LMZ23610/8/6 and LMZ22010/8/6 Current Sharing Evaluation Board
LMZ23610/8/6 and
LMZ22010/8/6 Current
Sharing Evaluation Board
Introduction
The LMZ23610/8/6 and LMZ22010/8/6 SIMPLE SWITCH-
ER® power modules are easy-to-use DC-DC solution capa-
ble of driving up to a 10, 8 or 6 ampere load. They are
available in an innovative package that enhances thermal
performance and allows for hand or machine soldering. The
LMZ23610/8/6 can accept an input voltage rail between 6V
and 36V and the LMZ22010/8/6 can accept an input voltage
rail between 6V and 20V.
The current sharing evaluation board is designed so that four
modules can be easily connected to supply up to a 40 amp
load. More can be connected as long as care is taken to not
exceed the current capabilities of the banana plug connectors
and the 5-amp per pin rating of the edge board connector.
The current sharing evaluation board is highly configurable.
The output voltage can be changed to 5V, 3.3V, 2.5V or 1.2V
with a jumper change. The external soft-start capacitor facil-
itates a controlled and adjustable startup rise time of the
output. The board temperature can be measured with the on-
board resistor. The UVLO can be adjusted by adding one
resistor. To simplify the synchronization of the modules an
onboard 555 timer provides an adjustable frequency clock
from 350 to 600 kHz.
The LMZ23610 and LMZ22010 family is a reliable and robust
solution with the following features: loss-less cycle-by-cycle
valley current limit to protect for over current or short-circuit
fault, thermal shutdown, input under-voltage lockout, and will
start up into a pre-biased output.
National Semiconductor
Application Note 2093
Marc Davis-Marsh
April 7, 2010
Board Specifications
•
•
•
V
IN
= 6V to 36V (LMZ23610/8/6)
V
IN
= 6V to 20V (LMZ22010/8/6)
V
OUT
= 1.2V, 2.5V, 3.3V or 5V (minimum input voltage of
7V required for 5V output)
• I
OUT
= 0 to 10, 8, or 6 Amps
•
θ
JA
= 8.8 °C / W,
θ
JC
= 1.0 °C/W
• Designed on four layers; Inner are 2 oz copper; Outer are
2 oz copper.
• Measures 3.54" x 3.54" (90 mm x 90 mm) and is 62 mils
(1.57 mm) thick of FR4 laminate material
For additional circuit considerations, including additional out-
put voltage options, refer to the Applications Section section
of the LMZ23610/8/6 or LMZ22010/8/6 data sheets. For neg-
ative output voltage connections see AN-2027.
Simplified Schematic
AN-2093
30138708
FIGURE 1.
© 2011 National Semiconductor Corporation
301387
www.national.com
AN-2093
Test Connections
The board should be connected to a power supply and load
as shown below in
Figure 2.
The EN post is connected to the
UVLO circuit on the back of the board. There is a resistive
divider implemented on the board, with the bottom resistor
unpopulated, that can be used to establish a precision UVLO
level of the board. A common user change to this circuit is to
adjust the value of RENT and RENB to adjust the operating
UVLO to that of the target application. Refer to the respective
data sheet for calculation. Note that if in the end application
the EN pin voltage does not exceed 5.5V at maximum Vin,
then the enable clamp zener D1 can be omitted. Pull EN low
to shutdown the module and clock circuitry.
The SYNC post is connected to the output of a 555 timer on
the back of the board and is fed to the SYNC pin of the device.
This clock is provided to simplify the testing of the current
sharing features of the device and is not required for stand
alone operation. The frequency of the clock can be adjusted
from 350kHz to 600kHz using the potentiometer labeled
R_freq_adj. Jumper J3 (SLAVE) can be used to disable the
555 timer and allow the use of external clocks from 314 to 600
kHz.
Board Connection Diagram
30138701
FIGURE 2.
www.national.com
2
AN-2093
Edge Connector Diagram
30138706
FIGURE 3.
The evaluation board is also compatible with the 44-pin edge
connector shown in
Figure 3.
The table below explains the
functionality of the pins.
