ZXSC100
SINGLE CELL DC-DC CONVERTER SOLUTION
DESCRIPTION
The ZXSC100 series is designed for DC-DC
applications where step-up voltage conversion from
very low input voltages is required. These applications
mainly operate from single nickel cadmium or nickel
metal hydride battery cells.
The ZXSC100 devices are non-synchronous PFM,
DC-DC controller ICs which drive an external
transistor. Zetex SuperSOT4
™
switching transistors,
with saturation resistance as low as 13mΩ, are
recommended as the external switching element.
These bipolar transistors are the best switching
devices available for this type of DC-DC conversion,
enabling high efficiency conversion with input
voltages down to below 1 volt.
The circuit can start up under full load with regulation
maintained down to an input voltage of only 0.926
volts. The solution configuration ensures optimum
FEATURES
•
•
SuperSOT4™ switching transistor
ZXT14N20DX:V
CE(sat)
45mV max @ 1A load
Efficiency maintained over a wide range of input
voltages and load currents
82% efficiency @ V
BATT
=1V
Startup under full load
Minimum operating input voltage V
BATT
=0.926V
Adjustable output voltage down to V
BATT
Quiescent current typically 150µA referred to
input voltage
MSOP8 Package
SO8 Package
Demonstration boards available
U1
EM
V
DRIVE
I
SENSE
FB
G
ND
BAS
RE
V
CC
efficiency over a wider range of load currents, several
circuit configurations are possible with power
dissipation up to 2W. The step up output voltage is
easily programmed with external resistors, the
non-synchronous architecture and SuperSOT4™
device enabling an output voltage down to the input
voltage level. For best performance the ZXSC100
quiescent current is a small 150µA ensuring minimum
battery drain in no load conditions.
For the best in space saving the ZXSC100 is offered in
the MSOP8 package, however the devices are also
available in SO8 packaging for applications where
space saving is not so critical.
The IC and discrete combination offers the ultimate
cost vs performance solution for single cell DC-DC
conversion.
APPLICATIONS(continued)
•
•
•
•
•
Hand Held Instruments
Portable Medical Equipment
Solar Powered Equipment
LED Flashlight
LED Backlight
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
TYPICAL APPLICATION CIRCUIT
V
BATT
L1
D1
ZHCS2000
3.3V/0.1A
R1
Q1
ZXT14N20DX
R3
C3
C2
APPLICATIONS
Cordless Telephones
MP3 Players
PDA
Pagers
Battery Backup Supplies
Electronic toothbrush
GPS Receivers
Digital Camera
Palmtop Computers
ZXSC100
C1
R2
R4
ISSUE 1 - JANUARY 2001
1
ZXSC100
ABSOLUTE MAXIMUM RATING
Supply Voltage
Maximum Voltage Other Pins
Power Dissipation
MSOP8
SO8
0.3 to 3.5V
0.3 to V
CC
+0.3V
500mW
780mW
Operating Temperature
Storage Temperature
Junction Temperature
0 to 70°C
-55 to 125°C
150°C
ELECTRICAL CHARACTERISTICS TEST CONDITIONS (Unless otherwise stated)
V
CC
=1.2V, T
A
= 25°C
Symbol
I
CC
I
DRIVE
V
DRIVE
V
FB
V
ISENSE
T
CVISENSE
V
DREF
T
CVDREF
V
CC(SRT)
V
CC(min)
V
CC(hys)
I
FB
I
ISENSE
V
O(min)
V
O(max)
Parameter
Quiescent current
Base drive current
V
DRIVE
o/p voltage
Feedback voltage
Output current
reference voltage
I
SENSE
voltage temp co.
Drive current reference
voltage
V
DREF
temp co.
