AIC AIC1577-CSTR External nmos step-down pwm controller Datasheet

AIC1577
External NMOS Step-Down PWM Controller
DESCRIPTION
FEATURES
N-Channel MOSFET Drive
Operating Input Voltage from 4.5V to 24V
Wide Ouput Range : 0.8V to 20V
±1.5% 0.8V Reference
Low Dropout Operation : 95% Duty Cycle
500KHz Fixed Constant Frequency
Low Standby Current, IQ Typically 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 an 8-Lead SO and MSOP Package
The AIC1577 is a current mode switching
regulator controller that drives external Nchannel power MOSFET using a fixed frequency architecure. 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 provide output overvolt-
APPLICATIONS
LCD Monitor
Palmtop Computers, PDAs
Wireless Modems
On-Card Switching Regulators
DC Power Distribution Systems
age 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. Package available are in
SOP8 and MSOP8 for SMD.
Analog Integrations Corporation
Si-Soft Research Center
DS-1577P-02 010405
3A1, No.1, Li-Hsin Rd. I , Science Park , Hsinchu 300, Taiwan , R.O.C.
TEL: 886-3-5772500
FAX: 886-3-5772510
www.analog.com.tw
1
AIC1577
TYPICAL APPLICATION CIRCUIT
1
2
C5
3
330pF
4
R3
24k
VIN
CS
ITH/RUN BOOST
DRI
FB
SW
GND
AIC1577
8
C2
0.1µF
7
6
5
RS
33m
+
CIN1
22µF
M1
FDS6694
C3
0.1µF
L1
+
CIN2
22µF
VOUT 3.3V 3A
10µH
D1
SL43
C4
R1
20k
VIN 6V~24V
C1
1000pF
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
ORDERING INFORMATION
AIC1577-XXXX
PIN CONFIGURATION
PACKING TYPE
TB: TUBE
TR: TAPING & REEL
TOP VIEW
PACKAGING TYPE
S: SMALL OUTLINE
O: MSOP8
CS 1
8
VIN
ITH/RUN 2
7
BOOST
FB 3
6
DRI
5
SW
GND
4
C: Commercial
P: Lead Free Commercial
Example: AIC1577COTR
in MSOP Package & Taping & Reel
Packing Type
AIC1577POTR
in MSOP Lead Free Package &
Taping & Reel Packing Type
2
AIC1577
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VIN)
Drive Supply Voltage (BOOST)
Switch Voltage (SW)
Differential Boost Voltage (BOOST to SW )
ITH/RUN,VFB Voltages
Peak Drive Output Current < 10µS (DRI )
Operating Temperature Range
Junction Temperatrue
Storage Temperature Range
Lead Temperature (Soldering. 10 sec)
Thernal Resistance (θJA) (Assume No Ambient Airflow, No Heatsink)
DIP8
SOP8
MSOP8
25V
32V
25V
8V
7V
2A
-40°C ~ 85°C
125°C
-65°C ~ 150°C
260°C
100°C/W
160°C/W
180°C/W
Absolute Maximum Ratings are those values beyond which the life of a device may be
Impaired.
TEST CIRCUIT
Refer to Typical Application Circuit.
ELECTRICAL CHARACTERISTICS
PARAMETER
(TA=25°C, VIN=15V, unless otherwise noted.) (note1)
TEST CONDITIONS
Input Voltage
Input Supply Current
UNIT
24
V
720
900
µA
Shutdown Mode, VITH/RUN=0V
16
20
µA
0.788
0.8
0.812
V
20
55
90
mV
0.002
0.015
%/V
ITH Sinking 5µA
0.7
1.1
ITH Sourcing 5µA
-0.4
-0.8
0.6
0.8
0.9
V
125
150
175
mV
450
500
550
KHz
VFB connect to Vout, ∆VOVL=VOVL-VFB
Reference Voltage Line
Regulation
VIN= 4.5V to 20 V
Run Threshold
Oscillator Frequency
MAX.
Normal Mode (Note 2)
∆Output Overvoltage Lockout
Maximum Current Sense
Threshold
TYP.
4.5
Feedback Voltage
Output Voltage Load Regulation
MIN.
VFB=0.72V
%
3
AIC1577
ELECTRICAL CHARACTERISTICS
PARAMETER
(Continued)
TEST CONDITIONS
MIN.
TYP.
MAX.
UNIT
DRI Rise Time
CLOAD = 3000PF
50
75
nS