Pin
1, 2, 3, 4, 5, 7, 8
9, 10, 11, 12, 13,
14, A, B, C, D, E
15, 16, 18, 19,
20, 21, 22, V, W,
X, Y, Z
H
M
T
N
J
Name
VIN
GND
VOUT
Description
Input supply — Nominal operating range is from 6V to 20V for the LMZLMZ22010/8/6 and from 6V
to 36V for the LMZLMZ23610/8/6.
Power Ground — Electrical path for the power circuits within the module.
Output Voltage — Regulated 5, 3.3, 2.5 or 1.2V.
VIN SENSE +
VIN SENSE -
Positive Kelvin Sense of Input voltage — Tied to VIN pin of the LMZ module.
Negative Kelvin Sense of Input voltage — Tied to PGND (EP) of the LMZ module.
VOUT SENSE + Positive Kelvin Sense of Output voltage — Tied to Vout banana jack.
VOUT SENSE - Negative Kelvin Sense of Output voltage — Tied to AGND of the LMZ module.
SYNC +
Synchronization Positive Input — This is the positive probe point for viewing the clock generated
by the 555 timer and is connected to the SYNC pin of the LMZ module. If the 555 timer is shutdown
using J3 then an external clock can be used. The external clock must provide a CMOS logic level
square wave whose frequency is between 314 kHz and 600 kHz.
Synchronization Negative Input — Tied to AGND of the LMZ module.
Share Positive Input — Connect this pin to the share pin of other LMZ modules to share the load
between the devices.
Share Negative Input — Tied to AGND of the LMZ module.
Enable — Input to the precision enable comparator of the LMZ Module. Also tied to a pull-up resistor
to enable the 5v bias supply and the 555 timer.
L
R
P
K
S
SYNC -
SHARE +
SHARE -
EN
TEMP SENSE Connected to top of the Rts temperature sensing resistor. Temperature measurements can be made
by measuring the temperature dependant resistance between TEMP SENSE and VIN SENSE -.
Convert the resistance to temperature with the following equation: Temperature (C)
≊
2.6245 x
Resistance (Ω)
- 262.7
3
www.national.com
AN-2093
Adjusting the Output Voltage
The output voltage of the evaluation board is adjusted to ei-
ther 5V, 3.3V, 2.5V, or 1.2V by moving jumper J1. For other
voltage options see the datasheet for adjusting the feedback
resistors.
Current Sharing
Current sharing is easy to evaluate. The next steps should be
implemented only while the power to the device is off.
Select which board will be the master. This is usually the
board closer to the load. Connect the master board as de-
scribed above in Test Connections. Insert the slave board into
the socket on the master. If there is no socket, connect a 44-
pin board-edge extender to the top of the master board and
solder the pins. The board-edge connector will connect Vin,
Gnd, Vout, Enable, Sync and the Share pin between the
boards to split the current demand between multiple boards.
On the slave board(s) remove the jumper J1 (MASTER) and
move it to jumper J2 (SLAVE). This disconnects the FB pin of
the slave converter(s) (J1) and disables the clock that is pro-
vided on the slave board (J2). The slave module's switching
frequency will now be controlled by the clock on the master
board. Turning the R_freq_adj pot counter clockwise lowers
the clock frequency and turning the pot clockwise increases
the frequency. By placing an additional jumper on J3 (SLAVE)
of the master board, the 555 timer is disabled on both boards.
With the clock disabled you can observe the parts perfor-
mance when the devices are not synchronized, or you can
supply an external clock through the SYNC post. J3 must be
in place (555 disabled) on all boards to use an external clock
on sync. The Sync pin of the slave can also be disconnected
from the master board by removing the RSHORT resistor.
This allows the user to provide a multiphase clock of their
choosing to the boards.
The advantage to running the clocks out of phase is to reduce
the current stress on the input and output capacitors. For two
modules the clocks should be run 180 degrees out of phase,
for three modules the clocks should be run 120 degrees out
of phase an so on. Although local input bypass capacitors are
still required, the bulk capacitance required for a given ripple
voltage can be greatly reduced.
Output Voltage Ripple with Two Boards Synchronized to Output Voltage Ripple with Two Boards Synchronized with
350Khz
180° Phase Shift
30138709
30138710
FIGURE 4.
www.national.com
4
AN-2093
Master Slave Connection
30138702
FIGURE 5.
5
www.national.com
