Rev. 5/23/01

SP6122 Evaluation Board Manual

© Copyright 2001 Sipex Corporation

2

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

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.

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.

SP6122

J1 Position

Mode

Condition

open

Enabled

Normal

1 to 2

Hiccup

Softstarts if Over-Current

2 to 3

Sleep

Iq = 20uA (max)