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PDF MIC68400 Data sheet ( Hoja de datos )
| Número de pieza | MIC68400 | |
| Descripción | 4A Sequencing LDO | |
| Fabricantes | Micrel Semiconductor | |
| Logotipo |  |
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MIC68400
4A Sequencing LDO with Tracking and
Ramp Control™
General Description
The MIC68400 is a high peak current LDO regulator
designed specifically for powering applications such as
FPGA core voltages that require high start up current with
lower nominal operating current. Capable of sourcing 4A of
current for start-up, the MIC68400 provides high power
from a small MLF® leadless package. The MIC68400 can
also implement a variety of power-up and power-down
protocols such as sequencing, tracking, and ratiometric
tracking.
The MIC68400 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,
DSP, microcontroller, etc.). The MIC68400 incorporates a
delay pin (Delay) for control of power on reset output
(POR) at turn-on and power-down delay at turn-off. In
addition there is a ramp control pin (RC) for either tracking
applications or output voltage slew rate adjustment at turn-
on and turn-off. This is important in applications where the
load is highly capacitive and in-rush currents can cause
supply voltages to fail and microprocessors or other
complex logic chips to hang up.
Multiple MIC68400s 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 and turns off before (or
after) the Master. This behavior is critical for power-up and
power-down control in multi-output power supplies. The
MIC68400 is fully protected offering both thermal, current
limit protection, and reverse current protection.
The MIC68400 has a junction temperature range of
–40°C to +125°C and is available in fixed as well as an
adjustable option. The MIC68400 is offered in the tiny
16-pin 4mm x 4mm MLF® package.
Features
• Stable with 10µF ceramic capacitor
• Input voltage range: 1.65V to 5.5V
• 0.5V reference
• ±2.0% output tolerance over temperature
• 4A maximum output current – peak start up
• 3A continuous operating current
• Tracking on turn-on and turn-off with pin strapping
• Timing controlled sequencing on/off
• Programmable Ramp Control™ for in-rush current
limiting and slew rate control of the output voltage
during turn-on and turn-off
• Power-on reset (POR) supervisor with programmable
delay time
• Single master can control multiple slave regulators
with tracking output voltages
• Tiny 4mm x 4mm MLF® 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.
MLF and MicroLeadFrame is a registered trademark of Amkor Technology, 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
August 2009
M9999-081809-C
1 page  
Micrel, Inc.
Pin Configuration
MIC68400
16-Pin 4mm × 4mm MLF® (ML)
Fixed Voltages
16-Pin 4mm × 4mm MLF® (ML)
Adjustable Voltages
Pin Description (Pin Numbering may change depending on layout considerations)
Pin Number
MIC68400YML
1, 2, 15, 16
3
4
5
6, 14
7, 8, Tab
9
10 (Fixed)
10 (ADJ)
11, 12, 13
Pin Name
VIN
Delay
RC
EN
NC
GND
POR
SNS
ADJ
VOUT
Pin Function
Input: Input voltage supply pin. Place a capacitor to ground to bypass the
input supply.
Delay: Capacitor to ground sets internal delay timer. Timer delays power-on
reset (POR) output at turn-on, and ramp down at turn-off.
Ramp Control: May be voltage driven for tracking applications or a capacitor
to ground will set the slew rate of output voltage during start-up.
Enable (Input): CMOS compatible input. Logic high = enable, logic low =
shutdown.
Not internally connected.
Ground.
Power-on Reset: Open-drain output device indicates when the output is in
regulation. High (open) means device is regulating within 10%. POR onset
can be delayed using a single capacitor from Delay to ground.
Output Voltage Sense Pin: Connect directly to output pin.
Adjustable regulators: Feedback input. Connect to resistor voltage divider.
Output Voltage: Output of voltage regulator. Place capacitor to ground to
bypass the output voltage. Minimum load current is 100µA. Nominal bypass
capacitor is 10µF.
August 2009
5 M9999-081809-C
5 Page 
Micrel, Inc.
