DATASHEET

1.5A Low Quiescent Current 1.6MHz High Efficiency
Synchronous Buck Regulator
ISL8009A
Features
The ISL8009A is a high efficiency, monolithic, synchronous
step-down DC/DC regulator that can deliver up to 1.5A
continuous output current. It is optimized for generating low
output voltages down to 0.8V. The supply voltage range of 2.7V to
5.5V allows for the use of single Li+cell, three NiMH cells or a
regulated 5V input. The ISL8009A uses current mode control
architecture to deliver very low duty cycle operation at high
frequency with fast transient response and excellent loop
stability. It has flexible operation mode selection of forced PWM
mode and automatic PFM/PWM with as low as 17µA quiescent
current, achieving high power conversion efficiency under light
load condition, hence maximizing battery life. High 1.6MHz
pulse-width modulation (PWM) switching frequency allows the
use of small external components.
• High Efficiency Synchronous Buck Regulator with up to 95%
Efficiency
The ISL8009A 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 400mV dropout voltage at 1.5A
output current.
• Internal Digital Soft-Start
The ISL8009A offers a 2ms Power-On-Reset (POR) timer at
power-up. The timer output can be reset by RSI. When shutdown,
ISL8009A discharges the output capacitor through a 100Ω
resistor. Other features include internal digital soft-start, enable
for power sequence, overcurrent protection, and thermal
shutdown.
• Soft Discharge Disable
The ISL8009A is offered in a 2mmx3mm 8 Ld DFN package with
1mm maximum height. The complete converter occupies less
than 1cm2 area.
• 2ms Reset Timer
• 2.7V to 5.5V Supply Voltage
• 3% Output Accuracy Over-Temperature/Load/Line
• 1.5A Guaranteed Output Current
• 17µA Quiescent Supply Current in PFM Mode
• Selectable Forced PWM Mode and PFM Mode
• Less Than 1µA Logic Controlled Shutdown Current
• 90% Maximum Duty Cycle for Lowest Dropout at 1.5A
• Internal Current Mode Compensation
• Peak Current Limiting, Short Circuit Protection
• Over-Temperature Protection
• Enable
• Small 8 Ld 2mmx3mm 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
Pin Configuration
ISL8009A
(8 LD DFN)
TOP VIEW
VIN
1
8 LX
EN
2
7 GND
POR
3
6 VFB
SKIP
4
5 RSI
*EXPOSED PAD MUST BE CONNECTED
TO THE GND PIN*
February 28, 2013
FN6656.3
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 LLC 2008, 2009, 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.
ISL8009A
Ordering Information
PART NUMBER
(Notes 1, 2, 3)
PART
MARKING
TEMP. RANGE
(°C)
PACKAGE
(Pb-free)
PKG.
DWG. #
ISL8009AIRZ-T
09A
-40 to +85
8 Ld 2x3 DFN
L8.2x3
ISL8009AIRZ-TK
09A
-40 to +85
8 Ld 2x3 DFN
L8.2x3
ISL8009AIRZ-T7A
09A
-40 to +85
8 Ld 2x3 DFN
L8.2x3
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 ISL8009A. For more information on MSL please see techbrief TB363.
2
FN6656.3
February 28, 2013
ISL8009A
Absolute Maximum Ratings (Reference to GND)
Thermal Information
Supply Voltage (VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6.5V
EN, RSI, SKIP, VFB, POR. . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to VIN + 0.3V
LX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -1.5V to 6.5V
VFB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 2.7V
Thermal Resistance (Typical)
θJA (°C/W) θJC (°C/W)
8 Ld 2x3 DFN (Notes 4, 5) . . . . . . . . . . .
55
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 1.5A
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.
5. For θJC, the “case temp” location is the center of the exposed metal pad on the package underside.
Electrical Specifications Typical specifications are measured at the following conditions: TA = +25°C, EN = VIN, RSI = SKIP = 0V, VIN = 5V,
L = 2.2µH, C1 = C2 = 20µF, IOUT = 0A to 1.5A. See “Typical Applications” on page 9.
