ILC 6370/71
Final
www.fairchildsemi.com
SOT-89 Step up Switching Regulator with Shutdown
General Description
50mA boost converter in 5-lead SOT-89 package. Only 3
external components are needed to complete the switcher
design, and frequency options of 50, 100, and 180kHz gives
the designer the ability to trade off system needs with
switcher design size.
87% max duty cycle gives conversion efficiencies of 85%.
Standard voltage options of 2.5V, 3.3V, and 5.0V at ±2.5%
accuracy feature on-chip phase compensation and soft-
start design.
ILC6371 drives an external transistor for higher current
switcher design, with all of the features and benefits of
the ILC6370.
Features
!
85% efficiency at 50mA
!
Start-up voltages as low as 900mV
!
±2.5% accurate outputs
!
Complete switcher design with only 3 external components
!
50, 100 and 180kHz switching frequency versions available
!
Shutdown to 0.5µA
!
External transistor option allows several hundred milliamp
switcher design
Applications
!
Cellular Phones, Pagers
!
Portable Cameras and Video Recorders
!
Palmtops and PDAs
Block Diagram
L
X
V
L X
LIMI TER
BUFFER
Slow Start
V
DD
V
OUT
V
SS
P WM Co ntrol led
OSC
V
re f
P hase com p
EXT
CE
50/ 100/180KHz
-
CHIP ENABLE
+
V
DD
is i nternall y connected to the V
O
UT
pi n.
Pin-Package Configurations
V
SS
5
L
X
4
V
S S
5
EXT
4
SOT -89-5
(TOP VI EW)
1
2
3
SOT -89-5
(TOP VI EW)
1
2
3
N/C V
O UT
CE
N/C
V
O UT
CE
ILC6370
ILC6371
Ordering Information*
ILC6370CP-25
2.5V±2.5%@50kHz
ILC6370CP-25
3.3V±2.5%@50kHz
ILC6370CP-50
5.0V±2.5%@50kHz
ILC6370BP-25
2.5V±2.5%@100kHz
ILC6370BP-33
3.3V±2.5%@100kHz
ILC6370BP-50
5.0V±2.5%@100kHz
ILC6370AP-25
2.5V±2.5%@180kHz
ILC6370AP-33
3.3V±2.5%@180kHz
ILC6370AP-50
5.0V±2.5%@180kHz
ILC6371CP-25
2.5V±2.5%@50kHz, external xtor
ILC6371CP-33
3.3V±2.5%@50kHz, external xtor
ILC6371CP-50
5.0V±2.5%@50kHz, external xtor
ILC6371BP-25
2.5V±2.5%@100kHz, external xtor
ILC6371BP-33
3.3V±2.5%@100kHz, external xtor
ILC6371BP-50
5.0V±2.5%@100kHz, external xtor
ILC6371AP-25
2.5V±2.5%@180kHz, external xtor
ILC6371AP-33
3.3V±2.5%@180kHz, external xtor
ILC6371AP-50
5.0V±2.5%@180kHz, external xtor
Standard Product offering comes in tape and reel,
quantity 1000 per reel, orientation right for SOT-89
1
Rev. 1.4 September 2001
SOT-89 Step up Switching Regulator with Shutdown
Electrical Characteristics ILC6370BP-50
V
OUT
= 5.0V, F
OSC
= 100kHz, T
A
= 25°C; Test Circuit of figure 1
Parameter
CE “High” Current
CE “Low” Current
L
X
Limit Voltage
Efficiency
Symbol
I
CEH
I
CEL
V
LXLMT
EFFI
Conditions
L
X
: 10kΩ pull-up to 5V, V
CE
= V
OUT
= 4.5V
=
L
X
: 10kΩ pull-up to 5V, V
OUT
4.5V, V
CE
= 0V
(1)
L
X
: 10kΩ pull-up to 5V, V
OUT
= 4.5V, F
OSC
> F
OSC
x 2
Min
Typ
Max
0.25
-0.25
1.1
Units
µA
µ
V
%
0.7
85
1. Switching frequency determined by delay time of internal comparator to turn L
X
“OFF,” and minimum “ON” time as
determined by MAXDTY spec.
Electrical Characteristics ILC6371BP-50
V
OUT
= 5.0V, F
OSC
= 100kHz, T
A
= 25°C; Test Curcuit of figure 2.
Parameter
Output Voltage
Input Voltage
Oscillation Startup Voltage
Supply Current 1
Supply Current 2
EXT “High” On-Resistance
EXT “Low” On-Resistance
Oscillator Frequency
Maximum Duty Ratio
Stand-by Current
CE “High” Voltage
CE “Low” Voltage
CE “High” Current
CE “Low” Current
Efficiency
Slow Start Time
Symbol
V
OUT
V
IN
V
ST
I
DD
1
I
DD
2
R
EXTH
R
EXTL
F
OSC
MAXDTY
I
STB
V
CEH
V
CEL
I
CEH
I
CEL
EFFI
T
SS
Conditions
Min
4.87
5
Typ
5.000
Max
5.125
10
0.8
64.1
13.8
50
50
115
92
0.5
0.75
0.20
0.25
-0.25
85
10
Units
V
V
V
µA
µA
Ω
Ω
kHz
%
µA
V
V
µA
µA
%
msec
EXT: 10kΩ pull-up to 5V, V
OUT
= V
ST
EXT: 10kΩ pull-up to 5V, V
OUT
= 4.5V
EXT: 10kΩ pull-up to 5V, V
OUT
= 5.5V
EXT: 10kΩ pull-up to 5V, V
OUT
= 4.5V,
V
EXT
= 4.1V
V
EXT
= 0.4V, V
OUT
= 5.5V
EXT: 10kΩ pull-up to 5V, V
OUT
= 4.5V,
Measuring of EXT pin
EXT: 10kΩ pull-up to 5V, V
OUT
= 4.5V,
Measuring of EXT pin
EXT: 10kΩ pull-up to 5V, V
OUT
= 4.5V
EXT: 10kΩ pull-up to 5V, V
OUT
= 4.5V,
Existance of L
X
Oscillation
EXT: 10kΩ pull-up to 5V, V
OUT
= 4.5V,
Stopped L
X
Oscillation
EXT: 10kΩ pull-up to 5V, V
OUT
= V
CE
= 4.5V
EXT: 10kΩ pull-up to 5V, V
OUT
= 4.5V, V
CE
= 0V
38.4
6.9
30
30
100
87
85
80
3
Rev. 1.4 September 2001
3
SOT-89 Step up Switching Regulator with Shutdown
Functions and Operation
The ILC6370 performs boost DC-DC conversion by controlling the
switch element shown in the circuit below.
