μF
R1
6 +0.6V 200kΩ 1%
5
R2
100kΩ 1%
9
80
70
60
50
VO
R 1 = R 2 ⎛ ----------- – 1⎞
⎝ VFB
⎠
(EQ. 1)
FIGURE 1. TYPICAL APPLICATION CIRCUIT CONFIGURATION
(INTERNAL COMPENSATION OPTION)
January 7, 2013
FN7888.1
90
GND
7
EFFICIENCY (%)
ISL8002
+2.7V …+5.5V 1
1
40
0.0
2.5VOUT
1.8VOUT
1.5VOUT
1.2VOUT
0.9VOUT
0.8VOUT
0.2
0.4
0.6
0.8 1.0 1.2 1.4
OUTPUT LOAD (A)
1.6
1.8
2.0
FIGURE 2. EFFICIENCY vs LOAD
FSW = 1MHz, VIN = 3.3V, MODE = PFM, TA = +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 2013. 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.
ISL8002, ISL8002A, ISL80019, ISL80019A
Table of Contents
Pin Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Pin Descriptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Functional Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Ordering Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Thermal Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Recommended Operating Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Typical Performance Curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Load Regulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Theory of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
PWM Control Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
PFM Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Overcurrent Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Short-Circuit Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Negative Current Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
PG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
UVLO. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Enable, Disable, and Soft Start-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Discharge Mode (Soft-Stop) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
100% Duty Cycle (1MHz Version) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Thermal Shut-Down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Applications Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Output Inductor and Capacitor Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Output Voltage Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Input Capacitor Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Output Capacitor Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Loop Compensation Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Layout Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
About Intersil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Package Outline Drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2
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ISL8002, ISL8002A, ISL80019, ISL80019A
TABLE 1. SUMMARY OF KEY DIFFERENCES
PART#
IOUT (MAX)
(A)
FSW
(MHz)
ISL80019
1.5
1
ISL80019A
1.5
2
ISL8002
2
1
ISL8002A
2
2
VIN RANGE
(V)
VOUT RANGE
(V)
PACKAGE
SIZE
2.7 to 5.5
0.6 to 5.5
8 pin 2mmx2mm TDFN
NOTE: In this datasheet, the parts in the table above are collectively called "device".
TABLE 2. COMPONENT VALUE SELECTION TABLE
VOUT
(V)
C1
(µF)
C5, C6
(µF)
C4
(pF)
L1
(µH)
R1
(kΩ)
R2
(kΩ)
0.8
22
22
22
1.0~2.2
33
100
1.2
22
22
22
1.0~2.2
100
100
1.5
22
22
22
1.0~2.2
150
100
1.8
22
22
22
1.0~3.3
200
100
2.5
22
22
22
1.5~3.3
316
100
3.3
22
22
22
1.5~4.7
450
100
3
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Pin Configuration
ISL8002, ISL8002A, ISL80019, ISL80019A
(8 LD 2x2 TDFN)
TOP VIEW
VIN
1
EN
2
MODE
3
PG
4
THERMAL
PAD
(GND)
PAD
PIN 9
8
PHASE
7
PGND
6
FB
5
COMP
Pin Descriptions
PIN NUMBER
SYMBOL
PIN DESCRIPTION
1
VIN
The input supply for the power stage of the PWM regulator and the source for the internal linear regulator that provides
bias for the IC. Place a minimum of 10µF ceramic capacitance from VIN to GND and as close as possible to the IC for
decoupling.
2
EN
Device enable input. When the voltage on this pin rises above 0.6V, the device is enabled. The device is disabled when
the pin is pulled to ground. When the device is disabled, a 100Ω resistor discharges the output through the PHASE pin.
See Figure 3, “FUNCTIONAL BLOCK DIAGRAM” on page 5 for details.
3
MODE
Mode selection pin. Connect to logic high or input voltage VIN for PWM mode. Connect to logic low or ground for PFM
mode. There is an internal 1MΩ pull-down resistor to prevent an undefined logic state in case the MODE pin is left
floating, however, it is not recommended to leave this pin floating.
4
PG
Power Good output is pulled to ground during the soft-start interval and also when the output voltage is below regulation
limits. There is an internal 5MΩ internal pull-up resistor on this pin.
5
COMP
COMP is the output of the error amplifier. When COMP is tied high to VIN, compensation is internal. When COMP is
connected with a series resistor and capacitor to GND, compensation is external. See “Loop Compensation Design” on
page 19 for more detail.
6
FB
Feedback pin for the regulator. FB is the negative input to the voltage loop error amplifier. The output voltage is set by
an external resistor divider connected to FB. In addition, the Power Good PWM regulator’s power-good and Undervoltage
protection circuits use FB to monitor the output voltage.
7
PGND
Power and analog ground connections. Connect directly to the board GROUND plane.
8
PHASE
Power stage switching node for output voltage regulation. Connect to the output inductor. This pin is discharged by an
100Ω resistor when the device is disabled. See Figure 3, “FUNCTIONAL BLOCK DIAGRAM” on page 5 for details.
9
THERMAL PAD Power ground. This thermal pad provides a return path for the power stage and switching currents, as well as a thermal
(T-PAD)
path for removing heat from the IC to the board. Place thermal vias to the PGND plane in this pad.
