Intersil ISL78213ARZ 3a low quiescent current, high efficiency synchronous buck regulator Datasheet

ISL78213
Features
The ISL78213 is a high efficiency, monolithic,
synchronous step-down DC/DC converter that can
deliver up to 3A continuous output current from a 2.8V 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 97% Efficiency
The ISL78213 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 300mV
dropout voltage at 3A output current. High 1MHz
pulse-width modulation (PWM) switching frequency, that
can be synchronized up to 4MHz with an external clock,
allows the use of small external components and SYNC
input enables multiple ICs to synchronize out of phase to
reduce ripple and eliminate beat frequencies.
• Power-Good (PG) Output with a 1ms Delay
• 2.8V to 5.5V Supply Voltage
• 2% Output Accuracy Over-Temperature/Load/Line
• 3A Output Current
• Start-Up with Pre-Biased Output
• Internal Soft-Start - 1ms
• Soft-Stop Output Discharge During Disabled
• 35µA Quiescent Supply Current in PFM Mode
• Selectable Forced PWM Mode and PFM Mode
• External Synchronization up to 4MHz
• Less than 1µA Logic Controlled Shutdown Current
• 100% Maximum Duty Cycle
The ISL78213 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.
• Internal Current Mode Compensation
Fault protection is provided by internal hiccup mode
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.
• Pb-Free (RoHS Compliant)
The ISL78213 is offered in a space saving 4x4 QFN lead
free package with exposed pad lead frames for low
thermal resistance.
The ISL78213 includes 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 300mV
dropout voltage at 3A.
• Peak Current Limiting and Hiccup Mode Short Circuit
Protection
• Over-Temperature Protection
• Small 16 Ld 4mmx4mm QFN
• TS16949 Compliant
• AECQ100 Tested
Applications*(see page 14)
• Automotive Power
• DC/DC POL Modules
• µC/µP, FPGA and DSP Power
Related Literature*(see page 14)
• See AN1365, “ISL8013AEVAL2Z: 3A Low Quiescent
Current 1MHz High Efficiency Synchronous Buck
Regulator”
The ISL78213 offers a 1ms Power Good (PG) timer at
power-up. When shutdown, ISL78213 discharges the
output capacitor. Other features include internal
soft-start, internal compensation, overcurrent protection,
and thermal shutdown.
The ISL78213 is offered in a 4mmx4mm 16 Ld QFN
package with 1mm maximum height. The complete
converter occupies less than 0.4in2 area.
The ISL78213 is both AEC-Q100-rated and fully
TS16949-compliant. The ISL78214 is rated for the
automotive temperature range (-40°C to +105°C).
March 16, 2010
FN7550.1
1
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. 2010. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
ISL78213
3A Low Quiescent Current, High Efficiency
Synchronous Buck Regulator
ISL78213
Ordering Information
PART NUMBER
(Notes 1, 2, 3)
PART
MARKING
ISL78213ARZ
TEMP. RANGE
(°C)
782 13ARZ
PACKAGE
(Pb-Free)
-40 to +105
16 Ld 4x4 QFN
PKG.
DWG. #
L16.4x4
NOTES:
1. Add “-T” 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 ISL78213. For more information on MSL please
see techbrief TB363.
Pin Configuration
VDD
3
SYNCH
4
LX
LX
LX
13
12 PGND
11 PGND
PD
10 SGND
9
5
6
7
8
VFB
2
14
PG
VIN
15
NC
1
16
EN
VIN
NC
ISL78213
(16 LD QFN)
TOP VIEW
SGND
Refer to Application Note AN1365 for more layout suggestions.
Pin Descriptions
PIN NUMBER
PIN NAME
1, 2
VIN
Input supply voltage. Connect a 10µF ceramic capacitor to power ground.
DESCRIPTION
3
VDD
Input supply voltage for the analog circuitry. Connect to VIN pin.
5
EN
Regulator 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.
7
PG
1ms timer output. At power-up or EN HI, this output is a 1ms delayed Power-Good signal
for the output voltage.
