DATASHEET

2A Low Quiescent Current 1MHz High Efficiency
Synchronous Buck Regulator
ISL8012
Features
The ISL8012 is a high efficiency, monolithic, synchronous
step-down DC/DC converter that can deliver up to 2A continuous
output current from a 2.7V to 5.5V input supply. It uses a current
control architecture to deliver very low duty cycle operation at
high frequency with fast transient response and excellent loop
stability.
• High Efficiency Synchronous Buck Regulator with up to 95%
Efficiency
The ISL8012 integrates a pair of low ON-resistance P-Channel
and N-Channel internal MOSFETs to maximize efficiency and
minimize external component count. The 100% duty-cycle
operation allows less than 240mV dropout voltage at 2A output
current. High 1MHz pulse width modulation (PWM) switching
frequency allows the use of small external components.
• 2A Guaranteed Output Current
The ISL8012 can be configured for discontinuous or forced
continuous operation at light load. Forced continuous operation
reduces noise and RF interference while discontinuous mode
provides high efficiency by reducing switching losses at light
loads.
• Selectable Forced PWM Mode and PFM Mode
Fault protection is provided by internal current limiting during
short circuit and overcurrent conditions, an output overvoltage
comparator and over-temperature monitor circuit. A power-good
output voltage monitor indicates when the output is in regulation.
• Peak Current Limiting and Hiccup Mode Short Circuit
Protection
The ISL8012 offers a 1ms Power-good (PG) timer at power-up.
When shutdown, ISL8012 discharges the output capacitor. Other
features include internal soft-start, internal compensation,
overcurrent protection, and thermal shutdown.
The ISL8012 is offered in a space saving 3mmx3mm 10 Ld DFN
package lead free package with exposed pad lead frames for low
thermal. The complete converter occupies less than 0.35in2
area.
• Power-Good (PG) Output with a 1ms Delay
• 2.7V to 5.5V Supply Voltage
• 3% Output Accuracy Over-Temperature/Load/Line
• Start-up with Pre-Biased Output
• Internal Soft-Start - 1ms
• Soft-Stop Output Discharge During Disabled
• 40µA Quiescent Supply Current in PFM Mode
• Less than 1µA Logic Controlled Shutdown Current
• 100% Maximum Duty Cycle
• Internal Current Mode Compensation
• Over-Temperature Protection
• Small 10 Ld 3mmx3mm DFN
• Pb-Free (RoHS Compliant)
Applications
• DC/DC POL Modules
• µC/µP, FPGA and DSP Power
• Plug-in DC/DC Modules for Routers and Switchers
• Portable Instruments
• Test and Measurement Systems
• Li-ion Battery Powered Devices
• Small Form Factor (SFP) Modules
• Bar Code Readers
Related Literature
• See AN1360 for “ISL8012EVAL1Z: 2A Synchronous Buck
Regulator with Integrated MOSFETs”
FN6616.2
December 1, 2011
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Copyright Intersil Americas Inc. 2008, 2010, 2011. 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.
ISL8012
Pin Configuration
ISL8012
(10 LD DFN)
TOP VIEW
VIN 1
10 LX
VCC 2
EN 3
9 PGND
PD
PG 4
MODE 5
8 SGND
7 VFB
6 RSI
Pin Descriptions
SYMBOL
PIN NUMBER
DESCRIPTION
VIN
1
Input supply voltage. Connect a 10µF ceramic capacitor to power ground.
VCC
2
Input supply for the logic. Connect to VIN.
EN
3
Regulator enable pin. Enable the output when driven to high. Shutdown the chip and discharge output capacitor
when driven to low. Do not leave this pin floating.
PG
4
1ms timer output. At power-up or EN HI, this output is a 1ms delayed Power-Good signal for the output voltage. This
output can be reset by a low RSI signal. 1ms starts when RSI goes to high.
MODE
5
Mode Selection pin. Connect to logic high or input voltage VIN for PFM mode; connect to logic low or ground for
forced PWM mode. Do not leave this pin floating.
RSI
6
This input resets the 1ms timer. When the output voltage is within the PGOOD window, an internal timer is started and
generates a PG signal 1ms later when RSI is low. A high RSI resets PG and RSI high to low transition restarts the
internal counter if the output voltage is within the window, otherwise the counter is reset by the output voltage
condition.
