ISL6842 Datasheet, PDF (6/9 Pages) Intersil Corporation – Improved Industry Standard Single Ended Current Mode PWM Controller

ISL6842, ISL6843, ISL6844, ISL6845
Typical Performance Curves
1.02
1.01
1
0.99
0.98
0.97
-40
-10
20
50
80
110
TEMPERATURE (^oC)
FIGURE 1. FREQUENCY vs TEMPERATURE
1.001
1
0.999
0.998
0.997
0.996
0.995
-40 -25 -10
5 20 35 50 65 80 95 110
TEMPERATURE (^oC)
FIGURE 2. REFERENCE VOLTAGE vs TEMPERATURE
1.002
1
0.998
0.996
0.994
-40 -25 -10 5 20 35 50 65 80 95 110
TEMPERATURE (^oC)
FIGURE 3. EA REFERENCE vs TEMPERATURE
Pin Descriptions
RTCT - This is the oscillator timing control pin. The
operational frequency and maximum duty cycle are set by
connecting a resistor, RT, between VREF and this pin and a
timing capacitor, CT, from this pin to GND. The oscillator
produces a sawtooth waveform with a programmable
frequency range up to 2.0MHz. The charge time, T_C, the
discharge time, T_D, the switching frequency, f, and the
maximum duty cycle, Dmax, can be calculated from the
following equations:
TC ≈ 0.583 • RT • CT
TD ≈ –RT • CT • ln_⁰⁰----^..--⁰⁰---⁰⁰---⁸⁸----³³----^••-----^RR----^TT------––----⁴²---^..--³⁴--_
(EQ. 1)
(EQ. 2)
f = 1 ⁄ (TC + TD)
(EQ. 3)
D = TC • f
(EQ. 4)
Figure 4 may be used as a guideline in selecting the
capacitor and resistor values required for a given frequency.
6
1-10³
100
10
CT=
100pF
220pF
330pF
470pF
1.0nF
2.2nF
3.3nF
4.7nF
1
10 20 30 40 50 60 70 80 90 100
RT (kΩ)
FIGURE 4. RTCT vs FREQUENCY
COMP - COMP is the output of the error amplifier and the
input of the PWM comparator. The control loop frequency
compensation network is connected between the COMP and
FB pins.
FB - The output voltage feedback is connected to the
inverting input of the error amplifier through this pin. The
non-inverting input of the error amplifier is internally tied to a
reference voltage.
CS - This is the current sense input to the PWM comparator.
The range of the input signal is nominally 0 to 1.0V and has
an internal offset of 100mV.
GND - GND is the power and small signal reference ground
for all functions.
OUT - This is the drive output to the power switching device.
It is a high current output capable of driving the gate of a
power MOSFET with peak currents of 1.0A. This GATE
output is actively held low when V_DD is below the UVLO
threshold.