ZXSC410
ZXSC420
VOLTAGE MODE BOOST CONVERTER
DESCRIPTION
The ZXSC410 is voltage mode boost converter in SOT23-6 package. Its excellent
load and line regulation means that for the full supply range from lithium Ion cells,
the output voltage will typically change by less than 1%. Using high efficiency
Zetex switching transistors allow output voltages of tens of volts depending on the
selected transistor. The ZXSC420 includes a battery low indicator. This operates
by indicating when the converter is no longer able to maintain the regulated
output voltage rather than setting a preset threshold, thereby making it suitable for
various battery options and load currents.
FEATURES
•
1.65V to 8V supply range
•
Typical output regulation of ±1%
•
Over 85% typical efficiency
•
Output currents up to 300mA
•
4.5 A typical shutdown current ZXSC410
•
End of regulation output ZXSC420
SOT23-6
ORDERING INFORMATION
DEVICE
ZXSC410E6TA
ZXSC420E6TA
REEL
SIZE
7”
7”
TAPE
WIDTH
8mm
8mm
QUANTITY
PER REEL
3000 units
3000 units
APPLICATIONS
•
System power for battery portable products
•
LCD bias
•
Local voltage conversion
TYPICAL APPLICATIONS DIAGRAM
L1
V
IN
ZHCS1000
D1
V
OUT
C1
Q1
U1
V
CC
DRIVE
STDN SENSE
GND
V
FB
FMMT617
R2
C2
ZXSC410
R1
R3
DEVICE MARKING
•
C410 ZXSC410
•
C420 ZXSC420
ISSUE 2 - May 2003
1
SEMICONDUCTORS
ZXSC410
ZXSC420
ABSOLUTE MAXIMUM RATINGS
V
CC
DRIVE
EOR
STDN
V
FB
, SENSE
Operating Temp.
Storage Temp.
Power Dissipation
-0.3V to
-0.3V to
-0.3V to
-0.3V to
-0.3V to
-40°C to
-55°C to
450mW
+10V
V
CC
+ 0.3V
V
CC
+ 0.3V
The lower of (+5.0V) or (V
CC
+ 0.3V)
The lower of (+5.0V) or (V
CC
+ 0.3V)
+85°C
+125°C
* (ZXSC420 only)
* (ZXSC410 only)
ELECTRICAL CHARACTERISTICS
Test Conditions V
CC
= 3V, T= -40°C to 85°C unless otherwise stated.
Symbol
Parameter
Conditions
Min
Supply parameters
V
CC
Iq
1
Limits
Typ
Max
Units
V
CC
Range
Quiescent Current
Shutdown Current
V
CC
= 8V
1.8
8
220
4.5
V
A
A
I
STDN
Eff
2
Acc
REF
TCO
REF
T
DRV
F
OSC
V
SENSE
I
SENSE
V
FB
I
FB
2
Efficiency
Reference tolerance
Reference Temp Co
Discharge pulse width
Operating Frequency
50mA > I
OUT
> 300mA
1.8V < V
CC
< 8V
1.8V < V
CC
< 8V
85
-3.0
0.005
1.7
200
3.0
%
%
%/ C
s
kHz
Input parameters
sense voltage
sense input current
Feedback voltage
Feedback input current
Shutdown high voltage
Shutdown low voltage
Line voltage regulation
V
FB
=0V;V
SENSE
=0V
T
A
= 25°C
V
FB
=0V;V
SENSE
=0V
22
-1
291
-1.2
1.5
0
0.5
1
28
-7
300
34
-15
309
-4.5
V
CC
0.55
V
V
%/V
mV
A
mV
A
V
IH
V
IL
dV
LN
I
OUT 3
I
DRIVE
V
DRIVE
C
DRIVE
VOH
EOR
VOL
EOR
T
EOR
dI
LD
Note
Output parameters
Output current
Transistor drive current
Transistor voltage drive
Mosfet gate drive cpbty
EOR Flag output high
EOR Flag output low
EOR delay time
Load current regulation
I
EOR
= -300nA
I
EOR
= 1mA
T
A
= 25°C
2.5
0
70
195
V
IN
> 2V, V
OUT
= V
IN
V
DRIVE
= 0.7V
1.8V < V
CC
< 8V
300
2
0
300
V
CC
1.15
250
0.01
3.4
5
V
CC
-0.4
mA
mA
V
pF
V
V
s
%mA
1
2
Excluding gate/base drive current.
3
I
FB
is typically half of these values at
3V
System not device spec, including recommended transistors.
ISSUE 2 - May 2003
SEMICONDUCTORS
2
ZXSC410
ZXSC420
TYPICAL CHARACTERISTICS
ISSUE 2 - May 2003
3
SEMICONDUCTORS
ZXSC410
ZXSC420
DEVICE DESCRIPTION
Bandgap Reference
All threshold voltages and internal currents are derived
from a temperature compensated bandgap reference
circuit with a reference voltage of 1.22V nominal.
