Intersil ISL9107IRZ-T 1.5a 1.6mhz low quiescent current high efficiency synchronous buck regulator Datasheet

ISL9107, ISL9108
®
Data Sheet
December 21, 2007
1.5A 1.6MHz Low Quiescent Current High
Efficiency Synchronous Buck Regulator
ISL9107 and ISL9108 are 1.6MHz synchronous step-down
regulators with integrated power switches capable of
delivering 1.5A output current, which is ideal for powering
low-voltage microprocessors in compact devices such as
PDAs and cellular phones. These devices are optimized for
generating low output voltages down to 0.8V. The supply
voltage range is from 2.7V to 5.5V allowing for the use of a
single Li+ cell, three NiMH cells or a regulated 5V input.
1.6MHz pulse-width modulation (PWM) switching frequency
allows using small external components. They have flexible
operation mode selection of forced PWM mode and Skip
(Low IQ) mode with typical 17μA quiescent current for
highest light load efficiency to maximize battery life.
FN6612.0
Features
• Integrated Synchronous Buck Regulator with up to 95%
Efficiency
• 2.7V to 5.5V Supply Voltage
• 1.5A Guaranteed Output Current
• 17μA Quiescent Supply Current in Skip (Low IQ) Mode
• Selectable Forced PWM Mode and Skip Mode
• Less Than 1µA Logic Controlled Shutdown Current
• 100% Maximum Duty Cycle for Lowest Dropout
• Discharge Output Capacitor when Shutdown
• Internal Digital Soft-Start
The ISL9107 and ISL9108 integrate a pair of low
ON-resistance P-Channel and N-Channel MOSFETs to
maximize efficiency and minimize external component
count.
• Enable, Peak Current Limiting, Short Circuit Protection
The ISL9107 offers a typical 215ms Power-Good (PG) timer
when powered up. The timer output can be reset by RSI.
When shutdown, ISL9107 and ISL9108 discharge the output
capacitor. Other features include internal digital soft-start,
enable for power sequence, overcurrent protection, and
thermal shutdown.
• 8 Ld 2mmx3mm DFN
The ISL9107 and ISL9108 are offered in 8 Ld 2mmx3mm
DFN package with 0.9mm typical height. The complete
converter can occupy less than 1cm2 area.
PART
MARKING
ISL9107IRZ-T 107
ISL9108IRZ-T 108
TEMP.
RANGE
(°C)
PACKAGE
(Pb-Free)
-40 to +85 8 Ld 2x3 DFN
-40 to +85 8 Ld 2x3 DFN
• Pb-Free (RoHS Compliant)
Applications
• Single Li-Ion Battery-Powered Equipment
• DSP Core Power
• PDAs and Palmtops
ISL9107
(8 LD 2X3 DFN)
TOP VIEW
PKG.
DWG. #
L8.2x3
L8.2x3
*Please refer to TB347 for details on reel specifications.
NOTE: 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.
1
• Power-Good Function (for ISL9107 only)
Pinouts
Ordering Information
PART
NUMBER
(Note)
• Over-Temperature Protection
VIN
1
8
SW
EN
2
7
GND
PG
3
6
FB
MODE
4
5
RSI
ISL9108
(8 LD 2X3 DFN)
TOP VIEW
VIN
1
8 SW
EN
2
7 GND
NC
3
6 FB
MODE
4
5 NC
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2007. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
ISL9107, ISL9108
Absolute Maximum Ratings (Reference to GND)
Thermal Information
VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6.5V
EN, MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to VIN + 0.3V
PG, RSI (Note 1) . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to VIN + 0.3V
SW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -1.5V to 6.5V
FB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 2.7V
Thermal Resistance (Notes 2, 3)
θJA (°C/W)
θJC (°C/W)
2x3 DFN Package . . . . . . . . . . . . . .
78
11
Junction Temperature Range. . . . . . . . . . . . . . . . . .-40°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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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:
1. For ISL9107 only.
2. 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.
3. θJC, “case temperature” location is at the center of the exposed metal pad on the package underside. See Tech Brief TB379.
