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PDF MIC68401 Data sheet ( Hoja de datos )
| Número de pieza | MIC68401 | |
| Descripción | 4A Sequencing LDO | |
| Fabricantes | Micrel Semiconductor | |
| Logotipo |  |
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MIC68401
4A Sequencing LDO with Tracking and
Ramp Control™
General Description
The MIC68401 is a high peak current LDO regulator
designed specifically for powering applications such as
FPGA core voltages that require high startup current with
lower nominal operating current. Capable of sourcing 4A of
current for start-up, the MIC68401 provides high power
from a small QFN package. The MIC68401 can also
implement a variety of power-up and power-down
protocols such as sequencing, tracking, and ratiometric
tracking.
The MIC68401 operates from a wide input range of 1.65V
to 5.5V, which includes all of the main supply voltages
commonly available today. It is designed to drive digital
circuits requiring low voltage at high currents (i.e., PLDs,
DSPs, microcontrollers, etc.). The MIC68401 incorporates
a delay pin (DELAY) for control of power-on-reset (POR)
output at turn-on. In addition, there is a ramp control (RC)
for either tracking applications or output voltage slew rate
control at turn-on. These features are important in
applications where the load is highly capacitive and inrush
currents can cause supply voltages to fail and
microprocessors or other complex logic chips to hang up.
Multiple MIC68401s can be “daisy chained” in two modes.
In tracking mode the output voltage of the master drives
the RC pin of a slave so that the slave tracks the main
regulator during turn-on and turn-off. In sequencing mode
the POR of the master drives the enable (EN) of the slave
so that it turns on after the master. This behavior is critical
for power-up control in multi-output power supplies. The
MIC68401 is fully protected offering both thermal, current
limit protection, and reverse current protection.
The MIC68401 has an adjustable output voltage. The
junction temperature range of part is rated from –40°C to
+125°C. The MIC68401 is offered in the small 16-pin 4mm
× 4mm QFN package.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Features
• Stable with 10µF ceramic capacitor
• Input voltage range: 1.65V to 5.5V
• Low 0.5V reference voltage
• ±2.0% output tolerance over temperature
• 4A output current
• Timing-controlled sequencing on/off
• Programmable Ramp Control™ for inrush current
limiting and slew rate control of the output voltage during
turn-on
• Power-on-reset (POR) supervisor with programmable
delay time
• Single master can control multiple slave regulators with
tracking output voltages
• Small 4mm × 4mm QFN package
• Maximum dropout (VIN – VOUT) of 500mV over
temperature at 3A output current
• Fixed and adjustable output voltages
• Excellent line and load regulation specifications
• Logic-controlled shutdown
• Thermal shutdown and current-limit protection
Applications
• FPGA/PLD power supply
• Networking/telecom equipment
• Microprocessor core voltage
• High-efficiency linear post regulator
• Sequenced or tracked power supply
Ramp Control is a trademark of Micrel, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
November 7, 2013
Revision 1.0
1 page  
Micrel, Inc.
MIC68401
Electrical Characteristics(5) (Continued)
TA = 25°C with VIN = VOUT + 1V; VEN = VIN; IOUT = 10mA; bold values indicate –40°C ≤ TJ ≤ +125°C, unless noted.
Parameter
Conditions
Min. Typ.
Max.
Units
POR Output
IPOR(LEAK)
VPOR(LO)
POR Threshold
POR Threshold Hysteresis
DELAY Pin Current
DELAY Threshold Voltage(6)
Ramp Control
POR pin inactive (open drain, high)
VPOR = 5.5V
POR pin active, output logic-low voltage
IPOR = 1mA
VOUT ramping up. % of VOUT below nominal
VOUT ramping down. Amount that the POR threshold shifts from
the ramp up threshold, when it is ramping down.
