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 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
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.
The IC and discrete combination offers the ultimate
cost vs performance solution for single cell DC-DC
conversion.
FEATURES
•
Efficiency maintained over a wide range of input
voltages and load currents
82% efficiency @ V
BATT
=1V
APPLICATIONS(continued)
•
Hand held instruments
•
Portable medical equipment
•
Solar powered equipment
•
•
•
•
Startup under full load
Minimum operating input voltage V
BATT
=0.926V
Adjustable output voltage down to V
BATT
TYPICAL APPLICATION CIRCUIT
V
BATT
Quiescent current typically 150µA referred to
input voltage
•
MSOP8 package
L1
D1
ZHCS1000
3.3V/0.1A
•
SO8 package
R1
Q1
R3
C3
C2
U1
EM
BAS
RE
V
CC
APPLICATIONS
•
•
•
•
•
•
•
•
•
Cordless telephones
MP3 players
PDA
Pagers
Battery backup supplies
Electronic toothbrush
GPS receivers
Digital camera
Palmtop computers
DEVICE
ZXSC100X8
ZXSC100N8
C1
FMMT617
V
DRIVE
I
SENSE
FB
G
ND
ZXSC100
R2
R4
ORDERING INFORMATION
Package
MSOP8
SO8
Partmarking
ZXSC100
ZXSC100
Reel
size
7”
7”
Tape
width
12mm
12mm
Quantity per
reel
1,000
500
ISSUE 3 - JANUARY 2004
1
SEMICONDUCTORS
ZXSC100
ABSOLUTE MAXIMUM RATING
Supply voltage
Maximum voltage other pins
Power dissipation (25°C)
MSOP8
SO8
500mW
780mW
0.3 to 3.5V
0.3 to V
CC
+0.3V
Operating temperature
Storage temperature
Junction temperature
0 to 70°C
-55 to 150°C
150°C
ELECTRICAL CHARACTERISTICS
(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)
T
OFF
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
Discharge pulse width
Conditions
Not switching
V
RE
= V
CC
V
RE
= V
CC
, I
DRIVE
= 5mA
Min.
Typ.
150
Max. Units
200
10
µA
mA
V
5
V
CC
- 0.17
708
12
730
17.5
0.4
752
24
mV
mV
%/°C
Measured with respect to V
CC
20
30
1
40
mV
%/°C
Any output load
1.01
0.926
1.06
0.98
80
100
1.1
1
V
V
mV
200
5.5
nA
µA
V
V
ISENSE
= 0V
3
V
CC
4
FMMT617as pass element
(1)
1.7
3
20
4
V
µs
(1)
Depends on breakdown voltage of pass device. See FMMT617 datasheet
ISSUE 3 - JANUARY 2004
SEMICONDUCTORS
2
ZXSC100
OPERATING CONDITIONS
Symbol
F
OSC
2
3
Parameter
Recommended operating frequency
3
Conditions
Min
Typ
Max
200
Units
kHz
These parameters guaranteed by design and characterization
Operating frequency is application circuit dependant. See applications section
FMMT617
For the circuits described in the applications section, Zetex FMMT617 is the recommended pass transistor. The
following indicates outline data for the transistor, more detailed information can be found 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.
15
TYP.
18
8
70
150
14
100
200
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
=3A, I
B
=50mA*
*Measured under pulsed conditions. Pulse width=300µs. Duty cycle
≤
2%
ZHCS1000
For the circuits described in the applications section Zetex ZHCS1000 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
12
MIN.
TYP.
MAX.
500
100
UNIT
mV
µA
ns
CONDITIONS
I
F
=1A
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 3 - JANUARY 2004
3
SEMICONDUCTORS
ZXSC100
TYPICAL CHARACTERISTICS
300
2.0
1.5
Quiescent Current (µA)
Output Voltage (%)
250
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-10
0
10
20
30
40
50
60
70
80
200
150
100
1.0
1.5
2.0
2.5
Input Voltage (V)
Temperature (°C)
Quiescent Current v Input Voltage
2.0
1.5
5.0
Output Voltage v Temperature
Load Regulation (%)
Line Regulation (%)
0
50m
100m
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
2.5
0.0
-2.5
-5.0
1.0
1.5
2.0
2.5
Output Current (A)
Input Voltage (V)
Load Regulation
Line Regulation
ISSUE 3 - JANUARY 2004
SEMICONDUCTORS
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.
V
CC
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.
Shutdown
Comp1
Drive
RE
I
EM
BAS
R1
V
REF
R2
Comp2
V
DRIVE
I
SENSE
FB
G
ND
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 3 - JANUARY 2004
5
SEMICONDUCTORS
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