VFB
7
Buck regulator output feedback. Connect to the output through a resistor divider for adjustable output voltage
(ISL8012-ADJ). For preset output voltage, connect this pin to the output.
SGND
8
System ground for the control logic. All voltage levels are measured with respect to this pin.
PGND
9
Ground connect for the IC and thermal relief for the package. The exposed pad must be connected to PGND and
soldered to the PCB.
LX
10
Switching node connection. Connect to one terminal of inductor.
Exposed Pad
PD
The exposed pad must be connected to the PGND and SGND pin for proper electrical performance. The exposed pad
must also be connected to as much as possible for optimal thermal performance.
2
December 1, 2011
FN6616.2
ISL8012
Typical Application
OUTPUT
L
INPUT 2.7V TO 5.5V
1.8V/2A
LX
VIN
C2
2x10µF
C1
2x10µF
R2
124k
PGND
C3*
220pF
ISL8012
SGND
EN
R3
100k
R1
100k
PG
VFB
MODE
RSI
*C3 is optional
FIGURE 1. TYPICAL APPLICATION DIAGRAM
Block Diagram
MODE
390k
SHUTDOWN
0.8V
BANDGAP
VIN
OSCILLATOR
+
EN
SHUTDOWN
27pF
SOFT-START
+
COMP
EAMP
PWM/PFM
LOGIC
CONTROLLER
PROTECTION
DRIVER
LX
+
GND
VFB
SLOPE
COMP
+
CSA
0.864V
+
+
OCP
1V
+
0.736V
+
SKIP
PG
1ms
DELAY
0.25V
ZERO-CROSS
SENSING
RSI
SCP
0.2V
+
FIGURE 2. FUNCTIONAL BLOCK DIAGRAM
3
December 1, 2011
FN6616.2
ISL8012
Ordering Information
PART NUMBER
(Notes 1, 2, 3)
ISL8012IRZ
PART
MARKING
012Z
TEMP. RANGE
(°C)
-40 to +85
PACKAGE
(Pb-Free)
10 Ld 3x3 DFN
PKG.
DWG. #
L10.3x3C
NOTES:
1. Add “-T*” or suffix for tape and reel. Please refer to TB347 for details on reel specifications.
2. These Intersil Pb-free plastic packaged products employ special Pb-free material sets, molding compounds/die attach materials, and 100% matte
tin plate plus anneal (e3 termination finish, which is RoHS compliant and compatible with both SnPb and Pb-free soldering operations). Intersil
Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020.
3. For Moisture Sensitivity Level (MSL), please see device information page for ISL8012. For more information on MSL please see techbrief TB363.
4
December 1, 2011
FN6616.2
ISL8012
Absolute Maximum Ratings (Reference to GND)
Thermal Information
VIN, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6V
EN, RSI, PG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to VIN+0.3V
LX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -1.5V (100ns)/-0.3V (DC) to 6.5V
VFB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 2.7V
Thermal Resistance (Typical)
JA (°C/W) JC (°C/W)
10 Ld 3x3 DFN (Notes 4, 5). . . . . . . . . . .
49
5.5
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
ESD Rating
Human Body Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5kV
Machine Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300V
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. 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.
