MAX15029 Datasheet, PDF (9/10 Pages) Maxim Integrated Products – 1.425V to 3.6V Input, 500mA Low-Dropout Regulators with BIAS Input

1.425V to 3.6V Input, 500mA Low-Dropout
Regulators with BIAS Input
Capacitor Selection and
Regulator Stability
Capacitors are required at the MAX15029/MAX15030’s
inputs and outputs for stable operation over the full
temperature range and with load currents up to
500mA. Connect a 1µF capacitor between IN and
ground and a 2.2µF capacitor with low equivalent
series resistance (ESR) between OUT and ground for
500mA output current.
The input capacitor (C_IN) lowers the source impedance
of the input supply. If input supply source impedance is
high, place a larger input capacitor close to IN to pre-
vent V_IN sagging due to load transients. Smaller output
capacitors can be used for output currents less than
500mA. Calculate the minimum C_OUT as follows:
C_OUT
=
I_OUT(MAX)
×
⎛
⎝⎜
1µF ⎞
0.25A ⎠⎟
Operating Region and
Power Dissipation
The maximum power dissipation depends on the ther-
mal resistance of the IC package and circuit board, the
temperature difference between the die junction and
ambient air, and the rate of airflow. The power dissipat-
ed in the device is P_DISS = I_OUT (V_IN - V_OUT). The
package features an exposed thermal pad on its
underside. This pad lowers the thermal resistance of
the package by providing a direct heat conduction
path from the die to the PCB. Additionally, the ground
pins (GND) perform the dual function of providing an
electrical connection to system ground and channeling
heat away. Connect the exposed backside pad and
GND to the system ground using a large pad or ground
plane and multiple vias to the ground plane layer.
Noise, PSRR, and Transient Response
The MAX15029/MAX15030 are designed to operate
with low-dropout voltages and low quiescent currents
while still maintaining good noise performance, tran-
sient response, and AC rejection (see the Typical
Operating Characteristics). When operating from noisy
sources, improved supply-noise rejection and transient
response can be achieved by increasing the values of
the input and output bypass capacitors and through
passive filtering techniques. The MAX15029/MAX15030
load-transient response graphs (see the Typical
Operating Characteristics) show two components of the
output response: a DC shift from the output impedance
due to the load current change, and the transient
response. A typical transient overshoot for a step
change in the load current from 100mA to 500mA is
10mV. Use ceramic output capacitors greater than
2.2µF (up to 100µF) to attenuate the overshoot.
Layout Guidelines
The TDFN package has an exposed thermal pad on its
underside. This pad provides a low thermal resistance
path for heat transfer into the PCB. This low thermally
resistive path carries a majority of the heat away from
the IC. The PCB is effectively a heatsink for the IC. The
exposed pad should be connected to a large ground
plane for proper thermal and electrical performance.
The minimum size of the ground plane is dependent
upon many system variables. To create an efficient
path, the exposed pad should be soldered to a thermal
landing, which is connected to the ground plane by
thermal vias. The thermal landing should be at least as
large as the exposed pad.
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