PARAMETER
MIN
(Note 7)
TYP
Rising
-
2.5
2.7
V
Falling
2.2
2.4
-
V
SKIP = VIN, no load at the output
-
17
30
µA
SKIP = VIN, no load at the output and no switches
switching, design info only
-
15
-
µA
SKIP = GND, no load at the output
-
3.7
6
mA
VIN = 5.5V, EN = low
-
0.1
2
µA
0.784
0.8
0.816
V
-
0.1
-
µA
SYMBOL
TEST CONDITIONS
MAX
(Note 7) UNITS
INPUT SUPPLY
VIN Undervoltage Lockout Threshold
Quiescent Supply Current
VUVLO
IVIN
Shutdown Supply Current
ISD
OUTPUT REGULATION
VFB Regulation Voltage
VVFB
VFB Bias Current
IVFB
VFB = 0.75V
Output Voltage Accuracy
VIN = VO + 0.5V to 5.5V, IO = 0A to 1A (Note 6)
-3
-
3
%
Line Regulation
VIN = VO + 0.5V to 5.5V (minimal 2.7V)
-
0.2
-
%/V
Adjustable version, design info only
-
20
-
µA/V
VIN = 5.5V, IO = 200mA
-
0.12
0.22
Ω
VIN = 2.7V, IO = 200mA
-
0.16
0.27
Ω
VIN = 5.5V, IO = 200mA
-
0.11
0.22
Ω
VIN = 2.7V, IO = 200mA
-
0.15
0.27
Ω
1.8
2.1
2.6
A
90
-
-
%
1.35
1.6
1.75
MHz
-
70
100
ns
-
1.1
-
ms
80
100
120
Ω
COMPENSATION
Error Amplifier Trans-Conductance
LX
P-Channel MOSFET ON-Resistance
N-Channel MOSFET ON-Resistance
P-Channel MOSFET Peak Current Limit
IPK
IO = 1.5A
LX Maximum Duty Cycle
PWM Switching Frequency
fS
LX Minimum On-Time
SKIP = low (forced PWM mode)
Soft-Start-Up Time
Soft-Discharge Resistor
Enable = 0
3
FN6656.3
February 28, 2013
ISL8009A
Electrical Specifications Typical specifications are measured at the following conditions: TA = +25°C, EN = VIN, RSI = SKIP = 0V, VIN = 5V,
L = 2.2µH, C1 = C2 = 20µF, IOUT = 0A to 1.5A. See “Typical Applications” on page 9.
PARAMETER
SYMBOL
TEST CONDITIONS
MIN
(Note 7)
TYP
MAX
(Note 7) UNITS
-
-
0.3
V
-
2
-
ms
-
0.01
0.1
µA
1.2
-
-
V
POR
Output Low Voltage
Sinking 1mA, VFB = 0.7V
Delay Time
POR Pin Leakage Current
POR = VIN = 3.6V
Minimum Supply Voltage for Valid POR Signal
Internal PGOOD Low Rising Threshold
Percentage of nominal regulation voltage
89.5
92
94.5
%
Internal PGOOD Low Falling Threshold
Percentage of nominal regulation voltage
85
88
91
%
Internal PGOOD High Rising Threshold
Percentage of nominal regulation voltage
108
112
114
%
Internal PGOOD High Falling Threshold
Percentage of nominal regulation voltage
104
107
110
%
-
6.5
-
µs
Logic Input Low
-
-
0.4
V
Logic Input High
1.4
-
-
V
-
0.1
1
µA
Thermal Shutdown
-
140
-
°C
Thermal Shutdown Hysteresis
-
25
-
°C
Internal PGOOD Delay Time
EN, SKIP, RSI
Logic Input Leakage Current
Pulled up to 5.5V
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.
Pin Descriptions
VFB
VIN
Buck regulator output feedback. Connect to the output through a
resistor divider for adjustable output voltage (ISL8009A-ADJ). For
preset output voltage, connect this pin to the output.