Electrical Specifications
Unless otherwise noted, all parameter limits are guaranteed over the recommended operating conditions and
the typical specifications are measured at the following conditions: TA = +25°C, VIN = VEN = 3.6V, L = 2.2µH,
C1 = 10µF, C2 = 10µF, IOUT = 0A (see the Typical Application Circuit on page 7).
PARAMETER
SYMBOL
TEST CONDITIONS
MIN
TYP
MAX
UNITS
Rising
-
2.5
2.7
V
Falling
2.2
2.4
-
V
MODE = VIN, no load at the output
-
17
30
µA
MODE = GND, no load at the output
-
5
8
mA
ISD
VIN = 5.5V, EN = LOW
-
0.05
2
μA
VFB
TA = 0°C to +85°C
0.784
0.8
0.816
V
TA = -40°C to +85°C
0.78
0.8
0.82
V
VFB = 0.75V
-
0.1
-
µA
VIN = VO + 0.5V to 5.5V (minimal 2.7V)
-
0.2
-
%/V
Design info only
-
20
-
µA/V
VIN = 3.6V, IO = 200mA
-
0.12
0.22
Ω
VIN = 2.7V, IO = 200mA
-
0.16
0.27
Ω
SUPPLY
Undervoltage Lockout Threshold
VUVLO
Quiescent Supply Current
IVIN
Shut Down Supply Current
OUTPUT REGULATION
FB Regulation Voltage
FB Bias Current
IFB
Line Regulation
COMPENSATION
Error Amplifier Trans-conductance
SW
P-Channel MOSFET ON-Resistance
N-Channel MOSFET ON-Resistance
VIN = 3.6V, IO = 200mA
-
0.11
0.22
Ω
VIN = 2.7V, IO = 200mA
-
0.15
0.27
Ω
-
90
-
Ω
1.8
2.1
2.6
A
-
100
-
%
1.35
1.6
1.75
MHz
-
-
100
ns
-
1.1
-
ms
N-Channel Bleeding MOSFET ON-Resistance
P-Channel MOSFET Peak Current Limit
IPK
VIN = 5.5V
Maximum Duty Cycle
PWM Switching Frequency
fS
SW Minimum On-Time
TA = -40°C to +85°C
MODE = LOW (forced PWM mode)
Soft Start-Up Time
2
FN6612.0
December 21, 2007
ISL9107, ISL9108
Electrical Specifications
Unless otherwise noted, all parameter limits are guaranteed over the recommended operating conditions and
the typical specifications are measured at the following conditions: TA = +25°C, VIN = VEN = 3.6V, L = 2.2µH,
C1 = 10µF, C2 = 10µF, IOUT = 0A (see the Typical Application Circuit on page 7). (Continued)
PARAMETER
SYMBOL
TEST CONDITIONS
MIN
TYP
MAX
UNITS
PG (NOTE 1)
Output Low Voltage
Sinking 1mA, VFB = 0.7V
Delay Time
PG = VIN = 3.6V
PG Pin Leakage Current
Minimum Supply Voltage for Valid PG Signal
-
-
0.3
V
150
215
275
ms
-
0.01
0.1
µA
1.2
-
-
V
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
108.2
110.7
113.2
%
Internal PGOOD High Falling Threshold
Percentage of Nominal Regulation Voltage
104
107
110
%
-
50
-
µs
Internal PGOOD Delay Time
RSI (NOTE 1), EN, MODE
Logic Input Low
-
-
0.4
V
Logic Input High
1.4
-
-
V
-
0.1
1
µA
Thermal Shutdown
-
150
-
°C
Thermal Shutdown Hysteresis
-
25
-
°C
Logic Input Leakage Current
Pulled up to 5.5V
Pin Descriptions
PIN #
ISL9107
ISL9108
PIN NAME PIN NAME
1
VIN
Input supply voltage pin. Connect a 10µF ceramic capacitor to power ground.
2
EN
Enable pin. Enable the output when driven to high. Shut down the chip and discharge output capacitor when
driven to low. Do not leave this pin floating.
4
MODE
Mode selection pin. Connect to logic high or VIN to enable skip mode; connect to logic low or ground for force
PWM mode.