Startup voltage
Minimum operating
input voltage
Supply start up to
shutdown hysteresis
Feedback input current
I
SENSE
input current
Minimum Output
Voltage
Maximum Output
Voltage
ZXT14N20DX as pass
element
1
V
ISENSE
= 0V
3
V
CC
20
Any output load
1.01
0.926
Measured with respect
to V
CC
20
Conditions
Not switching
V
RE
= V
CC
V
RE
= V
CC
, I
DRIVE
= 5mA
5
V
CC
- 0.17
708
12
730
17.5
0.4
30
1
1.06
0.98
80
100
4
200
5.5
1.1
1
40
752
24
Min
Typ
150
Max
200
10
Units
µA
mA
V
mV
mV
%/°C
mV
%/°C
V
V
mV
nA
µA
V
V
1
Depends on breakdown voltage of pass device. See ZXT14N20DX data sheet
ISSUE 1 - JANUARY 2001
2
ZXSC100
ELECTRICAL CHARACTERISTICS: AC PARAMETERS
2
TEST CONDITIONS (Unless otherwise stated) )
V
CC
=1.2V, T
A
= 25°C
Symbol
T
OFF
F
OSC
2
3
Parameter
Discharge Pulse Width
Recommended operating
frequency
3
Conditions
Min
1.7
3
Typ
4
Max
Units
µs
kHz
200
These parameters guaranteed by Design
Operating frequency is application circuit dependant. See applications section
ZXT14N20DX
For the circuits described in the applications section, Zetex ZXT14N20DX is the recommended pass transistor.
The following indicates outline data for the ZXT, more detailed information can be found in the Zetex SuperSOT4
data book or at www.zetex.com
ELECTRICAL CHARACTERISTICS (at T
A
= 25°C unless otherwise stated).
PARAMETER
Collector-Emitter Breakdown
Voltage
Collector-Emitter Saturation
Voltage
SYMBOL
V
(BR)CEO
V
CE(sat)
MIN.
20
TYP.
30
4.5
30
75
6
45
95
MAX.
UNIT
V
mV
mV
mV
CONDITIONS.
I
C
=10mA*
I
C
=0.1A, I
B
=10mA*
I
C
=1A, I
B
=10mA*
I
C
=4A, I
B
=40mA*
*Measured under pulsed conditions. Pulse width=300µs. Duty cycle
≤2%
ZHCS2000
For the circuits described in the applications section Zetex ZHCS2000 is the recommended Schottky diode. The
following indicates outline data for the ZHCS, more detailed information is available at www.zetex.com
ELECTRICAL CHARACTERISTICS (at T
amb
= 25°C unless otherwise stated).
PARAMETER
Forward Voltage
Reverse Current
Reverse Recovery
Time
SYMBOL
V
F
I
R
t
rr
5.5
MIN.
TYP.
MAX.
385
500
300
UNIT
mV
mV
µA
ns
CONDITIONS.
I
F
=1A
I
F
=2A
V
R
=30V
Switched from I
F
=
500mA to I
R
= 500mA.
Measured at I
R
=50mA
*Measured under pulsed conditions. Pulse width=300µs. Duty cycle
≤
2%
ISSUE 1 - JANUARY 2001
3
ZXSC100
TYPICAL CHARACTERISTICS
ISSUE 1 - JANUARY 2001
4
ZXSC100
DEVICE DESCRIPTION
The ZXSC100 is non-synchronous PFM, DC-DC
controller IC which, when combined with a high
performance external transistor, enables the
production of a high efficiency boost converter for use
in single cell applications. A block diagram is shown
for the ZXSC100 in Figure 1.
The driver circuit supplies the external switching
transistor with a defined current, which is
programmed by an external resistor connected
between the RE pin and V
CC
. The internal reference
voltage for the circuit is 25mV below V
CC
. To maximise
efficiency the external transistor is switched quickly,
typically being forced off within 20ns.
In higher power applications more current can be
supplied to the switching transistor by using a further
external component. The driver transistor in the IC can
be bypassed with the addition of a discrete PNP. More
information on this circuit configuration can be found
in the applications section.
Figure 1
ZXSC100 Block Diagram
A shutdown circuit turns the device on or off at V
CC
=1V
with a hysteresis of typically 80mV. At start up,
comparator Comp1 turns the driver circuit and
therefore the external switching transistor on. This
circuit will remain active until the feedback voltage at
the pin FB rises above V
REF
, which is set to 730mV. An
external resistive divider on the FB pin sets the output
voltage level.
Comparator Comp2 forces the driver circuit and the
external switching transistor off, if the voltage at
I
SENSE
exceeds 25mV. The voltage at I
SENSE
is taken
from a current sense resistor connected in series with
the emitter of the switching transistor.
A monostable following the output of Comp2 extends
the turn-off time of the output stage by a minimum of
2us. This ensures that there is sufficient time to
discharge the inductor coil before the next on period.
The AND gate between the monostable and Comp1
output ensures that the switching transistor always
remains on until the I
SENSE
threshold is reached and
that the minimum discharge period is always
asserted. The pulse width is constant, the pulse
frequency varies with the output load.
ISSUE 1 - JANUARY 2001
5
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