4
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January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Functional Block Diagram
COMP
MODE
27pF
SOFTSoft
START
*
SHUTDOWN
200kΩ
+
VREF
BANDGAP
VIN
OSCILLATOR
+
EN
+
EAMP
COMP
-
-
P
PWM/PFM
LOGIC
CONTROLLER
PROTECTION
SHUTDOWN
3pF
PHASE
N
HS DRIVER
+
PGND
FB
SLOPE
Slope
COMP
1.15*VREF
6kΩ
+
-
CSA
OV
+
+
OCP
-
0.85*VREF
+
UV
+
VIN
SKIP
5MΩ
PG
1ms
DELAY
-
NEG CURRENT
SENSING
ZERO-CROSS
SENSING
0.3V
SCP
+
100Ω
SHUTDOWN
* By default, when COMP is tied to VIN, the voltage loop is internally compensated with the 27pF and 200kΩ RC network.
Please see "COMP" pin in the “Pin Descriptions” table on page 4 for more details.
FIGURE 3. FUNCTIONAL BLOCK DIAGRAM
5
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Ordering Information
PART NUMBER
(Notes 1, 2, 3)
TAPE AND REEL
QUANTITY
PART
MARKING
TECHNICAL
SPECIFICATIONS
TEMP. RANGE
(°C)
PACKAGE
(Pb-Free)
PKG.
DWG. #
ISL8002IRZ-T
1000
002
2A, 1MHz
-40 to +85
8 Ld TDFN
L8.2x2C
ISL8002IRZ-T7A
250
002
2A, 1MHz
-40 to +85
8 Ld TDFN
L8.2x2C
ISL8002AIRZ-T
1000
02A
2A, 2MHz
-40 to +85
8 Ld TDFN
L8.2x2C
ISL8002AIRZ-T7A
250
02A
2A, 2MHz
-40 to +85
8 Ld TDFN
L8.2x2C
ISL80019IRZ-T
1000
019
1.5A, 1MHz
-40 to +85
8 Ld TDFN
L8.2x2C
ISL80019IRZ-T7A
250
019
1.5A, 1MHz
-40 to +85
8 Ld TDFN
L8.2x2C
ISL80019AIRZ-T
1000
19A
1.5A, 2MHz
-40 to +85
8 Ld TDFN
L8.2x2C
ISL80019AIRZ-T7A
250
19A
1.5A, 2MHz
-40 to +85
8 Ld TDFN
L8.2x2C
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 device information page for ISL8002, ISL8002A, ISL80019, ISL80019A. For more information on
MSL please see techbrief TB363.
6
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Absolute Maximum Ratings
Thermal Information
VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6V (DC) or 7V (20ms)
PHASE . . . . . . . . . . . . . . -1.5V (100ns)/-0.3V (DC) to 6V (DC) or 7V (20ms)
EN, COMP, PG, MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to VIN+0.3V
FB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 2.7V
Thermal Resistance (Typical, Notes 4, 5)
θJA (°C/W) θJC (°C/W)
2x2 TDFN Package . . . . . . . . . . . . . . . . . . .
71
7
Junction Temperature Range . . . . . . . . . . . . . . . . . . . . . . .-55°C to +125°C
Storage Temperature Range. . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
Pb-Free Reflow Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . see link below
http://www.intersil.com/pbfree/Pb-FreeReflow.asp
Recommended Operating Conditions
VIN Supply Voltage Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7V to 5.5V
Load Current Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0A to 2A
Ambient Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . -40°C to +85°C
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:
4. θJA 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 for details.
5. For θJC, the “case temp” location is the center of the exposed metal pad on the package underside.
Electrical Specifications
TA = -40°C to +85°C, VIN = 2.7V to 5.5V, unless otherwise noted. Typical values are at TA = +25°C. Boldface
limits apply over the operating temperature range, -40°C to +85°C.
PARAMETER
SYMBOL
TEST CONDITIONS
MIN
(Note 6)
TYP
MAX
(Note 6)
UNITS
2.5
2.7
V
INPUT SUPPLY
VIN Undervoltage Lockout Threshold
VUVLO
Rising, no load
Falling, no load
Quiescent Supply Current
IVIN
Shut Down Supply Current
ISD
2.2
2.4
V
MODE = PFM (GND), FSW = 2MHz, no load at
the output
35
60
µA
MODE = PWM (VIN), FSW = 1MHz, no load at
the output
7
15
mA
MODE = PWM (VIN), FSW = 2MHz, no load at
the output
10
22
mA
MODE = PFM (GND), VIN = 5.5V, EN = low
5
10
µA
0.600
0.605
V
OUTPUT REGULATION
Reference Voltage
VREF
VFB Bias Current
IVFB
Line Regulation
0.595
VFB = 0.75V
0.1
µA
VIN = VO + 0.5V to 5.5V (minimal 2.7V)
0.2
%/V
1
ms
Soft-Start Ramp Time Cycle
PROTECTIONS
Positive Peak Current Limit
IPLIMIT
2A application
1.5A application
Peak Skip Limit
ISKIP
3.5
4
A
2.1
2.5
2.9
A
VIN = 3.6, VOUT = 1.8V (See “Applications
Information” on page 18 for more detail)
Zero Cross Threshold
Negative Current Limit
3
INLIMIT
450
mA
-170
-70
30
mA
-2.3
-1.5
-1
A
Thermal Shutdown
Temperature rising
150
°C
Thermal Shutdown Hysteresis
Temperature falling
25
°C
7
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Electrical Specifications
TA = -40°C to +85°C, VIN = 2.7V to 5.5V, unless otherwise noted. Typical values are at TA = +25°C. Boldface
limits apply over the operating temperature range, -40°C to +85°C. (Continued)
PARAMETER
SYMBOL
TEST CONDITIONS
MIN
(Note 6)
TYP
MAX
(Note 6)
UNITS
COMPENSATION
Error Amplifier Trans-Conductance
Trans-Resistance
COMP tied VIN
40
µA/V
COMP with RC
120
µA/V
RT
0.24
0.3
0.40
Ω
LX
P-Channel MOSFET ON-Resistance
VIN = 5V, IO = 200mA
117
mΩ
N-Channel MOSFET ON-Resistance
VIN = 5V, IO = 200mA
86
mΩ
100
%
LX Maximum Duty Cycle
LX Minimum On-Time
MODE = PWM (High) 1MHz
60
80
ns
OSCILLATOR
Nominal Switching Frequency
FSW
ISL8002, ISL80019
850
1000
1150
kHz
ISL8002A, ISL80019A
1700
2000
2300
kHz
0.3
V
2
ms
PG
Output Low Voltage
1mA sinking current
Delay Time (Rising Edge)
0.5
PGOOD Delay Time (Falling Edge)
1
15
PG Pin Leakage Current
PG = VIN
OVP PG Rising Threshold
110
OVP PG Hysteresis
µs
0.01
0.1
µA
115
120
%
5
UVP PG Rising Threshold
80
UVP PG Hysteresis
85
%
90
5
%
%
EN AND MODE LOGIC
Logic Input Low
0.4
Logic Input High
1.4
Logic Input Leakage Current
IMODE
Pulled up to 5.5V
V
V
5.5
8
µA
NOTE:
6. Parameters with MIN and/or MAX limits are 100% tested at +25°C, unless otherwise specified. Temperature limits established by characterization
and are not production tested.
