ISL6845 Intersil Corporation, ISL6845 Datasheet - Page 8

• Manufacturer Part Number: ISL6845
• Description: (ISL6840 - ISL6845) Improved Industry Standard Single-Ended Current Mode PWM Controller
• Manufacturer: Intersil Corporation

Typical Performance Curves
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
discharge time, t
maximum duty cycle, Dmax, can be calculated from
Equations 1, 2, 3 and 4:
Figure 4 may be used as a guideline in selecting the
capacitor and resistor values required for a given frequency.
t
f
D
t D
C
=
=
≈
≈
1
0.583 RT CT
–
t
C
RT
⁄
(
t C
•
FIGURE 3. EA REFERENCE vs TEMPERATURE
1.002
1.000
0.998
0.996
0.994
f
FIGURE 1. FREQUENCY vs TEMPERATURE
•
1.02
1.01
1.00
0.99
0.98
0.97
•
+
CT
t D
-40 -25 -10
-40
•
)
•
ln
D
⎛
⎝
, the switching frequency, f, and the
0.0083 RT 4.3
----------------------------------------------
0.0083 RT 2.4
-10
•
•
5
TEMPERATURE (°C)
TEMPERATURE (°C)
ISL6840, ISL6841, ISL6842, ISL6843, ISL6844, ISL6845
20
20
–
–
8
35
⎞
⎠
50
50
65
80
80
95 110
C
, the
110
(EQ. 1)
(EQ. 2)
(EQ. 3)
(EQ. 4)
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 0V 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
threshold.
VDD - V
supply current will depend on the load applied to OUT. Total
I
FIGURE 4. RESISTANCE FOR CT CAPACITOR VALUES GIVEN
DD
current is the sum of the operating current and the
FIGURE 2. REFERENCE VOLTAGE vs TEMPERATURE
10
100
10
1.001
1.000
0.999
0.998
0.997
0.996
0.995
3
1
DD
10
-40 -25 -10
is the power connection for the device. The total
20
30
40
5
TEMPERATURE (°C)
50
RT (kΩ)
20
60
35
DD
70
50
is below the UVLO
65
80
80
90
95 110
100
April 16, 2007
100pF
220pF
330pF
470pF
1.0nF
2.2nF
3.3nF
4.7nF
FN9124.8