Datasheet

“E” Model External Enable On/Off Control (see fi g. 6)
The forced On/Off enable option for “E” models uses positive logic for the
external control. The converter may be powered ON by applying a positive volt-
age (logic HI) between the On/Off pin and the negative power input (-Vin). This
positive voltage is referred to –Vin and must be in the range of at least +2.0V
and not to exceed the power supply input voltage (+Vin). The current drain is 1
mA max. when turned on.
If the On/Off pin is left open, an internal 100 Kilohm pulldown resistor will
turn the converter OFF. The OFF condition may also be commanded by ground-
ing the pin or from an external logic LO voltage not to exceed +0.4 Volts. All
voltages are referred to the –Vin negative power input.
If you wish to control the On/Off circuit by external logic rather than a switch,
carefully compare your logic threshold voltages with that of the On/Off input.
The circuit below indicates the equivalent input. Please avoid false signals
from ground bounce errors on the On/Off control. Also note that the external
control signal is wired directly into the Q3 BSS138W gate which can be dam-
aged by electrostatic transient voltages. Do not exceed the specifi cations.
Output Capacitive Load
These converters do not require external capacitance added to achieve rated
specifi cations. Users should only consider adding capacitance to reduce
switching noise and/or to handle spike current load steps. Install only enough
capacitance to achieve noise objectives. Excess external capacitance may
cause regulation problems, degraded transient response and possible oscilla-
tion or instability.
Figure 6. On/Off Control Circuit for “E” Models
Pos. Vin
To
PWM
10KΩ
Q3
BSS 138W
100
KΩ
Neg. Vin
On/O Control
Min. Vgs for turn-on = 2.0V.
Max. Vgs for turn-o = 0.4V.
OKR-T/3 Series
Adjustable Output 3-Amp SIP-mount DC/DC Converters
MDC_OKR-T/3-W12.B05 Page 18 of 18
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