8
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
100
100
90
90
80
80
EFFICIENCY (%)
EFFICIENCY (%)
Typical Performance Curves
70
60
50
40
0.0
2.5VOUT
1.8VOUT
1.5VOUT
1.2VOUT
0.9VOUT
0.8VOUT
0.2
0.4
0.6
0.8
1.0
1.2
OUTPUT LOAD (A)
1.4
1.6
1.8
40
0.0
2.0
90
90
80
80
EFFICIENCY (%)
EFFICIENCY (%)
100
70
50
40
0.0
2.5VOUT
1.8VOUT
1.5VOUT
1.2VOUT
0.9VOUT
0.8VOUT
0.2
0.4
0.8
1.0
1.2
OUTPUT LOAD (A)
1.4
1.6
1.8
60
40
0.0
2.0
100
90
90
80
80
EFFICIENCY (%)
100
70
50
40
0.0
3.3VOUT
2.5VOUT
1.8VOUT
1.5VOUT
1.2VOUT
0.9VOUT
0.2
0.4
0.8
1.0
1.2
OUTPUT LOAD (A)
1.4
1.6
1.8
FIGURE 8. EFFICIENCY vs LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
9
0.8
1.0
1.2
OUTPUT LOAD (A)
1.4
1.6
1.8
2.0
2.5VOUT
1.8VOUT
1.5VOUT
1.2VOUT
0.9VOUT
0.8VOUT
0.2
0.4
0.6
0.8
1.0
1.2
OUTPUT LOAD (A)
1.4
1.6
1.8
2.0
70
3.3VOUT
2.5VOUT
1.8VOUT
1.5VOUT
1.2VOUT
0.9VOUT
60
50
0.6
0.6
FIGURE 7. EFFICIENCY vs LOAD
FSW = 1MHz, VIN = 3.3V, MODE = PWM, TA = +25°C
FIGURE 6. EFFICIENCY vs LOAD
FSW = 1MHz, VIN = 3.3V, MODE = PFM, TA = +25°C
60
0.4
70
50
0.6
0.2
FIGURE 5. EFFICIENCY vs LOAD
FSW = 2MHz, VIN = 3.3V, MODE = PWM, TA = +25°C
100
60
2.5VOUT
1.8VOUT
1.5VOUT
1.2VOUT
0.9VOUT
0.8VOUT
60
50
FIGURE 4. EFFICIENCY vs LOAD
FSW = 2MHz, VIN = 3.3V, MODE = PFM, TA = +25°C
EFFICIENCY (%)
70
2.0
40
0.0
0.2
0.4
0.6
0.8
1.0
1.2
OUTPUT LOAD (A)
1.4
1.6
1.8
2.0
FIGURE 9. EFFICIENCY vs LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
(Continued)
100
100
90
90
80
80
70
60
50
40
0.0
EFFICIENCY (%)
EFFICIENCY (%)
Typical Performance Curves
3.3VOUT
2.5VOUT
1.8VOUT
1.5VOUT
1.2VOUT
0.9VOUT
0.8VOUT
0.2
0.4
70
3.3VOUT
2.5VOUT
1.8VOUT
1.5VOUT
1.2VOUT
0.9VOUT
0.8VOUT
60
50
0.6
0.8
1.0
1.2
1.4
1.6
1.8
40
0.0
2.0
0.2
0.4
0.6
OUTPUT LOAD (A)
1.6
1.8
FIGURE 11. EFFICIENCY vs LOAD
FSW = 1MHz, VIN = 5V, MODE = PWM, TA = +25°C
0.925
1.230
5VIN PFM
5VIN PWM
3.3VIN PWM
3.3VIN PFM
0.915
0.910
0.905
0.900
0.895
0.0
1.220
1.215
1.210
1.205
0.2
0.4
0.6
0.8
1.0
1.2
OUTPUT LOAD (A)
1.4
1.6
1.8
1.200
0.0
2.0
FIGURE 12. VOUT REGULATION vs LOAD,
FSW = 2MHz, VOUT = 0.9V, TA = +25°C
0.6
0.8
1.0
1.2
OUTPUT LOAD (A)
1.4
1.6
1.8
2.0
5VIN PFM
5VIN PWM
3.3VIN PWM
3.3VIN PFM
1.805
OUTPUT VOLTAGE (V)
1.510
0.4
1.810
5VIN PFM
5VIN PWM
3.3VIN PWM
3.3VIN PFM
1.515
0.2
FIGURE 13. VOUT REGULATION vs LOAD,
FSW = 2MHz, VOUT = 1.2V, TA = +25°C
1.520
1.505
1.500
1.800
1.795
1.790
1.785
1.495
1.490
0.0
2.0
5VIN PFM
5VIN PWM
3.3VIN PWM
3.3VIN PFM
1.225
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
1.4
FIGURE 10. EFFICIENCY vs LOAD
FSW = 1MHz, VIN = 5V, MODE = PFM, TA = +25°C
0.920
OUTPUT VOLTAGE (V)
0.8
1.0
1.2
OUTPUT LOAD (A)
0.2
0.4
0.6
0.8
1.0
1.2
OUTPUT LOAD (A)
1.4
FIGURE 14. VOUT REGULATION vs LOAD,
FSW = 2MHz, VOUT = 1.5V, TA = +25°C
10
1.6
1.8
2.0
1.780
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
OUTPUT LOAD (A)
FIGURE 15. VOUT REGULATION vs LOAD,
FSW = 2MHz, VOUT = 1.8V, TA = +25°C
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Typical Performance Curves
(Continued)
3.335
2.505
OUTPUT VOLTAGE (V)
2.500
2.495
2.490
2.485
3.325
3.320
3.315
3.310
2.480
2.475
0.0
5VIN PFM MODE
5VIN PWM MODE
3.330
OUTPUT VOLTAGE (V)
5VIN PFM
5VIN PWM
3.3VIN PWM
3.3VIN PFM
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
OUTPUT LOAD (A)
FIGURE 16. VOUT REGULATION vs LOAD,
FSW = 2MHz, VOUT = 2.5V, TA = +25°C
3.305
0.0
0.2
0.4
0.6
0.8
1.0
1.2
OUTPUT LOAD (A)
1.4
1.6
1.8
2.0
FIGURE 17. VOUT REGULATION vs LOAD,
FSW = 2MHz, VOUT = 3.3V, TA = +25°C
LX 5V/DIV
LX 5V/DIV
VOUT 1V/DIV
VOUT 1V/DIV
VEN 1V/DIV
VEN 2V/DIV
PG 5V/DIV
PG 5V/DIV
1ms/DIV
1ms/DIV
FIGURE 18. START-UP AT NO LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
LX 5V/DIV
LX 5V/DIV
VOUT 1V/DIV
VOUT 1V/DIV
VEN 2V/DIV
VEN 2V/DIV
PG 5V/DIV
PG 5V/DIV
1ms/DIV
