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PDF MAX17083 Data sheet ( Hoja de datos )
| Número de pieza | MAX17083 | |
| Descripción | Step-Down Regulator | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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19-4458; Rev 0; 2/09
www.DataSheet4U.com
Low-Voltage, Internal Switch,
Step-Down Regulator
General Description
The MAX17083 is a fixed-frequency, current-mode,
step-down regulator optimized for low-voltage, low-
power applications. This regulator features dual internal
n-channel MOSFET power switches for high efficiency
and reduced component count. External Schottky
diodes are not required. An integrated boost switch
eliminates the need for an external boost diode. The
internal 25mΩ low-side power MOSFET easily supports
continuous load currents up to 5A. The MAX17083 pro-
duces an adjustable 0.75V to 2.7V output voltage from
the system’s 3.3V or 5V input supply.
This step-down regulator uses a peak current-mode
control scheme to eliminate the additional external
compensation required by voltage-mode architectures,
providing an easy-to-implement architecture without
sacrificing fast transient response. The MAX17083 pro-
vides peak current-limit protection and operates in
light-load pulse-skipping mode to maintain high effi-
ciency under light-load conditions.
Independent enable input and open-drain power-good
output allow flexible system power sequencing. The volt-
age soft-start gradually ramps up the output voltage
within a predictable time period, effectively limiting the
inrush current. The MAX17083 features output undervolt-
age, output overvoltage, and thermal-fault protection.
The MAX17083 is available in a 24-pin 4mm x 4mm x
0.75mm TQFN package. The exposed backside pad
improves thermal characteristics.
Features
o Fixed-Frequency, Current-Mode Controller
o 2.4V to 5.5V Input Range
o Internal 5A Step-Down Regulator
o Internal BST Switch
o Fault Protection: Undervoltage, Overvoltage,
Thermal, Peak Current Limit
o Enable Input and Power-Good Output
o Voltage-Controlled Soft-Start
o High-Impedance Shutdown
o < 1µA (typ) Shutdown Current
Applications
Low-Power Architectures
Ultra-Mobile PCs
Netbook and Nettop PCs
Portable Gaming
Notebook and Subnotebook Computers
PDAs and Mobile Communicators
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX17083ETG+
-40°C to +85°C
24 TQFN
+Denotes a lead(Pb)-free/RoHS-compliant package.
TOP VIEW
18 17 16 15 14 13
N.C. 19
12 FB
PGND 20
11 N.C.
PGND 21
PGND 22
MAX17083
10 GND
9 GND
PGND 23
N.C. 24 +
8 GND
7 REF
12 3456
Pin Configuration
TQFN
4mm x 4mm
________________________________________________________________ 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  
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Low-Voltage, Internal Switch,
Step-Down Regulator
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 5V, VOUT = 1.1V, FREQ = open. TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(VIN = 3.3V, 750kHz)
100
VOUT = 1.8V
VOUT = 1.5V
90
80
VOUT = 1.1V
70
VOUT = 0.75V
60
50
0.001
0.01 0.1
1
LOAD CURRENT (A)
10
SMPS OUTPUT VOLTAGE
vs. LOAD CURRENT (1MHz)
0.78
0.77
VIN = 5V
0.76
0.75 VIN = 3.3V
0.74
0
1234 5
LOAD CURRENT (A)
6
REGULATOR STARTUP WAVEFORM
(HEAVY LOAD)
MAX17083 toc06
EN
POK
OUT
IL
LX
400μs/div
fSW = 750kHz, VIN = 5V,
VOUT = 1.1V
EN: 5V/div
OUT: 1V/div
RLOAD = 0.22Ω
POK: 2V/div
IL: 5A/div
LX: 5V/div
REGULATOR STARTUP WAVEFORM
(NO LOAD)
MAX17083 toc07
EN
POK
OUT
IL
LX
400μs/div
fSW = 1MHz, VIN = 5V,
VOUT = 1.1V
EN: 5V/div
OUT: 1V/div
POK: 2V/div
IL: 5A/div
LX: 5V/div
_______________________________________________________________________________________ 5
5 Page 
www.DataSheet4U.com
Low-Voltage, Internal Switch,
Step-Down Regulator
curve, while higher values result in higher full-load effi-
ciency (assuming that the coil resistance remains fixed)
and less output voltage ripple. Penalties for using high-
er inductor values include larger physical size and
degraded load-transient response (especially at low
input-voltage levels).
