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PDF MAX15020 Data sheet ( Hoja de datos )
| Número de pieza | MAX15020 | |
| Descripción | Step-Down DC-DC Converter | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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19-0811; Rev 0; 4/07
EVAALVUAAILTAIOBNLEKIT
2A, 40V Step-Down DC-DC Converter with
Dynamic Output-Voltage Programming
General Description
The MAX15020 high-voltage step-down DC-DC con-
verter operates over an input voltage range of 7.5V to
40V. The device integrates a 0.2Ω high-side switch and
is capable of delivering 2A load current with excellent
load and line regulation. The output is dynamically
adjustable from 0.5V to 36V through the use of an exter-
nal reference input (REFIN). The MAX15020 consumes
only 6µA in shutdown mode.
The device utilizes feed-forward voltage-mode architec-
ture for good noise immunity in the high-voltage switch-
ing environment and offers external compensation for
maximum flexibility. The switching frequency is selec-
table to 300kHz or 500kHz and can be synchronized to
an external clock signal of 100kHz to 500kHz by using
the SYNC input. The IC features a maximum duty cycle
of 95% (typ) at 300kHz.
The device includes configurable undervoltage lockout
(UVLO) and soft-start. Protection features include
cycle-by-cycle current limit, hiccup-mode for output
short-circuit protection, and thermal shutdown. The
MAX15020 is available in a 20-pin TQFN 5mm x 5mm
package and is rated for operation over the
-40°C to +125°C temperature range.
Applications
Printer Head Driver Power Supply
Automotive Power Supply
Industrial Power Supply
Step-Down Power Supply
VIN
(7.5V TO 40V)
Features
o Wide 7.5V to 40V Input Voltage Range
o 2A Output Current, Up to 96% Efficiency
o Dynamic Programmable Output Voltage (0.5V to
36V)
o Maximum Duty Cycle of 95% (typ) at 300kHz
o 100kHz to 500kHz Synchronizable SYNC
Frequency Range
o Configurable UVLO and Soft-Start
o Low-Noise, Voltage-Mode Step-Down Converter
o Programmable Output-Voltage Slew Rate
o Lossless Constant Current Limit with Fixed
Timeout to Hiccup Mode
o Extremely Low-Power Consumption (< 6µA typ) in
Shutdown Mode
o 20-Pin (5mm x 5mm) Thin QFN Package
Ordering Information
PART
TEMP RANGE
PIN-
PACKAGE
PKG
CODE
MAX15020ATP+
-40°C to +125°C
20 TQFN-EP*
(5mm x 5mm)
T2055-5
+Denotes a lead-free package.
*EP = Exposed pad.
Pin Configuration appears at end of data sheet.
Typical Operating Circuit
PWM
INPUT
IN
ON/OFF
REG
DVREG BST
LX
REFOUT
REFIN
EP SS
MAX15020
FB
SYNC GND FSEL PGND COMP
VOUT
(0.5V TO 36V)
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1 page  
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2A, 40V Step-Down DC-DC Converter with
Dynamic Output-Voltage Programming
Typical Operating Characteristics (continued)
(VIN = 36V, Circuit of Figure 2, TA = +25°C, unless otherwise noted.)
TURN-ON/TURN-OFF WAVEFORM
MAX15020 toc09
TURN-ON/TURN-OFF WAVEFORM
MAX15020 toc10
VON/OFF
5V/div
0V VON/OFF
5V/div
0V
VOUT
VIN = 12V, RLOAD = 27Ω
10ms/div
1V/div
0V
VOUT
VIN = 40V, RLOAD = 27Ω
10ms/div
1V/div
0V
REFOUT VOLTAGE vs. TEMPERATURE
1.05
1.03
1.01
0.99
0.97
0.95
-40 -15 10 35 60 85 110 135
TEMPERATURE (°C)
EFFICIENCY vs. LOAD CURRENT
100
90 VIN = 7.5V
80 VIN = 12V
70
60
50
40
30
20
10
0
0.01
VIN = 24V
VIN = 40V
fS = 500kHz
VOUT = 3.3V
0.1 1
OUTPUT CURRENT (A)
10
EFFICIENCY vs. LOAD CURRENT
100
90
80
70
60
50
40
30
20
10
0
0.01
fS = 500kHz
VIN = 40V
VOUT = 30V
0.1 1
OUTPUT CURRENT (A)
10
LOAD TRANSIENT
MAX15020 toc14
LOAD TRANSIENT
MAX15020 toc15
VOUT
50mV/div
AC-COUPLED
IOUT
50mV/div
AC-COUPLED
IOUT
VIN = 12V, VOUT = 3.3V
200µs/div
2A
1A
VOUT
VIN = 12V, VOUT = 3.3V
200µs/div
1.2A
0.2A
_______________________________________________________________________________________ 5
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2A, 40V Step-Down DC-DC Converter with
Dynamic Output-Voltage Programming
Soft-Start (SS)
At startup, after VIN is applied and the UVLO threshold
is reached, a 15µA (typ) current is sourced into the
capacitor (CSS) connected from SS to GND forcing the
VSS voltage to ramp up slowly. If VREFIN is set to a DC
voltage or has risen faster than the CSS charge rate,
then VSS will stop rising once it reaches VREFIN. If
VREFIN rises at a slower rate, VSS will follow the VREFIN
voltage rise rate. VOUT rises at the same rate as VSS
since VFB follows VSS.
