Evaluates: MAX8815A
MAX8815A Evaluation Kit
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Quick Start
Recommended Equipment
• A 1.2V to 5.5V power supply capable of delivering
2.5A
• One voltmeter (DMM)
• Load capable of sinking 1A
• Ammeter (optional)
Procedure
The MAX8815A EV kit is fully assembled and tested.
Follow the steps below to verify board operation.
1) Preset the power supply to 3.6V.
2) Turn off the power supply. Do not turn on the
power supply until all connections are completed.
3) Verify that the shunt on JU1 is connected to OFF
(pins 2 and 3). Verify that the shunt on JU2 is con-
nected to NORM (pins 2 and 3).
4) Connect the positive power-supply terminal to the
pad on the EV kit labeled IN. Connect the power-
supply ground terminal to the pad on the EV kit
labeled GND.
5) Connect a voltmeter across the OUT pad on the EV
kit and the GND pad on the EV kit.
6) Connect the 1A load between OUT and GND with
the load set to minimum.
7) Turn on the power supply.
8) Verify that the voltmeter is reading 0V and input
current is less than 1µA.
9) Remove the shunt from the OFF position (pins 2
and 3) of JU1 and place it on the ON position (pins
1 and 2) of JU1.
10) Verify the voltmeter is measuring between 4.95V
and 5.05V.
11) Slowly increase the load up to 1A and verify the
output voltage.
Detailed Description
Normal and FPWM Mode
The MAX8815A operates in two modes, normal mode
and FPWM mode, depending on the voltage at SKIPB.
SKIPB is assigned to pin 2 on jumper JU2. Connecting
a shunt to pins 2 and 3 of JU2 sets the IC to normal
operation. Connecting a shunt to pins 1 and 2 sets the
IC to FPWM mode only.
Normal Mode
Drive SKIPB low to select the normal mode of opera-
tion. In this mode, the device operates in PWM only
when driving medium to heavy loads. As the load cur-
rent decreases and crosses the low-power idle-mode
threshold, the PWM comparator and oscillator are dis-
abled. In this low-power mode, switching occurs only
as needed to service the output. This improves the effi-
ciency for light loads, and the device consumes only
35µA under no-load conditions. The threshold for enter-
ing skip mode is approximately 90mA load with a 3.6V
input and 5V output. When switching in normal mode,
the inductor current terminates at zero for each switch-
ing cycle.
FPWM Mode
Drive SKIPB high to select the FPWM mode of opera-
tion. The IC switches at a constant frequency (2MHz)
and modulates the MOSFET switch pulse width
to control the power transferred per cycle to regulate
the output voltage. Switching harmonics gene-
rated by fixed-frequency operation are consistent
and easily filtered. This is important in noise-sensitive
applications.
The MAX8815A does not allow for dynamic switching
between normal and FPWM modes.
Shutdown Mode
Connect ON to GND or connect a shunt to pins 2 and 3
of JU1 to place the MAX8815A in shutdown mode and
reduce supply current to 0.1µA. In shutdown, the
control circuitry, internal switching MOSFET, and
synchronous rectifier turn off and LX becomes high
impedance. Connect ON to IN or connect a shunt to
pins 1 and 2 of JU1 for normal operation.
Evaluating Other Output Voltages
The MAX8815A EV kit is designed for the preset output
voltage of 5V. To set other output voltages, use external
feedback resistors.
To set the output voltage between 3.3V and 5V, cut the
PCB short on resistor R1, and connect FB to the center
of an external resistor voltage-divider between OUT
and GND, as shown in Figure 2. Select the value of R2
no more than 500kΩ, and then calculate the value for
R1 as follows:
R1 = R2 (V
OUT
/V
FB
- 1)
where V
FB
is the FB regulation voltage, 1.265V (typ).
