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ZXSC440 Schematic ( Datenblatt PDF ) - Diodes

Teilenummer ZXSC440
Beschreibung DC-DC BOOST SWITCHING CONTROLLERS
Hersteller Diodes
Logo Diodes Logo 



Gesamt 17 Seiten
		
ZXSC440 Datasheet, Funktion
ZXSC410/ZXSC420/ZXSC440
DC-DC BOOST SWITCHING CONTROLLERS
Description
The ZXSC410/420/440 are DC-DC boost controllers. Their wide input
voltage range makes them suitable for operation for a number of
battery configurations including single Li-Ion cell and 2~3
alkaline/NiCd/NiMH cells. Using high gain Diodes Zetex-brand
switching npn-transistors allows high-voltage boost ratios and/or high
output current depending on the transistor. The ZXSC410/440 has a
shutdown feature that can also be used for some dimming
functionality. ZXSC420/440 includes an End of Regulation flag that
can be used to indicate when the regulator is no longer able to
maintain the regulated output voltage/current or has reached the
required current/voltage. The ZXSC440 combines the features of the
ZXSC410 and ZXSC420 into one device.
Pin Assignments
ZXSC410 (SOT26)
VCC 1
GND 2
STDN 3
8 DRIVE
7 VFB
6 SENSE
ZXSC420 (SOT26)
VCC 1
GND 2
EOR 3
8 DRIVE
7 VFB
6 SENSE
Features
1.65V to 8V Supply Range
Typical Output Regulation of ±1%
Over 85% Typical Efficiency
Output Currents Up to 300mA
4.5µA Typical Shutdown Current ZXSC410/440
End of Regulation Output ZXSC420/440
Available in SOT26 and MSOP-8
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
ZXSC440 (MSOP-8)
DRIVE 1
VFB 2
SENSE 3
N/C 4
8 VCC
7 GND
6 EOR
5 STDN
Applications
System Power for Battery Portable Products
LCD Bias
Local Voltage Conversion
High-Brightness LED Driving
Notes:
1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.
2. See http://www.diodes.com/quality/lead_free.html for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green"
and Lead-free.
3. Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and
<1000ppm antimony compounds.
Typical Applications Circuit
22µH
ZHCS2000
ZXTN25012EFH
100µF
22µF ZXSC410
18m
820m
ZXSC410/ZXSC420/ZXSC440
Document number: DS33618 Rev. 6 - 2
1 of 17
www.diodes.com
August 2015
© Diodes Incorporated






ZXSC440 Datasheet, Funktion
ZXSC410/ZXSC420/ZXSC440
Application Information (continued)
External Component Selection
Switching Transistor Selection
The choice of switching transistor has a major impact on the converter efficiency. For optimum performance, a bipolar transistor with low VCE(SAT)
and high gain is required. The VCEO of the switching transistor is also an important parameter as this sees the full output voltage when the
transistor is switched off. Diodes SOT26 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 Diodes ZHCS Series meets these needs.
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 500mΩ or less should be used.
Output Capacitors
Output capacitors are a critical choice in the overall performance of the solution. They are required to filter the output and supply load transient
currents. There are three parameters which are paramount in the selection of the output capacitors, capacitance, IRIPPLE and ESR. The
capacitance value is selected to meet the load transient requirements. The capacitors IRIPPLE rating must meet or exceed the current ripple of the
solution.
The ESR of the output capacitor can also affect loop stability and transient performance. The capacitors selected for the solutions and indicated
in the reference designs are optimized to provide the best overall performance.
Input Capacitors
The input capacitor is chosen for its voltage and RMS current rating. The use of low ESR electrolytic or tantalum capacitors is recommended.
Capacitor values for optimum performance are suggested in the reference design section.
Also
note
that
the
ESR
of
the
input
capacitor
is
effectively
in
series
with
the
input
and
hence
contributes
to
efficiency
losses
in
the
order
of
I
2
RMS
ESR.
Peak Current Definition
In general, the IPK 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 temperatureextremes.Once IPK is decided, the value of RSENSE can be
determined by:
RSENSE
VSENSE
IPK
Sense Resistor
A low-value sense resistor is required to set the peak current. Power in this resistor is negligible due to the low sense voltage threshold, VSENSE.
ZXSC410/ZXSC420/ZXSC440
Document number: DS33618 Rev. 6 - 2
6 of 17
www.diodes.com
August 2015
© Diodes Incorporated

6 Page







ZXSC440 pdf, datenblatt
ZXSC410/ZXSC420/ZXSC440
Application Examples (continued)
Triple Output TFT Bias Generator
VIN
4.2V ~ 3V
L1
22µH Q1 ZXTN
U1 25012EFH
C1
10µF
VCC VDRIVE
STDN ISENSE
GND VFB
ZXSC410
R1
22mΩ
C7
1µF
BAT54S
C3
1µF
BAT54S
C4
1µF
D1
BAT54
R2
30kΩ
C2
47µF
R3
1kΩ
C5 BAT54S
1µF
C6
1µF
ZXSC410 as Triple Output TFT Bias
VON
27V, 10mA
C8
1µF
AVDD
9V, 180mA
VOFF
-9V, 10mA
Sequencing AVDD and VON
By adding the circuit below to the LCD bias output (VON) of
the converter, a 10ms delay can be achieved between AVDD
power up and VON power up. The circuit operates by a delay
in turning the PMOS transistor on, which transfers to a 10ms
delay between input and output of the circuit.
The delay is set by the RC time constant of R1 and C1. The
diode, D1, discharges the gate of the PMOS when the main
system supply is turned off, guaranteeing a delay every turn
on cycle.
LCD Bias
Voltage
VON
System
Voltage
AVDD
Q1
ZXMP3A13F
C1
0.1µF
Sequenced Output
10ms Delay
R1
470k
ZXSC410/ZXSC420/ZXSC440
Document number: DS33618 Rev. 6 - 2
12 of 17
www.diodes.com
August 2015
© Diodes Incorporated

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