MIC68400-1.5YML TR Micrel Inc, MIC68400-1.5YML TR Datasheet - Page 11

• Manufacturer Part Number: MIC68400-1.5YML TR
• Description: IC REG LDO SEQ 4A 1.5V 16-MLF
• Manufacturer: Micrel Inc

Specifications of MIC68400-1.5YML TR

• Regulator Topology: Positive Fixed
• Voltage - Output: 1.5V
• Voltage - Input: Up to 5.5V
• Voltage - Dropout (typical): 0.36V @ 4A
• Number Of Regulators: 1
• Current - Output: 3A
• Current - Limit (min): 4A
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-MLF®, QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: MIC68400-1.5YMLTR; MIC68400-1.5YMLTR

Adjustable Regulator Design
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 (C
instability due to phase lag at the ADJ/SNS input.
The output resistor divider values are calculated by:
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:
Micrel, Inc.
August 2009
V
Adjustable Regulator with Resistors
OUT
FF
=
= 0.1µF bypass capacitor) to avoid
0.5V
⎛
⎜
⎝
R2
R1
+
1
⎞
⎟
⎠
11
Scale Factor is:
T
ramp down on the off cycle. T
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.
DLYOFF
is the time from lowering of EN to the start of
1.1 seconds/microfarad,
1.1 milliseconds/nanofarad, or
1.1 microseconds/picofarad.
T
DLY
=
( )
1.1
⎛
⎜ ⎜
⎝
C
1
DLY
μ
A
⎞
⎟ ⎟
⎠
POR
is the time from the
M9999-081809-C
MIC68400