Input supply voltage. Connect a 10µF ceramic capacitor to power
ground.
EN
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.
POR
2ms timer output. At power-up or EN HI, this output is a 2ms
delayed Power-Good signal for the output voltage. This output can
be reset by a low RSI signal. 2ms starts when RSI goes to high.
SKIP
RSI
This input resets the 2ms timer. When the output voltage is within
the PGOOD window, an internal timer is started and generates a
POR signal 2ms later when RSI is low. A high RSI resets POR 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.
Exposed Pad
The exposed pad must be connected to the GND pin for proper
electrical performance. The exposed pad must also be connected
to as much as possible for optimal thermal performance.
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.
LX
Switching node connection. Connect to one terminal of inductor.
GND
System ground.
4
FN6656.3
February 28, 2013
ISL8009A
Typical Operating Performance
(Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 5V,
EN = VIN, RSI = SKIP = 0V, L = 2.2µH, C1 = 20µF, C2 = 20µF, IOUT = 0A)
100
100
90
90
70
2.5VOUT - PWM
1.5VOUT - PWM
60
EFFICIENCY (%)
EFFICIENCY (%)
80
1.8VOUT - PWM
50
1.2VOUT - PWM
40
30
20
2.5VOUT - PFM
80
1.5VOUT - PFM
1.8VOUT - PFM
70
1.2VOUT - PFM
60
50
10
0
0.00
0.25
0.50
0.75
1.00
1.25
40
0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
1.50
OUTPUT LOAD (A)
OUTPUT LOAD (A)
FIGURE 1. EFFICIENCY vs LOAD, VIN = 3.3V PWM
FIGURE 2. EFFICIENCY vs LOAD, V IN = 3.3V PFM
100
100
90
90
2.5VOUT - PWM
70
1.5VOUT - PWM
60
3.3VOUT - PWM
1.8VOUT - PWM
50
EFFICIENCY (%)
EFFICIENCY (%)
80
40
30
1.2VOUT - PWM
20
2.5VOUT - PFM
80
3.3VOUT - PFM
1.5VOUT - PFM
70
1.8VOUT - PFM
60
1.2VOUT - PFM
50
10
0
0.00
0.25
0.50
0.75
1.00
1.25
40
0.05
1.50
0.15
0.25
FIGURE 3. EFFICIENCY vs LOAD, VIN = 5V PWM
0.55
0.65
0.75
1.54
2.8VIN - PWM
5VIN - PWM
1.53
5VIN - PFM
1.21
3.3VIN-PFM
1.20
1.19
3.3VIN - PWM
1.18
2.8VIN - PFM
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
1.22
0.45
FIGURE 4. EFFICIENCY vs LOAD, VIN = 5V PFM
1.24
1.23
0.35
OUTPUT LOAD (A)
OUTPUT LOAD (A)
1.52 2.8VIN - PWM
5VIN - PWM
5VIN - PFM
1.51
1.50
3.3VIN-PFM
1.49
3.3VIN - PWM
1.48
2.8VIN - PFM
1.47
1.17
1.16
0.00
0.25
0.50
0.75
1.00
OUTPUT LOAD (A)
1.25
FIGURE 5. VOUT REGULATION vs LOAD, VOUT = 1.2V
5
1.50
1.46
0.00
0.25
0.50
0.75
1.00
1.25
1.50
OUTPUT LOAD (A)
FIGURE 6. VOUT REGULATION vs LOAD, VOUT = 1.5V
FN6656.3
February 28, 2013
ISL8009A
Typical Operating Performance
(Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 5V,
EN = VIN, RSI = SKIP = 0V, L = 2.2µH, C1 = 20µF, C2 = 20µF, IOUT = 0A) (Continued)
1.84
2.54
2.53
5.5VIN - PFM
5.5VIN - PWM
1.82
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
