DS_ND12S10A_07172008
8
FEATURES DESCRIPTIONS (CON.)
Input Under-Voltage Lockout
The input under-voltage lockout prevents the converter
from being damaged while operating when the input
voltage is too low. The lockout occurs between 7.6V to
9.0V.
Over-Current and Short-Circuit Protection
The ND series modules have non-latching over-current
and short-circuit protection circuitry. When over current
condition occurs, the module goes into the non-latching
hiccup mode. When the over-current condition is
removed, the module will resume normal operation.
An over current condition is detected by measuring the
voltage drop across the MOSFETs. The voltage drop
across the MOSFET is also a function of the MOSFET’s
Rds(on). Rds(on) is affected by temperature, therefore
ambient temperature will affect the current limit inception
point.
The detection of the Rds(on) of MOSFETs also acts as
an over temperature protection since high temperature
will cause the Rds(on) of the MOSFETs to increase,
eventually triggering over-current protection.
Remote sense
The ND50 provide Vo remote sensing to achieve proper
regulation at the load points and reduce effects of
distribution losses on output line. In the event of an open
remote sense line, the module shall maintain local sense
regulation through an internal resistor. The module shall
correct for a total of 0.5V of loss. The remote sense
connects as shown in Figures 25.
Figure 25:
circuit configuration for remote sense
Over Temperature Protection (OTP)
To provide additional over-temperature protection in a
fault condition, the unit is equipped with a non-latching
thermal shutdown circuit. The shutdown circuit engages
when the temperature of monitored component exceeds
approximately 125°C. The unit will cycle on and off while
the fault condition exists. The unit will recover from
shutdown when the cause of the over temperature
condition is removed
Output Voltage Programming
The output voltage of the ND series is trimmable by
connecting an external resistor between the trim pin and
output ground as shown Figure 26 and the typical trim
resistor values are shown in Figure 27.
Figure 26:
Trimming Output Voltage
The ND50 module has a trim range of 0.9V to 3.63V.
The trim resistor equation for the ND50A is:
Vout is the output voltage setpoint
Rs is the resistance between Trim and Ground
Rs values should not be less than
3.32k
Ω
Output Voltage
Rs (
Ω
)
0.9V open
+1.2 V
38.3k
+1.5 V
18.7k
+1.8V 12.1k
+2.5 V
6.34k
+3.3V
3.92k
+3.63V 3.32k
Figure 27:
Typical trim resistor values