4
SYNCH
Mode Selection pin. Connect to logic high or input voltage VDD for PWM mode. Connect
to logic low or ground for PFM mode. Connect to an external function generator for
synchronization with the negative edge trigger. Do not leave this pin floating.
13, 14, 15
LX
11, 12
PGND
Power ground
9, 10
SGND
Signal ground.
8
VFB
Buck regulator output feedback. Connect to the output through a resistor divider for
adjustable output voltage. For 0.8V output voltage, connect this pin to the output.
6, 16
NC
No connect.
PD
Exposed Pad
Switching node connection. Connect to one terminal of the inductor.
2
The exposed pad must be connected to the SGND pin for proper electrical performance.
Place as much vias as possible under the pad connecting to SGND plane for optimal
thermal performance.
FN7550.1
March 16, 2010
ISL78213
Typical Application
INPUT 2.8V TO 5.5V
VIN
LX
OUTPUT
1.8V
L
1.5µH
C2
2 x 22µF
VDD
C1
2 x 22µF
R2
124k
PGND
C3
47pF
ISL78213
EN
R1
100k
VFB
R3
100k
PG
SYNCH
SGND
FIGURE 1. TYPICAL APPLICATION DIAGRAM
Block Diagram
SYNCH
SHUTDOWN
SOFT
Soft
START
SHUTDOWN
27pF
390k
BANDGAP 0.8V
+
EN
OSCILLATOR
+
COMP
-
EAMP
3pF
+
VIN
PWM/PFM
LOGIC
CONTROLLER
PROTECTION
DRIVER
LX
PGND
VFB
SLOPE
Slope
COMP
6k
+
0.736V -
PG
1ms
DELAY
SGND
+
CSA
+
OCP
-
1.4V
+
SKIP
-
0.5V
ZERO-CROSS
SENSING
0.2V
SCP
+
FIGURE 2. FUNCTIONAL BLOCK DIAGRAM
3
FN7550.1
March 16, 2010
ISL78213
Absolute Maximum Ratings (Reference to GND)
Thermal Information
VIN, VDD . . . . . . . . . . . . . . -0.3V to 6V (DC) or 7V (20ms)
EN, SYNCH, PG . . . . . . . . . . . . . . . . . . -0.3V to VIN + 0.3V
LX . . . -1.5V (100ns)/-0.3V (DC) to 6.5V (DC) or 7V (20ms)
VFB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 2.8V
ESD Ratings
Human Body Model . . . . . . . . . . . . . . . . . . . . . . . 3000V
Charged Device Model . . . . . . . . . . . . . . . . . . . . . 2000V
Machine Model . . . . . . . . . . . . . . . . . . . . . . . . . . . 250V
Latch-up . . . . . . . . . . . . . . Tested and passed per JESD78A
Thermal Resistance (Typical)
θJA (°C/W) θJC (°C/W)
16 Ld QFN Package (Notes 4, 5) .
39
3
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 . . . . . . . . . . . . . . . . 2.8V to 5.5V
Load Current Range . . . . . . . . . . . . . . . . . . . . . . 0A to 3A
Ambient Temperature Range . . . . . . . . . . -40°C to +105°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. θJC, “case temperature” location is at 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 specification are measured at the following conditions
unless otherwise noted: TA = -40°C to +105°C, VIN = 3.6V, EN = VDD. Typical values are at
TA = +25°C. Boldface limits apply over the operating temperature range, -40°C to
+105°C.