FIGURE 20. SHUTDOWN AT NO LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
11
FIGURE 19. START-UP AT NO LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
1ms/DIV
FIGURE 21. SHUTDOWN AT NO LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Typical Performance Curves
(Continued)
LX 5V/DIV
LX 5V/DIV
VOUT 1V/DIV
VOUT 1V/DIV
VEN 2V/DIV
PG 5V/DIV
VEN 2V/DIV
PG 5V/DIV
1ms/DIV
1ms/DIV
FIGURE 22. START-UP AT 2A LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
FIGURE 23. SHUTDOWN AT 2A LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
LX 5V/DIV
LX 5V/DIV
VOUT 1V/DIV
VOUT 1V/DIV
VEN 2V/DIV
PG 5V/DIV
VEN 2V/DIV
PG 5V/DIV
1ms/DIV
1ms/DIV
FIGURE 24. START-UP AT 2A LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
FIGURE 25. SHUTDOWN AT 2A LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
VEN 5V/DIV
VEN 5V/DIV
VOUT 1V/DIV
VOUT 1V/DIV
IL 1A/DIV
PG 5V/DIV
IL 1A/DIV
PG 5V/DIV
1ms/DIV
FIGURE 26. START-UP AT 1.5A LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
12
1ms/DIV
FIGURE 27. SHUTDOWN AT 1.5A LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Typical Performance Curves
(Continued)
VEN 5V/DIV
VEN 5V/DIV
VOUT 1V/DIV
VOUT 1V/DIV
IL 1A/DIV
PLACEHOLDER
PG 5V/DIV
IL 1A/DIV
PG 5V/DIV
1ms/DIV
1ms/DIV
FIGURE 28. START-UP AT 1.5A LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
FIGURE 29. SHUTDOWN AT 1.5A LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
VIN 5V/DIV
VIN 5V/DIV
VOUT 1V/DIV
VOUT 1V/DIV
IL 1A/DIV
IL 1A/DIV
PG 5V/DIV
PG 5V/DIV
500µs/DIV
500µs/DIV
FIGURE 30. START-UP VIN AT 2A LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
FIGURE 31. START-UP VIN AT 2A LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
VIN 5V/DIV
VIN 5V/DIV
IL 1A/DIV
IL 1A/DIV
VOUT 1V/DIV
VOUT 1V/DIV
PG 5V/DIV
1ms/DIV
FIGURE 32. SHUTDOWN VIN AT 2A LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
13
PG 5V/DIV
1ms/DIV
FIGURE 33. SHUTDOWN VIN AT 2A LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Typical Performance Curves
(Continued)
LX 5V/DIV
LX 5V/DIV
VOUT 1V/DIV
VOUT 1V/DIV
VIN 5V/DIV
VIN 5V/DIV
PG 5V/DIV
PG 5V/DIV
500µs/DIV
500µs/DIV
FIGURE 34. START-UP VIN AT NO LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
FIGURE 35. START-UP VIN AT NO LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
LX 5V/DIV
LX 5V/DIV
VOUT 1V/DIV
VOUT 1V/DIV
VIN 5V/DIV
VIN 5V/DIV
PG 5V/DIV
PG 5V/DIV
100ms/DIV
50ms/DIV
FIGURE 36. SHUTDOWN VIN AT NO LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
FIGURE 37. SHUTDOWN VIN AT NO LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
LX 1V/DIV
10ns/DIV
FIGURE 38. JITTER AT NO LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
14
LX 1V/DIV
10ns/DIV
FIGURE 39. JITTER AT FULL LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Typical Performance Curves
(Continued)
LX 5V/DIV
LX 5V/DIV
VOUT 20mV/DIV
VOUT 10mV/DIV
IL 0.5A/DIV
IL 0.5A/DIV
50ms/DIV
500ns/DIV
FIGURE 40. STEADY STATE AT NO LOAD
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
FIGURE 41. STEADY STATE AT NO LOAD
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
VOUT RIPPLE 50mV/DIV
VOUT RIPPLE 50mV/DIV
IL 1A/DIV
200µs/DIV
IL 1A/DIV
200µs/DIV
FIGURE 42. LOAD TRANSIENT
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
FIGURE 43. LOAD TRANSIENT
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
LX 5V/DIV
VOUT 0.5V/DIV
IL 1A/DIV
IL 2A/DIV
VOUT 1V/DIV
PG 5V/DIV
PG 5V/DIV
5µs/DIV
FIGURE 44. OUTPUT SHORT-CIRCUIT
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
15
500µs/DIV
FIGURE 45. OVERCURRENT PROTECTION
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Typical Performance Curves
(Continued)
LX 5V/DIV
LX 5V/DIV
675mA MODE TRANSITION, COMPLETELY
ENTER TO PWM AT 770mA
BACK TO PFM AT 121mA
VOUT RIPPLE 20mV/DIV