VDELAY = 0.75V
VPOR = High
7.5
0.7
1.185
60
10
2.5
1
1.235
1
2
90
12.5
3
1.3
1.285
µA
mV
%
%
µA
V
IRC
IDISCHARGE(7)
Tracking Accuracy(8)
Ramp Control Current (VRC = 0.75V)
VOUT = 0.5VNOM, VRAMP = 0V
Measure (VOUT − VRC × (VTARGET / 500mV))
0.7 1 1.3 µA
25 45 70 mA
−10 15 50 mV
Notes:
6. Timer high voltage along with DELAY pin current (1µA, nominal) determines the delay per µF of capacitance. Typical delay is 1.235sec/µF.
7. The discharge current (IDISCHARGE), is the current drawn from the output to ground to actively discharge the output capacitor during the
shutdown process.
8. VTARGET is the desired output voltage.
November 7, 2013
5
Revision 1.0
5 Page 
Micrel, Inc.
TPOR is the time period from the rising of EN to the
assertion (low-to-high transition) of the POR output, and
is calculated by Equation 3:
TPOR = TDELAY + TRC
Eq. 3
Where:
TRC
=
(0.45V
)
CRC
1μA
At turn off, the DELAY capacitor is discharged via a 1µA
current sink when the EN pin is driven low.
Ramp Control
When the RC pin voltage is less than 0.5V, the output
voltage is controlled by the voltage on the RC pin. When
the RC pin voltage is greater than 0.5V, the output
voltage is held in regulation by the FB pin. The RC
capacitor is charged by an internal 1µA current source
when the EN pin goes high and discharged by an N-
channel when the EN pin is low and the output voltage is
discharged below 0.1V. The size of the capacitor on the
RC pin will control the slew rate of the output voltage
during startup. The startup slew rate at the FB pin may
be calculated from Equation 4:
TRC
=
0.5
V
CRC
1μA
Eq. 4
Ramp Down − Turn Off Slew Rate
When the EN pin goes low, the output will begin to turn
off within 5µs. The time that it takes for the output voltage
to fully discharge to 0V is dependent upon the value of
the output capacitor and the load current. In the absence
of a load, the internal discharge current (IDISCHARGE) will
assure that the output voltage is discharged to 0V. The
RC pin and the DELAY pin are quickly discharged
through an internal N-channel pull down device when the
EN pin goes low and the output voltage is discharged
below 0.1V.
MIC68401
Sequencing Configurations
Sequencing allows a master device to control the start
and stop timing of a single or multiple Slave MIC68401
devices. In a typical sequencing application, the master
device POR output drives the slave EN inputs. The
sequence begins with the master EN driven high. The
master output ramps up and triggers the master DELAY.
When the master output reaches 90% of its final value,
the master POR is released which enables the Slave
device(s).
Ratiometric Tracking
Ratiometric tracking allows independent ramping rates for
multiple MIC68401 regulators, such that their final output
voltages ramp up, and regulation occurs at the same
time. This is accomplished by adding a resistor divider
between the master output pin and the slave RC pin.
The divider should be scaled such that the slave RC pin
reaches or exceeds 0.5V when the master reaches its
target output voltage.
Ratiometric tracking can also be accomplished by simply
connecting the RC pins of the master and slave(s)
together. When the RC pins are connected, the current
from each of the MIC68401’s RC pin current sources
adds together. In order to maintain the desired slew rate,
the RC capacitor size needs to be increased by the total
number of RC pins that are connected together. For
example: One master and two slaves will require three
times the RC cap size as compared to a single device.
Final Note on Tracking
The MIC68401 does not fully shutdown until the output
voltage is discharged below 100mV. If the RC is driven
from an external source in a tracking configuration, and
the external source does not go to zero on shutdown, it
may prevent complete shutdown of the MIC68401. This
will not cause damage to the device, but a higher
quiescent will be drawn from the source. A potential
cause for concern in battery operated portable
equipment. When the RC pin is driven in tracking mode,
pulling EN low will cause the output to turn-off. The
MIC68401 cannot enter tracking mode unless EN is
pulled high.
November 7, 2013
11
Revision 1.0
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet MIC68401.PDF ] | |
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