PARAMETER
SYMBOL
TEST CONDITIONS
MIN
MAX
(Note 7) TYP (Note 7) UNITS
INPUT SUPPLY
VIN Undervoltage Lockout Threshold
Quiescent Supply Current
VUVLO
IVIN
Shut Down Supply Current
ISD
Rising, no load
-
2.6
2.8
V
Falling, no load
2.15
2.35
-
V
SYNCH = GND, no load at the output
-
35
-
µA
SYNCH = GND, no load at the output
and no switches switching
-
30
45
µA
SYNCH = VDD, FS = 1MHz, no load at
the output
-
6.5
10
mA
VIN = 5.5V, EN = low
-
0.1
4
µA
0.790
0.8
0.810
V
VFB = 0.75V
-
0.1
-
µA
VIN = VO + 0.5V to 5.5V (minimal 2.8V)
-
0.2
-
%/V
-
1
-
ms
OUTPUT REGULATION
Reference Voltage
VREF
VFB Bias Current
IVFB
Line Regulation
Soft-Start Ramp Time Cycle
OVERCURRENT PROTECTION
Current Limit Blanking Time
tOCON
-
17
-
Clock
pulses
Overcurrent and Auto Restart Period
tOCOFF
-
4
-
SS
cycle
Switch Current Limit
ILIMIT
(Note 6)
4.0
4.8
5.9
A
Peak Skip Limit
ISKIP
(Note 6)
-
1.2
-
A
-
20
-
µA/V
COMPENSATION
Error Amplifier Trans-Conductance
4
FN7550.1
March 16, 2010
ISL78213
Electrical Specifications
PARAMETER
Unless otherwise noted, all parameter limits are established over the recommended
operating conditions and the typical specification are measured at the following conditions
unless otherwise noted: TA = -40°C to +105°C, VIN = 3.6V, EN = VDD. Typical values are at
TA = +25°C. Boldface limits apply over the operating temperature range, -40°C to
+105°C. (Continued)
SYMBOL
Trans-Resistance
TEST CONDITIONS
RT
MIN
MAX
(Note 7) TYP (Note 7) UNITS
0.213
0.25
0.287
Ω
VIN = 5V, IO = 200mA
-
50
75
mΩ
VIN = 2.8V, IO = 200mA
-
70
100
mΩ
VIN = 5V, IO = 200mA
-
50
75
mΩ
VIN = 2.8V, IO = 200mA
-
70
100
mΩ
-
100
-
%
0.80
1.00
1.20
MHz
SYNCH = High
-
-
140
ns
Sinking 1mA
-
-
0.3
V
0.65
1
1.35
ms
-
0.01
2.0
µA
LX
P-Channel MOSFET ON-Resistance
N-Channel MOSFET ON-Resistance
LX Maximum Duty Cycle
PWM Switching Frequency
fS
LX Minimum On-Time
PG
Output Low Voltage
Delay Time (Rising Edge)
PG Pin Leakage Current
PG = VIN = 3.6V
PGOOD Rising Threshold
Percentage of regulation voltage
89
92
95
%
PGOOD Falling Threshold
Percentage of regulation voltage
85
88
91.5
%
-
15
-
µs
Logic Input Low
-
-
0.4
V
Logic Input High
1.4
-
-
V
-
0.1
4
µA
-
0.1
4
µA
Thermal Shutdown
-
140
-
°C
Thermal Shutdown Hysteresis
-
25
-
°C
PGOOD Delay Time (Falling Edge)
EN, SYNCH
Synch Logic Input Leakage Current
ISYNCH
Enable Logic Input Leakage Current
IEN
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.
5
FN7550.1
March 16, 2010
ISL78213
Typical Operating Performance
Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 2.5V to 5.5V, EN = VIN, SYNCH = 0V, L = 1.5µH,
C1 = 2x22µF, C2 = 2x22µF, IOUT = 0A to 3A.
