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PDF ZT7184 Data sheet ( Hoja de datos )

Número de pieza ZT7184
Descripción Synchronous Step-Down DC/DC Converter
Fabricantes ZillTek Technology 
Logotipo ZillTek Technology Logotipo



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ZT7184
3A, 23V, 340kHz, Synchronous Step-Down DC/DC Converter
FEATURES
4.75V to 23V input voltage
Output adjustable from 0.925V to 20V
Output current up to 3A
Integrated 85mΩ power MOSFET switches
Shutdown current 1μA typical
Efficiency up to 95%
340kHz fixed frequency
Programmable soft start
Over current protection
Over temperature protection
RoHS Compliant and 100% Lead (Pb) Free
APPLICATIONS
FPGA, DSP, ASIC power supplies
Notebook computers
Green electronics or appliance
ORDERING INFORMATION
PART
PACKAGE RoHS
ZT7184S SOP-8L(EP) Yes
Ship, Quantity
Tape and Reel
DESCRIPTION
The ZT7184 is a 340kHz fixed frequency PWM
synchronous step-down regulator. The ZT7184
is operated from 4.75V to 23V, the generated
output is adjustable from 0.925V to 20V, and
the output current can be up to 3A.
The integrated two MOSFET switches is with
turn on resistance of 85mΩ. Current mode
control provides fast transient response and
cycle-by-cycle over current protection. The
shutdown current is 1μA typical. Adjustable
soft start prevents inrush current at turn on.
The ZT7184 is with thermal shutdown.
The ZT7184 is available in the SOP-8L package,
and it is RoHS compliant and 100% lead (Pb)
free.
Pins Configuration
Typical Application Circuit
DS-07; Sep. 04, 2009
Copyright © ZillTek Technology Corp.
-1-
5F, No.2, Industry E. 9th Rd., Science-Based
Industrial Park, Hsinchu 30075 Taiwan
Tel: (886) 3577 7509; Fax: (886) 3577 7390
Free Datasheet http://www.datasheet4u.com/

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ZT7184 pdf
ZT7184
maximum switch current limit. Also, make sure that the
peak inductor current is below the maximum switch
current limit. The inductance value can be calculated by:
L = [ VOUT / (fS × ΔIL) ] × (1 VOUT/VIN)
Where VOUT is the output voltage, VIN is the input voltage,
fS is the switching frequency, and ΔIL is the peak-to-peak
inductor ripple current.
Choose an inductor that will not saturate under the
maximum inductor peak current. The peak inductor
current can be calculated by:
ILP = ILOAD + [ VOUT / (2 × fS × L) ] × (1 VOUT/VIN)
Where ILOAD is the load current.
The choice of which style inductor to use mainly
depends on the price vs. size requirements and any EMI
requirements.
Optional Schottky Diode
During the transition between high-side switch and
low-side switch, the body diode of the low-side power
MOSFET conducts the inductor current. The forward
voltage of this body diode is high. An optional Schottky
diode may be paralleled between the SW pin and GND
pin to improve overall efficiency. Table 1 lists example
Schottky diodes and their Manufacturers.
Part
Number
B130
SK13
Voltage and
Current Rating
30V, 1A
30V, 1A
Vendor
Diodes Inc.
Diodes Inc.
MBRS130
30V, 1A
International Rectifier
Table 1: Diode selection guide.
Input Capacitor
The input current to the step-down converter is
discontinuous, therefore a capacitor is required to
supply the AC current to the step-down converter while
maintaining the DC input voltage. Use low ESR
capacitors for the best performance. Ceramic capacitors
are preferred, but tantalum or low-ESR electrolytic
capacitors may also suffice. Choose X5R or X7R
dielectrics when using ceramic capacitors.
Since the input capacitor (C1) absorbs the input
switching current it requires an adequate ripple current
rating. The RMS current in the input capacitor can be
estimated by:
IC1 = ILOAD × [ (VOUT/VIN) × (1 VOUT/VIN) ]1/2
The worst-case condition occurs at VIN = 2VOUT, where IC1
= ILOAD/2. For simplification, choose the input capacitor
whose RMS current rating greater than half of the
maximum load current.
The input capacitor can be electrolytic, tantalum or
ceramic. When using electrolytic or tantalum capacitors,
a small, high quality ceramic capacitor, i.e. 0.1μF, should
be placed as close to the IC as possible. When using
ceramic capacitors, make sure that they have enough
capacitance to provide sufficient charge to prevent
excessive voltage ripple at input. The input voltage
ripple for low ESR capacitors can be estimated by:
ΔVIN = [ ILOAD/(C1 × fS) ] × (VOUT/VIN) × (1 VOUT/VIN)
Where C1 is the input capacitance value.
Output Capacitor
The output capacitor is required to maintain the DC
output voltage. Ceramic, tantalum, or low ESR
electrolytic capacitors are recommended. Low ESR
capacitors are preferred to keep the output voltage
ripple low. The output voltage ripple can be estimated
by:
ΔVOUT = [ VOUT/(fS × L) ] × (1 VOUT/VIN)
× [ RESR + 1 / (8 × fS × C2) ]
Where C2 is the output capacitance value and RESR is the
equivalent series resistance (ESR) value of the output
capacitor.
In the case of ceramic capacitors, the impedance at the
switching frequency is dominated by the capacitance.
The output voltage ripple is mainly caused by the
capacitance. For simplification, the output voltage ripple
can be estimated by:
ΔVOUT = [ VOUT/(8 × fS2 × L × C2) ] × (1 VOUT/VIN)
In the case of tantalum or electrolytic capacitors, the
ESR dominates the impedance at the switching
frequency. For simplification, the output ripple can be
approximated to:
ΔVOUT = [ VOUT/(fS × L) ] × (1 VOUT/VIN) × RESR
The characteristics of the output capacitor also affect
the stability of the regulation system. The ZT7184 can be
optimized for a wide range of capacitance and ESR
values.
Compensation Components
ZT7184 employs current mode control for easy
DS-07; Sep. 04, 2009
Copyright © ZillTek Technology Corp.
-5-
5F, No.2, Industry E. 9th Rd., Science-Based
Industrial Park, Hsinchu 30075 Taiwan
Tel: (886) 3577 7509; Fax: (886) 3577 7390
Free Datasheet http://www.datasheet4u.com/

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