Final
Impala Linear Corporation
ILC6370/1
SOT-89 Step-up Switching Regulator with Shutdown
General Description
50 mA 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 2.5, 3.3, and 5.0V at
±2.5% accuracy feature on-chip phase compensation
and soft-start design.
ILC6371 drives an external transistor for higher cur-
rent switcher design, with all of the features and bene-
fits of the ILC6370.
Features
u
u
u
u
u
u
u
July 1996
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
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u
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Cellular Phones, Pagers
Portable Cameras and Video Recorders
Palmtops and PDAs
Ordering Information*
Block Diagram
ILC6370CP-25
ILC6370CP-33
V
DD
Slow Start
2.5V±2.5%@50kHz
3.3V±2.5%@50kHz
5.0V±2.5%@50kHz
2.5V±2.5%@100kHz
3.3V±2.5%@100kHz
5.0V±2.5%@100kHz
2.5V±2.5%@180kHz
3.3V±2.5%@180kHz
5.0V±2.5%@180kHz
2.5V±2.5%@50kHz, external xtor
3.3V±2.5%@50kHz, external xtor
5.0V±2.5%@50kHz, external xtor
2.5V±2.5%@100kHz, external xtor
3.3V±2.5%@100kHz, external xtor
5.0V±2.5%@100kHz, external xtor
2.5V±2.5%@180kHz, external xtor
3.3V±2.5%@180kHz, external xtor
5.0V±2.5%@180kHz, external xtor
L
X
V
LX
LIMITER
BUFFER
ILC6370CP-50
V
OUT
V
SS
PWM Controlled
OSC
50/100/180KHz
V
ref
ILC6370BP-25
ILC6370BP-33
ILC6370BP-50
ILC6370AP-25
ILC6370AP-33
ILC6370AP-50
ILC6371CP-25
ILC6371CP-33
ILC6371CP-50
Phase comp
EXT
CE
-
CHIP ENABLE
+
V
DD
is internally connected to the V
OUT
pin.
Pin-Package Configurations
V
SS
5
L
X
4
V
SS
5
EXT
4
ILC6371BP-25
ILC6371BP-33
ILC6371BP-50
ILC6371AP-25
ILC6371AP-33
ILC6371AP-50
SOT -89-5
(TOP VIEW)
1
2
3
SOT -89-5
(TOP VIEW)
1
2
3
N/C
V
OUT
CE
N/C
V
OUT
CE
ILC6370
ILC6371
Impala Linear Corporation
* Standard product offering comes in tape & reel, quantity 1000
per reel, orientation right for SOT-89.
1
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
Symbol
I
CEH
I
CEL
V
LxLMT
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
L
X
: 10kΩ pull-up to 5V, V
OUT
=4.5V,
F
OSC
> F
OSC
x 2
(1)
Min
Typ
Max
0.25
-0.25
Units
µA
µA
V
0.7
1.1
Efficiency
EFFI
85
%
1. Switching frequency determined by delay time of internal comparator to turn Lx “
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 Circuit 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
4.875
Typ
5.000
Max
5.125
10
Units
V
V
V
µA
µA
Ω
Ω
kHz
%
µA
V
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, Vout = 5.5V
EXT: 10kΩ pull-up to 5V, V
OUT
=4.5V, Measuring
of EXTpin
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, Existence
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
85
10
0.75
85
80
38.4
6.9
30
30
100
87
0.8
64.1
13.8
50
50
115
92
0.5
0.20
0.25
-0.25
V
µA
µA
%
msec
Note: Unless otherwise specified, V
IN
=V
OUT
x 0.6, I
OUT
=50mA. See the Schematic, Fig. 2.
Impala Linear Corporation
3
Functions and Operation
The ILC6370 performs boost DC-DC conversion by control-
ling the switch element shown in the circuit below.
conditions, there is some point where the load current gets
too small to be handled efficiently. 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 currents this can be of the
same magnitude as the load current itself, driving switching
efficiencies down to 50% and below!
The other limitation of PWM techniques is that, while the
fundamental 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 filter-
ing requirements, though, will vary by application 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
datasheets.]
However, PWM control for boost DC-DC conversion is
widely used, especially in audio-noise sensitive applica-
tions or applications requiring strict filtering of the high fre-
quency components. Impala’s products give very good
efficiencies of 85% at 50mA output (5V operation), 87%
maximum duty cycles for high load conditions, while main-
taining 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 sup-
presses ringing or overshoot on the output during start-up.
The following diagram illustrates this start-up condition’s
typical performance.
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 switching continues, the output capacitor volt-
age builds up due to the charge it is storing from the inductor
current. In this way, the output voltage gets boosted relative
to the input. The ILC6370 monitors 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 Mod-
ulation technique. The parts come in one of three fixed inter-
nal frequencies: 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 max-
imum 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 the PWM type controllers.
First, because the controller automatically varies the duty
cycle of the switch’s on-time in response to changing load
conditions, the PWM controller will always have an opti-
mized 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 constantly
accepting and storing the charge received from the inductor,
and delivering charge as required by the load. The “pump-
ing” action of the switch produces a sawtooth-shaped volt-
age as seen by the output.]
The other key advantage of the PWM type controllers is that
the radiated noise due to the switching 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
minimize the high frequency interference within their system
as much as is possible. Using a boost converter requires a
certain amount of higher frequency noise to be generated;
using a PWM converter makes that noise highly predictable,
and thus easier to filter out.
But there are downsides of PWM approaches, especially at
very low currents. Because the PWM technique relies on
constant switching and varying duty cycle to match the load
V
OUT MIN
V
IN
- V
f
T
SOFT-START (~10msec)
t=0
External Components and Layout Consideration
The ILC6370 is designed to provide a complete DC-DC
convertor solution with a minimum 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, typi-
cally 1Ω value. Toroidal wound inductors have better field
containment (less high frequency noise radiated out) but
tend to be more expensive. Some manufacturers like Coil-
craft have new bobbin-wound inductors 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 current will determine the inductor size used.
Impala Linear Corporation
5
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