1.83
1.81 2.7VIN - PWM
1.80
4VIN-PFM
1.79
1.78
4VIN - PWM
1.77
1.76
0.00
0.25
2.7VIN - PFM
2.51
2.50
2.49
3.3VIN - PWM
2.47
0.50
0.75
1.00
OUTPUT LOAD (A)
1.25
2.46
0.00
1.50
0.50
0.75
1.00
OUTPUT LOAD (A)
0.7
4VIN - PWM
POWER DISSIPATION (W)
5.5VIN - PFM
5.5VIN - PWM
3.38
3.36
3.34
4VIN - PFM
3.3VIN - PWM
3.32
5VIN-PFM
3.30
3.28
3.26
0.00
0.25
0.50
0.75
1.00
OUTPUT LOAD (A)
1.25
1.25
1.50
2.8VIN - PWM
0.6
0.5
0.4
0.3
0.2
2.8VIN - PFM
3.3VIN - PWM
3.3VIN-PFM
5VIN - PWM
0.1
5VIN - PFM
0.0
0.00
1.50
FIGURE 9. VOUT REGULATION VS LOAD, VOUT = 3.3V
0.25
0.50
0.75
1.00
OUTPUT LOAD (A)
1.25
1.50
FIGURE 10. POWER DISSIPATION vs LOAD, 1.6 MHz,
VOUT = 1.8V
45
2.5
0.75A LOAD
40
35
NO LOAD- PWM
OUTPUT VOLTAGE (V)
POWER DISSIPATION (mW)
0.25
FIGURE 8. VOUT REGULATION vs LOAD, VOUT = 2.5V
3.42
OUTPUT VOLTAGE (V)
3.3VIN - PFM
2.48
FIGURE 7. VOUT REGULATION vs LOAD, VOUT = 1.8V
3.40
5VIN - PFM
5VIN - PWM
2.52
30
25
20
15
NO LOAD - PFM
10
2.0
1.5
1.5A LOAD
1.0
NO LOAD
0.5
5
0
2.75
3.25
3.75
4.25
4.75
5.25
VIN (V)
FIGURE 11. POWER DISSIPATION vs VIN AT NO LOAD, VOUT =
1.8V
6
0.0
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
FIGURE 12. OUTPUT VOLTAGE REGULATION vs VIN PWM MODE
FN6656.3
February 28, 2013
ISL8009A
Typical Operating Performance
(Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 5V,
EN = VIN, RSI = SKIP = 0V, L = 2.2µH, C1 = 20µF, C2 = 20µF, IOUT = 0A) (Continued)
OUTPUT VOLTAGE (V)
2.0
NO LOAD
1.5
0.75A LOAD
1.0
LX 2V/DIV
1.5A LOAD
0.5
VOUT RIPPLE
20mV/DIV
0.0
-0.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
IL 0.2A/DIV
INPUT VOLTAGE (V)
FIGURE 13. OUTPUT VOLTAGE REGULATION vs VIN SKIP MODE
FIGURE 14. STEADY STATE OPERATION AT NO LOAD (PWM),
1µs/DIV
LX 2V/DIV
VOUT RIPPLE
20mV/DIV
LX 2V/DIV
IL 0.5A/DIV
VOUT RIPPLE
20mV/DIV
IL 0.2A/DIV
FIGURE 15. STEADY STATE OPERATION AT NO LOAD (PFM),
1µs/DIV
FIGURE 16. STEADY STATE OPERATION WITH FULL LOAD,
1µs/DIV
LX 2V/DIV
LX 2V/DIV
VOUT RIPPLE
50mV/DIV
VOUT RIPPLE
50mV/DIV
IL 1A/DIV
IL 1A/DIV
FIGURE 17. LOAD TRANSIENT (PWM), 200µs/DIV
7
FIGURE 18. LOAD TRANSIENT (PFM), 200µs/DIV
FN6656.3
February 28, 2013
ISL8009A
Typical Operating Performance
(Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 5V,
EN = VIN, RSI = SKIP = 0V, L = 2.2µH, C1 = 20µF, C2 = 20µF, IOUT = 0A) (Continued)
EN 2V/DIV
EN 2V/DIV
VOUT
1V/DIV
VOUT
0.5V/DIV
IL 1A/DIV
IL 1A/DIV
POR 1V/DIV
POR 2V/DIV
FIGURE 19. SOFT-START AT NO LOAD, 500µs/DIV
FIGURE 20. SOFT-START WITH PRE-BIASED 1V, 500µs/DIV
LX 2V/DIV
EN 2V/DIV
VOUT
0.5V/DIV
IL 0.5A/DIV
IL 1A/DIV
VOUT
1V/DIV
POR 5V/DIV
POR 2V/DIV
FIGURE 21. SOFT-START AT FULL LOAD, 500µs/DIV
FIGURE 22. OUTPUT SHORT CIRCUIT, 10.0µs/DIV
VOUT 1V/DIV
IL 1A/DIV
POR 5V/DIV
