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YB1692
2A Synchronous Step-Down Converter
Description
The YB1692 is a monolithic synchronous
buck regulator. The device integrates
130mMOSFETS that provide 2A
continuous load cur- rent over a wide
operating input voltage of 4.75V to 18V.
Current mode control provides fast
transient response and cycle-by-cycle cur-
rent limit.
An adjustable soft-start prevents inrush
current at turn-on. In shutdown mode, the
supply cur- rent drops below 1μA.
This device, available in an 8-pin SOP
pack- age, provides a very compact system
solution with minimal reliance on external
components.
Features
„ 2A Output Current
„ Wide 4.75V to 18V Operating Input
Range
„ Integrated 130mPower MOSFET
Switches
„ Output Adjustable from 0.923V to 15V
„ Up to 93% Efficiency
„ Programmable Soft-Start
„ Stable with Low ESR Ceramic Output
Capaci- tors
„ Fixed 340KHz Frequency
„ Cycle-by-Cycle Over Current
Protection
„ Input Under Voltage Lockout
„ Thermally Enhanced 8-Pin SOP
Package
Applications
„ Distributed Power Systems
„ Networking Systems
„ FPGA, DSP, ASIC Power Supplies
„ Green Electronics/ Appliances
„ Notebook Computers
Typical Application Circuit
YB1692 Rev.1.0
Figure1 Typical Application Circuit
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Pin Configuration
YB1692
2A Synchronous Step-Down Converter
SOP-8
Figure 2 Pin Configuration
Pin Description
Table 1
Pin Name
Description
High-Side Gate Drive Boost Input. BS supplies the drive for the
1 BS high-side N-Channel MOSFET switch. Connect a 0.01μF or greater
capacitor from SW to BS to power the high side switch.
Supply Voltage Input Pin. YB1692 operates from a 4.75V to 18VDC
2
VIN
voltage.
Bypass VIN to GND with a suitably large capacitor to eliminate noise
on the input.
3
SW
Power Switch Output Pin. SW is the switch node that supplies power
to the output.
4 GND Ground Pin.
Feedback Pin. Through an external resistor divider network,
5 FB FBsenses the output voltage and regulates it. The feedback threshold
voltage is 0.923V
Compensation Node. COMP is used to compensate the regulation
control loop. Connect a series RC network from COMP to GND to
6 COMP compensate the regulation control loop. In some cases, an additional
capacitor from COMP to GND is required. See Compensation
Components.
7
EN
Enable Pin. EN is a digital input that turns the regulator on or off.
Drive EN pin high to turn on the regulator, drive it low to turn it off.
Soft-Start Control Input. SS controls the soft-start period. Connect a
8
SS
capacitor from SS to GND to set the soft-start period. A 0.1μF
capacitor sets the soft-start period to 15ms. To disable the soft-start
feature, leave SS unconnected.
Ordering Information
Order Number
Package Type
YB1692SPX8
SOP-8
Supplied As
2500 units
Tape & Reel
Package Marking
YB1692
YB1692 Rev.1.0
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YB1692
2A Synchronous Step-Down Converter
Absolute Maximum Ratings(1)
Supply Voltage............................-0.3V to 20V
Switch Voltage..........................................21V
Bootstrap Voltage...... VSW -0.3V to VSW + 6V
Enable/UVLO Voltage...............–0.3V to +6V
Comp Voltage...........................–0.3V to +6V
Feedback Voltage.....................–0.3V to +6V
Junction Temperature ....................... +150
Lead Temperature ............................. +260
Storage Temperature........... –65°C to +150
Recommended Operating Conditions(2)
Input Voltage............................. 4.75V to 18V
Output Voltage.......................... 0.923 to 15V
Operating Temperature............–45to +85
Thermal Resistance(3) θJA θJC
SOP8 ................................ 90...... 45... /W
Notes:
(1) Exceeding these ratings may damage the
device.
(2) The device is not guaranteed to function
outside of its operating conditions.
(3) Measured on approximately 1”square of 1
oz copper.
Electrical and Optical Characteristics
Table 2 VIN = 12V, TA=25°C, Test Circuit Figure 1, unless otherwise noted.