5. For JC, the “case temp” location is the center of the exposed metal pad on the package underside.
Electrical Specifications
Unless otherwise noted, all parameter limits are established over the recommended operating conditions and
the typical specifications are measured at the following conditions: TA = -40°C to +85°C, VIN = 3.6V, EN = VCC, 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 7)
TYP
MAX
(Note 7) UNITS
INPUT SUPPLY
VIN Undervoltage Lockout Threshold
VUVLO
Rising
Falling
Quiescent Supply Current
IVIN
Shut Down Supply Current
2.5
2.2
2.7
2.4
V
V
MODE = VIN, no load at the output
40
MODE = VIN, no load at the output and no switches
switching; design info only
15
MODE = SGND, no load at the output
6
8
mA
0.1
2
µA
0.8
0.816
V
ISD
VIN = 5.5V, EN = low
VFB Regulation Voltage
VVFB
TA = 0°C to +85°C
VFB Bias Current
IVFB
VFB = 0.75V
60
µA
µA
OUTPUT REGULATION
0.784
0.1
-3
µA
Output Voltage Accuracy
VIN = VO + 0.5V to 5.5V, IO = 0A to 2A (Note 6)
3
%
Line Regulation
VIN = VO + 0.5V to 5.5V (minimal 2.7V), IOUT = 400mA
0.2
%/V
Adjustable version, design info only
20
µA/V
COMPENSATION
Error Amplifier Trans-Conductance
LX
P-Channel MOSFET ON-Resistance
N-Channel MOSFET ON-Resistance
P-Channel MOSFET Peak Current Limit
VIN = 5.5V, IO = 200mA
0.12
0.22

VIN = 2.7V, IO = 200mA
0.21
0.27

VIN = 5.5V, IO = 200mA
0.11
0.22

VIN = 2.7V, IO = 200mA
0.13
0.27

3.00
3.50
A
2.65
IPK
LX Maximum Duty Cycle

100
PWM Switching Frequency
fS
5
TA = 0°C to +85°C
0.840
1
1.16
MHz
December 1, 2011
FN6616.2
ISL8012
Electrical Specifications
Unless otherwise noted, all parameter limits are established over the recommended operating conditions and
the typical specifications are measured at the following conditions: TA = -40°C to +85°C, VIN = 3.6V, EN = VCC, 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 7)
TYP
LX Minimum On-Time
MODE = low (forced PWM mode)
80
Soft-Start-Up Time
VIN = 3.6V
1.1
MAX
(Note 7) UNITS
100
ns
ms
PG
Output Low Voltage
Sinking 1mA, VFB = 0.7V
0.3
Delay Time
1
PG Pin Leakage Current
PG = VIN = 3.6V
Minimum Supply Voltage for Valid PG Signal
0.01
V
ms
0.1
1.2
µA
V
Internal PGOOD Low Rising Threshold
Percentage of nominal regulation voltage
89
92
95
%
Internal PGOOD Low Falling Threshold
Percentage of nominal regulation voltage
85
88
91
%
Internal PGOOD High Rising Threshold
Percentage of nominal regulation voltage
107
110
113
%
Internal PGOOD High Falling Threshold
Percentage of nominal regulation voltage
104
107
110
Internal PGOOD Delay Time
30
%
µs
EN, MODE, RSI
Logic Input Low
0.4
Logic Input High
1.4
Logic Input Leakage Current
Pulled up to 5.5V
V
V
0.1
1
µA
NOTES:
6. Limits established by characterization and are not production tested.
7. 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.
6
December 1, 2011
FN6616.2
ISL8012
Typical Operating Performance
100
100
90
90
80
80
1.5VOUT
70
EFFICIENCY (%)
EFFICIENCY (%)
(Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 2.5V to 5.5V,
EN = VIN, MODE = 0V, L = 2.2µH, C1 = 2x10µF, C2 = 2x10µF, IOUT = 0A to 2A).
1.2VOUT
60
50
40
30
20
0.00