90
90
80
70
2.5VOUT-PWM
1.8VOUT-PWM
1.5VOUT-PWM
1.2VOUT-PWM
60
EFFICIENCY (%)
100
EFFICIENCY (%)
100
50
40
0.0
2.5VOUT-PFM
80
70
1.8VOUT-PFM 1.5VOUT-PFM
1.2VOUT-PFM
60
50
0.5
1.0
1.5
2.0
2.5
40
0.0
3.0
0.1
0.2
0.3
OUTPUT LOAD (A)
FIGURE 3. EFFICIENCY vs LOAD (1MHz 3.3 VIN PWM)
90
70
1.2VOUT-PWM
3.3VOUT-PWM
60
EFFICIENCY (%)
90
EFFICIENCY (%)
100
1.8VOUT-PWM 1.5VOUT-PWM
2.5VOUT-PWM
80
70
60
2.5VOUT-PFM
3.3VOUT-PFM
0.5
1.0
1.5
2.0
2.5
40
0.0
3.0
0.1
0.2
0.3
1.2VOUT-PFM
1.5VOUT-PFM
1.8VOUT-PFM
0.4
0.5
0.6
0.7
0.8
0.9
1.0
FIGURE 6. EFFICIENCY vs LOAD (1MHz 5VIN PFM)
2.00
125
POWER DISSIPATION (mW)
POWER DISSIPATION (mW)
FIGURE 5. EFFICIENCY vs LOAD (1MHz 5VIN PWM)
1.75
1.50
1.25
1.00
3.3VIN-PWM
0.75
3.3VIN-PFM 5VIN-PFM
5VIN-PWM
0.25
0.00
0.0
1.0
OUTPUT LOAD (A)
OUTPUT LOAD (A)
0.50
0.9
50
50
40
0.0
0.8
FIGURE 4. EFFICIENCY vs LOAD (1MHz 3.3 VIN PFM)
100
80
0.4 0.5 0.6 0.7
OUTPUT LOAD (A)
0.5
1.0
1.5
2.0
2.5
3.0
OUTPUT LOAD (A)
FIGURE 7. POWER DISSIPATION vs LOAD (1MHz,
VOUT = 1.8V)
6
100
75
50
25
0
2.0
2.5
3.0
3.5
4.0
VIN (V)
4.5
5.0
5.5
FIGURE 8. POWER DISSIPATION WITH NO LOAD vs
VIN (PWM VOUT = 1.8V)
FN7550.1
March 16, 2010
ISL78213
Typical Operating Performance
Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 2.5V to 5.5V, EN = VIN, SYNCH = 0V, L = 1.5µH,
C1 = 2x22µF, C2 = 2x22µF, IOUT = 0A to 3A. (Continued)
1.24
OUTPUT VOLTAGE (V)
POWER DISSIPATION (mW)
0.25
0.20
0.15
0.10
0.05
0
2.5
3.0
3.5
4.0
VIN (V)
4.5
5.0
1.21
1.20
1.19
5VIN-PWM 3.3V
1.18
0.5
OUTPUT VOLTAGE (V)
1.50
5VIN-PWM
5VIN-PFM
3.3VIN-PWM
1.49
1.48
1.47
0.0
0.5
1.0
1.5
2.0
2.5
1.81
2.0
2.5
3.0
3.3VIN-PFM
1.80
1.79
1.78
5VIN-PFM
1.77
1.75
0.0
3.0
5VIN-PWM 3.3V
IN-PWM
1.76
0.5
OUTPUT LOAD (A)
1.0
1.5
2.0
2.5
3.0
OUTPUT LOAD (A)
FIGURE 11. VOUT REGULATION vs LOAD (1MHz,
VOUT = 1.5V)
FIGURE 12. VOUT REGULATION vs LOAD (1MHz,
VOUT = 1.8V)
2.52
3.36
3.3VIN-PFM
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
1.5
FIGURE 10. VOUT REGULATION vs LOAD (1MHz,
VOUT = 1.2V)
1.82
3.3VIN-PFM
1.51
2.50
1.0
1.83
1.52
2.51
IN-PWM
5VIN-PFM
OUTPUT LOAD (A)
1.55
OUTPUT VOLTAGE (V)
3.3VIN-PFM
1.16
0.0
5.5
FIGURE 9. POWER DISSIPATION WITH NO LOAD vs
VIN (PFM VOUT = 1.8V)
1.53
1.22
1.17
2.0
1.54
1.23
3.3VIN-PWM
2.49
2.48
2.47
2.46
2.45
2.44
0.0
5VIN-PWM
5VIN-PFM
0.5
3.35
3.34
4.5VIN-PWM
5VIN-PWM
3.33
3.32
3.31
3.30
4.5VIN-PFM
5VIN-PFM
3.29
1.0
1.5
2.0
OUTPUT LOAD (A)
2.5
FIGURE 13. VOUT REGULATION vs LOAD (1MHz,
VOUT = 2.5V)
7
3.0
3.28
0.0
0.5
1.0
1.5
2.0
OUTPUT LOAD (A)
2.5
3.0
FIGURE 14. VOUT REGULATION vs LOAD (1MHz,
VOUT = 3.3V)
FN7550.1
March 16, 2010
ISL78213
Typical Operating Performance
Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 2.5V to 5.5V, EN = VIN, SYNCH = 0V, L = 1.5µH,
C1 = 2x22µF, C2 = 2x22µF, IOUT = 0A to 3A. (Continued)
1.830
OUTPUT VOLTAGE (V)
1.820
0A LOAD PWM
3A LOAD PWM
1.810
1.800
1.790
1.780
1.770
1.820
3A LOAD
1.810
0A LOAD
1.800
1.790
1.780
1.770
1.760
1.760
1.750
2.0
OUTPUT VOLTAGE (V)
