Datasheet

2016-2019 Microchip Technology Inc. DS20005685B-page 25
MIC2915X/30X/50X/75X
thermal resistance (θ
JA
) of the D-Pak adhering to the
following criteria for the PCB design: 2 oz. copper and
100 mm
2
copper area for the MIC29152.
For example, given an expected maximum ambient
temperature (T
A
) of +75°C with V
IN
= 3.3V, V
OUT
=
2.5V, and I
OUT
= 1.5A, first calculate the expected P
D
using Equation 4-3:
EQUATION 4-3:
Next, calculate the junction temperature for the
expected power dissipation.
EQUATION 4-4:
Now determine the maximum power dissipation
allowed that would not exceed the IC’s maximum
junction temperature (+125°C) without the use of a
heat sink.
EQUATION 4-5:
4.2 Capacitor Requirements
For stability and minimum output noise, a capacitor on
the regulator output is necessary. The value of this
capacitor is dependent upon the output current; lower
currents allow smaller capacitors. The
MIC2915x/2930x/2950x/2975x regulators are stable
with the following minimum capacitor values at full load,
as noted in Tab le 4 -1.
This capacitor need not be an expensive low ESR type:
aluminum electrolytics are adequate. In fact, extremely
low ESR capacitors may contribute to instability.
Tantalum capacitors are recommended for systems
where fast load transient response is important.
Where the regulator is powered from a source with high
AC impedance, a 0.1 µF capacitor connected between
Input and GND is recommended. This capacitor should
have good characteristics to above 250 kHz.
4.3 Minimum Load Current
The MIC2915x–2975x regulators are specified
between finite loads. If the output current is too small,
leakage currents dominate and the output voltage
rises. The following minimum load current swamps any
expected leakage current across the operating
temperature range, as shown in Ta ble 4- 2.
4.4 Adjustable Regulator Design
The adjustable regulator versions, MIC29xx2 and
MIC29xx3, allow programming the output voltage
anywhere between 1.25V and the 25V. Two resistors
are used. The resistor values are calculated by
Equation 4-6.
EQUATION 4-6:
In the equation above, V
OUT
is the desired output
voltage. Figure 4-2 shows component definition.
Applications with widely varying load currents may
scale the resistors to draw the minimum load current
required for proper operation (see the Minimum Load
Current sub-section).
TABLE 4-1: MINIMUM CAPACITOR
VALUES AT FULL LOAD
Device Full-Load Capacitor
MIC2915x 10 µF
MIC2930x 10 µF
MIC2950x 10 µF
MIC2975x 22 µF
P
D
3.3V 2.5V1.5A 3.3V 0.016A1.1472W==
T
J
JA
P
D
T
A
+
56
o
C/W 1.1472W75
o
C+ 139.24
o
C
=
==
P
DMAX
T
JMAX
T
A

JA
125
o
C 75
o
C56
o
C/W 0.893W
=
==
TABLE 4-2: MINIMUM LOAD CURRENTS
Device Minimum Load
MIC2915x 5 mA
MIC2930x 7 mA
MIC2950x 10 mA
MIC2975x 10 mA
R1 R2
V
OUT
1.240
-------------
1


=