2.5VOUT
0.50
1.5VOUT
60
50
40
0.75
1.00
1.25
1.50
1.75
20
0.1
2.00
0.2
0.3
100
100
90
90
80
80
70
1.2VOUT
1.8VOUT
2.5VOUT
60
50
40
30
3.3VOUT
20
0.00
0.25
0.50
70
1.5VOUT
60
0.7
0.8
1.8VOUT
2.5VOUT
3.3VOUT
1.2VOUT
40
30
0.75
1.00
1.25
1.50
1.75
20
0.1
2.00
0.2
0.3
0.4
0.5
0.6
OUTPUT LOAD (A)
0.7
0.8
FIGURE 6. EFFICIENCY vs LOAD (1MHz 5VIN PFM)
FIGURE 5. EFFICIENCY vs LOAD (1MHz 5VIN PWM)
1.000
160
0.875
POWER DISSIPATION (mW)
3.3VIN PWM
0.750
0.625
0.500
0.375
5VIN PFM
5VIN PWM
3.3VIN PFM
0.125
0
0.00
0.6
50
OUTPUT LOAD (A)
0.250
0.5
FIGURE 4. EFFICIENCY vs LOAD (1MHz 3.3VIN PFM)
EFFICIENCY (%)
EFFICIENCY (%)
FIGURE 3. EFFICIENCY vs LOAD (1MHz 3.3VIN PWM)
POWER DISSIPATION (W)
0.4
OUTPUT LOAD (A)
OUTPUT LOAD (A)
1.5VOUT
2.5VOUT
1.8VOUT
1.2VOUT
30
1.8VOUT
0.25
70
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
OUTPUT LOAD (A)
FIGURE 7. POWER DISSIPATION vs LOAD (1MHz, VOUT = 1.8V)
7
140
120
100
80
PWM MODE
60
40
20
0
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
VIN (V)
FIGURE 8. POWER DISSIPATION WITH NO LOAD vs VIN (PWM
VOUT = 1.8V)
December 1, 2011
FN6616.2
ISL8012
Typical Operating Performance
0.50
1.24
0.45
1.23
OUTPUT VOLTAGE (V)
POWER DISSIPATION (mW)
(Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 2.5V to 5.5V,
EN = VIN, MODE = 0V, L = 2.2µH, C1 = 2x10µF, C2 = 2x10µF, IOUT = 0A to 2A). (Continued)
0.40
0.35
0.30
0.25
PFM
0.20
0.15
0.10
2.0
2.5
3.0
3.5
4.0
VIN (V)
4.5
5.0
5.5
1.19
1.18
OUTPUT VOLTAGE (V)
1.53
3.3VIN PWM
5VIN PWM
1.51
1.50
1.47
0.00
0.25
5VIN PFM
0.50
0.75
0.25
0.50
1.00
1.25
1.50
1.75
1.75
2.00
3.3VIN PWM
1.79
1.78 3.3VIN PFM
1.77
5VIN PFM
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
OUTPUT LOAD (A)
FIGURE 12. VOUT REGULATION vs LOAD (1MHz, VOUT = 1.8V)
3.36
2.57
3.35
5VIN PWM
2.55
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
1.50
5VIN PWM
1.80
1.75
0.00
2.00
2.59
2.53
2.51
2.49
2.43
0.00
1.25
1.76
FIGURE 11. VOUT REGULATION vs LOAD (1MHz, VOUT = 1.5V)
2.45
1.00
1.81
OUTPUT LOAD (A)
2.47
0.75
FIGURE 10. VOUT REGULATION vs LOAD (1MHz, VOUT = 1.2V)
1.82
3.3VIN PFM
5VIN PFM
OUTPUT LOAD (A)
1.83
1.48
3.3VIN PFM
1.17
1.54
1.49
3.3VIN PWM
1.20
1.55
1.52
5VIN PWM
1.21
1.16
0.00
6.0
FIGURE 9. POWER DISSIPATION WITH NO LOAD vs VIN
(PFM VOUT = 1.8V)
OUTPUT VOLTAGE (V)
1.22
3.3VIN PWM
5VIN PFM
3.3VIN PFM
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
FIGURE 13. VOUT REGULATION vs LOAD (1MHz, VOUT = 2.5V)
8
4.5VIN PWM
3.34
5VIN PWM
3.33
3.32
3.31
3.30
3.29
OUTPUT LOAD (A)
5VIN PFM
3.28
0.00
4.5VIN PFM
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
OUTPUT LOAD (A)
FIGURE 14. VOUT REGULATION vs LOAD (1MHz, VOUT = 3.3V)
December 1, 2011
FN6616.2
ISL8012
Typical Operating Performance
(Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 2.5V to 5.5V,
EN = VIN, MODE = 0V, L = 2.2µH, C1 = 2x10µF, C2 = 2x10µF, IOUT = 0A to 2A). (Continued)
LX 2V/DIV
LX 2V/DIV
VOUT RIPPLE
20mV/DIV
VOUT RIPPLE
20mV/DIV
IL 0.5A/DIV
IL 0.5A/DIV
FIGURE 15. STEADY STATE OPERATION AT NO LOAD (PWM),
(1µs/DIV)
FIGURE 16. STEADY STATE OPERATION AT NO LOAD (PFM),
(1µs/DIV)
LX 2V/DIV