6
FB
7
GND
8
SW
E-PAD
-
DESCRIPTION
Buck regulator output feedback pin. Connect to the output voltage through voltage divider resistors for
adjustable output voltage.
System ground.
Switching node pin. Connect to one terminal of the inductor.
Exposed pad. It should be connected to ground for proper electrical performance. The exposed pad must also
be connected to as much as possible for optimal thermal performance.
3
PG
NC
For ISL9107, it is 215ms timer output. It outputs 215ms delayed power-good signal when output voltage is
within power-good window. It can be reset by a high RSI signal, then 215ms starts when RSI goes from high
to low.
For ISL9108, do not connect. Leave this pin floating.
5
RSI
NC
For ISL9107, this input resets the 215ms timer. Please refer to “Theory of Operation” on page 9 for more
details.
For ISL9108, do not connect. Leave this pin floating.
3
FN6612.0
December 21, 2007
ISL9107, ISL9108
100
100
95
95
90
90
VIN = 3.6V
85
VIN = 4.2V
EFFICIENCY (%)
EFFICIENCY (%)
Typical Operating Performance
80
75
70
65
85
75
70
65
60
55
55
50
0
500
1000
VIN = 3.6V
80
60
50
VIN = 4.2V
1500
0
500
LOAD CURRENT (mA)
FIGURE 1. EFFICIENY vs LOAD CURRENT (VOUT = 3.3V)
1500
FIGURE 2. EFFICIENCY vs LOAD CURRENT (VOUT = 2.5V)
30
100
QUIESCENT CURRENT (µA)
EFFICIENCY @ 4.2V
95
90
EFFICIENCY (%)
1000
LOAD CURRENT (mA)
85
80
75
EFFICIENCY @ 3.6V
70
EFFICIENCY @ 2.7V
65
60
25
20
15
10
5
55
50
0
500
1000
0
2.7
1500
3.4
LOAD CURRENT (mA)
4.1
4.8
5.5
INPUT VOLTAGE (V)
FIGURE 3. EFFICIENCY vs LOAD CURRENT (VOUT = 1.6V)
FIGURE 4. IQ vs VIN (MODE = VIN, VOUT = 1.6V, IOUT = 0)
QUIESCENT CURRENT (mA)
8
7
6
5
4
3
2
1
0
2.7
3.4
4.1
4.8
5.5
INPUT VOLTAGE (V)
FIGURE 5. IQ vs VIN (MODE = GND, VOUT = 1.6V, IOUT = 0)
4
FN6612.0
December 21, 2007
ISL9107, ISL9108
Typical Operating Performance (Continued)
5V/DIV
5V/DIV
VSW
VSW
1V/DIV
1A/DIV
1V/DIV
VOUT
VOUT
500mA/DIV
IL
IL
EN
EN
5V/DIV
5V/DIV
200µs/DIV
FIGURE 6. SOFT-START (VIN = 4.2V, VOUT = 1.6V,
IOUT = 1.5A)
200µs/DIV
FIGURE 7. SOFT-START (VIN = 4.2V, VOUT = 1.6V,
IOUT = 1mA)
VSW
5V/DIV
5V/DIV
VSW
VOUT (AC COUPLED)
VOUT (AC COUPLED)
20mV/DIV
50mV/DIV
IL
IL
1A/DIV
200mA/DIV
1µs/DIV
2µs/DIV
FIGURE 8. STEADY-STATE IN SKIP MODE (VIN = 5.0V,
VOUT = 1.6V, IOUT = 35mA)
FIGURE 9. STEADY-STATE IN PWM MODE (VIN = 5.0V,
VOUT = 1.6V, IOUT = 1.5A)
VVSW
SW
VSW
5V/DIV
5V/DIV
VOUT (AC COUPLED)
100mV/DIV
VOUT (AC COUPLED)
100mV/DIV
IL
IL
1A/DIV
1A/DIV
100µs/DIV
FIGURE 10. LOAD TRANSIENT TEST (MODE = VIN = 5.0V;
VO = 1.6V; IO = 0.01A~1A)
5
100µs/DIV
FIGURE 11. LOAD TRANSIENT TEST (MODE = GND,
