SP6124

®
Advanced
SP6124
External NMOS PWM Buck Controller
FEATURES
■ N-Channel MOSFET Drive
■ Operating Input Voltage: 4.5V - 24V
■ Wide Output Range : 0.8V to 20V
■ ±1.5% 0.8V Reference
■ Low Dropout Operation : 95% Duty
Cycle
■ 500KHz Fixed Constant Frequency
■ Low Standby Current, IQ Typ: 720µA
■ Logic-Control Micropower Shutdown
■ Output Overvoltage Protection
■ Internal Diode for Bootstrapped Gate
Drive
■ Current Mode Operation for Excellent
Line and Load Transient Response
■ Available in 8 pin MSOP package
CS 1
8 V IN
SP6124
ITH/RUN 2
7 BOOST
8 Pin MSOP
FB 3
6 DRI
GND 4
5 SW
Now Available in Lead Free Packaging
APPLICATIONS
■ LCD Monitor
■ PDA
■ Wireless Modems
■ On Card Switching Regulators
■ DC Power Distribution Systems
DESCRIPTION
The SP6124 is a current mode switching regulator controller that drives an external Nchannel power MOSFET using a fixed frequency architecture. It uses external divider to
adjust output voltage from 0.8V to 20V with excellent line and load regulation. A maximum
high duty cycle limit of 95% provides low dropout operation which extends operating time
in battery-operated systems. Switching frequency up to 500KHz are achievable thus
allowing smaller sized filter components. The operating current level is user-programmable
via an external current sense resistor. It also provides output overvoltage protection under
fault conditions. A multifunction pin (ITH/RUN) allows external compensation for optimum
load step response plus shutdown. Soft start can also be implemented with this pin to
properly sequence supplies. The SP6124 is available in 8 pin MSOP package.
TYPICAL APPLICATION CIRCUIT
1000pF
1 CS
2 ITH/RUN
C5
330pF
3 FB
SP6124
4 GND
®
VIN 8
Boost
DRI
SW
C2
0.1µF
7
6
5
C3
0.1µF
R3
24k
C4
VIN 6V - 24V
C1
RS
33m
+
M1
FDS6694
D1
SL43
R1
20k
CIN1
22µF
L1
+
CIN2
22µF
VOUT 3.3V 3A
10µH
COUT
220µF
C6
2.2µF
1nF
R2 62k
CIN1, CIN2: HER-MEI 22µF/35V Electrolytic capacitors
M1: FAIRCHILD FDS6694 N -MOSFET
D1: GS SL43
L1: TDK SLF12555T-100M3R4
COUT: HER-MEI 220µF /16V Electrolytic capacitor
C6: TAIYO YUDEN LMK212BJ225KG -T Ceramic capacitor
Date: 01/26/05
SP6124, External NMOS PWM Buck Controller
1
© Copyright 2005 Sipex Corporation
ABSOLUTE MAXIMUM RATINGS
These are stress ratings only and functional operation of the device at these ratings or any other above those indicated
in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions
for extended periods of time may affect reliability.
Supply Voltage (VIN)............................................25V
Drive Supply Voltage (BOOST).......................32V
Switch Voltage (SW)...........................................25V
Differential Boost Voltage (BOOST to SW)........7.0V
ITH/RUN, VFB Voltages.......................................8.0V
Peak Drive Output Current < 10µs (DRI)...............2A
Operating Temperature Range.............-40ûC to +85ûC
Storage Temperature Range..............-65ûC to +150ûC
Lead Temperature Range (10 sec).....-65ûC to +150ûC
Thermal Resistance (TJA)
8 Pin NSOIC...................................................160ûC/W
8 Pin MSOP....................................................180ûC/W
ELECTRICAL CHARACTERISTICS
Unless otherwise noted, the following specifications apply for VIN = +15V, TA = 25°C.
PARAMETER
MIN.
Input Voltage
4.5
TYP.
720
MAX.