LX 2V/DIV
VOUT RIPPLE
50mV/DIV
IL 0.5A/DIV
VOUT RIPPLE
20mV/DIV
FIGURE 17. STEADY STATE OPERATION WITH FULL LOAD,
(5µs/DIV)
IL 0.5A/DIV
FIGURE 18. MODE TRANSITION CCM TO DCM, (5µs/DIV)
VOUT RIPPLE
50mV/DIV
LX 2V/DIV
VOUT RIPPLE
50mV/DIV
IL 1A/DIV
IL 0.5A/DIV
FIGURE 19. MODE TRANSITION DCM TO CCM, (50µs/DIV)
9
FIGURE 20. LOAD TRANSIENT (PWM), (50µs/DIV)
December 1, 2011
FN6616.2
ISL8012
Typical Operating Performance
(Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 2.5V to 5.5V,
EN = VIN, MODE = 0V, L = 2.2µH, C1 = 2x10µF, C2 = 2x10µF, IOUT = 0A to 2A). (Continued)
LX 2V/DIV
EN 5V/DIV
VOUT
0.5V/DIV
VOUT RIPPLE
50mV/DIV
IL 0.5A/DIV
IL 1A/DIV
PG 5V/DIV
FIGURE 21. LOAD TRANSIENT (PFM), (500µs/DIV)
FIGURE 22. SOFT-START WITH NO LOAD (PWM), (500µs/DIV)
EN 2V/DIV
EN 2V/DIV
VOUT
0.5V/DIV
VOUT
0.5V/DIV
IL 0.5A/DIV
IL 0.5A/DIV
PG 5V/DIV
PG 5V/DIV
FIGURE 23. SOFT-START AT NO LOAD (PFM), (500µs/DIV)
FIGURE 24. SOFT-START WITH PRE-BIASED 1V, (500µs/DIV)
EN 2V/DIV
EN 5V/DIV
VOUT
0.5V/DIV
VOUT
0.5V/DIV
IL 1A/DIV
IL 1A/DIV
PG 5V/DIV
PG 5V/DIV
FIGURE 25. SOFT-START AT FULL LOAD, (2ms/DIV)
10
FIGURE 26. SOFT-DISCHARGE SHUTDOWN, (2ms/DIV)
December 1, 2011
FN6616.2
ISL8012
Typical Operating Performance
(Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 2.5V to 5.5V,
EN = VIN, MODE = 0V, L = 2.2µH, C1 = 2x10µF, C2 = 2x10µF, IOUT = 0A to 2A). (Continued)
RSI 2V/DIV
RSI 2V/DIV
VOUT RIPPLE
20mV/DIV
VOUT RIPPLE
20mV/DIV
PG 2V/DIV
PG 2V/DIV
FIGURE 27. RSI RESET, (200µs/DIV)
FIGURE 28. RSI RESET (ZOOM OUT), (200µs/DIV)
VOUT
1V/DIV
LX 2V/DIV
PHASE 2V/DIV
IL 2A/DIV
IL 2A/DIV
VOUT
0.5V/DIV
PG 5V/DIV
PG 5V/DIV
FIGURE 29. OUTPUT SHORT CIRCUIT, (500µs/DIV)
FIGURE 30. OUTPUT SHORT CIRCUIT RECOVERY, (500µs/DIV)
OUTPUT CURRENT LIMIT (A)
3.2
5.5VIN
3.1
3.0
2.9
2.8
2.7
3.3VIN
2.6
2.5
2.4
-50
-25
0
25
50
75
100
TEMPERATURE (°C)
FIGURE 31. OUTPUT CURRENT LIMIT vs TEMPERATURE
11
December 1, 2011
FN6616.2
ISL8012
Theory of Operation
The ISL8012 is a step-down switching regulator optimized for
battery-powered handheld applications. The regulator operates at
1MHz fixed switching frequency under heavy load conditions to
allow smaller external inductors and capacitors to be used for
minimal printed-circuit board (PCB) area. At light load, the regulator
reduces the switching frequency (unless forced to the fixed
frequency) to minimize the switching loss and to maximize the
battery life. The quiescent current when the output is not loaded is
typically only 40µA. The supply current is typically only 0.1µA when
the regulator is shut down.
VEAMP
VCSA
DUTY
CYCLE
IL
VOUT
PWM Control Scheme
Pulling the MODE pin LOW (<0.4V) forces the converter into PWM
mode, regardless of output current. The ISL8012 employs the
current-mode pulse-width modulation (PWM) control scheme for
fast transient response and pulse-by-pulse current limiting. Figure 2
shows the 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 gain for the current
sensing circuit is typically 285mV/A. The control reference for the
current loops comes from the error amplifier's (EAMP) output.