STDN
Shutdown
VCC
Block Diagrams
Dynamic Drive Output
Depending on the input signal, the output is either
“LOW” or “HIGH”. In the high state a 2.5mA current
source (max drive voltage = VCC-0.4V) drives the base
or gate of the external transistor. In order to operate the
external switching transistor at optimum efficiency,
both output states are initiated with a short transient
current in order to quickly discharge the base or the
gate of the switching transistor.
Switching Circuit
The switching circuit consists of two comparators,
Comp1 and Comp2, a gate U1, a monostable and the
drive output. Normally the DRIVE output is “HIGH”; the
external switching transistor is turned on. Current
ramps up in the inductor, the switching transistor and
external current sensing resistor. This voltage is
sensed by comparator, Comp2, at input I
SENSE
. Once
the current sense voltage across the sensing resistor
exceeds 20mV, comparator Comp2 through gate U1
triggers a re-triggerable monostable and turns off the
output drive stage for 2µs. The inductor discharges to
the load of the application. After 2µs a new charge cycle
begins, thus ramping the output voltage. When the
output voltage reaches the nominal value and V
FB
gets
an input voltage of more than 300mV, the monostable
is forced “on” from Comp1 through gate U1, until the
feedback voltage falls below 300mV. The above action
continues to maintain regulation.
EOR, End of Regulation Detector
The EOR circuit is a retriggerable 120µs monostable,
which is re-triggered by every down regulating action
of comparator Comp1. As long as regulation takes
place, output EOR is “HIGH“ (high impedance, 100K to
V
CC
). Short dips of the output voltage of less than
120µs are ignored. If the output voltage falls below the
nominal value for more than 120µs, output EOR goes
”LOW“. The reason for this to happen is usually a
slowly progressing drop of input voltage from the
discharging battery. Therefore the output voltage will
also start to drop slowly. With the EOR detector,
batteries can be used to the ultimate end of discharge,
with enough time left for a safe shutdown.
R3
R1
Bandgap
Reference
Bias Generator
+
Comp 1
_
R2
+
Comp 2
_
U1
Monostable
2µs
Dynamic
Drive
DRIVE
GND V
FB
SENSE
Fig. 1 ZXSC410
Fig. 1 ZXSC420
ISSUE 2 - May 2003
SEMICONDUCTORS
4
ZXSC410
ZXSC420
PIN DESCRIPTIONS
Pin No.
1
2
3
4
5
6
Name
V
CC
GND
STDN/EOR
SENSE
V
FB
DRIVE
Description
Supply voltage, 1.8V to 8V.
Ground
Shutdown ZXSC410 / End of regulation ZXSC420
Inductor current sense input. Internal threshold voltage set to
28mV. Connect external sense resistor.
Reference voltage. Internal threshold set to 300mV. Connect
external resistor network to set output voltage.
Drive output for external switching transistor. Connect to base or
gate of external switching transistor.
APPLICATIONS INFORMATION
Switching transistor selection
The choice of switching transistor has a major impact
on the converter efficiency. For optimum performance,
a bipolar transistor with low V
CE(SAT)
and high gain is
required. The V
CEO
of the switching transistor is also an
important parameter as this sees the full output
voltage when the transistor is switched off. Zetex
SuperSOT™ transistors are an ideal choice for this
application.
Schottky diode selection
As with the switching transistor, the Schottky rectifier
diode has a major impact on the converter efficiency. A
Schottky diode with a low forward voltage and fast
recovery time should be used for this application.
The diode should be selected so that the maximum
forward current rating is greater or equal to the
maximum peak current in the inductor, and the
maximum reverse voltage is greater or equal to the
output voltage. The Zetex ZHCS Series meet these
needs.
Combination devices
To minimise the external component count Zetex
recommends the ZX3CDBS1M832 combination of
NPN transistor and Schottky diode in a 3mm x 2mm
MLP package. This device is recommended for use in
space critical applications.
The IC is also capable of driving MOSFETs. Zetex
recommends the ZXMNS3BM832 combination of low
threshold voltage N-Channel MOSFET and Schottky
diode in a 3mm x 2mm MLP package. This device is
recommended for use in space critical applications.
Inductor Selection
The inductor value must be chosen to satisfy
performance, cost and size requirements of the overall
solution.
Inductor selection has a significant impact on the
converter performance. For applications where
efficiency is critical, an inductor with a series resistance
of 500m or less should be used.
A list of recommended inductors is listed in the table
below:
Part No.
Manufacture
L
I
PK
R
DC
(A) ( )
CMD4D11-100MC Sumida
CMD4D11-220MC Sumida
LPO2506OB-103
ST2006103
Coilcraft
Standex
Electronics Inc
10µH 0.5 0.457
22µH 0.4 0.676
10µH 1.0 0.24
10µH 0.6
0.1
Peak current definition
In general, the I
PK
value must be chosen to ensure that
the switching transistor, Q1, is in full saturation with
maximum output power conditions, assuming
worse-case input voltage and transistor gain under all
operating temperature extremes.
Once I
PK
is decided the value of R
SENSE
can be
determined by:
RSENSE
=
VSENSE
IPK
ISSUE 2 - May 2003
5
SEMICONDUCTORS
