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PDF MAX17112 Data sheet ( Hoja de datos )
| Número de pieza | MAX17112 | |
| Descripción | DC-DC Converter | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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19-4393; Rev 0; 12/08
www.DataSheet4EUV.cAAoLVmUAAILTAIOBNLEKIT
High-Performance, Step-Up, DC-DC Converter
General Description
The MAX17112 is a high-performance, step-up, DC-DC
converter that provides a regulated supply voltage for
active-matrix thin-film transistor (TFT) liquid-crystal dis-
plays (LCDs). The MAX17112 incorporates current-
mode, fixed-frequency (1MHz), pulse-width modulation
(PWM) circuitry with a built-in, n-channel power MOSFET
to achieve high efficiency and fast-transient response.
The input overvoltage protection (OVP) function pre-
vents damage to the MAX17112 from an input surge
voltage (up to 24V).
The high switching frequency (1MHz) allows the use of
ultra-small inductors and low-ESR ceramic capacitors.
The current-mode architecture provides fast-transient
response to pulsed loads. A compensation pin (COMP)
gives users flexibility in adjusting loop dynamics. The
internal MOSFET can generate output voltages up to
20V from an input voltage between 2.6V and 5.5V.
Soft-start slowly ramps the input current and is pro-
grammable with an external capacitor. The MAX17112
is available in a 10-pin TDFN package.
Applications
Notebook Computer Displays
LCD Monitor Panels
Features
o Input Overvoltage Protection
o Adjustable Output from VIN to 20V
o 2.6V to 5.5V Input Supply Range
o Input Supply Undervoltage Lockout
o 1MHz Fixed Switching Frequency
o Programmable Soft-Start
o Small 10-Pin, TDFN Package
o Thermal-Overload Protection
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX17112ETB+
-40°C to +85°C
10 TDFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Simplified Operating Circuit
Pin Configuration
VIN
2.6V TO 5.5V
6
LX
8
IN
7
LX
FB 2
MAX17112
9
SHDN
GND 5
3 VL
GND 4
10
SS
GND
EP
COMP 1
VOUT
TOP VIEW
COMP 1 +
FB 2
VL 3
GND 4
GND 5
MAX17112
*EP
10 SS
9 SHDN
8 IN
7 LX
6 LX
*EXPOSED PAD
TDFN
3mm × 3mm
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1 page  
www.DataSheet4U.com
High-Performance, Step-Up, DC-DC Converter
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 5V, VMAIN = 15V, TA = +25°C, unless otherwise noted.)
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
1100
1000
900
2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
4.0
3.5
3.0
2.5
SWITCHING
2.0
0
1.5
1.0
0.5 NONSWITCHING
0
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
SUPPLY VOLTAGE (V)
SOFT-START
(RLOAD = 30Ω)
MAX17112 toc06
VOUT
5V/div
2ms/div
INDUCTOR
CURRENT
1A/div
LOAD-TRANSIENT RESPONSE
(ILOAD = 50mA TO 550mA)
MAX17112 toc07
15V
VOUT
0 500mV/div
AC-COUPLED
PULSED LOAD-TRANSIENT RESPONSE
(ILOAD = 100mA TO 1.1A)
MAX17112 toc08
15V
VOUT
200mV/div
AC-COUPLED
IOUT
1A/div
50mA
IOUT
500mA/div
0
L = 2.7μH
RCOMP = 47kΩ
CCOMP1 = 560pF
100μs/div
INDUCTOR
CURRENT
2A/div
SWITCHING WAVEFORMS
(ILOAD = 600mA)
MAX17112 toc09
0.1A
INDUCTOR
CURRENT
1A/div
0
L = 2.7μH
RCOMP = 47kΩ
CCOMP1 = 560pF
10μs/div
VIN OVP PROTECTION
MAX17112 toc10
LX
10V/div
0
INDUCTOR
CURRENT
1A/div
0
1μs/div
VIN
5V/div
0
VL
0 5V/div
10ms/div
_______________________________________________________________________________________ 5
5 Page 
www.DataSheet4U.com
High-Performance, Step-Up, DC-DC Converter
and:
VRIPPLE(ESR) ≈ IPEAKRESR(COUT)
where IPEAK is the peak inductor current (see the
Inductor Selection section). For ceramic capacitors, the
output voltage ripple is typically dominated by VRIPPLE(C).