VOUT RIPPLE 20mV/DIV
IL 2A/DIV
IL 1A/DIV
2µs/DIV
2µs/DIV
FIGURE 46. PFM TO PWM TRANSITION
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
FIGURE 47. PWM TO PFM TRANSITION
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +25°C
LX 5V/DIV
IL 2A/DIV
VOUT 0.5V/DIV
VOUT 2V/DIV
PG 2V/DIV
PG 5V/DIV
10µs/DIV
FIGURE 48. OVERVOLTAGE PROTECTION
FSW = 2MHz, VIN = 5V, MODE = PFM, TA = +25°C
16
1ms/DIV
FIGURE 49. OVER-TEMPERATURE PROTECTION
FSW = 2MHz, VIN = 5V, MODE = PWM, TA = +163°C
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Theory of Operation
VEAMP
The device is a step-down switching regulator optimized for battery
powered applications. It operates at high switching frequency (1MHz
or 2MHz) which enables the use of smaller inductors resulting in
small form factor, while also providing excellent efficiency. Further,
at light loads while in PFM mode, the regulator reduces the
switching frequency, thereby minimizing the switching loss and
maximizing battery life. The quiescent current when the output is
not loaded is typically only 35µA. The supply current is typically only
5µA when the regulator is shut down.
VCSA
DUTY
CYCLE
IL
VOUT
PWM Control Scheme
Pulling the MODE pin HI (>2.5V) forces the converter into PWM
mode, regardless of output current. The device employs the
current-mode pulse-width modulation (PWM) control scheme for
fast transient response and pulse-by-pulse current limiting. Page 5
shows the “Functional Block Diagram”. The current loop consists of
the oscillator, the PWM comparator, current sensing circuit and the
slope compensation for the current loop stability. The slope
compensation is 900mV/Ts, which changes with frequency. The
gain for the current sensing circuit is typically 300mV/A. The control
reference for the current loops comes from the error amplifier's
(EAMP) output.
FIGURE 50. PWM OPERATION WAVEFORMS
The output voltage is regulated by controlling the VEAMP voltage
to the current loop. The bandgap circuit outputs a 0.6V reference
voltage to the voltage loop. The feedback signal comes from the
VFB pin. The soft-start block only affects the operation during the
start-up and will be discussed separately. The error amplifier is a
transconductance amplifier that converts the voltage error signal
to a current output. The voltage loop is internally compensated
with the 27pF and 200kΩ RC network. The maximum EAMP
voltage output is precisely clamped to 1.6V.
The PWM operation is initialized by the clock from the oscillator.
The P-Channel MOSFET is turned on at the beginning of a PWM
cycle and the current in the MOSFET starts to ramp up. When the
sum of the current amplifier CSA and the slope compensation
reaches the control reference of the current loop, the PWM
comparator COMP sends a signal to the PWM logic to turn off the
P-FET and turn on the N-Channel MOSFET. The N-FET stays on until
the end of the PWM cycle. Figure 50 shows the typical operating
waveforms during the PWM operation. The dotted lines illustrate
the sum of the slope compensation ramp and the current-sense
amplifier’s CSA output.
PWM
PFM Mode
Pulling the MODE pin LO (<0.4V) forces the converter into PFM
mode. The device enters a pulse-skipping mode at light load to
minimize the switching loss by reducing the switching frequency.
Figure 51 illustrates the skip-mode operation. A zero-cross
sensing circuit shown in Figure 51 monitors the N-FET current for
zero crossing. When 16 consecutive cycles of the inductor current
crossing zero are detected, the regulator enters the skip mode.
During the eight detecting cycles, the current in the inductor is
allowed to become negative. The counter is reset to zero when
the current in any cycle does not cross zero.