DRI Fall Time
CLOAD = 3000PF
50
75
nS
BOOST Voltage
VIN=8V, IBOOST=5mA, SW=0V
4.9
5.3
5.7
V
Maximum Duty Cycle
90
94
%
Soft Start Time
5
7.5
mS
Run Current Source
VITH/RUN=0V, VFB=0V
1.0
2.3
4.0
µA
Run Pullup Current
VITH/RUN=1V
100
190
250
µA
Note 1: Specifications are production tested at TA=25°C. Specifications over the -40°C to 85°C operating
temperature range are assured by design, characterization and correlation with Statistical Quality
Controls (SQC).
Note 2: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency.
TYPICAL PERFORMANCE CHARACTERISTICS
100
100
VOUT=3.3V
VOUT=5V
95
VIN=6V
Efficiency (%)
Efficiency (%)
95
90
VIN=12V
85
VIN=19V
80
VIN=6V
VIN=12V
90
85
VIN=19V
80
75
75
70
70
1
10
100
1000
10000
Load Current (mA)
Fig. 1 Efficiency vs Load Current (VOUT=3.3V)
1
10
100
1000
10000
Load Current (mA)
Fig. 2 Efficiency vs Load Current (VOUT=5.0V)
4
AIC1577
TYPICAL PERFORMANCE CHARACTERISTICS
100
100
VOUT=3.3V
90
85
ILOAD=1A
80
ILOAD=0.1
A
75
5
10
15
20
25
90
ILOAD=1A
85
80
ILOAD=0.1A
75
70
0
VOUT=5V
95
Efficiency (%)
Efficiency (%)
95
70
30
0
5
Input Voltage (V)
Fig. 3 Efficiency vs Input Voltage
10
15
20
25
30
Input Voltage (V)
Fig. 4 Efficiency vs Input Voltage
900
7
800
Supply Current (µA)
(Continued)
Normal Mode
6
Boost Voltage (V)
700
600
500
40
Shutdown
20
3
2
0
5
10
15
VCC=5V
4
1
0
0
VCC=15V
5
20
25
30
VPHASE=0V
0
5
Input Voltage (V)
Fig. 5 Supply Current vs Input Voltage
10
20
15
Boost Load Current (mA)
Fig. 6 Boost Load Regulation
7
0.805
0.804
Boost Voltage (V)
Reference Voltage (V)
VCC UP
6
5
4
3
VCC DOWN
2
IBOOST=2mA
1
0
5
10
15
20
Input Voltage (V)
Fig. 7 Boost Line Regulation
25
0.802
0.801
0.800
0.799
0.798
0.797
0.796
0.795
0.794
0.793
0.792
VPHASE=0V
0
0.803
0.791
30
0.790
-40
-20
0
20
40
60
80
100
120
140
Temperature (°C)
Fig. 8 Reference Voltage vs Temperature
5
AIC1577
TYPICAL PERFORMANCE CHARACTERISTICS
500
480
5.5
Frequency (KHz)
Boost Voltage (V)
6.0
(Continued)
5.0
4.5
IBOOST=1mA
460
440
420
VPHASE=0V
4.0
-40
400
-20
0
20
40
60
80
100
120
140
Temperature (°C)
Fig. 9 Boost Voltage vs Temperature
-40
-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
6
AIC1577
BLOCK DIAGRAM
CS
VINT VINT
VIN
VIN
R1
+
+
R2
2.5µA
ICOMP
Q2
+
40mV
VIN
VINT
LC_COMP
*
VIN
Slope
*
SD
LEB
Blank
Clock
Q3 Q4
SS
0.8V
2.4V
+
-
1.33V
+
ITH
+
EA
-
ITH
SD
0.855V
+
REF
0.8V
FB
OVDT
Switching
Logic
Floating
Driver
DRI
Burst_Mode
Clock
0.8V
Thermal
+
-
Buffer_ITH
BOOST
SD
R
S
SW
Q
VINT
Dropout
DET
VIN
FB
INTVCC
Q1
1.2V
ITH
VIN
OSC
1_SHUT
M1
*
Slope
GND
7
AIC1577
PIN DESCRIPTIONS
PIN 1: CS
PIN 2:
- Current sense comparator inverting input, not to exceed VIN voltage. Built in offsets between the
CS and VIN pins in conjunction
with RSENSE set the current trip
thresholds.
ITH/RUN -Combination of error amplifier
compensation point and run control inputs. The current comparator threshold increases with this
control voltage. Forcing this pin
below 0.8V causes the device to
be shutdown.
PIN 3: FB
- Feedback error amplifier input, to
compare the feedback voltage
with the internal reference voltage.
Connecting a resistor R2 to converter output node and a resistor
R1 to ground yields the output
voltage:
