AN34

Applications Note 34
Issue1 August 2001
ZXSC100 Power Supply for Digital Still Camera.
The ZXSC100 is a DC-DC boost converter
designed for single or multi-cell portable
equipment. A typical application is shown in
Figure 1. The application is for a digital still
camera DSP power supply, providing a
regulated 3.3V/250mA supply from two cell
input.
Other typical applications for this reference
design are MP3 players and PDA’s where
high efficiency step-up conversion is
required.
L1
D1
47uH
ZHCS1000
VBATT
U1
EM
Vdrive
BAS
Isense
Q1
R2 C1
FMMT617
110k
1nF
C2
2V to 3V
RE
100uF/80mR
FB
Vcc
Gnd
ZXSC100
R1
R3
0.033R
30k
Figure 1. Digital still camera power supply solution.
Materials List
Ref
Value
Part Number
Manufacture
Comments
U1
ZXSC100X8
Zetex
DC-DC boost converter
Q1
FMMT617
Zetex
SuperSOT
D1
ZHCS1000
Zetex
1A Schottky diode in SOT23
TM
NPN transistor
R1
33m⍀
Generic
R2
110k
Generic
R3
30k
Generic
C1
1nF
C2
100uF
TPSD107M010R0080
AVX
100uF/80mohm SMT
L1
47uH
DO3316P-473
Coilcraft
47uF/500mohm SMT
Generic
AN 33 - 1
Applications Note 34
Issue1 August 2001
The ZXSC100 is an adjustable converter
allowing the end user maximum flexibility in
output voltage selection. The output voltage
is determined by:
VOUT = VFB (1+R2/R3),
where VFB=730mV.
The solution achieves a peak efficiency of
85%. The graphs are shown below in figures 2
and 3. Line and load regulation are also
shown in figures 4 and 5 respectively. Figures
6 and 7 show waveforms of the output
voltage ripple at 2V and 3V input.
Figure 4. Line Regulation
Figure 2. Efficiency v Input Voltage.
Figure 5. Load Regulation
Figure 3. Efficiency v Load Current.
AN 34 - 2
Applications Note 34
Issue1 August 2001
Low Battery Detect.
In many portable equipment applications a
low battery flag is necessary. Two
cost-effective solutions, to be used with the
ZXSC100 power supply, are given below.
Both solutions have been designed for low
battery indication between 2.1V and 2.3V.
Figure 8 shows a simple linear low battery
detect circuit. This circuit would be ideal for
driving an LED to indicate low power.
Figure 6. Output ripple at 2V input,
IOUT=250mA.
Figure 8. Low Battery Detect using BC858.
Figure 7. Output ripple at 3V input,
IOUT=250mA.
Materials List
Ref
Value
Q2
Part Number
Manufacture
Comments
BC858C
Generic
Small signal PNP transistor
R4
1M
Generic
R5
100k
Generic
R6
1M
Generic
C3
1nF
Generic
AN 34 - 3
Applications Note 34
Issue1 August 2001
Low Battery Detect cont.
Figure 9 shows a solution using the ZR431L
configured as a comparitor. The ZR431L is an
adjustable Zener shunt regulator with a 1.25V
reference voltage. When the batteries voltage
is above the 2.2V threshold the low battery
flag is set to the reference voltage of the
ZR431L, 1.25V. As the battery discharges and
approaches the 2.2V threshold the low
battery flag pulls up to the output voltage.
This type of flag is best suited for use with a
microprocessor.
Another alternative to the circuits in figure 9
are supply voltage monitors such as the
ZXCM series for Zetex. The ZXCM209 are
reset low and the ZXCM210 are reset high.
They are available in a range of threshold
voltages from 4.63V to 2.63V.
Figure 9 . Low Battery Detect using ZR431L.
Materials List
Ref
Value
U2
Part Number
Manufacture
Comments
ZR431LF01
Zetex
1.25V adjustable voltage reference - 1% tol
R1
100K
Generic
R2
130k
Generic
R3
1k
Generic
C1*
1uF
Generic
*Optional - used for noise suppression
© Zetex plc 2001
Zetex plc
Fields New Road
Chadderton
Oldham, OL9 8NP
United Kingdom
Telephone (44) 161 622 4422
Fax: (44) 161 622 4420
Zetex GmbH
Streitfeldstraße 19
D-81673 München
Germany
Telefon: (49) 89 45 49 49 0
Fax: (49) 89 45 49 49 49
Zetex Inc
Suite 315
700 Veterans Memorial Highway
Hauppauge NY11788
USA
Telephone: (631) 360 2222
Fax: (631) 360 8222
Zetex(Asia)Ltd
3701-04 Metroplaza, Tower 1
Hing Fong Road
Kwai Fong, Hong Kong
China
Telephone: (852) 26100 611
Fax: (852) 24250 494
These offices are supported by agents and distributors in major countries world-wide.
This publication is issued to provide outline information only which (unless agreed by the Company in writing) may not be
used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating
to the products or services concerned. The Company reserves the right to alter without notice the specification, design, price
or conditions of supply of any product or service.
For the latest product information, log on to www.zetex.com
AN 34 - 4
Applications Note 34
Issue1 August 2001
© Zetex plc 2001
Zetex plc
Fields New Road
Chadderton
Oldham, OL9 8NP
United Kingdom
Telephone (44) 161 622 4422
Fax: (44) 161 622 4420
Zetex GmbH
Streitfeldstraße 19
D-81673 München
Germany
Telefon: (49) 89 45 49 49 0
Fax: (49) 89 45 49 49 49
Zetex Inc
Suite 315
700 Veterans Memorial Highway
Hauppauge NY11788
USA
Telephone: (631) 360 2222
Fax: (631) 360 8222
Zetex(Asia)Ltd
3701-04 Metroplaza, Tower 1
Hing Fong Road
Kwai Fong, Hong Kong
China
Telephone: (852) 26100 611
Fax: (852) 24250 494
These offices are supported by agents and distributors in major countries world-wide.
This publication is issued to provide outline information only which (unless agreed by the Company in writing) may not be
used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating
to the products or services concerned. The Company reserves the right to alter without notice the specification, design, price
or conditions of supply of any product or service.
For the latest product information, log on to www.zetex.com
AN 34 - 5
Similar pages