PFM
PWM
CLOCK
16 CYCLES
IL
PFM CURRENT LIMIT
LOAD CURRENT
0
NOMINAL +1.5%
VOUT
NOMINAL
NOMINAL -1.5%
FIGURE 51. SKIP MODE OPERATION WAVEFORMS
17
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Once the skip mode is entered, the pulse modulation starts being
controlled by the SKIP comparator shown in the “Functional
Block Diagram” on page 5. Each pulse cycle is still synchronized
by the PWM clock. The P-FET is turned on at the clock's rising
edge and turned off when the output is higher than 1.5% of the
nominal regulation or when its current reaches the peak Skip
current limit value. Then the inductor current is discharging to 0A
and stays at zero. The internal clock is disabled. The output
voltage reduces gradually due to the load current discharging the
output capacitor. When the output voltage drops to the nominal
voltage, the P-FET will be turned on again at the rising edge of
the internal clock as it repeats the previous operations.
The regulator resumes normal PWM mode operation when the
output voltage drops 1.5% below the nominal voltage.
Overcurrent Protection
The overcurrent protection is realized by monitoring the CSA
output with the OCP comparator, as shown in the “Functional
Block Diagram” on page 5. The current sensing circuit has a gain
of 300mV/A, from the P-FET current to the CSA output. When the
CSA output reaches a threshold, the OCP comparator is tripped to
turn off the P-FET immediately. The overcurrent function protects
the switching converter from a shorted output by monitoring the
current flowing through the upper MOSFET.
Upon detection of overcurrent condition, the upper MOSFET will
be immediately turned off and will not be turned on again until
the next switching cycle. If the overcurrent condition goes away,
the output will resume back into regulation point after the hiccup
mode expires.
Short-Circuit Protection
The short-circuit protection (SCP) comparator monitors the VFB
pin voltage for output short-circuit protection. When the VFB is
lower than 0.3V, the SCP comparator forces the PWM oscillator
frequency to drop to 1/3 of the normal operation value. This
comparator is effective during start-up or an output short-circuit
event.
Negative Current Protection
Similar to the overcurrent, the negative current protection is
realized by monitoring the current across the lowside N-FET, as
shown in the “Functional Block Diagram” on page 5. When the
valley point of the inductor current reaches -1.5A for 2 consecutive
cycles, both P-FET and N-FET shut off. The 100Ω in parallel to the
N-FET will activate discharging the output into regulation. The
control will begin to switch when output is within regulation. The
regulator will be in PFM for 20µs before switching to PWM if
necessary.
PG
PG is an output of a window comparator that continuously monitors
the buck regulator output voltage. PG is actively held low when EN is
low and during the buck regulator soft-start period. After 1ms delay
of the soft-start period, PG becomes high impedance as long as the
output voltage is within nominal regulation voltage set by VFB.
When VFB drops 15% below or raises 15% above the nominal
regulation voltage, the device pulls PG low. Any fault condition forces
PG low until the fault condition is cleared by attempts to soft-start.
There is an internal 5MΩ pull-up resistor to fit most applications. An
18
external resistor can be added from PG to VIN for more pull-up
strength.
UVLO
When the input voltage is below the undervoltage lock-out (UVLO)
threshold, the regulator is disabled.
Enable, Disable, and Soft Start-Up
After the VIN pin exceeds its rising POR trip point (nominal 2.7V),
the device begins operation. If the EN pin is held low externally,
nothing happens until this pin is released. Once the EN is
released and above the logic threshold, the internal default
soft-start time is 1ms.
Discharge Mode (Soft-Stop)
When a transition to shutdown mode occurs or the VIN UVLO is set,
the outputs discharge to GND through an internal 100Ω switch.
100% Duty Cycle (1MHz Version)
The device features 100% duty cycle operation to maximize the
battery life. When the battery voltage drops to a level that the
device can no longer maintain the regulation at the output, the
regulator completely turns on the P-FET. The maximum dropout
voltage under the 100% duty-cycle operation is the product of the
load current and the ON-resistance of the P-FET.
Thermal Shut-Down
The device has built-in thermal protection. When the internal
temperature reaches +150°C, the regulator is completely shut
down. As the temperature drops to +125°C, the device resumes
operation by stepping through the soft-start.
Applications Information
Output Inductor and Capacitor Selection
To consider steady state and transient operations,
ISL8002A/ISL80019A typically requires a 1.2µH and
ISL8002/ISL80019 typically requires a 2.2µH output inductor.
Higher or lower inductor value can be used to optimize the total
converter system performance. For example, for higher output
voltage 3.3V application, in order to decrease the inductor ripple
current and output voltage ripple, the output inductor value can
be increased. It is recommended to set the inductor ripple
current to be approximately 30% of the maximum output current
for optimized performance. The inductor ripple current can be
expressed as shown in Equation 2:
VO ⎞
⎛
V O • ⎜ 1 – --------⎟
V IN⎠
⎝
ΔI = --------------------------------------L • F SW
(EQ. 2)
The inductor’s saturation current rating needs to be at least
larger than the peak current.
The device uses internal compensation network and the output
capacitor value is dependent on the output voltage. The ceramic
capacitor is recommended to be X5R or X7R.
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Output Voltage Selection
If using electrolytic capacitors then:
The output voltage of the regulator can be programmed via an
external resistor divider that is used to scale the output voltage
relative to the internal reference voltage and feed it back to the
inverting input of the error amplifier. Refer to Figure 35.