FIGURE 23. OUTPUT SHORT CIRCUIT RECOVERY, 500µs/DIV
8
FN6656.3
February 28, 2013
ISL8009A
Typical Applications
L
2.2µH
INPUT 2.7V TO 5.5V
VIN
LX
C1
20µF
OUTPUT
1.8V TO 1.5A
C2
20µF
R2
124k
GND
ISL8009A
*C3
220pF
EN
R3
100k
R1
100k
POR
VFB
SKIP
RSI
*C3 IS OPTIONAL TO IMPROVE
TRANSIENT RESPONSE. CHECK
LOOP BANDWIDTH BEFORE USE.
FIGURE 24. TYPICAL APPLICATION DIAGRAM
Block Diagram
SKIP
SHUTDOWN
390k
BANDGAP
0.8V
EAMP
+
EN
SHUTDOWN
27pF
SOFT- START
+
COMP
VIN
OSCILLATOR
PWM/PFM
LOGIC
CONTROLLER
PROTECTION
DRIVER
+
LX
GND
VFB
SLOP
SLOPE
E
COMP
COMP
0.864V
+
+
CSA1
+
OCP
0.85V
+
0.736V
+
SKIP
POR
2ms
DELAY
0.17V
ZERO - CROSS
SENSING
RSI
0.2V
SCP
+
FIGURE 25. FUNCTIONAL BLOCK DIAGRAM
9
FN6656.3
February 28, 2013
ISL8009A
Theory of Operation
The ISL8009A is a step-down switching regulator optimized for
battery-powered handheld applications. The regulator operates
at 1.6MHz fixed switching frequency under heavy load condition
to allow small external inductor 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 17µA. The supply current is typically only
0.1µA when the regulator is shutdown.
PWM Control Scheme
The ISL8009A employes the current-mode pulse-width
modulation (PWM) control scheme for fast transient response
and pulse-by-pulse current limiting. Figure 25 shows the block
diagram. The current loop consists of the oscillator, the PWM
comparator COMP, the current sensing circuit, and the slope
compensation for the current loop stability. The current sensing
circuit consists of the resistance of the P-Channel MOSFET when
it is turned on and the current sense amplifier CSA. The gain for
the current sensing circuit is typically 0.4V/A. The control
reference for the current loops comes from the error amplifier
EAMP of the voltage loop.
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 compensation slope
(0.675V/µs) reach 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 to turn on the N-Channel MOSFET. The
N-MOSFET stays on until the end of the PWM cycle. Figure 26
shows the typical operating waveforms during the PWM operation.
The dotted lines illustrate the sum of the compensation ramp and
the current-sense amplifier CSA output.
The output voltage is regulated by controlling the reference
voltage to the current loop. The bandgap circuit outputs a 0.8V
reference voltage to the voltage control 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 30pF and 300kΩ RC network.
The maximum EAMP voltage output is precisely clamped to the
bandgap voltage (1.172V).
VEAMP
VCSA1
Duty
DUTY
Cycle
CYCLE
IL
VOUT
FIGURE 26. PWM OPERATION WAVEFORMS
SKIP Mode
The ISL8009A enters a pulse-skipping mode at light load to
minimize the switching loss by reducing the switching frequency.