UNITS
24
V
900
Input Supply Current
CONDITIONS
Normal Mode (Note 1)
µA
Feedback Voltage
Output Overvoltage Lockout
Shutdown Mode, VITH/RUN = 0V
16
20
0.788
0.8
0.812
V
20
55
90
mV
VFB connect to
VOUT, ∆ VOVL = VOVL - VFB
0.002
0.015
%/V
VIN = 4.5 to 20V
0.7
1.1
Reference Voltage Line Regulation
Output Voltage Load Regulation
%
-0.4
-0.8
ITH Sinking 5µA
ITH Sourcing 5µA
Run Threshold
0.6
0.8
0.9
V
Maximum Current Sense Threshold
125
150
175
mV
Oscillator Frequency
45 0
500
550
KHz
DRI Rise Time
50
75
ns
CLOAD = 3000pF
DRI FallTime
50
75
ns
CLOAD = 3000pF
5.7
V
VIN = 8V, IBOOST = 5mA,
SW = 0V
VFB = 0.72V
Boost Voltage
4.9
5.3
Maximum Duty Cycle
90
94
%
Soft Start Time
5
7.5
ms
Run Current Source
1.0
2.3
4.0
µA
VITH/RUN = 0V, VFB = 0V
Run Pullup Current
100
190
250
µA
VITH/RUN = 1V
Note 1: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency.
Date: 01/26/05
SP6124, External NMOS PWM Buck Controller
2
© Copyright 2005 Sipex Corporation
PIN DESCRIPTION
Pin Number
Pin Name
Description
1
CS
2
ITH/RUN
Combination of error amplifier compensation point and run con-trol inputs.
The current com-parator threshold increases with this control voltage. Forcing
this pin below 0.8V causes the device to be shutdown.
3
FB
Feedback error amplifier input, to compare the feedback voltage with the
internal reference volt-age. Connecting a resistor R2 to converter output node
and a re-sistor R1 to ground yields the out-put voltage:
VOUT = 0.8 x (R1+R2)/ R1
4
GND
Singal GND for IC. All voltage levels are measured with respect to this pin.
5
SW
Switch node connection to induc-tor. In buck converter applications the
voltage swing at this pin is from a schottky diode voltage drop below ground to
VIN
6
DRI
External high-side N-MOSFET gate drive pin. Connect DRI to gate of the
external high-side N-MOSFET.
7
BOOST
8
VIN
Current sense comparator invert-ing input, not to exceed VIN voltage. Built in
offsets between the CS and VIN pins in conjunction with RSENSE set the
current trip thresholds.
Supply to high-side floating driver. The bootstrap capacitor C3 is returned to
this pin.
Input voltage pin. It also provides bias to the IC and gate gias for all
MOSFETS controlled by the IC.
BLOCK DIAGRAM
VIN
CS
VINT VINT
VIN
R1
+
+
R2
2.5µA
ICOMP
Q2
+
40mV
-
VIN
VIN
VINT
LC_COMP
*
VIN
INTVCC
Q1
1.2V
Slope
*
SD
LEB
Blank
Clock
Q3 Q4
SS
0.8V
+
SD
2.4V
SD
1.33V
+
ITH
ITH
ITH
Thermal
-
FB
Date: 01/26/05
DRI
Switching
Logic
Burst_Mode
Clock
0.8V
R
S
SW
Q
VINT
Dropout
DET
VIN
T
0.855V
Floating
Driver
+
Buffer_ITH
+
EA
-
BOOST
1_SHUT
M1
*
+
REF
0.8V
FB
OSC
Slope
GND
OVDT
SP6124, External NMOS PWM Buck Controller
3
© Copyright 2005 Sipex Corporation
TYPICAL PERFORMANCE CHARACTERISTICS
100
100
VOUT=3.3V
VOUT=5V
95
95
Efficiency (%)
VIN=6V
Efficiency (%)
90
VIN =12V
85
VIN=19V
80
VIN =6V
VIN =12V
90
85
VIN =19V
80
75
75
70
1
10
100
1000
10000
70
Load Current (mA)
Fig. 1 Efficiency vs Load Current (VOUT=3.3V)
1
10
100
1000
100
100
VOUT=3.3V
95
VOUT=5V
95
90
85
Efficiency (%)
Efficiency (%)
10000
Load Current (mA)
Fig. 2 Efficiency vs Load Current (VOUT=5.0V)
