SP6122EB Datasheet, PDF (2/6 Pages) Sipex Corporation – Evaluation Board Manual

USING THE EVALUATION BOARD
1) Powering Up the SP6122 Circuit
The SP6122 Evaluation Board can be powered from inputs from a +3V to +7V power
supply. Connect with short leads directly to the “Vin” and “Gnd” posts. Monitor the
Output Voltage and connect the Load between the “Vout” post and the 2^nd “GND” post.
2) Using the J1 Jumper: Enabling the SP6122 Output and using the Hiccup Mode
As you can see in table 1, the SP6122 output will be Enabled if the J1 Jumper is left
open. If J1 is in the pin 2 to 3 position, the ENABLE pin is brought to GND, which puts
the SP6122 in the Sleep Mode. If the Jumper at J1 is in the pin 1 to 2 position, FFLAG
U1 pin 2 is connected to ENABLE U1 pin 4, and Hiccup Mode is activated. Hiccup
Mode occurs if the output current exceeds the Over-Current-Protection threshold, and
the part will “Soft-start”, which happens every 1.2msec for a CEN capacitor value of
4.7nF. This is determined by the following relationship:
I = CEN*dV/dt
which yields dt = CEN*dV/I = 1.2msec
where the value of the CEN capacitor is 4.7nF, dV is the 1V internal threshold for
charging, and I is the Enable pin source current of 4uA.
SP6122
J1 Position
Mode
Condition
open
Enabled
Normal
1 to 2
Hiccup
Softstarts if Over-Current
2 to 3
Sleep
Iq = 20uA (max)
Table 1. SP6122 Enable/Hiccup Jumper
3) Using External Divider Resistors: Programming the SP6122 Output Voltage
As you can see by the schematic in Figure 1, the SP6122 uses an internal feedback
divider to initially trim the output voltage using Rin1 and Rin2, where Rin2 is
approximately 62.5K. To accommodate the user who wants to externally program the
SP6122 output voltage, the SP6122 Evaluation Board has 2 external divider resistors,
R1 and R2, which can be used to program the output voltage above, but not below the
voltage set by the internal resistor divider. The relationships for the external divider
resistors are derived below:
i1 = Va/Rin2 = 1.25/62.5K = 20uA
Since Rin2 has +/-50% tolerance, ib change is +20uA/-7uA. If the SP6122 is trimmed to
1.5V output, Vb will be fixed at 1.5V in a closed loop. As a result, i2 is not affected by
the variation of the internal resistors, and the +20uA/-7uA current variation will be
passed on to i3.
Vout = Vb+i3*R1,
Therefore, ∆Vout = ∆i3*R1=+20uA/-7uA*R1.
That is, the additional variation on the output voltage is caused by the internal voltage
divider. For example, with R1 selected to be 500ohm, the variation on the output
voltage will be +10mV/-3.5mV.
Rev. 5/23/01
SP6122 Evaluation Board Manual
2
© Copyright 2001 Sipex Corporation