Figure 27 illustrates the skip-mode operation. A zero-cross
sensing circuit shown in Figure 25 monitors the N-MOSFET
current for zero crossing. When 8 consecutive cycles of the NMOSFET 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.
CLOCK
Clock
88CYCLES
Cycles
CURRENT
LIMIT
Current Limit
IL
LOAD
LoadCURRENT
Current
0
NOMINAL++1.5%
Nominal
1.5%
VOUT
NOMINAL
Nominal
FIGURE 27. SKIP MODE OPERATION WAVEFORMS
10
FN6656.3
February 28, 2013
ISL8009A
Once the skip mode is entered, the pulse modulation starts being
controlled by the SKIP comparator shown in Figure 25. Each
pulse cycle is still synchronized by the PWM clock. The P-MOSFET
is turned on at the clock and turned off when its current reaches
20% of the current limit value (0.2V at the CSA output). As the
average inductor current in each cycle is higher than the average
current of the load, the output voltage rises cycle over cycle.
When the output voltage reaches 1.5% above the nominal
voltage, the P-MOSFET is turned off immediately and the inductor
current is fully discharged to zero and stays at zero. 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 clock,
repeating the previous operations.
The regulator resumes normal PWM mode operation when the
output voltage drops 1.5% below the nominal voltage.
.
VO
MIN
25ns
RSI
2ms
2ms
POR
FIGURE 28. RSI AND POR TIMING DIAGRAM
UVLO
When the input voltage is below the undervoltage lock out (UVLO)
threshold, the regulator is disabled.
Soft-Start-Up
Mode Control
The ISL8009A has a SKIP pin that controls the operation mode.
When the SKIP 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.
Overcurrent Protection
The overcurrent protection is realized by monitoring the CSA
output with the OCP comparator, as shown in Figure 25. The
current sensing circuit has a gain of 0.4V/A, from the N-MOSFET
current to the CSA output. When the CSA output reaches 0.8V,
(which is equivalent to 2A for the switch current) the OCP
comparator is tripped to turn off the P-MOSFET immediately.
Short-Circuit Protection
A 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 1/3 of the normal operation value. This
comparator is effective during start-up or an output short-circuit
event.
The soft start-up eliminates the in-rush current during the
start-up. The soft-start block outputs a ramp reference to both
the voltage loop and the current loop. The two ramps limit the
inductor current rising speed as well as the output voltage speed
so that the output voltage rises in a controlled fashion. At the
very beginning of the start-up, the output voltage is less than
0.2V; hence the PWM operating frequency is 1/3 of the normal
frequency.
Power MOSFETs
The power MOSFETs are optimized for best efficiency. The
ON-resistance for the P-MOSFET is typically 120mΩ and the
ON-resistance for the N-MOSFET is typically 110mΩ.
Duty Cycle
The ISL8009A features duty cycle operation to maximize the
battery life. When the battery voltage drops to a level that the
ISL8009A can no longer maintain the regulation at the output,
the regulator completely turns on the P-MOSFET. The maximum
drop out voltage under the duty-cycle operation is the product of
the load current and the ON-resistance of the P-MOSFET.
Enable
RSI/POR Function
When powering up, the open-collector Power-On-Reset output
holds low for about 1ms after VO reaches the preset voltage.
When the active-HI reset signal RSI is issued, POR goes to low
immediately and holds for the same period of time after RSI
comes back to LOW. The output voltage is unaffected (Figure 28).
When the function is not used, connect RSI to ground and leave
the pull-up resistor, R1, open at the POR pin.
The POR 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 another resistor connected to
ground for this to function properly.
11
The Enable (EN) input allows the user to control the turning on or off
of 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, then the soft-start-up begins. When the
regulator is disabled, the P-MOSFET and the N-MOSFET are turned
off immediately. The 100Ω soft discharge resistor from LX to
GDN is activated and pulls the output to 0V.
