Design of a 2 phase pulse width modulator

[fantabulous68]

SPECIFICATIONS:

*PWM OUTPUT VOLTAGE OV (OFF) OR 5V (ON) WITH A MAX CURRENT CAPABILITY OF 0.1ma
*A constant pulse frequency of 100KHz(each phase is 50KHz)
*Accepts an input voltage of -5V.....+5V to create a duty cycle range D=0.0 to D=1.0

I want to know if i designed the components of the triangle wave generator correctly ie. R1, R2, R3 and the capacitor
(see diagram)

R1 & R2 will have the same current right?
therefore

current of R2 and R1 = pwm output voltage / R2 = input voltage / R1
= 5V/R2 = 10V/R1

choose R1=20K & R2=10K

so current in R1 & R2= 500uA

R3 = pwm output voltage/MAX CURRENT CAPABILITY = 5V / 0.1mA=50K

to solve the capacitor

T=Ton= R1 X C

each phase is 50KHz therefore Ton=20uS

C=20uS / 50K = 400pF