I LOAD=1A
80
I LOAD=0.1
A
75
90
ILOAD=1A
85
80
ILOAD=0.1A
75
70
0
5
10
15
20
25
30
70
Input Voltage (V)
Fig. 3 Efficiency vs Input Voltage
0
10
15
20
25
30
Input Voltage (V)
Fig. 4 Efficiency vs Input Voltage
900
7
800
Normal Mode
6
700
Boost Voltage (V)
Supply Current ( µA)
5
600
500
40
Shutdown
20
5
10
15
20
25
3
2
VPHASE=0V
0
30
0
Input Voltage (V)
Fig. 5 Supply Current vs Input Voltage
Date: 01/26/05
VCC=5V
4
1
0
0
VCC=15V
5
5
10
15
20
Boost Load Current (mA)
Fig. 6 Boost Load Regulation
SP6124, External NMOS PWM Buck Controller
4
© Copyright 2005 Sipex Corporation
TYPICAL PERFORMANCE CHARACTERISTICS
7
0.805
0.804
Boost Voltage (V)
Reference Voltage (V)
VCC UP
6
5
4
3
VCC DOWN
2
IBOOST=2mA
1
VPHASE=0V
0
0.803
0.802
0.801
0.800
0.799
0.798
0.797
0.796
0.795
0.794
0.793
0.792
0.791
0
5
10
15
20
25
30
0.790
-40
Input Voltage (V)
Fig. 7 Boost Line Regulation
-20
0
20
40
60
80
100
120
140
Temperature (° C)
Fig. 8 Reference Voltage vs Temperature
6.0
500
Frequency (KHz)
Boost Voltage (V)
480
5.5
5.0
4.5
IBOOST=1mA
460
440
420
VPHASE=0V
4.0
-40
-20
0
20
40
60
80
100
120
400
140
-40
Temperature (° C)
Fig. 9 Boost Voltage vs Temperature
-20
0
20
40
60
80
100
120
140
Temperature (° C)
Fig. 10 Operating Frequency vs Temperature
Current Sense Threshold (mV)
160
155
150
145
140
135
130
125
120
-40
-20
0
20
40
60
80
100
120
140
Temperature ( C)
Fig. 11 Maximum Current Sense Threshold vs
Temperature
Date: 01/26/05
SP6124, External NMOS PWM Buck Controller
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© Copyright 2005 Sipex Corporation
APPLICATION INFORMATION
Introduction
The Main control loop is shutdown when ITH/
RUN goes below 0.8V. When ITH/RUN pulled
up to 0.8V or up by error amplifier, main
control loop is enabled.
The SP6124 is a current mode switching
regulator controller that drives external Nchannel power MOSFET with constant
frequency architecture. It uses external
divider to adjust output voltage with
excellent line regulation and load regulation.
A maximum high duty cycle limit of 95%
provides low dropout operation, which
extends operating time in battery-operated
system.
Low Current Operation
During heavy load current operation,
SP6124 operates in PWM mode with a
frequency of 500KHz. Decreasing of the
current will cause a drop in ITH/RUN below
1.33V so that SP6124 enters PFM mode
operation for better efficiency. If the voltage
across RS does not exceed the offset of
current comparator within a cycle, then the
high-side and internal MOSFETs will disable
until ITH/RUN goes over 1.33V.
Wide input voltage ranges from 4.5V to
24V, and switching frequency (500KHz)
allows smaller sized filter components. The
operating current is user-programmable
via an external current sense resistor and
it automatically enters PFM operation at
low output current to boost circuit efficiency.
Component Selection
A multifunction pin (ITH/RUN) allows external
compensation plus shutdown. A built-in
soft start can properly provide sequence
supplies. Available packages are in SOP8
and MSOP8 for SMD.