The voltage rating and temperature characteristics of
the output capacitor must also be considered.
Input Capacitor Selection
The input capacitor (CIN) reduces the current peaks
drawn from the input supply and reduces noise injec-
tion into the IC. Two 4.7µF ceramic capacitors are used
in the typical operating circuit in Figure 1 because of
the high source impedance seen in typical lab setups.
Actual applications usually have much lower source
impedance since the step-up regulator often runs
directly from the output of another regulated supply.
Typically, CIN can be reduced below the values used in
Figure 1. Ensure a low-noise supply at IN by using ade-
quate CIN. Alternatively, greater voltage variation can
be tolerated on CIN if IN is decoupled from CIN using
an RC lowpass filter (see Figure 1).
Rectifier Diode Selection
The MAX17112 high switching frequency demands a
high-speed rectifier. Schottky diodes are recommended
for most applications because of their fast recovery time
and low forward voltage. The diode should be rated to
handle the output voltage and the peak switch current.
Make sure that the diode’s peak current rating is at least
IPEAK calculated in the Inductor Selection section and
that its breakdown voltage exceeds the output voltage.
Output Voltage Selection
The MAX17112 operates with an adjustable output from
VIN to 20V. Connect a resistive voltage-divider from the
output (VMAIN) to GND with the center tap connected to
FB (see Figure 1). Select R3 in the 10kΩ to 50kΩ range.
Calculate R4 with the following equation:
R4
=
R3
×
⎛
⎝⎜
VMAIN
VFB
⎞
- 1⎠⎟
where VFB, the step-up regulator’s feedback set point,
is 1.24V (typ). Place R3 and R4 as close as possible to
the IC.
Loop Compensation
Choose RCOMP to set the high-frequency integrator
gain for fast-transient response. Choose CCOMP to set
the integrator zero to maintain loop stability.
For low-ESR output capacitors, use the following equa-
tions to obtain stable performance and good transient
response:
RCOMP
≈
253 ×
VIN × VOUT
L × IOUT
×
COUT
CCOMP
≈
VOUT × COUT
10 × IOUT × RCOMP
To further optimize transient response, vary RCOMP in
20% steps and CCOMP in 50% steps while observing
transient response waveforms.
Soft-Start Capacitor
The soft-start capacitor should be large enough so that
it does not reach final value before the output has
reached regulation. Calculate CSS to be:
CSS
>
21× 10-6
×
COUT
×
⎡
⎢
⎣⎢ VIN
VOUT2 - VIN × VOUT
× IINRUSH - IOUT × VOUT
⎤
⎥
⎦⎥
where COUT is the total output capacitance including
any bypass capacitor on the output bus, VOUT is the
maximum output voltage, IINRUSH is the peak inrush
current allowed, IOUT is the maximum output current
during power-up, and VIN is the minimum input voltage.
The load must wait for the soft-start cycle to finish
before drawing a significant amount of load current.
The soft-start duration after which the load can begin to
draw maximum load current is:
tMAX = 2.4 × 105 × CSS
PCB Layout and Grounding
Careful PCB layout is important for proper operation.
Use the following guidelines for good PCB layout:
1) Minimize the area of high-current loops by placing
the inductor, output diode, and output capacitors
near the input capacitors and near the LX and GND
pins. The high-current input loop goes from the pos-
itive terminal of the input capacitor to the inductor,
to the IC’s LX pin, out of GND, and to the input
capacitor’s negative terminal. The high-current out-
put loop is from the positive terminal of the input
capacitor to the inductor, to the output diode (D1),
to the positive terminal of the output capacitors,
reconnecting between the output capacitor and
input capacitor ground terminals. Connect these
loop components with short, wide connections.
Avoid using vias in the high-current paths. If vias
are unavoidable, use many vias in parallel to
reduce resistance and inductance.
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet MAX17112.PDF ] | |
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