1.830
2.5
3.0
3.5
4.0
4.5
5.0
5.5
1.750
2.0
2.5
FIGURE 15. OUTPUT VOLTAGE REGULATION vs VIN
(PWM VOUT = 1.8 )
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
FIGURE 16. OUTPUT VOLTAGE REGULATION vs VIN
(PFM VOUT = 1.8V)
LX 2V/DIV
LX 2V/DIV
VOUT RIPPLE 20mV/DIV
VOUT RIPPLE 20mV/DIV
IL 0.5A/DIV
IL 0.5A/DIV
FIGURE 17. STEADY STATE OPERATION AT NO LOAD
(PWM)
FIGURE 18. STEADY STATE OPERATION AT NO LOAD
(PFM)
LX 2V/DIV
LX 2V/DIV
IL 1A/DIV
VOUT RIPPLE 50mV/DIV
IL 1A/DIV
VOUT RIPPLE 20mV/DIV
FIGURE 19. STEADY STATE OPERATION WITH FULL
LOAD
8
FIGURE 20. MODE TRANSITION CCM TO DCM
FN7550.1
March 16, 2010
ISL78213
Typical Operating Performance
Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 2.5V to 5.5V, EN = VIN, SYNCH = 0V, L = 1.5µH,
C1 = 2x22µF, C2 = 2x22µF, IOUT = 0A to 3A. (Continued)
LX 2V/DIV
VOUT RIPPLE 50mV/DIV
VOUT RIPPLE 50mV/DIV
IL 1A/DIV
IL 1A/DIV
FIGURE 21. MODE TRANSITION DCM TO CCM
LX 2V/DIV
FIGURE 22. LOAD TRANSIENT (PWM)
EN 5V/DIV
VOUT 0.5V/DIV
VOUT RIPPLE 50mV/DIV
IL 1A/DIV
FIGURE 23. LOAD TRANSIENT (PFM)
IL 1A/DIV
PG 5V/DIV
FIGURE 24. SOFT-START WITH NO LOAD (PWM)
EN 5V/DIV
EN 5V/DIV
VOUT 0.5V/DIV
VOUT 0.5V/DIV
IL 5A/DIV
IL 1A/DIV
PG 5V/DIV
PG 5V/DIV
FIGURE 25. SOFT-START AT NO LOAD (PFM)
9
FIGURE 26. SOFT-START WITH PRE-BIASED 1V
FN7550.1
March 16, 2010
ISL78213
Typical Operating Performance
Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 2.5V to 5.5V, EN = VIN, SYNCH = 0V, L = 1.5µH,
C1 = 2x22µF, C2 = 2x22µF, IOUT = 0A to 3A. (Continued)
EN 5V/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 27. SOFT-START AT FULL LOAD
LX 2V/DIV
FIGURE 28. SOFT-DISCHARGE SHUTDOWN
LX 2V/DIV
IL 1A/DIV
SYNCH 2V/DIV
VOUT RIPPLE 20mV/DIV
IL 1A/DIV
FIGURE 29. STEADY STATE OPERATION AT NO LOAD
WITH FREQUENCY = 2MHz
SYNCH 2V/DIV
VOUT RIPPLE 20mV/DIV
FIGURE 30. STEADY STATE OPERATION AT FULL
LOAD WITH FREQUENCY = 2MHz
LX 2V/DIV
LX 2V/DIV
IL 1A/DIV
SYNCH 2V/DIV
SYNCH 2V/DIV
VOUT RIPPLE 20mV/DIV
VOUT RIPPLE 20mV/DIV
IL 1A/DIV
FIGURE 31. STEADY STATE OPERATION AT NO LOAD
WITH FREQUENCY = 4MHz
10
FIGURE 32. STEADY STATE OPERATION AT FULL
LOAD (PWM) WITH FREQUENCY = 4MHz
FN7550.1
March 16, 2010
ISL78213
Typical Operating Performance
Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 2.5V to 5.5V, EN = VIN, SYNCH = 0V, L = 1.5µH,
C1 = 2x22µF, C2 = 2x22µF, IOUT = 0A to 3A. (Continued)
LX 2V/DIV
PHASE 2V/DIV
VOUT 1V/DIV
VOUT 0.5V/DIV
IL 2A/DIV
IL 2A/DIV
PG 5V/DIV
PG 5V/DIV
FIGURE 34. OUTPUT SHORT CIRCUIT RECOVERY
FIGURE 33. OUTPUT SHORT CIRCUIT
OUTPUT CURRENT (A)
5.000
4.875
4.750
OCP_3.3VIN
4.625
4.500
4.375
OCP_5VIN
4.250
4.125
4.000
-50
-25
0
25
50
75
100
TEMPERATURE (°C)
FIGURE 35. OUTPUT CURRENT LIMIT vs TEMPERATURE
Theory of Operation
The ISL78213 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 35µA. The
supply current is typically only 0.1µA when the regulator
is shut down.
PWM Control Scheme
Pulling the SYNCH pin HI (>2.5V) forces the converter