SMPS POR, UVLO, and Soft-Start
Power-on reset (POR) occurs when VCC rises above
approximately 2.1V, resetting the undervoltage, over-
voltage, and thermal-shutdown fault latches. The VCC
input undervoltage lockout (UVLO) circuitry prevents
the switching regulators from operating if the 5V bias
supply (VCC) is below its 4V UVLO threshold.
Soft-Startup
The internal step-down controller starts switching and the
output voltages ramp up using soft-start. If the bias supply
voltage drops below the UVLO threshold, the controller
stops switching and disables the drivers (LX becomes
high impedance) until the bias supply voltage recovers.
Once the 5V bias supply and IN rise above their respec-
tive input UVLO thresholds, and EN is pulled high, the
internal step-down controller becomes enabled and
begins switching. The internal voltage soft-starts gradu-
ally increment the feedback voltage by approximately
25mV every 61 switching cycles. Therefore, OUT reach-
es its nominal regulation voltage 1833/fSW after the regu-
lator is enabled (see the Soft-Start Waveforms in the
Typical Operating Characteristics section).
SMPS Power-Good Output (POK)
POK is the open-drain output of the window comparator
that continuously monitors the output for undervoltage
and overvoltage conditions. POK is actively held low in
shutdown (EN = GND) and during soft-start. Once the
soft-start sequence terminates, POK becomes high
impedance as long as the output remains within ±10%
of the nominal regulation voltage set by FB. POK goes
low once the output drops 12% (typ) below or rises 12%
(typ) above its nominal regulation point, or the output is
shut down. For a logic-level POK output voltage, con-
nect an external pullup resistor between POK and VCC.
A 100kΩ pullup resistor works well in most applications.
SMPS Fault Protection
Output Overvoltage Protection (OVP)
If the output voltage rises above 112% (typ) of its nomi-
nal regulation voltage, the controller sets the fault latch,
pulls POK low, shuts down the regulator, and immedi-
ately pulls the output to ground through its low-side
MOSFET. Turning on the low-side MOSFET with 100%
duty cycle rapidly discharges the output capacitors and
clamps the output to ground. However, this commonly
undamped response causes negative output voltages
due to the energy stored in the output LC at the instant
of 0V fault. If the load cannot tolerate a negative voltage,
place a power Schottky diode across the output to act
as a reverse-polarity clamp. If the condition that caused
the overvoltage persists (such as a shorted high-side
MOSFET), the input source also fails (short-circuit fault).
Cycle VCC below 1V or toggle the enable input to clear
the fault latch and restart the regulator.
Output Undervoltage Protection (UVP)
Each MAX17083 includes an output undervoltage
(UVP) protection circuit that begins to monitor the out-
put once the startup blanking period has ended. If the
output voltage drops below 88% (typ) of its nominal
regulation voltage, the regulator pulls the POK output
low and begins the UVP fault timer. Once the timer
expires after 1600/fSW, the regulator shuts down, forc-
ing the high-side off and disabling the low-side MOS-
FET once the zero-crossing threshold has been
reached. Cycle VCC below 1V, or toggle the enable
input to clear the fault latch and restart the regulator.
Thermal-Fault Protection
The MAX17083 features a thermal-fault protection
circuit. When the junction temperature rises above
+160°C (typ), a thermal sensor activates the fault latch,
pulls down the POK output, and shuts down the regu-
lator. Toggle EN to clear the fault latch, and restart the
controllers after the junction temperature cools by
15°C (typ).
SMPS Design Procedure
(Step-Down Regulator)
Firmly establish the input voltage range and maximum
load current before choosing a switching frequency
and inductor operating point (ripple-current ratio). The
primary design trade-off lies in choosing a good switch-
ing frequency and inductor operating point, and the fol-
lowing four factors dictate the rest of the design:
• Input Voltage Range. The maximum value (VIN(MAX)),
and minimum value (VIN(MIN)) must accommodate
the worst-case conditions accounting for the input
voltage soars and drops. If there is a choice at all,
lower input voltages result in better efficiency.
• Maximum Load Current. There are two values to
consider. The peak load current (ILOAD(MAX)) deter-
mines the instantaneous component stresses and fil-
tering requirements and thus drives output-capacitor
selection, inductor-saturation rating, and the design of
the current-limit circuit. The continuous load current
______________________________________________________________________________________ 11
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| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet MAX17083.PDF ] | |
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