some point where the load current gets to small to be handled effi-
ciently. If the ILC6370 had an ideal switch, this would not be such
a problem. But an actual switch consumes some finite amount of
current to switch on and off; at very low current this can be of the
same magnitude as the load current itself, driving switching effi-
ciencies down to 50% and below.
The other limitation of PWM techniques is that, while the funda-
mental switching frequency is easier to filter out since it’s constant,
the higher order harmonics of PWM will be present and may have
to be filtered out as well. Any filtering rquirements will vary by appli-
cation and by actual system design and layout, so generalizations
in this area are difficult, at best. [For
other boost converter tech-
niques, please see the ILC6380/81 and ILC6390/91 data sheets.]
However, PWM control for boost DC-DC conversion is widely
used, especially in audio-noise sensitive applications or applica-
tions requiring strict filtering of the high frequency components.
Impala’s products give very good efficiencies of 85% at 50mA out-
put (5V operation), 87% maximum duty cycles for high load con-
ditions, while maintaining very low shutdown current levels of
0.5µA. The only difference between the ILC6370 and ILC6371
parts is that the 6371 is configured to drive an external transistor
as the switch element. Since larger transistors can be selected for
this element, higher effective loads can be regulated.
Start-up Mode
The ILC6370 has an internal soft-start mode which suppresses
ringing or overshoot on the output during start-up. The following
diagram illustrates this start-up condition’s typical performance
V
OUT MIN
V
IN
- V
f
T
SOFT-START
(~10msec)
When the switch is closed, current is built up through the inductor.
When the switch opens, this current has to go somewhere and is
forced through the diode to the output. As this on and off switch-
ing continues, the output capacitor voltage builds up due to the
charge it is storing from the inductor current. In this way, the out-
put voltage gets boosted relative to the input. The ILC6370 mon-
itors the voltage on the output capacitor to determine how much
and how often to drive the switch.
In general, the switching characteristic is determined by the output
voltage desired and the current required by the load. Specifically
the energy transfer is determined by the power stored in the coil
during each switching cycle.
PL =
ƒ(t
ON
, V
IN
)
The ILC6370 and ILC6371 use a PWM or Pulse Width Modulation
technique. The parts come in one of three fixed internal frequen-
cies: 50, 100, or 180kHz. The switches are constantly driven at
these frequencies. The control circuitry varies the power being
delivered to the load by varying the on-time, or duty cycle, of the
switch. Since more on-time translates to higher current build up in
the inductor, the maxmim duty cycle of the switch determines the
maximum load current that the device can support. The ILC6370
and ILC6371 both support up to 87% duty cycles, for maximum
usable range of load currents.
There are two key advantages of PWM type controllers. First,
because the controller automatically varies the duty cycle of the
switche’s on-time in response to changing load conditions, the
PWM controller will always have an optimized waveform for a
steady-state load. This translates to very good efficiency at high
currents and minimal ripple on the output. [Ripple
is due to the
output cap constanty accepting and storing the charge recieved
from the inductor, and delivering charge as required by the load.
The “pumping” action of the switch produces a sawtooth-shaped
voltage as seen by the output.]
The other key advatage of the PWM type controllers is that the
radiated noise due to the swtiching transients will always occur at
the (fixed) switching frequency. Many applications do not care
much about switching noise, but certain types of applications,
especially communication equipment, need to minimze the high
frequency interference within their system as much as is possible.
Using a boost converter requires a certain amount of higher fre-
quency noise to be generated; using a PWM converter makes that
noise highly predictable; thus easier to filter out.
There are downsides of PWM approaches, especially at very low
currents. Because the PWM technique relies on constant switch-
ing and varying duty cycle to match the load conditions, there is
t=0
External Components and Layout Consideration
The ILC6370 is designed to provide a complete DC-DC convertor
solution with a minmum of external components. Ideally, only
three externals are required: the inductor, a pass diode, and an
output capacitor.
The inductor needs to be of low DC Resistance type, typically 1Ω
value. Toroidal wound inductors have better field containment (less
high frequency noise radiated out) but tend to be more expensive.
Some manufacturers like Coilcraft have new bobbin-wound induc-
tors with shielding included, which may be an ideal fit for these
applications. Contact the manufacturer for more information.
The inductor size needs to be in the range of 47µH to 1mH. In
general, larger inductor sizes deliver less current, so the load cur-
rent wil determine the inductor size used.
5
Rev. 1.4 September 2001
5
电源技术
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