VOUT=0.8 x (R1+R2)/ R1
PIN4: GND - Singal GND for IC. All voltage levels are measured with respect to
this pin.
PIN 5: SW
- Switch node connection to inductor. In buck converter applications
the voltage swing at this pin is
from a schottky diode voltage
drop below ground to VIN
PIN 6: DRI
- External high-side N-MOSFET
gate drive pin. Connect DRI to
gate of the external high-side NMOSFET.
PIN 7: BOOST - Supply to high-side floating
driver. The bootstrap capacitor C3
is returned to this pin.
PIN 8: VIN
- The chip power supply pin. It also
provides the gate bias charge for
all the MOSFETs controlled by
the IC. Recommend supply voltage is 4.5V~24V.
APPLICATION INFORMATION
Introduction
AIC1577 is a current mode switching regulator controller that drives external N-channel 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.
Wide input voltage ranges from 4.5V to 24V, and
switching frequency (500KHz) allows smaller sized
filter components. The operating current level is
user-programmable via an external current sense
resistor and it automatically enters PFM operation
at low output current to boost circuit efficiency.
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.
Principle of Operation
AIC1577 uses a current mode with a constant frequency architecture. Normally high-side MOSFET
turns on each cycle when oscillator sets RS latch
and it turns off when internal current comparator resets 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
8
AIC1577
in the voltage of VFB pin. Thus the ITH/RUN voltage
remains increasing until the average inductor current matches new load current. While the high-side
MOSFET turns off, the low-side MOSFET is turned
on to recharge bootstrap capacitor C3.
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.
Low Current Operation
During heavy load current operation, AIC1577 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 AIC1577 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.
Component Selection
AIC1577 can be used in many switching regulator
applications, such as step-down, step-up, SEPIC
and positive-to-negative converters. Among all,
step-down converter is the most common application. External component selection, beginning with
selecting RS, depends on load requirement of the
application. Once RS is decided, the choice of inductor, which is followed by selecting power
MOSFET and diode, can be easily chosen. Finally,
CIN and COUT can be determined.
RS Selection
The choice of RS has substantial connection with
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, ΔIL.
Allowing a margin for variation of AIC1577, external
component can be yielded as:
RS =
100mV
IMAX
Inductor Selection
With the operating frequency high to 500KHz,
smaller inductor value is favored. In general,
operating in high frequency will cause low efficiency
because of large MOSFET switching loss. Thus the
effect of inductor value on ripple current and low
current operation must be considered as well.
The inductor value has a direct influence on ripple
current ( Δ IL), which decreases with high inductance and increases with high VIN or VOUT:
∆IL =
VIN − VOUT
f ×L
 VOUT + VD 


