Simulating '4046 as VCO only ' in Proteus

Required output from pin 4 of 4046 is 25 - 37 kHz square pulses when the input is 2.5 - 3.7 V. The circuit which is simulated in proteus is given in .jpg format. I don't require 4046 to work as PLL. It only needs to get the output of vco as square pulses.
Pls check attachments. Still i ll describe the circuit here.
At pin 9, input of 2.5 -3.7 V is given. Between pin 6 and pin 7 capacitor of 100 pF is connected. Pin 5 is grounded.At pin 11, 10k resistor is connected to ground. And pin 4 gives output of vco. Simulation of the circuit described above gives triangular wave of 500 kHz frequency. How do i modify the circuit so that at pin 4 a square wave output is obtained ?