VIN = 5.0V; VO = 1.6V; IO = 0.01A~1A)
FN6612.0
December 21, 2007
ISL9107, ISL9108
Typical Operating Performance (Continued)
VSW
5V/DIV
VSW
5V/DIV
VOUT (AC COUPLED)
100mV/DIV
VOUT (AC COUPLED)
100mV/DIV
IL
IL
1A/DIV
1A/DIV
100µs/DIV
FIGURE 12. LOAD TRANSIENT TEST (MODE = VIN = 4.2V;
VO = 1.6V; IO = 0.01A~1A)
100µs/DIV
FIGURE 13. LOAD TRANSIENT TEST (MODE = GND,
VIN = 4.2V; VO = 1.6V; IO = 0.01A~1A)
VSW
VSW
5V/DIV
5V/DIV
VOUT (AC COUPLED)
VOUT (AC COUPLED)
100mV/DIV
100mV/DIV
IL
IL
1A/DIV
1A/DIV
100µs/DIV
FIGURE 14. LOAD TRANSIENT TEST (MODE = VIN = 3.6V;
VO = 1.6V; IO = 0.01A~1A)
6
100µs/DIV
FIGURE 15. LOAD TRANSIENT TEST (MODE = GND,
VIN = 3.6V; VO = 1.6V; IO = 0.01A~1A)
FN6612.0
December 21, 2007
ISL9107, ISL9108
Typical Applications
L
2.2µH
INPUT
2.7V TO 5.5V
OUTPUT
1.6V/0A~1.5A
SW
VIN
C2
10µF
C1
10µF
R2
100k
EN
R1
ISL9107
100k
C3
220pF
GND
R3
100k
PG
FB
RSI
MODE
E-PAD
L
2.2µH
INPUT
2.7V TO 5.5V
OUTPUT
1.6V/0A~1.5A
SW
VIN
C2
10µF
C1
10µF
R2
100k
EN
ISL9108
C3
220pF
GND
R3
100k
MODE
FB
NC
NC
E-PAD
PARTS
DESCRIPTION
MANUFACTURERS
PART NUMBER
SPECIFICATIONS
SIZE
L
Inductor
Sumida
CDRH4D15/SNP-2R2NC
2.2µH/2.0A/48mΩ
4.4mmx4.4mmx1.7mm
C1
Input capacitor
Murata
GRM21BR60J106KE19L
10µF/6.3V
2.0mmx1.25mmx1.25mm
C2
Output capacitor
Murata
GRM21BR60J106KE19L
10µF/6.3V
2.0mmx1.25mmx1.25mm
C3
Capacitor
Murata
GRM188R71H221KA01C
220pF/50V
1.6mmx0.8mmx0.8mm
R1(ISL9107)
Resistor
Various
100kΩ, SMD, 1%
1.6mmx0.8mmx0.45mm
R2, R3
Resistor
Various
100kΩ, SMD, 1%
1.6mmx0.8mmx0.45mm
FIGURE 16. TYPICAL APPLICATION DIAGRAM FOR ISL9107 AND ISL9108
7
FN6612.0
December 21, 2007
ISL9107, ISL9108
Block Diagram
MODE
SOFTSTART
SHUTDOWN
SHUTDOWN
0.8V
BANDGAP
+
EN
OSCILLATOR
EAMP
VIN
+
COMP
PWM/PFM
LOGIC
CONTROLLER
SW
PROTECTION
SLOPE
COMP
DRIVER
+
GND
RSI*
+
VREF5
SCP
FB
+
*Note
CSA
+
+
VREF3
OCP
VREF1
+
+
VREF4
SKIP
PG*
VREF2
PGOOD
DELAY
ZERO-CROSS
SENSING
*Note: Only applies to ISL9107.
FIGURE 17. FUNCTIONAL BLOCK DIAGRAM
8
FN6612.0
December 21, 2007
ISL9107, ISL9108
Theory of Operation
The ISL9107 and ISL9108 are step-down switching
regulators optimized for battery-powered handheld
applications. The regulators operate at typical 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 regulators
can be selected to enter skip mode to reduce the switching
frequency, unless forced to the fixed frequency, to minimize
the switching loss and to maximize the battery life. The
quiescent current under skip mode with no loading is
typically only 17µA. The supply current is typically only
0.1µA when the regulator is disabled.
