MIC79110-4.2YML Evaluation Board User Guide

MIC79110 Evaluation Board
Simple 1.2A Linear Li-ion Battery Charger
General Description
The Micrel MIC79110 is a simple and accurate Li-ion
battery charger. Featuring a built-in pass transistor,
precision programmable current limiting (±5%), precision
voltage termination (±1% over temperature) and a very
small package, the MIC79110 packs full functionality into a
very small space.
Other features of the MIC79110 include two independent
end-of-charge indications including a digital indication that
is programmable with a resistor-to-ground and an analog
current output that is proportional to the output current,
allowing for monitoring of the actual charging current.
Additional features include very low dropout (550mV over
the temperature range), thermal shutdown, and reverse
polarity protection. In the event that the input voltage to the
charger is disconnected, the MIC79110 also provides
minimal reverse-current and reversed-battery protection.
Available in both fixed 4.2V and adjustable outputs, the
MIC79110 is offered in the leadless 10-pin 3mm × 3mm
DFN with an operating junction temperature range of
−40°C to +125°C.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Getting Started
1. Connect an external supply to VIN (J1) and GND
(J2 or J6) terminals.
With the output of the power supply disabled, set its
voltage to the desired input test voltage (2.5V ≤ VIN ≤
16V). An ammeter may be placed between the input
supply and the VIN terminal. Be sure to monitor the
supply voltage at the VIN terminal, as ammeter and/or
power lead resistance can reduce the voltage supplied
to the device.
2. Connect a Lithium-ion battery to VBAT (J3) and GND
(J2 or J6) terminals.
The load at the VBAT pin is the Lithium-ion battery. A
voltage meter may be placed across VBAT and GND to
monitor the output voltage.
3. Monitor the DEOC (J5) and AEOC (J7)
Connect a voltage meter across DEOC and GND to
monitor end of charge. To monitor the charging
current, connect a voltage meter across AEOC and
GND terminals.
4. Enable the SD pin (J4)
Connect SD to GND terminal to initiate charging.
Ordering Information
Part Number
MIC79110-4.2YML EV
Evaluation Board
Evaluation Board
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
May 28, 2013
Revision 2.0
Micrel, Inc.
MIC79110 Evaluation Board
SD – Shutdown Pin
The MIC79110 comes with an active-high shutdown pin
feature that allows the regulator to be disabled. Forcing the
SD pin high disables the regulator and sends it into a
“zero” off-mode-current state. In this state, current
consumed by the regulator goes nearly to zero. Forcing
the SD pin low enables the output voltage. This part is
CMOS and the SD pin cannot be left floating; a floating SD
pin may cause an indeterminate state on the output.
VIN – Input Voltage
Input voltage range is from 2.5V to 16V. Default bypass
capacitor value is 2.2µF rated for maximum voltage of 16V
for the input pin.
ACHG – Analog Charge Indicator Output
Output charge current for the MIC79110 can be monitored
using the ACHG pin. The current sourced from this pin is
1/1000th of the output charge current.
The evaluation board has R5 set to 1kΩ, so that the
voltage measured at pin J7 is equal to the output current of
the battery charger.
On the evaluation board, the SD pin can be tied to the
DEOC pin by installing a 0Ω resistor for R8 to place it in
shutdown mode. The pin can also be tied to ground via R7
during test to keep the part on. The third option is tying it to
J4 and controlling the shutdown pin externally.
DEOC – Digital End of Charge Indicator
This is an N-Channel open drain output on the MIC79110
that pulls high when the charge current falls below the
minimum charge current that is set by REOC. Low indicates
charging a current that is higher than the programmed
current set by REOC. When the current drops to less than
the programmed current set by REOC, the output goes high
impedance, indicating end-of-charge.
On the evaluation board, resistors R7 and R8 are left
open. Shutdown can be toggled externally using pin J4.
RSET – Current-Limit Sensing
The MIC79110 features output current limit sensing from a
range of 50mA to 1.2A. Current limit is set by an external
resistor-to-ground by Equation 1:
IRSET = (0.2/RSET) x 1000
The default setting on the evaluation board has the DEOC
pin connected to VIN via R6 with a 10kΩ pull up resistor.
There is also the option of connecting to the SD pin via R8.
This will automatically turn off the part at the end of
Eq. 1
Default setting for the evaluation board is RSET = 165Ω with
the current limit set at 1.21A.
The DEOC pin can also be used to shut down the charger
by using a resister divider with R7 and R8. Shutdown
threshold is approximately 1.05V and for an output voltage
of 4.2V, use Equation 3 to find the correct resistor values:
SNS or ADJ – Output Voltage Setting
The evaluation board comes with the fixed output version
of the MIC79110. Output voltage is set at 4.2V and the
SNS pin is shorted to the VBAT pin via R1 with a 0Ω
For the adjustable version of the MIC79110, the output
voltage must be set with two external resistors R1 and R2.
The reference voltage for the MIC79110 is 0.6V and VBAT
is set by Equation 2:
VBAT = 0.6 × (1 + (R1/R2))
Eq. 3
REOC – End of Charge Sensing
The MIC79110 monitors the output charge current and
indicates end of charge when the current drops below a
minimum current. This minimum current is set by the
resistor R4 that is connected to ground.
Eq. 2
End of charge limit is set by R4 with Equation 4:
VBAT – Lithium-ion Battery
Lithium-ion battery is connected to this pin. Default
evaluation board is set to charge 4.2V batteries. Bypass
capacitor on the VBAT pin is 4.7µF.
IREOC = (0.2/REOC) x 1000
Eq. 4
Default setting for the evaluation board is REOC = 4 kΩ,
which calculates to an end of charge current of 50mA.
May 28, 2013
Revision 2.0
Micrel, Inc.
MIC79110 Evaluation Board
PCB Layout Recommendations
Top Layer
Bottom Layer
May 28, 2013
Revision 2.0
Micrel, Inc.
MIC79110 Evaluation Board
Bill of Materials
Part Number
4.7µF, 6.3V, X5R, 0603
2.2µF, 16V, X5R, 0805
0Ω, 1%, 1/10W, 0603
165Ω, 1%, 1/10W, 0603
4.02kΩ, 1%, 1/10W, 0603
1kΩ, 1%, 1/10W, 0603
10kΩ, 1%, 1/10W, 0603
Simple 1.2A Linear Li-ion Battery Charger
Micrel, Inc.
1. Murata: www.murata.com.
2. TDK: www.tdk.com.
3. AVX: www.avx.com.
4. Vishay: www.vishay.com.
5. Micrel, Inc.: www.micrel.com.
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
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May 28, 2013
Revision 2.0