Zetex ZXSC100N8, ZXSC100X8 Datasheet

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
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

™

switching transistors,

ZXSC100

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 isasmall 150µA ensuring minimum
battery drain in no load conditions.

For the best in space saving theZXSC100 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.

FEATURES

• SuperSOT4™ switching transistor

ZXT14N20DX:V

45mV max @ 1A load

CE(sat)

• Efficiency maintained over a wide range of input

voltages and load currents
82% efficiency @ V

•

Startup under full load

•

Minimum operating input voltage V

•

Adjustable output voltage down to V

•

Quiescent current typically 150µA referred to
input voltage

•

MSOP8 Package

•

SO8 Package

•

Demonstration boards available

BATT

=1V

BATT

BATT

=0.926V

APPLICATIONS

•

Cordless Telephones

•

MP3 Players

•

PDA

•

Pagers

•

Battery Backup Supplies

•

Electronic toothbrush

•

GPS Receivers

•

Digital Camera

•

Palmtop Computers

APPLICATIONS(continued)

• Hand Held Instruments

• Portable Medical Equipment

• Solar Powered Equipment

• LED Flashlight

•

LED Backlight

TYPICAL APPLICATION CIRCUIT

V

BATT

C1

L1 D1

R1

U1

V

EM

DRIVE

I

BAS

SENSE

RE

FB

V

G

CC

ND

ZXSC100

ZHCS2000

Q1

ZXT14N20DX

R2

3.3V/0.1A

R3

C3

C2

R4

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ZXSC100

ABSOLUTE MAXIMUM RATING

Supply Voltage 0.3 to 3.5V
Maximum Voltage Other Pins 0.3 to V

CC

+0.3V
Power Dissipation
MSOP8 500mW
SO8 780mW

ELECTRICAL CHARACTERISTICS TEST CONDITIONS (Unless otherwise stated)

=1.2V, TA= 25°C

V

CC

Symbol Parameter Conditions Min Typ Max Units

I

CC

I

DRIVE

V

DRIVE

V

FB

V

ISENSE

Quiescent current Not switching 150 200 µA

Base drive current VRE=V

V

o/p voltage VRE=VCC,I

DRIVE

Feedback voltage 708 730 752 mV

Output current
reference voltage

Operating Temperature 0 to 70°C
Storage Temperature -55 to 125°C
Junction Temperature 150°C

CC

= 5mA VCC- 0.17 V

DRIVE

510mA

12 17.5 24 mV

T

CVISENSEISENSE

V

DREF

T

CVDREF

V

CC(SRT)

V

CC(min)

V

CC(hys)

I

FB

I

ISENSE

V

O(min)

V

O(max)

1

Depends on breakdown voltage of pass device. See ZXT14N20DX data sheet

voltage temp co. 0.4 %/°C

Drive current reference
voltage

V

temp co. 1 %/°C

DREF

Measured with respect
to V

CC

20 30 40 mV

Startup voltage Any output load 1.01 1.06 1.1 V

Minimum operating

0.926 0.98 1 V

input voltage

Supply start up to
shutdown hysteresis

Feedback input current 100 200 nA

I

input current V

SENSE

Minimum Output
Voltage

Maximum Output
Voltage

ZXT14N20DX as pass
element

= 0V 3 4 5.5 µA

ISENSE

V

CC

1

80 mV

V

20 V

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ZXSC100

ELECTRICAL CHARACTERISTICS: AC PARAMETERS

2

TEST CONDITIONS (Unless otherwise stated) )
V

=1.2V, TA= 25°C

CC

Symbol Parameter Conditions Min Typ Max Units

T

OFF

F

OSC

2

These parameters guaranteed by Design

3

Operating frequency is application circuit dependant. See applications section

Discharge Pulse Width 1.7 3 4 µs

Recommended operating
frequency

3

200 kHz

ZXT14N20DX

For the circuits described in the applications section, Zetex ZXT14N20DX is the recommended pass transistor.
The following indicatesoutlinedata for the ZXT,moredetailed information can befoundin the Zetex SuperSOT4
data book or at www.zetex.com

ELECTRICAL CHARACTERISTICS (at TA= 25°C unless otherwise stated).

PARAMETER SYMBOL MIN. TYP. MAX. UNIT CONDITIONS.

Collector-Emitter Breakdown
Voltage

Collector-Emitter Saturation
Voltage

V

(BR)CEO

V

CE(sat)

20 30 V IC=10mA*

4.5
30
75

45
95

6

mV
mV
mV

IC=0.1A, IB=10mA*
I

=1A, IB=10mA*

C

I

=4A, IB=40mA*

C

*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

PARAMETER SYMBOL MIN. TYP. MAX. UNIT CONDITIONS.

Forward Voltage V

Reverse Current I

Reverse Recovery
Time

*Measured under pulsed conditions. Pulse width=300µs. Duty cycle ≤2%

ISSUE 1 - JANUARY 2001

F

R

t

rr

= 25°C unless otherwise stated).

amb

385
500mVmV

300

µA

5.5 ns Switched from IF=

3

3

IF=1A
I

=2A

F

VR=30V

500mA to I
Measured at I

R

= 500mA.

=50mA

R

ZXSC100

TYPICAL CHARACTERISTICS

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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 ofa high efficiencyboost converter for use
in single cell applications. A block diagram is shown
for the ZXSC100 in Figure 1.

Figure 1
ZXSC100 Block Diagram

A shutdown circuitturnsthe device on oroffat V
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

, which is set to 730mV. An

REF

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

exceeds 25mV. The voltage at I

SENSE

SENSE

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

threshold is reached and

SENSE

that the minimum discharge period is always
asserted. The pulse width is constant, the pulse
frequency varies with the output load.

=1V

CC

is taken

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
voltage for thecircuitis 25mV below V

. The internal reference

CC

. To maximise

CC

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. Thedriver transistor in theICcan
be bypassedwiththe addition ofa discrete PNP. More
information on this circuit configuration can be found
in the applications section.

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ZXSC100

PIN DESCRIPTIONS

Pin

Name Description

No.
1 EM Emitter of internal drive transistor. Connect to RE in lower power applications.

2 BAS Not connected in lower power applications. Connect to base of external drive

3 RE Drive current sense input. Internal threshold voltage set 25mV below V

4V
5I

CC

SENSE

6 FB Feedback sense. Internal threshold set to 730mV. Connect external resistive

7G
8V

DRIVE

Must be unconnected in higher power applications

transistor in higher power applications

Connected external sense resistor. Connect emitter of external drive transistor in
higher power applications

Supply voltage, generally NiMH, NiCd single cell
Inductor current sense input. Internal threshold voltage set to 25mV. Connect

external sense resistor

divider to output voltage
Ground

ND

Drive output for external switching transistor. Connect to base of external
switching transistor. Also connect to collector of external drive transistor in
higher power applications

CC

.

EM

BAS

RE
V

CC

1

2

3

4

V

8

DRIVE

G

7

ND

FB

6

5

I

SENSE

REFERENCE DESIGNS

Three typical DC-DC step-up converter applications
for the ZXSC100 are shown. Firstly with a maximum
output power of 0.33W, secondly with a maximum

Low Power Solution (330mW) Efficiency

output power of1.0Wand finally driving whiteLED’sin
a flashlight application.

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