MIC2215 Datasheet, PDF (9/11 Pages) Micrel Semiconductor – Tirple High PSRR, Low Noise uCap LDO

MIC2215
Applications Information
Enable/Shutdown
The MIC2215 comes with three active-high enable pins that
allow control of each individual regulator to be either disabled
or enabled. Forcing the enable pin low disables the respec-
tive regulator and sends it into a “zero” off-mode-current
state. In this state, current consumed by the individual regu-
lator goes nearly to zero. This is true for both regulators 2 and
3. Regulator 1’s input supply pin is also used to power the
internal reference. When any regulator, either 1, 2, or 3 is
enabled, an additional 20µA for the reference will be drawn
through V_IN1. All three must be disabled to enter the “zero”
current-off-mode-state. Forcing the enable pin high enables
each respective output voltage. This part is CMOS and none
of the enable pins can be left floating; a floating enable pin
may cause an indeterminate state on the output.
Input Capacitor
The MIC2215 is a high performance, high bandwidth device.
Therefore, it requires a well-bypassed input supply for opti-
mal performance. A small 0.1µF capacitor placed close to the
input is recommended to aid in noise performance. Low-ESR
ceramic capacitors provide optimal performance at a mini-
mum of space. Additional high-frequency capacitors such as
small valued NPO dielectric type capacitors help to filter out
high frequency noise and are good practice in any RF-based
circuit.
Output Capacitor
The MIC2215 requires an output capacitor for stability. The
design requires 1µF or greater on the output to maintain
stability. The design is optimized for use with low-ESR
ceramic chip capacitors. X7R/X5R dielectric-type ceramic
capacitors are recommended because of their temperature
performance. X7R-type capacitors change capacitance by
15% over their operating temperature range and are the most
stable type of ceramic capacitors. Z5U and Y5V dielectric
capacitors change value by as much as 50% and 60%,
respectively, over their operating temperature ranges. To use
a ceramic chip capacitor with Y5V dielectric, the value must
be much higher than an X7R ceramic capacitor to ensure the
same minimum capacitance over the equivalent operating
temperature range.
Bypass Pin
A capacitor can be placed from the noise bypass pin to
ground to reduce output voltage noise. The capacitor by-
passes the internal reference. There is one single internal
reference shared by each output, therefore the bypassing
affects each regulator. A 0.1µF capacitor is recommended for
applications that require low-noise outputs. The bypass ca-
pacitor can be increased, further reducing noise and im-
proving PSRR. Turn-on time increases slightly with respect to
bypass capacitance.
Internal Reference
The internal bandgap, or reference, is powered from the V_IN1
input. Due to some of the input noise (PSRR) contributions
being imposed on the bandgap, it is important to make V_IN1
as clean as possible with good bypassing close to the input.
Micrel
Multiple Input Supplies
The MIC2215 can be used with multiple input supplies when
desired. The only requirement, aside from maintaining the
voltages within the operating ranges, is that V_IN1 always
remains the highest voltage potential.
No-Load Stability
The MIC2215 will remain stable and in regulation with no
load, unlike many other voltage regulators. This is especially
important in CMOS RAM keep-alive applications.
Thermal Considerations
The MIC2215 is designed to provide up to 250mA of current
per channel in a very small package. Maximum power dissi-
pation can be calculated based on the output current and the
voltage drop across the part. To determine the maximum
power dissipation of the package, use the junction-to-ambi-
ent thermal resistance of the device and the following basic
equation:
P_D (max) = (T_J (max) – T_A) ÷ θ_JA
T_J ^(max) is the maximum junction temperature of the die,
125°C, and T_A is the ambient operating temperature. θ_JA is
layout dependent; Table 2 shows examples of the junction-
to-ambient thermal resistance for the MIC2215.
Package
θ_JA Recommended
Minimum Footprint
16-Pin MLF™
43°C/W
Table 2. MLF™ Thermal Resistance
The actual power dissipation of the regulator circuit can be
determined using the equation:
P_DTOTAL = P_DLDO1 + P_DLDO2 + P_DLDO3
P_DLDO1 = (V_IN1 – V_OUT1) × I_OUT1
P_DLDO2 = (V_IN2 – V_OUT2) × I_OUT2
P_DLDO3 = (V_IN3 – V_OUT3) × I_OUT3
Substituting P_D (max) for P_D and solving for the operating
conditions that are critical to the application will give the
maximum operating conditions for the regulator circuit. For
example, when operating the MIC2215 at 60°C with a mini-
mum footprint layout, the maximum load currents can be
calculated as follows:
P_D (max) = (125°C – 60°C)/43 °C/W
P_D (max) = 1.511W
The junction-to-ambient thermal resistance for the minimum
footprint is 43°C/W, from Table 2. The maximum power
dissipation must not be exceeded for proper operation. Using
a lithium-ion battery as the supply voltage, 2.8V/250mA for
channel 1, 3V/100mA for channel 2 and 2.8V/50mA for
channel 3, maximum power can be calculated as follows:
P_DLDO1 = (V_IN1 – V_OUT1) × I_OUT1
P_DLDO1 = (4.2V – 2.8V) × 250mA
P_DLDO1 = 350mW
April 2004
9
M9999-042704