Set the soft-start time (tSS) using following equation:
tSS
=
VREFIN × CSS
15µA
where tSS is in seconds and CSS is in Farads.
Reference Input and
Output (REFIN, REFOUT)
The MAX15020 features a reference input for the inter-
nal error amplifier. The IC regulates FB to the SS voltage
which is driven by the DC voltage applied to REFIN.
Connect REFIN to REFOUT to use the internal 0.98V ref-
erence. Connect REFIN to a variable DC voltage source
to dynamically control the output voltage. Alternatively,
REFIN can also be driven by a duty-cycle control PWM
source through a lowpass RC filter (Figure 2).
Internal Digital Power Supply (DVREG)
DVREG is the supply input for the internal digital power
supply. The power for DVREG is derived from the out-
put of the internal regulator (REG). Connect a 10Ω
resistor from REG to DVREG. Bypass DVREG to GND
with at least a 1µF ceramic capacitor.
Error Amplifier
The output of the internal error amplifier (COMP) is
available for frequency compensation (see the
Compensation Design section). The inverting input is
FB, the noninverting input is SS, and the output is
COMP. The error amplifier has an 80dB open-loop gain
and a 1.8MHz GBW product. When an external clock is
used, connect FSEL to REG.
Oscillator/Synchronization Input (SYNC)
With SYNC connected to GND, the IC uses the internal
oscillator and switches at a fixed frequency of 300kHz or
500kHz based upon the selection of FSEL. For external
synchronization, drive SYNC with an external clock from
100kHz to 500kHz and connect FSEL to REG. When dri-
ven with an external clock, the device synchronizes to
the rising edge of SYNC.
PWM Comparator/Voltage Feed-Forward
An internal ramp generator is compared against the
output of the error amplifier to generate the PWM sig-
nal. The maximum amplitude of the ramp (VRAMP) auto-
matically adjusts to compensate for input voltage and
oscillator frequency changes. This causes the VIN /
VRAMP to be a constant 9V/V across the input voltage
range of 7.5V to 40V and the SYNC frequency range of
100kHz to 500kHz. This simplifies loop compensation
design by allowing large input voltage ranges and
large frequency range selection.
Output Short-Circuit
Protection (Hiccup Mode)
The MAX15020 protects against an output short circuit
by utilizing hiccup-mode protection. In hiccup mode, a
series of sequential cycle-by-cycle current-limit events
cause the part to shut down and restart with a soft-start
sequence. This allows the device to operate with a con-
tinuous output short circuit.
During normal operation, the switch current is measured
cycle-by-cycle. When the current limit is exceeded, the
internal power MOSFET turns off until the next on-cycle
and the hiccup counter increments. If the counter
counts four consecutive overcurrent limit events, the
device discharges the soft-start capacitor and shuts
down for 512 clock periods before restarting with a soft-
start sequence. Each time the power MOSFET turns on
and the device does not exceed the current limit, the
counter is reset.
Thermal-Overload Protection
The MAX15020 features an integrated thermal-over-
load protection. Thermal-overload protection limits the
total power dissipation in the device and protects it in
the event of an extended thermal fault condition. When
the die temperature exceeds +160°C, an internal ther-
mal sensor shuts down the part, turning off the power
MOSFET and allowing the IC to cool. After the temper-
ature falls by 20°C, the part restarts beginning with the
soft-start sequence.
______________________________________________________________________________________ 11
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| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet MAX15020.PDF ] | |
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