Thermal Shutdown
The ISL8009A has built-in thermal protection. When the internal
temperature reaches +140°C, the regulator is completely
shutdown. As the temperature drops to +120°C, the ISL8009A
resumes operation by stepping through a soft-start-up.
FN6656.3
February 28, 2013
ISL8009A
Applications Information
Input Capacitor Selection
Output Inductor and 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 from flowing back to the
battery rail. A 10µF, X5R or X7R ceramic capacitor is a good
starting point for the input capacitor selection.
To consider steady state and transient operation, ISL8009A
typically uses a 3.3µH output inductor. Higher or lower inductor
values 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.
The inductor ripple current can be expressed in Equation 1:
VO ⎞
⎛
V O • ⎜ 1 – --------⎟
V
⎝
IN⎠
ΔI = -----------------------------------L • fS
(EQ. 1)
Output Voltage Setting Resistor Selection
The resistors R2 and R3 shown in Figure 24 set the output
voltage for the adjustable version. The output voltage can be
calculated by Equation 2:
R 2⎞
⎛
V O = 0.8 • ⎜ 1 + -------⎟
R
⎝
3⎠
The inductor’s saturation current rating needs be at least larger
than the peak current. The ISL8009A protects the typical peak
current 2.1A. The saturation current needs to be over 2.4A for
maximum output current application.
ISL8009A uses internal compensation network and the output
capacitor value is dependant on the output voltage. The ceramic
capacitor is recommended to be X5R or X7R. The recommended
minimum output capacitor values are shown in Table 1.
TABLE 1. OUTPUT CAPACITOR VALUE vs VOUT
VOUT (V)
COUT (µF)
L (µH)
0.8
10
1.0~2.2
1.2
10
1.2~2.2
1.6
10
1.8~2.2
1.8
10
1.8~3.3
2.5
10
1.8~3.3
3.3
10
1.8~4.7
3.6
10
1.8~4.7
(EQ. 2)
where the 0.8V is the reference voltage.
The voltage divider consists of R2 and R3 and increases the
quiescent current by VO/(R2 + R3), so larger resistance is
desirable. On the other hand, the VFB pin has leakage current
that will cause error in the output voltage setting. The leakage
current has a typical value of 0.1µA. To minimize the accuracy
impact on the output voltage, select the R3 no larger than
200kΩ. For VO = 0.8V, it is recommended to short R2 and open
R3.
Layout Recommendation
The layout is a very important converter design step to make sure
the designed converter works well. For the ISL8009A buck
converter, the power loop is composed of the output inductor L,
the output capacitor COUT, the LX pin and the GND pin. It is
necessary to make the power loop as small 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 EMI
performance. It is recommended to add 5 vias under the thermal
pad connection to the solid ground plane.
In Table 1, the minimum output capacitor value is given for
different output voltages to make sure the whole converter
system is stable. Maximum output capacitance should be limited
to 50µF or less.
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12
FN6656.3
February 28, 2013
ISL8009A
Package Outline Drawing
L8.2x3
8 LEAD DUAL FLAT NO-LEAD PLASTIC PACKAGE
Rev 1, 3/10
2.00
A
2X 1.50
PIN 1
INDEX AREA
6
PIN #1
INDEX AREA
6X 0.50
1
1.80 +0.10/-0.15
3.00
B
(4X)
0.15
8
8X 0.40 ±0.10
TOP VIEW
1.65 +0.10/-0.15
8X 0.25 +0.07/-0.05 4
0.10 M C A B
BOTTOM VIEW
SEE DETAIL "X"
0.90 ±0.10
0.10 C
(1.65)
(1.50)
(8X 0.60)
C
BASE PLANE
SEATING PLANE
0.08 C
0.05 MAX
SIDE VIEW
(2.80)(1.80)
0.20 REF
C
(6X 0.50)
0.05 MAX
(8X 0.25)
DETAIL "X"
TYPICAL RECOMMENDED LAND PATTERN
NOTES:
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 0.25mm 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
7.
Compies to JEDEC MO-229 VCED-2.
either a mold or mark feature.
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FN6656.3
February 28, 2013
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