PWM Control Scheme
These devices use the peak-current-mode pulse-width
modulation (PWM) control scheme for fast transient
response and pulse-by-pulse current limiting. Figure 17
shows the circuit functional block diagram. The current loop
consists of the oscillator, the PWM comparator COMP,
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 control
reference for the current loops comes from the Error
Amplifier (EAMP) of the voltage loop.
vEAMP
vCSA
d
iL
vOUT
FIGURE 18. PWM OPERATION WAVEFORMS
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 P-Channel
MOSFET starts ramping up. When the sum of the CSA
output and the compensation slope reaches the control
reference of the current loop, the PWM comparator COMP
sends a signal to the PWM logic to turn off the P-Channel
MOSFET and to turn on the N-Channel MOSFET. The
N-MOSFET remains on till the end of the PWM cycle. Figure 18
shows the typical operating waveforms during the normal PWM
operation. The dotted lines illustrate the sum of the slope
compensation ramp and the CSA output.
feedback signal comes from the FB pin. The soft-start block
only affects the operation during the start-up and will be
discussed separately in “Soft Start-Up” on page 10. The
EAMP is a transconductance amplifier, which converts the
voltage error signal to a current output. The voltage loop is
internally compensated by a RC network. The maximum
EAMP voltage output is precisely clamped to the bandgap
voltage.
Skip Mode
With the MODE pin connected to logic high, the device
enters a pulse-skipping mode at light load to minimize the
switching loss by reducing the switching frequency.
Figure 19 illustrates the skip mode operation. A zero-cross
sensing circuit (as shown in Figure 17) monitors the
N-Channel MOSFET current for zero crossing. When it is
detected to cross zero for 8 consecutive cycles, the regulator
enters the skip mode. During the 8 consecutive cycles, the
inductor current could be negative. The counter is reset to
zero when the sensed N-Channel MOSFET current does not
cross zero during any cycle within the 8 consecutive cycles.
Once the device enters the skip mode, the pulse modulation
starts being controlled by the SKIP comparator shown in
Figure 17. Each pulse cycle is still synchronized by the PWM
clock. The P-Channel MOSFET is turned on at the rising
edge of clock and turned off when its current reaches 20% of
the peak current limit. 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 it’s nominal voltage, the
P-Channel 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-Channel MOSFET will
be turned on again, repeating the previous operations.
The regulator resumes normal PWM mode operation when
the output voltage is sensed to drop below 1.5% of its
nominal voltage value.
Enable
The enable (EN) pin allows the user to enable or disable the
converter for purposes such as power-up sequencing. With
the EN pin pulled to high, the converter is enabled, the
internal reference circuit wakes up first and then the soft
start-up begins. When the EN pin is pulled to logic low, the
converter is disabled, the P-Channel MOSFET is turned off
immediately and the output capacitor is discharged through
internal discharge path.
Undervoltage Lockout (UVLO)
When the input voltage is below the Undervoltage Lockout
(UVLO) threshold, the device is disabled.
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
9
FN6612.0
December 21, 2007
ISL9107, ISL9108
Mode Selection
Power MOSFETs
The MODE pin is provided on ISL9107 and ISL9108 to
select the operation mode. When it is driven to logic low or
ground, the regulator operates in forced PWM mode. Under
forced PWM mode, the device remains at the fixed PWM
operation (typical at 1.6MHz), regardless of if the load
current is high or low.
The power MOSFETs are optimized to achieve better
efficiency. The ON-resistance for the P-Channel MOSFET is
typically 0.16Ω and the typical ON-resistance for the
N-Channel MOSFET is 0.15Ω.
When the MODE pin is driven to logic high or connected to
input voltage VIN, the regulator operates in either SKIP
mode or fixed PWM mode depending on the different load
conditions.
Overcurrent Protection
The overcurrent protection is provided when an overload
condition happens. It is realized by monitoring the CSA output
with the OCP comparator, as shown in Figure 17. When the
current at P-Channel MOSFET is sensed to reach the current
limit, the OCP comparator is triggered to turn off the
P-Channel MOSFET immediately.