into PWM mode, regardless of output current. The
ISL78213 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.
11
The gain for the current sensing circuit is typically
250mV/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 (237mV/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 36 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
FN7550.1
March 16, 2010
ISL78213
transconductance amplifier that converts the voltage
error signal to a current output. The voltage loop is
internally compensated with the 27pF and 390kΩ RC
network. The maximum EAMP voltage output is precisely
clamped to 1.6V.
VEAMP
Synchronization Control
The frequency of operation can be synchronized up to
4MHz by an external signal applied to the SYNCH pin.
The falling edge on the SYNCH triggers the rising edge of
the LX pulse. Make sure that the minimum ON time of
the LX node is greater than 140ns.
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
250mV/A, from the P-MOSFET current to the CSA output.
When the CSA output reaches 1.4V, which is equivalent
to 4.8A for the switch current, 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.
VCSA
DUTY
CYCLE
IL
VOUT
FIGURE 36. PWM OPERATION WAVEFORMS
SKIP Mode
Pulling the SYNCH pin LO (<0.4V) forces the converter
into PFM mode. The ISL78213 enters a pulse-skipping
mode at light load to minimize the switching loss by
reducing the switching frequency. Figure 37 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 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.
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 0A and stays at zero.
The internal clock is disabled and 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.
Upon detection of an overcurrent condition, the upper
MOSFET will be immediately turned off and will not be
turned on again until the next switching cycle. Upon
detection of the initial overcurrent condition, the
overcurrent fault counter is set to 1. If, on the
subsequent cycle, another overcurrent condition is
detected, the OC fault counter will be incremented. If
there are 17 sequential OC fault detections, the regulator
will be shut down under an overcurrent fault condition.
An overcurrent fault condition will result in the regulator
attempting to restart in a hiccup mode within the delay of
four soft-start periods. At the end of the fourth soft-start
wait period, the fault counters are reset and soft-start is
attempted again. If the overcurrent condition goes away
during the delay of four soft-start periods, the output will
resume back into regulation point after 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 0.2V, the SCP comparator forces
the PWM oscillator frequency to drop to 1/3 of the normal
operation value. This comparator is effective during startup or an output short-circuit event.
The regulator resumes normal PWM mode operation when
the output voltage drops 1.5% below the nominal voltage.