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 (675mV/µs)
reaches the control reference of the current loop, the PWM
comparator COMP sends a signal to the PWM logic to turn off the
P-MOSFET and turn on the N-Channel MOSFET. The N-MOSFET stays
on until the end of the PWM cycle. Figure 32 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.
The output voltage is regulated by controlling the VEAMP voltage
to the current loop. The bandgap circuit outputs a 0.8V 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 390k RC network. The maximum EAMP
voltage output is precisely clamped to 1.47V.
FIGURE 32. PWM OPERATION WAVEFORMS
SKIP Mode
Pulling the MODE pin HIGH (>1.4V) forces the converter into PFM
mode. The ISL8012 enters a pulse-skipping mode at light load to
minimize the switching loss by reducing the switching frequency.
Figure 33 illustrates the skip-mode operation. A zero-cross
sensing circuit shown in Figure 2 monitors the N-MOSFET current
for zero crossing. When 8 consecutive cycles of the inductor
current crossing zero are detected, the regulator enters the skip
mode. During the 8 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.
Once the skip mode is entered, the pulse modulation starts being
controlled by the SKIP comparator shown in Figure 2. Each pulse
cycle is still synchronized by the PWM clock. The P-MOSFET 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 zero Ampere 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-MOSFET 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.
CLOCK
8 CYCLES
SKIP CURRENT LIMIT
LOAD CURRENT
IL
0
NOMINAL +1.5%
VOUT
NOMINAL
FIGURE 33. SKIP MODE OPERATION WAVEFORMS
12
December 1, 2011
FN6616.2
ISL8012
Mode Control
Soft Start-Up
The ISL8012 has a MODE pin that controls the operation mode.
When the MODE pin is driven to low or shorted to ground, the
regulator operates in a forced PWM mode. The forced PWM
mode remains the fixed PWM frequency at light load instead of
entering the skip mode.
The soft-start-up reduces the in-rush current during the start-up.
The soft-start block outputs a ramp reference to the input of the
error amplifier. This voltage ramp limits the inductor current as
well as the output voltage speed so that the output voltage rises
in a controlled fashion. When VFB is less than 0.2V at the
beginning of the soft-start, the switching frequency is reduced to
1/3 of the nominal value so that the output can start up
smoothly at light load condition. During soft-start, the IC operates
in the SKIP mode to support pre-biased output condition.
Overcurrent Protection
The overcurrent protection is realized by monitoring the CSA
output with the OCP comparator, as shown in Figure 2. The current
sensing circuit has a gain of 285mV/A, from the P-MOSFET current
to the CSA output. When the CSA output reaches 1V, which is
equivalent to 2.9A for the switch current (0.15V offset), the OCP
comparator is tripped to turn off the P-MOSFET 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.
Short-Circuit Protection
Enable
The enable (EN) input allows the user to control the turning on or
off the regulator for purposes such as power-up sequencing.
When the regulator is enabled, there is typically a 600µs delay
for waking up the bandgap reference and then the soft-start-up
begins.
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 100
switch.
The short-circuit protection SCP comparator monitors the VFB pin
voltage for output short-circuit protection. When the VFB is lower
than 0.2V, the SCP comparator forces the PWM oscillator
frequency to drop to minimum value to reduce the power
dissipation. This comparator is effective during start-up or an
output short-circuit event.
Power MOSFETs
RSI/PG Function
The ISL8012 features 100% duty cycle operation to maximize
the battery life. When the battery voltage drops to a level that the
ISL8012 can no longer maintain the regulation at the output, the
regulator completely turns on the P-MOSFET. The maximum
dropout voltage under the 100% duty-cycle operation is the
product of the load current and the ON-resistance of the
P-MOSFET.
When powering up, the open-collector Power-Good output holds
low for about 1ms after VO reaches the preset voltage. When the
active-HI reset signal RSI is issued, PG goes to low immediately
and holds for the same period of time after RSI comes back to
LOW. The output voltage is unaffected. Please refer to the timing
diagram in Figure 34. When the function is not used, connect RSI
to ground and leave the pull-up resistor R4 open at the PG pin.
The PG output also serves as a 1ms delayed Power-Good signal
when the pull-up resistor R1 is installed. The RSI pin needs to be
directly (or indirectly through a resistor) connected to Ground for
PG to be actively monitoring the output voltage.