Short-Circuit Protection
As shown in Figure 17, the device has a Short-Circuit
Protection (SCP) comparator, which monitors the FB pin
voltage for output short-circuit protection. When the FB
voltage is lower than 0.2V, the SCP comparator forces the
PWM oscillator frequency to drop to 1/3 of its normal
operation frequency.
Low Dropout Operation
The ISL9107 and ISL9108 feature low dropout operation to
maximize the battery life. When the input voltage drops to a
level that the device can no longer operate under switching
regulation to maintain the output voltage, the P-Channel
MOSFET is completely turned on (100% duty cycle). The
dropout voltage under such condition is the product of the
load current and the ON-resistance of the P-Channel
MOSFET. Minimum required input voltage VIN under this
condition is the sum of the output voltage plus the voltage
drop cross the inductor and the P-Channel MOSFET switch.
Thermal Shut Down
The ISL9107 and ISL9108 provide a built-in thermal
protection function. The thermal shutdown threshold
temperature is typical +160°C with typical +25°C hysteresis.
When the internal temperature is sensed to reach +150°C,
the regulator is completely shut down and as the
temperature is sensed to drop to +125°C (typical), the device
resumes operation starting from the soft start-up.
RSI Signal
Soft Start-Up
The soft start-up eliminates the inrush current during the
circuit 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.
The RSI signal is an input signal, which can reset the PG
signal. As shown in Figure 17, the power-good signal is
gated by the RSI signal. When the RSI is high, the PG signal
remains low, regardless of the output voltage condition. This
function is provided on ISL9107 only.
Power-Good
The ISL9107 offers a power-good (PG) signal. When the
output voltage is not within the power-good window, the PG
pin outputs an open-drain low signal. When the output
voltage is within the power-good window, an internal
power-good signal is issued to turn off the open-drain
MOSFET so that the PG pin can be externally pulled to high.
8 CYCLES
CLOCK
20% PEAK CURRENT LIMIT
IL
0
1.015*VOUT_NOMINAL
VOUT
VOUT_NOMINAL
FIGURE 19. SKIP MODE OPERATION WAVEFORMS
10
FN6612.0
December 21, 2007
ISL9107, ISL9108
The rising edge of the PG output is delayed by 215ms
(typical) from the time the power-good signal is issued. This
function is provided on ISL9107 only.
Inductor and Output Capacitor Selection
calculated as VO/(R2 + R3), so larger resistance is desirable
to minimize this current. On the other hand, the FB 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.
To achieve better steady state and transient response,
typically a 2.2µH inductor can be used. The peak-to-peak
inductor current ripple can be expressed as in Equation 1:
C3 (shown in Figure 16) is highly recommended to be added
for improving stability and achieving better transient
response. C3 can be calculated using Equation 3:
VO ⎞
⎛
V O • ⎜ 1 – ---------⎟
V
⎝
IN⎠
ΔI = --------------------------------------L • fS
1
C 3 = ----------------------------------------------------2 × π × R 2 × 7.3kHz
Applications Information
(EQ. 1)
In Equation 1, usually the typical values can be used but to
have a more conservative estimation, the inductance should
consider the value with worst case tolerance; and for
switching frequency (fS), the minimum fS from the “Electrical
Specifications” table on page 2 can be used.
To select the inductor, its saturation current rating should be
at least higher than the sum of the maximum output current
and half of the delta calculated from Equation 1. Another
more conservative approach is to select the inductor with the
current rating higher than the P-Channel MOSFET peak
current limit.
(EQ. 3)
Table 1 provides the recommended component values for
some output voltage options.
Layout Recommendation
The PCB layout is a very important converter design step to
make sure the designed converter works well, especially
under the high current, high switching frequency condition.
Another consideration is the inductor DC resistance since it
directly affects the efficiency of the converter. Ideally, the
inductor with the lower DC resistance should be considered
to achieve higher efficiency.