V OUTripple = ΔI*ESR
VO
R 1 = R 2 ⎛ ----------- – 1⎞
⎝ VFB
⎠
(EQ. 3)
If the output voltage desired is 0.6V, then R2 is left unpopulated
and R1 is shorted. There is a leakage current from VIN to LX. It is
recommended to preload the output with 10µA minimum. For
better performance, add 22pF in parallel with R1. Check loop
analysis before use in application.
Input Capacitor Selection
The main functions for the input capacitor are to provide
decoupling of the parasitic inductance and to provide filtering
function to prevent the switching current flowing back to the
battery rail. At least two 22µF X5R or X7R ceramic capacitors are
a good starting point for the input capacitor selection.
Output Capacitor Selection
An output capacitor is required to filter the inductor current.
Output ripple voltage and transient response are 2 critical factors
when considering output capacitance choice. The current mode
control loop allows for the usage of low ESR ceramic capacitors
and thus smaller board layout. Electrolytic and polymer
capacitors may also be used.
The following equations allow calculation of the required
capacitance to meet a desired ripple voltage level. Additional
capacitance may be used.
For the ceramic capacitors (low ESR) =
ΔI
V OUTripple = --------------------------------------8∗ F SW∗ C OUT
(EQ. 4)
I OUT 2 * L
C OUT = -------------------------------------------------------------------------------------------V OUT 2 * ( V OUTMAX ⁄ V OUT ) 2 – 1 )
(EQ. 6)
where VOUTMAX/VOUT is the relative maximum overshoot
allowed during the removal of the load. For an overshoot of 5%,
the equation becomes as follows:
I OUT 2 * L
C OUT = ---------------------------------------------------V OUT 2 * ( 1.05 2 – 1 )
(EQ. 7)
Loop Compensation Design
When COMP is not connected to VDD, the COMP pin is active for
external loop compensation. The ISL8002, ISL8002A, ISL80019,
and ISL80019A use constant frequency peak current mode
control architecture to achieve 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 52 shows the small signal model of the synchronous buck
regulator.
^
i in
^
Vin
+
Additional consideration applies to ceramic capacitors. While
they offer excellent overall performance and reliability, the actual
in-circuit capacitance must be considered. Ceramic capacitors
are rated using large peak-to-peak voltage swings and with no DC
bias. In the DC/DC converter application, these conditions do not
reflect reality. As a result, the actual capacitance may be
considerably lower than the advertised value. Consult the
manufacturers data sheet to determine the actual in-application
capacitance. Most manufacturers publish capacitance vs DC bias
so that this effect can be easily accommodated. The effects of
AC voltage are not frequently published, but an assumption of
~20% further reduction will generally suffice. The result of these
considerations can easily result in an effective capacitance 50%
lower than the rated value. Nonetheless, they are a very good
choice in many applications due to their reliability and extremely
low ESR.
Regarding transient response needs, a good starting point is to
determine the allowable overshoot in VOUT if the load is suddenly
removed. In this case, energy stored in the inductor will be
transferred to COUT causing its voltage to rise. After calculating
capacitance required for both ripple and transient needs, choose
the larger of the calculated values. The following equation
determines the required output capacitor value in order to
achieve a desired overshoot relative to the regulated voltage.
ILd^
1:D
^
iL
LP
^
vo
RLP
Vin d^
+
GAIN (VLOOP (S(fi))
The output voltage programming resistor, R2, will depend on the
value chosen for the feedback resistor and the desired output
voltage of the regulator. The value for the feedback resistor is
typically between 10kΩ and 100kΩ, as shown in Equation 3.
(EQ. 5)
RT
Rc
Ro
Co
T i(S)
d^
K
Fm
+
Tv (S)
He(S)
v^comp
-Av(S)
FIGURE 52. SMALL SIGNAL MODEL OF SYNCHRONOUS BUCK
REGULATOR
where ΔI is the inductor’s peak to peak ripple current, FSW is the
switching frequency and COUT is the output capacitor.
19
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Put compensator zero 2 to 5 times fc:
VOUT
R1
1
C 4 = ---------------πf c R 1
C4
VFB
VREF
R2
-
(EQ. 12)
Example: VIN = 5V, VOUT = 1.8V, IO = 2A, FSW = 1MHz,
R1 = 200kΩ, R2 = 100kΩ, COUT = 2x22µF/3mΩ, L = 2.2µH,
fc = 100kHz, then compensator resistance R14:
VCOMP
GM
+
3
(EQ. 13)
R 14 = 26 ×10 ⋅ 100kHz ⋅ 1.8V ⋅ 44μF = 205kΩ
R14
C8
Using the closest standard value for R14 value is fine (200kΩ).
C7
1.8V ⋅ 44 μF
C 7 = -------------------------------- = 198pF
2A ⋅ 200kΩ
(EQ. 14)
3mΩ ⋅ 44μF
1
C 8 = max (---------------------------------,------------------------------------------------) = (1pF,2.3pF)
200kΩ
π ⋅ 1MHz ( 200kΩ )
(EQ. 15)
FIGURE 53. TYPE II COMPENSATOR
Figure 53 shows the type II compensator and its transfer function
is expressed as Equation 8:
S ⎞⎛
S
⎛ 1 + ------------ 1 + -------------⎞
⎝
GM ⋅ R 2
ω cz1⎠ ⎝
ω cz2⎠
v̂ comp
A v ( S ) = ----------------- = -------------------------------------------------------- --------------------------------------------------------------( C7 + C8 ) ⋅ ( R1 + R2 ) ⎛
S
S
v̂ FB
S 1 + -------------⎞ ⎛ 1 + -------------⎞
⎝
⎠⎝
⎠
ω
ω
cp1
cp2
(EQ. 8)
where,
C7 + C8
R1 + R2
1
1
ω cz1 = ------------------ , ω cz2 = ---------------, ω cp1 = --------------------------, ω cp2 = ---------------------R 14 C 7 C 8
R 14 C 7
C4 R1 R2
R1 C4
The closest standard values for C7 and C8 are also fine. There is
approximately 3pF parasitic capacitance from VCOMP to GND;
Therefore, C8 is optional. Use C7 = 220pF and C8 = OPEN.
