MIC2954-07YM Micrel Inc, MIC2954-07YM Datasheet - Page 10

• Manufacturer Part Number: MIC2954-07YM
• Description: IC,VOLT REGULATOR,FIXED/ADJUSTABLE,+5V/+1.24 TO +29V,BIPOLAR,SOP,8PIN,PLASTIC
• Manufacturer: Micrel Inc

Specifications of MIC2954-07YM

• Rohs Compliant: YES
• Regulator Topology: Positive Fixed or Adjustable
• Voltage - Output: 5V, 1.24 ~ 29 V
• Voltage - Input: 2 ~ 30 V
• Voltage - Dropout (typical): 0.375V @ 250mA
• Number Of Regulators: 1
• Current - Output: 250mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Limit (min): -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-1155

Application Information
External Capacitors
A 2.2µF (or greater) capacitor is required between the
MIC2954 output and ground to prevent oscillations due
to instability. Most types of tantalum or aluminum
electrolytics will be adequate; film types will work, but
are costly and therefore not recommended. Many
aluminum electrolytics have electrolytes that freeze at
about –30°C, so solid tantalums are recommended for
operation below –25°C. The important parameters of the
capacitor are an effective series resistance of about 5Ω
or less and a resonant frequency above 500kHz. The
value of this capacitor may be increased without limit.
At
capacitance is required for output stability. The capacitor
can be reduced to 0.5µF for current below 10mA or
0.15µF for currents below 1mA. Adjusting the MIC2954-
07/-08 to voltages below 5V runs the error amplifier at
lower gains so that more output capacitance is needed.
For the worst-case situation of a 250mA load at 1.23V
output (output shorted to feedback) a 5µF (or greater)
capacitor should be used.
The MIC2954 will remain in regulation with a minimum
load of 1mA. When setting the output voltage of the
MIC2954-07/-08 version with external resistors, the
current through these resistors may be included as a
portion of the minimum load.
A 0.1µF capacitor should be placed from the MIC2954
input to ground if there is more than 10 inches of wire
between the input and the ac filter capacitor or if a
battery is used as the input.
Error Detection Comparator Output (MIC2954-07/-08)
A logic-low output will be produced by the comparator
whenever the MIC2954-07/-08 output falls out of
regulation by more than approximately 5%. This figure is
the comparator’s built-in offset of about 60mV divided by
the 1.235V reference voltage. (Refer to the block
diagram on page 1). This trip level remains “5% below
normal” regardless of the programmed output voltage of
the MIC2954-07/-08. For example, the error flag trip
level is typically 4.75V for a 5V output or 11.4V for a12V
output. The out of regulation condition may be due either
to low input voltage, current limiting, or thermal limiting.
Figure 1 is a timing diagram depicting the /ERR signal
and the regulated output voltage as the MIC2954-07/-08
input is ramped up and down. The /ERR signal becomes
valid (low) at about 1.3V input. It goes high at about 5V
input (the input voltage at which V
MIC2954-07/-08’s dropout voltage is load-dependent
(see curve in “Typical Characteristics”), the input voltage
trip point (about 5V) will vary with the load current. The
output voltage trip point (approximately 4.75V) does not
vary with load.
Micrel, Inc.
September 2007
lower
values
of
output
current,
OUT
= 4.75). Since the
less
output
10
The error comparator has an open-collector output which
requires an external pull-up resistor. Depending on
system requirements, this resistor may be returned to
the 5V output or some other supply voltage. In
determining a value for this resistor, note that while the
output is rated to sink 400µA, this sink current adds to
battery drain in a low battery condition. Suggested
values range from 100k to 1MΩ. The resistor is not
required if this output is unused.
Programming the Output Voltage (MIC2954-07/-08)
The MIC2954-07/-08 may be pin-strapped for 5V using
its internal voltage divider by tying pin 1 (OUT) to pin 2
(SNS) and pin 7 (FB) to pin 6 (TAP). Alternatively, it may
be programmed for any output voltage between its
1.235V reference and its 30V maximum rating. An
external pair of resistors is required, as shown in Figure
3.
The complete equation for the output voltage is:
where:
The minimum recommended load current of 1µA forces
an upper limit of 1.2MΩ on the value of R2, if the
regulator must work with no load (a condition often found
in CMOS in standby), IFB will produce a 2% typical error
in V
trimming R1. For better accuracy, choosing R2 = 100k
reduces this error to 0.17% while increasing the resistor
program current to 12µA. Since the MIC2954-07/-08
typically draws 60µA at no load with pin 2 (SNS) open-
circuited, this is a negligible addition.
Reducing Output Noise
In reference applications it may be advantageous to
reduce the ac noise present at the output. One method
is to reduce the regulator bandwidth by increasing the
size of the output capacitor. This is relatively inefficient,
as increasing the capacitor from 1µF to 220µF only
decreases the noise from 430µV to 160µV
100kHz bandwidth at 5V output. Noise can be reduced
fourfold by a bypass capacitor across R1, since it
reduces the high frequency gain from 4 to unity.
Pick:
OUT
which may be eliminated at room temperature by
V
I
C
V
FB
REF
OUT
BYPASS
= nominal FB pin bias current (–20nA)
= nominal 1.235V reference voltage
=
V
≅
REF
2
π
⎛
⎜
⎝
R1
1
+
×
R2
R1
1
200Hz
⎞
⎟
⎠
+
I
FB
R1
M9999-090607
MIC2954
RMS
for a