SP6124 can be used in many switching
regulator applications, such as step-down,
step-up, SEPIC and positive-to-negative
converters. Of these, the step-down
converter is the most common application.
External component selection, beginning
with selecting RS, depends on the load
requirement of the application. Once RS is
determined, the choice of inductor, power
MOSFET and diode can be easily chosen.
Finally, CIN and COUT can be determined.
Theory of Operation
SP6124 uses a current mode with a
constant frequency architecture. Normally
the high-side MOSFET turns on each cycle
when oscillator sets the RS latch and it
turns off when internal current comparator
resets the RS latch. Voltage on ITH/RUN
pin, which is the output voltage of voltage
error amplifier, will control peak inductor
current. The output voltage feeds back to
VFB pin so that the error amplifier receives
a voltage through external resistor divider.
When load current increases, it causes a
slight decrease in the voltage of VFB pin.
Thus the ITH/RUN voltage increases until
the average inductor current matches the
new load current. While the high-side
MOSFET turns off, the low-side MOSFET
is turned on to recharge bootstrap capacitor
C3.
Date: 01/26/05
RS Selection
The choice of RS depends on the required
output current. The threshold voltage of
current comparator decides peak inductor
current, which yields a maximum average
output current (IMAX). And the peak current is
less than half of the peak-to-peak ripple
current, ∆IL.
Allowing a margin for variation of SP6124,
RS can be calculated as follows:
R
SP6124, External NMOS PWM Buck Controller
6
S
=
100mV
I
MAX
© Copyright 2005 Sipex Corporation
APPLICATION INFORMATION
Inductor Selection
Output Diode Selection
Since SP6124 operates at a high frequency
of 500KHz a smaller inductor value is
preferred. In general, operating in high
frequency will cause low efficiency because
of large MOSFET switching loss. Therefore
the effect of inductor value on ripple current
and low current operation must be
considered as well.
In order not to exceed the diode ratings, it is
important to specify the diode peak current
and average power dissipation.
CIN and COUT Selection
To prevent high voltage spikes resulting
from high frequency switching, a low ESR
input capacitor for the maximum RMS
current must be used. Usually capacitors
may be paralleled to meet size or height
requirements in the design.
The inductor value has a direct influence
on ripple current (∆IL), which decreases
with high inductance and increases with
high VIN or VOUT:
V −V
+ V
V
OUT  OUT
D
ÄI = IN
∆
L
 V +V
f ×L
D
 IN
The selection of COUT depends on the
required effective series resistance (ESR).
In general once the ESR requirement is
met, the capacitance is suitable for filtering.
The output ripple voltage (∆V OUT ) is
determined by:




VD is the drop voltage of the output Schottky
diode.

1
∆VOUT ≈ ∆I L  ESR +
4 fC OUT

Accepting a large value of ∆IL allows the
use of low inductance, but yields high output
ripple voltage and large core loss. The
inductor value also has an effect on low
current operation. Low inductor value
causes the PFM operation to begin at high
load current. The efficiency of the circuit
decreases at the beginning of low current
operation. Generally speaking, low
inductance in PFM mode will cause the
efficiency to decrease.
where f = operating frequency, COUT = output
capacitance and ∆IL = ripple current of the
inductor. Once the ESR requirement for
COUT has been met, the RMS current rating
generally exceeds the IRIPPLE(P-P) requirement.
Topside MOSFET Driver Supply (C3)
External bootstrap capacitor C3 connecting
to the BOOST pin supplies the gate drive
voltage for highside MOSFET. C3 is charged
from INTVCC when SW pin is low. When the
high-side MOSFET turns on, the driver
places the C3 voltage across the gate and
the source of MOSFET. It will enhance the
MOSFET and turn on the high-side switch.
Then the switch node voltage SW rises to
VIN and BOOST pin rises to VIN + INTVCC. In
general, 0.1mF is acceptable.
Power MOSFET Selection
For an application of SP6124, an external
N-channel power MOSFET, used as the
high-side switch, must be properly selected.