1
C 4 = ------------------------------------------------ = 16pF
π100kHz ⋅ 200kΩ
(EQ. 16)
Use C4 = 15pF. Note that C4 may increase the loop bandwidth
from previously estimated value. Figure 54 shows the simulated
voltage loop gain. It is shown that it has 114kHz loop bandwidth
with 52° phase margin and 10dB gain margin. It may be more
desirable to achieve more phase margin. This can be
accomplished by lowering R14 by 20% to 50%.
60
COMPENSATOR DESIGN GOAL
45
• High DC gain
• Choose Loop bandwidth fc less than 100kHz
30
GAIN (dB)
• Gain margin: >10dB
• Phase margin: >50°
The compensator design procedure is as follows:
The loop gain at crossover frequency of fc has unity gain.
Therefore, the compensator resistance R14 is determined by
Equation 9.
2πf c V o C o R t
3
- = 26 ×10 ⋅ f c V o C o
R 14 = --------------------------------GM ⋅ V FB
-30
100
(EQ. 9)
10k
100k
1M
100k
1M
180
150
(EQ. 11)
An optional zero can boost the phase margin. ωCZ2 is a zero due
to R1 and C4.
120
PHASE (°)
(EQ. 10)
Rc Co
1
C 8 = max (--------------,-------------------)
R 14 πf s R 14
1k
FREQUENCY (Hz)
Compensator capacitors C7 and C8 are then given by
Equations 10 and 11.
Vo Co
-------------I o R 14
0
-15
Where GM is the trans-conductance of the voltage error
amplifier.
Ro Co
C 7 = --------------- =
R 14
15
90
60
30
0
100
1k
10k
FREQUENCY (Hz)
FIGURE 54. SIMULATED LOOP GAIN
20
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Layout Considerations
The PCB layout is a very important converter design step to make
sure the designed converter works well. The power loop is
composed of the output inductor L’s, the output capacitor COUT,
the PHASE’s pins, and the PGND pin. It is necessary to make the
power loop as small as possible and the connecting traces
among them should be direct, short and wide. The switching
node of the converter, the PHASE pins, and the traces connected
to the node are very noisy, so keep the voltage feedback trace
away from these noisy traces. The input capacitor should be
placed as closely as possible to the VIN pin and the ground of the
input and output capacitors should be connected as closely as
possible. The heat of the IC is mainly dissipated through the
thermal pad. Maximizing the copper area connected to the
thermal pad is preferable. In addition, a solid ground plane is
helpful for better EMI performance. It is recommended to add at
least 4 vias ground connection within the pad for the best
thermal relief.
Revision History
The revision history provided is for informational purposes only and is believed to be accurate, but not warranted. Please go to web to make sure you
have the latest revision.
DATE
January 7, 2013
REVISION
CHANGE
FN7888.1 Initial release.
About Intersil
Intersil Corporation is a leader in the design and manufacture of high-performance analog, mixed-signal and power management
semiconductors. The company's products address some of the fastest growing markets within the industrial and infrastructure,
personal computing and high-end consumer markets. For more information about Intersil or to find out how to become a member of
our winning team, visit our website and career page at www.intersil.com.
For a complete listing of Applications, Related Documentation and Related Parts, please see the respective product information page.
Also, please check the product information page to ensure that you have the most updated datasheet: ISL8002, ISL8002A, ISL80019,
ISL80019A
To report errors or suggestions for this datasheet, please go to: www.intersil.com/askourstaff
Reliability reports are available from our website at: http://rel.intersil.com/reports/search.php
For additional products, see www.intersil.com/product_tree
Intersil products are manufactured, assembled and tested utilizing ISO9000 quality systems as noted
in the quality certifications found at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time
without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be
accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third
parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com
21
FN7888.1
January 7, 2013
ISL8002, ISL8002A, ISL80019, ISL80019A
Package Outline Drawing
L8.2x2C
8 LEAD THIN DUAL FLAT NO-LEAD PLASTIC PACKAGE (TDFN) WITH E-PAD
Rev 0, 07/08
2.00
6
PIN #1 INDEX AREA
A
B
6
PIN 1
INDEX AREA
8
1
0.50
2.00
1.45±0.050
Exp.DAP
(4X)
0.15
0.10 M C A B
0.25
( 8x0.30 )
TOP VIEW
0.80±0.050
Exp.DAP
BOTTOM VIEW
( 8x0.20 )
Package Outline
( 8x0.30 )
SEE DETAIL "X"
( 6x0.50 )
1.45
2.00
0.10 C
0 . 75 ( 0 . 80 max)
C
BASE PLANE
SEATING PLANE
0.08 C
SIDE VIEW
( 8x0.25 )
0.80
2.00
TYPICAL RECOMMENDED LAND PATTERN
C
0 . 2 REF
0 . 00 MIN.
0 . 05 MAX.
DETAIL "X"
NOTES:
1. Dimensions are in millimeters.
Dimensions in ( ) for Reference Only.
2. Dimensioning and tolerancing conform to AMSE Y14.5m-1994.
3. Unless otherwise specified, tolerance : Decimal ± 0.05
4. Dimension b 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.
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.
22
FN7888.1
January 7, 2013