GE Industrial Solutions PicoTLynx 3A - Manual (Page 15)

GE
Data Sheet
PicoTLynx TM 3A: Non-Isolated DC-DC Power Modules
2.4Vdc –5.5Vdc input; 0.6Vdc to 3.63Vdc output; 3A Output Current
September 11, 2013 ©2013 General Electric Company. All rights reserved. Page 15
saturation thus preventing output overshoot during the start
of the sequencing ramp. By selecting resistor R1 (see fig. 43)
according to the following equation
05 . 0
24950
1
−
=
IN
V
R ohms,
the voltage at the sequencing pin will be 50mV when the
sequencing signal is at zero.
R1
GND
VIN+
SEQ
+
-
OUT
10K
499K
MODULE
Figure 43. Circuit showing connection of the sequencing
signal to the SEQ pin.
After the 10msec delay, an analog voltage is applied to the
SEQ pin and the output voltage of the module will track this
voltage on a one-to-one volt bases until the output reaches
the set-point voltage. To initiate simultaneous shutdown of
the modules, the SEQ pin voltage is lowered in a controlled
manner. The output voltage of the modules tracks the
voltages below their set-point voltages on a one-to-one
basis. A valid input voltage must be maintained until the
tracking and output voltages reach ground potential.
When using the EZ-SEQUENCE
TM feature to control start-up
of the module, pre-bias immunity during start-up is disabled.
The pre-bias immunity feature of the module relies on the
module being in the diode-mode during start-up. When
using the EZ-SEQUENCE TM feature, modules goes through an
internal set-up time of 10msec, and will be in synchronous
rectification mode when the voltage at the SEQ pin is applied.
This will result in the module sinking current if a pre-bias
voltage is present at the output of the module. When pre-
bias immunity during start-up is required, the EZ-
SEQUENCE
TM feature must be disabled. For additional
guidelines on using the EZ-SEQUENCE TM feature please refer
to Application Note AN04-008 “Application Guidelines for
Non-Isolated Converters: Guidelines for Sequencing of
Multiple Modules”, or contact the GE technical representative
for additional information.
Tunable Loop
The 5V Pico TLynx TM 3A modules have a new feature that
optimizes transient response of the module called Tunable
Loop
TM .
External capacitors are usually added to the output of the
module for two reasons: to reduce output ripple and noise
(see Figures 36 and 37) and to reduce output voltage
deviations from the steady-state value in the presence of
dynamic load current changes. Adding external capacitance
however affects the voltage control loop of the module,
typically causing the loop to slow down with sluggish
response. Larger values of external capacitance could also
cause the module to become unstable.
The Tunable Loop TM allows the user to externally adjust the
voltage control loop to match the filter network connected to
the output of the module. The Tunable Loop is implemented
by connecting a series R-C between the SENSE and TRIM pins
of the module, as shown in Fig. 44. This R-C allows the user to
externally adjust the voltage loop feedback compensation of
the module.
Figure. 44. Circuit diagram showing connection of R
TUME
and C
TUNE
to tune the control loop of the module.
Recommended values of R
TUNE
and C
TUNE
for different output
capacitor combinations are given in Tables 2, 3, 4 and 5.
Tables 2 and 4 show the recommended values of R
TUNE
and
C
TUNE
for different values of ceramic output capacitors up to
470uF that might be needed for an application to meet
output ripple and noise requirements for 5Vin and 3.3Vin
respectively. Selecting R
TUNE
and C
TUNE
according to Table 2
will ensure stable operation of the module.
In applications with tight output voltage limits in the presence
of dynamic current loading, additional output capacitance
will be required. Tables 3 and 5 list recommended values of
R
TUNE
and C
TUNE
in order to meet 2% output voltage deviation
limits for some common output voltages in the presence of a
1.5A to 3A step change (50% of full load), with an input
voltage of 5Vin and 3.3Vin respectively
Please contact your GE technical representative to obtain
more details of this feature as well as for guidelines on how to
select the right value of external R-C to tune the module for
best transient performance and stable operation for other
output capacitance values or input voltages other than 3.3 or
5V.
MODULE
VOUT
SENSE
TRIM
GND
RTUNE
CTUNE
RTrim
C O