Detailed Descriptions
5
SNVU579 – September 2017
Copyright © 2017, Texas Instruments Incorporated
LM73605 / LM73606 EVM User’s Guide
The divider, R
ENT
and R
ENB
, locates right above the EN jumper on the PCB.
The default setting is jumper on PIN-2 and PIN-3. The board will start when V
IN
is about 3.5 V with
this setting. The EN voltage is calculated by
V
EN
= V
IN
× R
ENB
/ (R
ENT
+ R
ENB
)
(1)
When PIN-1 and PIN-2 are connected, the EN voltage is calculated by
.
V
EN
= V
EN-EXT
× R
ENB
/ (R
ENT
+ R
ENB
)
(2)
If a resistor divider is not desired, the R
ENB
can be removed from the board and the EN pin voltage
will be equal to either EN-EXT or V
IN
voltage, depending on the jumper location. It is recommended
to keep R
ENT
as a current limiting and noise filtering resistor at EN pin.
EN-EXT —
External voltage input to drive EN
When EN jumper has PIN-1 and PIN-2 connected, the enable threshold is driven by the voltage on
the EN-EXT test point. The EN pin voltage can be found by
Remove R
ENB
from the board if it is desired to have the same voltage on the EN pin as the EN-EXT
voltage.
PGOOD —
Test point to monitor the PGOOD pin
PGOOD test point is used to monitor the power-good flag. This flag indicates whether the output
voltage has reached its regulation level. The PGOOD pin of the device is an open-drain output that
is pulled up to V
OUT
on this board through R
PG
resistor.
SYNC/MODE Jumper —
Operation mode setting and synchronization clock input
As noted on the PCB, the SYNC/MODE jumper is used to select the desired light-load operation
mode.
1. PIN-1 to PIN-2: FPWM mode;
2. PIN-2 to PIN-3 (default): auto mode;
3. Open, connect external clock input to SYNC test point for synchronization and FPWM mode.
The default is PIN-2 and PIN-3 connected together and the device will operate in auto mode at light
loads. With auto mode, discontinuous conduction mode (DCM) and pulse frequency modulation
(PFM) mode are employed at light loads to provide high efficiency. PFM mode also provides very
low quiescent current at no load. At heavier load, when inductor current is in DCM or continuous
conduction mode (CCM) operation, the switching frequency is determined by the RT resistor on the
board, which is either 400 kHz or 2.2 MHz.
When PIN-1 and PIN-2 are connected, the device operates in the force PWM (FPWM) mode. In
FPWM, the inductor current will be in CCM regardless of load. The switching frequency is the same
at light loads as that of heavier loads. The switching frequency will be programmed by RT resistor
on the board, which is either 400 kHz or 2.2 MHz.
If synchronization to an external clock is desired, leave the SYNC/MODE jumper open and connect
the clock input between SYNC test point and a GND test point. The device will operate in FPWM
when it is synchronized to an external clock.
SYNC —
Test point to monitor the SYNC/MODE pin and external clock input
The SYNC test point can used to monitor the SYNC/MODE pin voltage on the device. It is also the
external clock input if synchronization is needed. Connect the external clock input to the SYNC test
point with the SYNC/MODE jumper open on all pins. The external clock frequency must be
between 350 kHz and 2.2 MHz if used. The device operates in FPWM when synchronized to a
clock.
VCC —
Test point to monitor the VCC pin
This test point is to monitor the voltage at the VCC output.
Edge Connector —
Additional connector to attach the EVM to a cable harness.
The edge connector provides the option of connecting the EVM to a cable harness if available. It
includes the power connections: VIN, GND, VOUT, and VIN-EMI. It also has Kelvin sense
connections for VIN (VIS), VOUT (VOS_P), and GND (VSNS-). See the schematic in
for
all the signals connected to the edge connector.