 V +V 
 IN D 
VD is the drop voltage of the output Schottky diode.
Accepting a large value ofΔIL 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.
Power MOSFET Selection
For an application of AIC1577, an external Nchannel power MOSFET, used as the high-side
switch, must be properly selected. To prevent
MOSFET from damage during high input voltage
operation, attention should be taken to the BVDSS
specification for MOSFET.
Other important selection criteria for the power
MOSFET include the “ON” resistance RDS(ON), input voltage and maximum output current.
9
AIC1577
Output Diode Selection
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 the high voltage spike resulted 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 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 (ΔVOUT) is
determined by:

1 

∆VOUT ≈ ∆IL  ESR +
4fC OUT 

where f = operating frequency, COUT = output capacitance and ΔIL = ripple current of the inductor.
Once the ESR requirement for COUT has been met,
the RMS current rating generally far exceeds the
IRIPPLE(P-P) requirement.
 R2 
VOUT = 0.8 V 1 +

R1 

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.
ITH/RUN Function
The ITH/RUN pin, also as a dual-purpose pin, provides loop compensation as well as shutdown function. An internal current source at 2.5µA charges up
the external capacitor C5. When the voltage on
ITH/RUN pin reaches 0.8V, the AIC1577 begins to
operate.
VIN 4.5V~24V
R4
1.2M
C7
1µF
D2
LL4148
ITH/RUN
C5
330pF
R3
24k
Fig. 12 ITH/RUN pin interfacing
Topside MOSFET Driver Supply (C3)
External bootstrap capacitor C3 connecting to
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
to 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,
0.1µF is acceptable.
Output Voltage Programming
The typical AIC1577 application circuit is shown in
figure18. A resistive divider, as in the following formula, sets the output voltage.
Over Current Protection
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(Maxi mum current sense threshold)
IMAX =
RS
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
10
AIC1577
return to its designed value when the peak inductor
value no longer exceeds over current protection
point.
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.
PCB Layout
Since operating in a high switching frequency,
500KHz, proper PCB layout and component placement may enhance the performance of AIC 1577
application circuit. For a better efficiency, major loop
from input terminal to output terminal should be as
Fig. 13 Top Layer
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.
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 in the shortest distance. Recommended layout diagrams and
component placement are as shown as figures 13
to 16. No sensitive components, which may cause
noise interference to the circuit, should be allowed
to be close to SW pin.
Furthermore, AIC1577 is a current mode controller.
Remaining 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
connect to AIC1577 as close as possible.
Fig. 14 Bottom Layer
11
AIC1577
Fig. 15 Placement (Top Overlay)
Fig. 16 Placement (Bottom Overlay)
APPLICATION CIRCUIT
** VIN 6V~24V
R4
1.2M
C7
1µF
1
D2
LL4148
2
C5
330pF
R3
24k
3
4
VIN
CS
ITH/RUN BOOST
DRI
FB
SW
GND
AIC1577
8
1000pF
6
5
C3
0.1µF
C4
R1
20k
R2
C2
0.1µF
7
VIN 6V~24V
C1
RS
33m
+
M1
FDS6694
D1
SL43
CIN1
22µF
L1
+
CIN2
22µF
VOUT 3.3V 3A
10µH
COUT
220µF
C6
2.2µF
1nF
62k
Fig. 17 3.3V Step-Down Converter with External Soft-Start Circuit
12
AIC1577
1
2
C5
C7
3
330pF
4
1nF
R3
24k
VIN
CS
ITH/RUN BOOST
DRI
FB
SW
GND
AIC1577
C2
0.1µF
7
D2
6
5
LL4148
C3
R2
+
RS
33m
CIN1
+
22µF
M1
FDS6694
D1
SL43
C4
R1
20k
VIN 5V
C1
1000pF
8
CIN2
22µF
VOUT 3.3V 3A
L1
10µH
COUT
220µF
C6
2.2µF
1nF
62k
Fig. 18 5V to 3.3V Step-Down Converter
PHYSICAL DIMENSIONS (unit: mm)
8 LEAD PLASTIC SO
D
h X 45°
E
A
H
S
Y
M
B
O
L
A
e
SEE VIEW B
SOP-8
MILLIMETERS
MIN.
MAX.
A
1.35
1.75
A1
0.10
0.25
B
0.33
0.51
C
0.19
0.25
D
4.80
5.00
E
3.80
A
e
H
5.80
6.20
h
0.25
0.50
L
0.40
1.27
0°
8°
θ
WITH PLATING
C
A1
B
4.00
1.27 BSC
0.25
BASE METAL
GAUGE PLANE
SEATING PLANE
θ
L
VIEW B
13
AIC1577
MSOP 8
D
S
Y
M
B
O
L
MSOP-8
MILLIMETERS
MIN.
MAX.
E
E1
A
A A
A1
0.05
0.15
A2
0.75
0.95
b
0.25
0.40
c
0.13
0.23
D
2.90
E
A2
e
SEE VIEW B
1.10
E1
2.90
A
e
L
A1
θ
3.10
4.90 BSC
3.10
0.65 BSC
0.40
0.70
0°
6°
b
0.25
c
WITH PLATING
BASE METAL
SECTION A-A
θ
L
VIEW B
Note:
Information provided by AIC is believed to be accurate and reliable. However, we cannot assume responsibility for use of any circuitry
other than circuitry entirely embodied in an AIC product; nor for any infringement of patents or other rights of third parties that may result
from its use. We reserve the right to change the circuitry and specifications without notice.
Life Support Policy: AIC does not authorize any AIC product for use in life support devices and/or systems. Life support devices or systems are devices or systems which, (I) are intended for surgical implant into the body or (ii) support or sustain life, and whose failure to
perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a
significant injury to the user.
14
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