12
FN7550.1
March 16, 2010
ISL78213
PWM
PFM
CLOCK
8 CYCLES
PFM CURRENT LIMIT
IL
LOAD CURRENTT
0
NOMINAL +1.5%
VOUT
NOMINAL
FIGURE 37. SKIP MODE OPERATION WAVEFORMS
PG
During power-up, the open-drain power good output
holds low for about 1ms after VOUT reaches the
regulation voltage. The PG output also serves as a 1ms
delayed the Power Good signal when the pull-up resistor
R1 is installed.
UVLO
When the input voltage is below the undervoltage
lock-out (UVLO) threshold, the regulator is disabled.
Soft Start-Up
The soft-start-up reduces the inrush 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.
Enable
The enable (EN) input allows the user to control 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 100Ω switch.
Power MOSFETs
The power MOSFETs are optimized for best efficiency. The
ON-resistance for the P-MOSFET is typically 50mΩ and the
ON-resistance for the N-MOSFET is typically 50mΩ.
100% Duty Cycle
The ISL78213 features 100% duty cycle operation to
maximize the battery life. When the battery voltage
drops to a level that the ISL78213 can no longer
maintain the regulation at the output, the regulator
13
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.
Thermal Shut-Down
The ISL78213 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 ISL78213 resumes operation by stepping
through the soft-start.
Applications Information
Output Inductor and Capacitor Selection
To consider steady state and transient operations,
ISL78213 typically uses a 1.5µH 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 applications, 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 performance. The inductor ripple current can
be expressed as shown in Equation 1:
VO ⎞
⎛
V O ⋅ ⎜ 1 – ---------⎟
V IN⎠
⎝
ΔI = ------------------------------------L ⋅ fS
(EQ. 1)
The inductor’s saturation current rating needs to be at
least larger than the peak current. The ISL78213
protects the typical peak current 4.8A. The saturation
current needs be over 5.5A for maximum output current
application.
ISL78213 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. 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. Additional output capacitance
should be added for better performances in applications
FN7550.1
March 16, 2010
ISL78213
where high load transient or low output ripple is required.
It is recommended to check the system level
performance along with the simulation model.
TABLE 1. OUTPUT CAPACITOR VALUE vs VOUT
VOUT
(V)
COUT
(µF)
L
(µH)
0.8
2 x 22
1.0~2.2
1.2
2 x 22
1.0~2.2
1.5
2 x 22
1.5~3.3
1.8
2 x 22
1.5~3.3
2.5
2 x 22
1.5~3.3
3.3
2 x 22
2.2~4.7
3.6
2 x 22
2.2~4.7
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 10kΩ and 100kΩ,
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. There is a leakage
current from VIN to LX. It is recommended to preload the
output with 10µA minimum. For better performance, add
47pF in parallel with R2 (100kΩ).
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. Two 22µF X5R or X7R ceramic
capacitors are a good starting point for the input
capacitor selection.
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
3/11/10
FN7550.1
On Page 5, under PG, corrected typo for MAX limit from 0.2 to 2.0.
3/8/10
FN7550.0
Initial release.
Products
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*For a complete listing of Applications, Related Documentation and Related Parts, please see the respective device
information page on intersil.com: ISL78213
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14
FN7550.1
March 16, 2010
ISL78213
Package Outline Drawing
L16.4x4
16 LEAD QUAD FLAT NO-LEAD PLASTIC PACKAGE
Rev 6, 02/08
4X 1.95
4.00
12X 0.65
A
B
13
6
PIN 1
INDEX AREA
6
PIN #1 INDEX AREA
16
1
4.00
12
2 . 10 ± 0 . 15
9
4
0.15
(4X)
5
8
TOP VIEW
0.10 M C A B
+0.15
16X 0 . 60
-0.10
4 0.28 +0.07 / -0.05
BOTTOM VIEW
SEE DETAIL "X"
0.10 C
1.00 MAX
C
BASE PLANE
( 3 . 6 TYP )
SEATING PLANE
0.08 C
SIDE VIEW
(
2 . 10 )
( 12X 0 . 65 )
( 16X 0 . 28 )
C
0 . 2 REF
5
( 16 X 0 . 8 )
0 . 00 MIN.
0 . 05 MAX.
DETAIL "X"
TYPICAL RECOMMENDED LAND PATTERN
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.
15
FN7550.1
March 16, 2010