To prevent damage to the MOSFET during
high input voltage operation, the BVDSS
specification of the MOSFET should be
considered. Other important selection
criteria for the power MOSFET include the
“ON” resistance RDS(ON), maximum gate
voltage and maximum output current.
Date: 01/26/05




SP6124, External NMOS PWM Buck Controller
7
© Copyright 2005 Sipex Corporation
APPLICATION INFORMATION
Output Voltage Programming
Over Current Protection
The typical SP6124 application circuit is
shown in figure17. A resistive divider, as in
the following formula, sets the output
voltage.

R2 
V OUT = 0 .8 V  1 +

R1 

Over current protection occurs when the
peak inductor current reaches maximum
current sense threshold divided by sense
resistor. The maximum current under over
current protection can be calculated by the
following formula.
150mV(Maximum current sense threshold)
I
=
MAX
The feedback reference voltage 0.8V
allows low output voltages from 0.8V to
input voltage. A small capacitor at 1nF in
parallel to the upper feedback resistor is
required for a stable feedback.
The ITH/RUN pin, also as a dual-purpose
pin, provides loop compensation as well
as shutdown function. An internal current
source at 2.5mA charges up the external
capacitor C5. When the voltage on ITH/
RUN pin reaches 0.8V, the SP6124 begins
to operate.
Over Voltage Protection
Over voltage protection occurs when the FB
pin voltage (the negative input of error
amplifier) exceeds 0.855V. The over voltage
comparator will force driver to pull low until
output over voltage is removed.
VIN 4.5V - 24V
C7
1µF
D2
LL4148
S
At the same time, the frequency of oscillator
will be reduced to sixteenth of original value,
500kHz. This lower frequency allows the
inductor current to safely discharge, thereby
preventing current runaway. The frequency
of oscillator will automatically return to its
designed value when the peak inductor
value no longer exceeds over current
protection point.
ITH/RUN Function
R4
1.2M
R
ITH/RUN
PCB Layout
Since the switching frequency of SP6124 is
500KHz, proper PCB layout and component
placement may enhance the performance
of SP6124 application circuit. For a better
efficiency, major loop from input terminal to
output terminal should be as short as
possible. In addition, in the case of a large
current loop, the track width of each
component in the loop should maintain as
wide as possible.
C5
330pF
R3
24k
Fig. 12 ITH/RUN pin interfacing
Date: 01/26/05
SP6124, External NMOS PWM Buck Controller
8
© Copyright 2005 Sipex Corporation
APPLICATION INFORMATION
In order to prevent the effect from noise,
the GND pin should be placed close to the
ground. Also keep the IC’s GND pin and
the ground leads at the shortest distance.
Recommended layout diagrams and
component placement are as shown as
figures 13 &16. No sensitive components,
which may cause noise interference to the
circuit, should be allowed to be close to SW
pin.
Furthermore, SP6124 is a current mode
controller. Keeping the sense resistor close
to both VIN and CS pins is recommended for
better efficiency and output performance. In
addition, all filtering and decoupling
capacitors, such as C1 and C2 should be
connected as close as possible to SP6124.