Description
Input Voltage
Shutdown Supply Current
Supply Current
Feedback Voltage
Feedback Overvoltage Threshold
High-Side Switch Leakage
Soft-star Current
Soft-Start Period
Switch Current Limit
Oscillator Frequency
EN Pin Threshold
Internal MOS RDSON
Maximum Duty Cycle
Minimum On Time
Efficiency
Thermal Shutdown
Symbol
VIN
ISTBY
ICC
VFB
Test Conditions
VEN=0V
VEN=2V , VFB=1.0V
4.75VVIN 18
Min
4.75
900
ISS
ILIM
FOSC
VEN
RDSON
DMAX
VEN=0V , VSW=0V
VSS
CSS = 0.1μF
Minimum Duty Cycle
From Drain to Source
2.4
1.1
η
TOSTD
VIN=8V VOUT=3.3 IOUT=500mA
Typ.
1
1.3
923
1.1
6
15
3.4
1.1
340
1.5
130
90
220
93
160
Max Units
18 V
3 μA
1.5 mA
946 mV
V
10 μA
μA
ms
A
A
KHz
2.0 V
m
nS
°C
YB1692 Rev.1.0
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BLOCK DIAGRAM
YB1692
2A Synchronous Step-Down Converter
Figure 3
FUNCTIONAL DESCRIPTIONS
The YB1692 is a synchronous rectified, cur-
rent-mode,step-down regulator. It regulates
in- put voltages from 4.75V to 18V down to an
out- put voltage as low as 0.923V,and
supplies up to 2A of load current.
The YB1692 uses current-mode control to
regulate the output voltage. The output
voltage is measured at FB through a resistive
voltage di- vider and amplified through the
internal trans- conductance error amplifier.
The voltage at the COMP pin is compared to
the switch current measured internally to
control the output voltage.
The converter uses internal N-Channel
MOSFET switches to step-down the input
voltage to the regu- lated output voltage.Since
the high side MOSFET requires a gate
voltage greater than
the input voltage, a boost capacitor connected
between SW and BS is needed to drive the
high side gate. The boost capaci- tor is
charged from the internal 5V rail when SW is
low.
When the YB1692 FB pin exceeds 20% of the
nominal regulation voltage of 0.923V, the over
volt- age comparator is tripped and the COMP
pin and the SS pin are discharged to
GND,forcing the high-side switch off.
YB1692 Rev.1.0
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YB1692
2A Synchronous Step-Down Converter
Application Information
Component Selection
Setting the Output Voltage
The output voltage is set using a resistive
volt-age divider from the output voltage to FB
(see Typical Application circuit on page 1).
The volt - age divider divides the output
voltage down by the ratio:
Where VFB is the feedback voltage and VOUT is
the output voltage.
Thus the output voltage is:
R2 can be as high as 100k, but a typical
value is 10k.Using the typical value for R2,
R1 is determined by:
For example, for a 3.3V output voltage, R2 is
10k, and R1 is 26.1k. Table 3 lists recom-
mended resistance values of R1 and R2 for
standard output voltages.
Table 3
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:
Where ILOAD is the load current.
The choice of which style inductor to use
mainly de- pends 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
lowside power MOSFET conducts the
inductor current. The forward voltage of this
body diode is high. An optional Schot- tky
diode may be paralleled between the SW pin
and GND pin to improve overall efficiency.
Table 4 lists example Schottky diodes and
their Manufacturers.
Table 4
Inductor
The inductor is required to supply constant
cur- rent to the output load while being driven
by the switched input voltage.A larger value
inductor will result in less ripple current that
will result in lower output ripple voltage.
However, the larger value inductor will have a
larger physical size, higher series resistance,
and/or lower saturation current. A good rule
for determining the induc- tance to use is to
allow the peak-to-peak ripple current in the
inductor to be approximately 30% of the
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:
Where VOUT is the output voltage, VIN is the
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 ca- pacitors 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
absorbs the input switching current it requires
an adequate ripple current rating. The RMS
current in the input capacitor can be
estimated by:
The worst-case condition occurs at VIN =
2VOUT, where ICIN = ILOAD/2. For simplification,
choose the input capacitor whose RMS
YB1692 Rev.1.0
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