MCP16251 One-Cell Boost Converter with External UVLO Circuit
DS50002561A-page 18
2017 Microchip Technology Inc.
To test the MCP16251 One-Cell Boost Converter with External UVLO Circuit, follow the
following steps:
1. Make sure SW1 is in the Off position.
2. Insert an AA alkaline battery in the holder, paying attention to the polarity. Also,
make sure jumper J1 “Connect to battery” is placed (shorted).
3. Connect a resistive or an electronic load and a voltmeter between the V
OUT
and
GND test pads, as shown in
Figure 2-3
.
4. Switch SW1 in the On position to enable the UVLO circuit.
5. Measure the input voltage between the V
IN
and GND test pads. Also, measure
the voltage at the EN test point. If V
IN
is higher than 1.1V, the EN voltage should
be approximately equal to the input voltage.
6. Measure the output voltage; it should be 3.3V.
7. Switch SW1 Off or decrease V
IN
below 0.8V and measure the output voltage; it
should be 0V.
2.2.1.3
TEST PADS, TEST POINTS AND JUMPERS
Several external test pads, test points and a jumper are placed on the top side of the
PCB:
2.2.2
MCP16251 One-Cell Boost Converter with External UVLO
Circuit Operation
The board can be powered from an AA alkaline battery, which typically has 2500 mAh
capacity at low currents, as specified by OEM. If jumper J1 “Connect to battery” is on
(connected) and switch SW1 is turned off, the application will start in Sleep mode.
While in this state, the EN voltage is 0V (because it is being pulled down by resistor R5)
and the Boost Converter is disabled. Turning SW1 on, the UVLO circuit is active and
starts monitoring the V
IN
voltage. If the battery voltage is higher than 1.1V,
transistor
Q1 turns
on, injecting current in the base of transistor Q2, which also turns on and
biases resistor R3. This causes the voltage at the EN pin to go high. Because resistor
R5 acts as a load for transistor Q1, the collector current of Q1 is small, meaning its
Collector-Emitter Saturation Voltage, V
CE
, can be neglected; thus, V
EN
V
IN
and the
MCP16251 turns on.
As transistor Q2 bypasses resistor R3, its Base-Emitter Voltage, V
BE
, begins to grow,
keeping transistor Q1 on as long as V
IN
> 0.8V. Transistor Q2 and resistor R3 form the
hysteresis block.
• Jumper
J1
“Connect to battery” for selecting between battery or external power supply. J1
shorted connects V
IN
to the battery’s positive terminal.
• Test Pads
V
IN
For measuring the input voltage or powering the board from an external supply.
V
OUT
For connecting the load and measuring the output voltage.
GND Connected to the battery’s negative terminal.
• Test Points
EN
For measuring the enable signal. It is connected to the MCP16251 device’s EN pin.
SW
Connected to the switching node.
Note:
MCP16251 device’s enable pin is a logic-level input used to enable or
disable device switching. A logic high (>70% of V
IN
) on the EN pin will start
the output regulation and a logic low (<20% of V
IN
) will ensure that the IC
is disabled.
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