Fig. 13 Top Layer
Fig. 14 Bottom Layer
Fig. 15 Placement (Top Overlay)
Fig. 16 Placement (Bottom Overlay)
Date: 01/26/05
SP6124, External NMOS PWM Buck Controller
9
© Copyright 2005 Sipex Corporation
APPLICATION INFORMATION
** VIN 6V~24V
R4
1.2M
1
D2
2
LL4148
C7
1µF
C5
330pF
3
4
CS
®
ITH/RUN
SP6124
FB
GND
VIN
Boost
DRI
SW
1000pF
8
VIN 6V - 24V
C1
C2
0.1µF
7
6
5
CIN2
22µF
VOUT 3.3V 3A
L1
10µH
D1
SL43
C4
R1
20k
+
22µF
M1
FDS6694
C3
0.1µF
R3
24k
CIN1
+
RS
33m
COUT
220µF
C6
2.2µF
1nF
R2 62k
Fig. 17: 3.3V Step-Down Converter with external soft start circuit
1 CS
®
2 ITH/RUN
C5
330pF
C7
3 FB
SP6124
VIN 8
1000pF
Boost 7
D2
DRI 6
SW 5
4 GND
1nF
C2
0.1µF
LL4148
R3
24k
VIN 5V
C1
C3
C4
R1
20k
RS
33m
+
M1
FDS6694
D1
SL43
CIN1
22µF
+
CIN2
22µF
L1
VOUT 3.3V 3A
10µH
COUT
220µF
C6
2.2µF
1nF
R2 62k
Fig. 18: 5V to 3.3V Step-Down Converter
Date: 01/26/05
SP6124, External NMOS PWM Buck Controller
10
© Copyright 2005 Sipex Corporation
PACKAGE: 8 Pin NSOIC
D
Ø
e
E/2
L2
E1/2 E1
E
Seating Plane
L1
1
Gauge Plane
VIEW C
b
INDEX AREA
(D/2 X E1/2)
Ø
L
Ø1
TOP VIEW
A1
A
Seating Plane
A2
8 Pin NSOIC JEDEC MO-012 (AA) Variation
MIN
NOM
MAX
SYMBOL
A
1.35
1.75
A1
0.1
0.25
A2
1.25
1.65
b
0.31
0.51
c
0.17
0.24
4.90 BSC
D
6.00 BSC
E
3.90 BSC
E1
1.27 BSC
e
L
0.4
1.27
1.04 REF
L1
0.25 BSC
L2
ø
0º
8º
ø1
5º
15º
SIDE VIEW
B
B
SEE VIEW C
b
c
Note: Dimensions in (mm)
BASE METAL
SECTION B-B
WITH PLATING
Date: 01/26/05
SP6124, External NMOS PWM Buck Controller
11
© Copyright 2005 Sipex Corporation
PACKAGE: 8 Pin MSOP
D
e1
Ø1
E/2
R1
R
E1
E
Gauge Plane
L2
Ø1
Seating Plane
Ø
L
L1
1
2
e
Pin #1 indentifier must be indicated within this shaded area (D/2 * E1/2)
8 Pin MSOP JEDEC MO-187 (AA) Variation
MIN
NOM
MAX
SYMBOL
A
1.1
A1
0
0.15
A2
0.75
0.85
0.95
b
0.22
0.38
c
0.08
0.23
3.00 BSC
D
4.90 BSC
E
3.00 BSC
E1
0.65 BSC
e
1.95 BSC
e1
L
0.4
0.6
0.8
0.95 REF
L1
0.25 BSC
L2
N
8
R
0.07
R1
0.07
ø
0º
8º
ø1
0º
15º
B
B
A2
A
b
A1
WITH PLATING
b
c
BASE METAL
Note: Dimensions in (mm)
Section B-B
Date: 01/26/05
SP6124, External NMOS PWM Buck Controller
12
© Copyright 2005 Sipex Corporation
ORDERING INFORMATION
Part Number
Temperature Range
Package Types
SP6124-EN ...................................................... -40°C to +85°C ................................................... 8-pin NSOIC
SP6124-EN/TR ................................................ -40°C to +85°C .................................................. 8-pin NSOIC
SP6124-EU ...................................................... -40°C to +85°C .................................................... 8-pin MSOP
SP6124-EU/TR ................................................ -40°C to +85°C ................................................... 8-pin MSOP
Available in lead free packaging. To order add “-L” suffix to part number.
Example: SP6124-1EN/TR = standard; SP6124-EN-L/TR = lead free
/TR = Tape and Reel
Pack quantity is 2,500 for NSOIC and MSOP.
Corporation
ANALOG EXCELLENCE
Sipex Corporation
Headquarters and
Sales Office
233 South Hillview Drive
Milpitas, CA 95035
TEL: (408) 934-7500
FAX: (408) 935-7600
Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the
application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others.
Date: 01/26/05
SP6124, External NMOS PWM Buck Controller
13
© Copyright 2005 Sipex Corporation