For ISL9107 and ISL9108, the power loop is composed of
the output inductor (L), the output capacitor (COUT), the SW
pin and the GND 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 same type of traces
should be used to connect the VIN pin, the input capacitor
CIN and its ground. The switching node of the converter, the
SW pin, and the traces connected to this node are very
noisy, so keep the voltage feedback trace and other noise
sensitive traces away from these noisy traces.
Inductor specifications could be different from different
manufacturers so please check with each manufacturer if
additional information is needed.
The input capacitor should be placed as close as possible to
the VIN pin. The ground of the input and output capacitors
should be connected as close as possible as well.
For the output capacitor, a ceramic capacitor can be used
because of the low ESR values, which helps to minimize the
output voltage ripple. A typical value of 10µF/6.3V ceramic
capacitor should be enough for most of the applications and
the capacitor should be X5R or X7R.
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.
Input Capacitor Selection
The main function for the input capacitor is 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/6.3V ceramic capacitor (X5R or X7R)
is a good starting point for the input capacitor selection.
Output Voltage Setting Resistor Selection
The voltage divider resistors (R2 and R3), as shown in
Figure 16, set the desired output voltage value. The output
voltage can be calculated using Equation 2:
R 2⎞
⎛
V O = V FB • ⎜ 1 + -------⎟
R 3⎠
⎝
TABLE 1. ISL9107 AND ISL9108 RECOMMENDED CIRCUIT
CONFIGURATION vs VOUT
VOUT (V)
L (µH)
C2 (µF)
R2 (kΩ)
C3 (pF)
R3 (kΩ)
0.8
2.2
10
0
N/A
100
1.0
2.2
10
44.2
470
178
1.2
2.2
10
80.6
270
162
1.5
2.2
10
84.5
270
97.6
1.8
2.2
10
100
220
80.6
2.5
2.2~3.3
10~22
100
220
47.5
2.8
2.2~3.3
10~22
100
220
40.2
3.3
2.2~3.3
10~22
102
220
32.4
(EQ. 2)
where VFB is the feedback voltage (typically it is 0.8V). The
current flowing through the voltage divider resistors can be
11
FN6612.0
December 21, 2007
ISL9107, ISL9108
Dual Flat No-Lead Plastic Package (DFN)
L8.2x3
2X
0.15 C A
A
D
8 LEAD DUAL FLAT NO-LEAD PLASTIC PACKAGE
2X
MILLIMETERS
0.15 C B
SYMBOL
E
MIN
A
0.80
A1
-
6
A3
INDEX
AREA
b
TOP VIEW
D2
0.20
0.10
SIDE VIEW
C
SEATING
PLANE
D2
(DATUM B)
0.08 C
A3
7
0.90
1.00
-
-
0.05
-
0.25
0.32
1.50
1.65
1.75
1
7,8
3.00 BSC
-
8
1.65
e
1.80
1.90
7,8
0.50 BSC
-
k
0.20
-
-
-
L
0.30
0.40
0.50
8
N
8
Nd
4
D2/2
6
INDEX
AREA
5,8
C
E2
A
NOTES
2.00 BSC
E
//
MAX
0.20 REF
D
B
NOMINAL
2
3
Rev. 0 6/04
2
NX k
NOTES:
1. Dimensioning and tolerancing conform to ASME Y14.5-1994.
2. N is the number of terminals.
3. Nd refers to the number of terminals on D.
(DATUM A)
E2
4. All dimensions are in millimeters. Angles are in degrees.
E2/2
5. Dimension b applies to the metallized terminal and is measured
between 0.25mm and 0.30mm from the terminal tip.
NX L
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.
N N-1
NX b
e
8
5
0.10
(Nd-1)Xe
REF.
M C A B
7. Dimensions D2 and E2 are for the exposed pads which provide
improved electrical and thermal performance.
8. Nominal dimensions are provided to assist with PCB Land
Pattern Design efforts, see Intersil Technical Brief TB389.
BOTTOM VIEW
CL
(A1)
NX (b)
L
5
SECTION "C-C"
C C
TERMINAL TIP
e
FOR EVEN TERMINAL/SIDE
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.
Intersil Corporation’s quality certifications can be viewed 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
12
FN6612.0
December 21, 2007