The power MOSFETs are optimized for best efficiency. The
ON-resistance for the P-MOSFET is typically 120m and the
ON-resistance for the N-MOSFET is typically 110m.
100% Duty Cycle
Thermal Shut-Down
The ISL8012 has built-in thermal protection. When the internal
temperature reaches +140°C, the regulator is completely shut
down. As the temperature drops to +115°C, the ISL8012 resumes
operation by stepping through the soft-start.
Applications Information
VO
Output Inductor and Capacitor Selection
MIN
25ns
RSI
1ms
1ms
PG
FIGURE 34. RSI AND PG TIMING DIAGRAM
UVLO
To consider steady state and transient operations, ISL8012
typically uses a 2.2µH output inductor. The 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 current ripple and
output voltage ripple, the output inductor value can be increased.
It is recommended to set the ripple inductor current
approximately 30% of the maximum output current for optimized
When the input voltage is below the undervoltage lock-out (UVLO)
threshold, the regulator is disabled.
13
December 1, 2011
FN6616.2
ISL8012
performance. The inductor ripple current can be expressed as
shown in Equation 1:
VO 

V O   1 – ---------
V

IN
I = --------------------------------------L  fS
(EQ. 1)
The inductor’s saturation current rating needs to be at least
larger than the peak current. The ISL8012 protects the typical
peak current 3A. The saturation current needs be over 4A for
maximum output current application.
ISL8012 uses an internal compensation network and the output
capacitor value is dependent on the output voltage. The ceramic
capacitor is recommended to be X5R or X7R. The recommended
X5R or X7R minimum output capacitor values are shown in
Table 1.
TABLE 1. OUTPUT CAPACITOR VALUE vs VOUT
Output Voltage Selection
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 1.
The output voltage programming resistor, R3, 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 10k and 100kas shown in Equation 2.
R 2  0.8V
R 3 = ---------------------------------V OUT – 0.8V
(EQ. 2)
If the output voltage desired is 0.8V, then R3 is left unpopulated
and R2 is shorted. For better performance, add 220pF in parallel
with R2 (124k
Input Capacitor Selection
VOUT
(V)
COUT
(µF)
L
(µH)
0.8
2x10
1.5~3.3
1.2
2x10
1.5~3.3
1.5
2x10
1.8~3.3
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 from flowing back to the
battery rail. Two 10µF X5R or X7R ceramic capacitors are a good
starting point for the input capacitor selection.
1.8
2x10
2.2~3.3
Layout Recommendation
2.5
2x10
2.2~4.7
3.3
2x10
2.2~4.7
3.6
2x10
2.2~4.7
The layout is a very important converter design step to make sure
the designed converter works well. For the ISL8012 buck
converter, the power loop is composed of the output inductor L,
the output capacitor COUT, LX pin and SGND pin. It is necessary to
make the power loop as small as possible.
In Table 1, the minimum output capacitor value is given for the
different output voltage to make sure that the whole converter
system is stable. The maximum output capacitor should be
limited to 50µF or less.
14
The heat of the IC is mainly dissipated through the thermal pad.
Maximizing the copper area connected to the thermal epad is
preferable. In addition, a solid ground plane on the second layer
is helpful for EMI performance. Then connect the epad to the
ground plane with at least 5 vias for best thermal performance.
December 1, 2011
FN6616.2
ISL8012
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 Rev.
DATE
REVISION
CHANGE
2011-10-18
FN6616.2
Updated Tape & Reel note in “Ordering Information” on page 4 from "Add “-T” suffix for tape and reel." to new standard
"Add “-T*” suffix for tape and reel." The "*" covers all possible tape and reel options
On page 14, changed "The ISL8012 protects the typical peak current 6A. The saturation current needs be over 7A for
maximum output current application." to "The ISL8012 protects the typical peak current 3A. The saturation current
needs be over 4A for maximum output current application."
Added "The maximum output capacitor should be limited to 50µF or less."
2010-03-17
FN6616.1
Added “Related Literature” to page 1 per new data sheet standards.
Moved “Pin Configuration” to page 2 and converted “Pin Descriptions” on page 2 to tabular format, per new data sheet
standards.