Adjustable Regulator Design
Adjustable Regulator with Resistors
The adjustable MIC68400 output voltage can be
programmed from 0.5V to 5.5V using a resistor divider
from output to the SNS pin. Resistors can be quite
large, up to 1MΩ because of the very high input
impedance and low bias current of the sense
amplifier. Typical sense input currents are less than
30nA which causes less than 0.3% error with R1 and
R2 less than or equal to 100KΩ. For large value
resistors (>50KΩ) R1 should be bypassed by a small
capacitor (CFF = 0.1µF bypass capacitor) to avoid
instability due to phase lag at the ADJ/SNS input.
The output resistor divider values are calculated by:
VOUT
=
0.5V⎜⎛
⎝
R1
R2
+
1⎟⎞
⎠
Power on Reset (POR) and Delay (DLY)
The power-on reset output (POR) is an open-drain
N-Channel device requiring a pull-up resistor to either
the input voltage or output voltage for proper voltage
levels. POR is driven by the internal timer so that the
release of POR at turn-on can be delayed for as much
as 1 second. POR is always pulled low when enable
(EN) is pulled low or the output goes out of regulation
by more than 10% due to loading conditions.
The internal timer is controlled by the DLY pin which
has a bidirectional current source and two limiting
comparators. A capacitor connected from DLY to
GND sets the delay time for two functions. On start
up, DLY sets the time from the nominal output voltage
is reached to the release of the POR. At shut down,
the delay sets the time from disable (EN pin driven
low) to actual ramp down of the output voltage. The
current source is ±1µA, which charges the capacitor
from ~150mV (nominal disabled DLY voltage) to
~1.25V. At turn on, the DLY cap begins to charge
when the output voltage reaches 90% of the target
value. When the capacitor reaches 1.25V, the output
of the POR is released to go high. At turn off, the DLY
cap begins to discharge when the EN is driven low.
When the cap reaches ~150mV the output is ramped
down. Both delays are nominally the same, and are
calculated by the same formula:
MIC68400
TDLY
=
(1.1)⎜⎜⎝⎛
CDLY
1μA
⎟⎟⎠⎞
Scale Factor is:
1.1 seconds/microfarad,
1.1 milliseconds/nanofarad, or
1.1 microseconds/picofarad.
TDLYOFF is the time from lowering of EN to the start of
ramp down on the off cycle. TPOR is the time from the
rising of EN to the release (low to high edge) of the
POR. This behavior means that a µP or other complex
logic system is guaranteed that the nominal output
voltage is stable for a known time before the POR is
released, and they are further guaranteed that once
POR is pulled low, they have a known time to ‘tidy up’
memory or other registers for a well controlled
shutdown. In Master/Slave configurations the timers
can be used to assure that the Master is always
accurately regulating when the Slave is on.
Ramp Control
The ramp control (RC) has a bidirectional current
source and a sense amplifier, which together are used
to control the voltage at the output. When RC is below
the target voltage (nominal output voltage for fixed
voltage parts, 0.5V for adjustable parts) the RC pin
controls the output voltage. When RC is at or above
the target voltage, the output is controlled by the
internal regulator.
Tracking Applications: Driving RC from a Voltage
Source
Fixed Parts: If RC is driven from another (Master)
regulator the two outputs will track each other until the
Master exceeds the target voltage of the Slave
regulator. Typically the output of the MIC68400 will
track above the RC input by 30mV to 70mV. This
offset is designed to allow Master/Slave tracking of
same-voltage regulators. Without the offset, same-
voltage Master/Slave configurations could suffer poor
regulation.
Adjustable Parts: The RC pin on adjustable versions
operates from 0V to 0.5V. To implement tracking on
an adjustable version, an external resistor divider
must be used. This divider is the nearly same ratio as
the voltage setting divider used to drive the
Sense/Adjustable pin. It is recommended that the ratio
be adjusted to track ~50mV (2% to 3%) above the
target voltage if the Master and Slave are operating at
the same target voltage.
August 2009
11 M9999-081809-C
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet MIC68400.PDF ] | |
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