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ZXSC420 PDF 데이터시트 : 부품 기능 및 핀배열

부품번호 ZXSC420
기능 VOLTAGE MODE BOOST CONVERTER
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ZXSC420 데이터시트, 핀배열, 회로
VOLTAGE MODE BOOST CONVERTER
ZXSC410
ZXSC420
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
4.5A typical shutdown current ZXSC410
End of regulation output ZXSC420
APPLICATIONS
System power for battery portable products
LCD bias
Local voltage conversion
SOT23-6
ORDERING INFORMATION
DEVICE
ZXSC410E6TA
ZXSC420E6TA
REEL TAPE QUANTITY
SIZE WIDTH PER REEL
7” 8mm 3000 units
7” 8mm 3000 units
TYPICAL APPLICATIONS DIAGRAM
VIN
C1
L1
D1
ZHCS1000
VOUT
U1
VCC DRIVE
STDN SENSE
GND VFB
ZXSC410
Q1
FMMT617
R2
C2
R1 R3
DEVICE MARKING
C410 ZXSC410
C420 ZXSC420
ISSUE 2 - May 2003
1 SEMICONDUCTORS




ZXSC420 pdf, 반도체, 판매, 대치품
ZXSC410
ZXSC420
DEVICE DESCRIPTION
Block Diagrams
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.
Dynamic Drive Output
Depending on the input signal, the output is either
LOWor 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 ISENSE. 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 VFB gets
an input voltage of more than 300mV, the monostable
is forced onfrom Comp1 through gate U1, until the
feedback voltage falls below 300mV. The above action
continues to maintain regulation.
STDN
Shutdown
VCC
Bandgap
Reference
Bias Generator
R1
+
Comp 1
_
R2
+
Comp 2
_
R3
Monostable
U1 2µs
Dynamic
Drive
GND VFB SENSE
Fig. 1 ZXSC410
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
VCC). 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.
Fig. 1 ZXSC420
DRIVE
SEMICONDUCTORS
4
ISSUE 2 - May 2003

4페이지










ZXSC420 전자부품, 판매, 대치품
ZXSC410
ZXSC420
Output voltage adjustment
The ZXSC410/420 are adjustable output converters
allowing the end user the maximum flexibilty. For
adjustable operation a potential divider network is
connected as follows:
VOUT
RA
VFB
RB
GND
The output voltage is determined by the equation:
Layout issues
Layout is critical for the circuit to function in the most
efficient manner in terms of electrical efficiency,
thermal considerations and noise.
For step-up convertersthere are four main current
loops, the input loop, power-switch loop, rectifier loop
and output loop. The supply charging the input
capacitor forms the input loop. The power-switch loop
is defined when Q1 is on, current flows from the input
through the inductor, Q1, RSENSE and to ground. When
Q1 is off, the energy stored in the inductor is
transferred to the output capacitor and load via D1,
forming the rectifier loop. The output loop is formed by
the output capacitor supplying the load when Q1 is
switched back off.
To optimise for best performance each of these loops
kept separate from each other and interconnected with
short, thick traces thus minimising parasitic
inductance, capacitance and resistance. Also the
RSENSE resistor should be connected, with minimum
trace length, between emitter lead of Q1 and ground,
again minimising stray parasitics.
VOUT
=
VFB
1+
RA 
RB
where VFB=300mV
The resistor values, RA and RB, should be maximised
to improve efficiency and decrease battery drain.
Optimisation can be achieved by providing a minimum
current of IFB(MAX)=200nA to the VFB pin. Output is
adjustable from VFB to the (BR)VCEO of the switching
transistor, Q1.
Note: For the reference designs, RA is assigned the
label R2 and RB the label R3.
CONNECTION DIAGRAMS
ZXSC410
SOT23-6
ZXSC420
SOT23-6
VCC
GND
STDN
DRIVE
VFB
SENSE
VCC
GND
EOR
DRIVE
VFB
SENSE
ISSUE 2 - May 2003
7 SEMICONDUCTORS

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관련 데이터시트

부품번호상세설명 및 기능제조사
ZXSC420

VOLTAGE MODE BOOST CONVERTER

Zetex Semiconductors
Zetex Semiconductors
ZXSC420

DC-DC BOOST SWITCHING CONTROLLERS

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