Added inverter symbol on the RSI pin in the “Block Diagram” on page 3.
Added ESD ratings to “Absolute Maximum Ratings (Reference to GND)” on page 5 per new data sheet standards.
Added “Revision History” on page 15 and “Products” on page 16 per new data sheet standards.
2009-10-29
On page 2: Redrew chamfered corner on Pinout to look like POD on page 15
On page 7 to page 11 in common conditions of “Typical Performance Curves”: Changed "L = 1.5µH to 2.2µH" to "L =
2.2µH”
“Input Capacitor Selection” on page 14: changed "Two 22µF X5R or X7R ceramic capacitors are a good starting point.."
to "Two 10µF X5R or X7R ceramic capacitors are a good starting point.."
2009-10-27
On page 17: Updated POD to latest revision (changes from Rev 0 to Rev 1 were to add land pattern and move dimensions
from table onto drawing)
“Typical Application” on page 3: Changed value of C1 & C2 from 22µF to 2x10µF.
n page 7 to page 11 in common conditions of “Typical Performance Curves”: Changed "L = 1.5µH" to "L = 1.5µH to
2.2uH"
On page 14 in Table 1: Changed value of all COUT caps from 22µF to 2x10µF.
“Input Capacitor Selection” on page 14: changed "One 22µF X5R or X7R ceramic capacitor is a good starting point.." to
"Two 22µF X5R or X7R ceramic capacitors are a good starting point.."
Throughout: Converted to new format. Added new required content as follows:
On page 4: Added MSL Note 3 to “Ordering Information”
On page 5: In the “Electrical Specifications”: Adding standard over temp note to common conditions ("Boldface limits
apply...) Moved Note 7 "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" from common conditions to MIN MAX
columns as part of new standard
“Thermal Information” on page 5: Updated Theta JC Note 5 from "ThetaJC, “case temperature” location is at the center
of the exposed metal pad on the package underside. See Tech Brief TB379." to "For ThetaJC, the “case temp” location
is the center of the exposed metal pad on the package underside." per ASYD record and new standards
2009-07-15
On page 2 in Pinout: Deleted the circle and chamfered the corner of thermal pad (to match POD). Re-drew pins 1, 5, 6,
10 to look the same as the other pins
Updated Pb-free Note 2 in “Ordering Information” on page 4 based on lead finish, per packaging.
On page 5: In the “Electrical Specifications”: Removed Note "Parts are 100% tested at +25°C. Temperature limits
established by characterization and are not production tested." from MIN MAX columns and replaced with new verbiage
in common conditions "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."
2008-03-11
FN6616.0
Initial release.
15
December 1, 2011
FN6616.2
ISL8012
Products
Intersil Corporation is a leader in the design and manufacture of high-performance analog semiconductors. The Company's products
address some of the industry's fastest growing markets, such as, flat panel displays, cell phones, handheld products, and notebooks.
Intersil's product families address power management and analog signal processing functions. Go to www.intersil.com/products for a
complete list of Intersil product families.
For a complete listing of Applications, Related Documentation and Related Parts, please see the respective device information page on
intersil.com: ISL8012
To report errors or suggestions for this datasheet, please go to www.intersil.com/askourstaff
FITs 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
16
December 1, 2011
FN6616.2
ISL8012
Package Outline Drawing
L10.3x3C
10 LEAD DUAL FLAT PACKAGE (DFN)
Rev 2, 09/09
3.00
6
PIN #1 INDEX AREA
A
B
10
6
PIN 1
INDEX AREA
1
2.38
3.00
0.50
2
10 x 0.25
6
(4X)
0.10 C B
1.64
TOP VIEW
10x 0.40
BOTTOM VIEW
5
(4X)
PACKAGE
OUTLINE
0.10 M C B
SEE DETAIL "X"
(10 x 0.60)
(10x 0.25)
0.90
MAX
0.10 C
BASE PLANE
2.38
0.20
C
SEATING PLANE
0.08 C
SIDE VIEW
(8x 0.50)
1.64
TYPICAL RECOMMENDED LAND PATTERN
C
0.20 REF
5
0.05
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 0.18mm 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 indentifier may be
either a mold or mark feature.
7. COMPLAINT TO JEDEC MO-229-WEED-3 except for E-PAD
dimensions.
17
December 1, 2011
FN6616.2