ISL6754 Datasheet, PDF (8/19 Pages) Intersil Corporation – ZVS Full-Bridge PWM Controller with Adjustable Synchronous Rectifier Control

ISL6754
Typical Performance Curves
1.02
1.01
1
0.99
0.98
-40 -25 -10 5 20 35 50 65 80 95 110
TEMPERATURE (¬¨Ð
FIGURE 1. REFERENCE VOLTAGE vs TEMPERATURE
25
24
23
22
21
20
19
18
0
200
400
600
800
RTD CURRENT (¬¨¬
1000
FIGURE 2. CT DISCHARGE CURRENT GAIN vs RTD CURRENT
1-10⁴
CT = 680pF
CT = 470pF
1-10³
CT = 1000pF
CT = 100pF
CT = 220pF
100
CT = 330pF
1-10³
RTD = 10kΩ
100
RTD = 50kΩ
RTD = 100kΩ
10
0 10 20 30 40 50 60 70 80 90 100
RTD (kΩ)
FIGURE 3. DEADTIME (DT) vs CAPACITANCE
Pin Descriptions
VDD - VDD is the power connection for the IC. To optimize
noise immunity, bypass VDD to GND with a ceramic
capacitor as close to the VDD and GND pins as possible.
VDD is monitored for supply voltage undervoltage lock-out
(UVLO). The start and stop thresholds track each other
resulting in relatively constant hysteresis.
GND - Signal and power ground connections for this device.
Due to high peak currents and high frequency operation, a
low impedance layout is necessary. Ground planes and
short traces are highly recommended.
VREF - The 5.00V reference voltage output having 3%
tolerance over line, load and operating temperature. Bypass
to GND with a 0.1μF to 2.2μF low ESR capacitor.
CT - The oscillator timing capacitor is connected between
this pin and GND. It is charged through an internal 200μA
current source and discharged with a user adjustable current
source controlled by RTD.
RTD - This is the oscillator timing capacitor discharge
current control pin. The current flowing in a resistor
connected between this pin and GND determines the
10
0.1
1
10
CT (nF)
FIGURE 4. CAPACITANCE vs FREQUENCY
magnitude of the current that discharges CT. The CT
discharge current is nominally 20x the resistor current. The
PWM deadtime is determined by the timing capacitor
discharge duration. The voltage at RTD is nominally 2.00V.
CS - This is the input to the overcurrent comparator. The
overcurrent comparator threshold is set at 1.00 V nominal.
The CS pin is shorted to GND at the termination of either
PWM output.
Depending on the current sensing source impedance, a
series input resistor may be required due to the delay
between the internal clock and the external power switch.
This delay may result in CS being discharged prior to the
power switching device being turned off.
RAMP - This is the input for the sawtooth waveform for the
PWM comparator. The RAMP pin is shorted to GND at the
termination of the PWM signal. A sawtooth voltage
waveform is required at this input. For current-mode control
this pin is connected to CS and the current loop feedback
signal is applied to both inputs. For voltage-mode control,
the oscillator sawtooth waveform may be buffered and used
to generate an appropriate signal, RAMP may be connected
to the input voltage through a RC network for voltage feed
forward control, or RAMP may be connected to VREF
8
FN6754.1
September 29, 2008