ISL6522A Datasheet, PDF (5/13 Pages) Intersil Corporation – Buck and Synchronous Rectifier Pulse-Width Modulator (PWM) Controller

ISL6522A
Typical Performance Curves
1000
100
10
R_T PULLUP
TO +12V
R_T PULLDOWN
TO V_SS
10
100
SWITCHING FREQUENCY (kHz)
FIGURE 1. R_T RESISTANCE vs FREQUENCY
1000
Functional Pin Descriptions
RT
This pin provides oscillator switching frequency adjustment.
By placing a resistor (R_T) from this pin to GND, the nominal
200kHz switching frequency is increased according to the
following equation:
Fs ≈ 200kHz + -⁵----^•-----¹---⁰----⁶-
R_T
(R_T to GND)
Conversely, connecting a pull-up resistor (R_T) from this pin
to V_CC reduces the switching frequency according to the
following equation:
Fs ≈ 200kHz – ⁴-----^•-----¹---⁰----⁷-
R_T
(R_T to 12V)
OCSET
Connect a resistor (R_OCSET) from this pin to the drain of the
upper MOSFET. R_OCSET, an internal 200µA current source
(I_OCS), and the upper MOSFET on-resistance (r_DS(ON)) set
the converter overcurrent (OC) trip point according to the
following equation:
I_PEAK
=
I_{--O-----C----S-----}•_----R_{-----O----C-----S----E---T--}
r_DS(ON)
An overcurrent trip cycles the soft-start function.
SS
Connect a capacitor from this pin to ground. This capacitor,
along with an internal 10µA current source, sets the
soft-start interval of the converter.
COMP and FB
COMP and FB are the available external pins of the error
amplifier. The FB pin is the inverting input of the error
80
70
60
C_GATE = 3300pF
50
40
30
C_GATE = 1000pF
20
10
C_GATE = 10pF
0
100 200 300 400 500 600 700 800 900 1000
SWITCHING FREQUENCY (kHz)
FIGURE 2. BIAS SUPPLY CURRENT vs FREQUENCY
amplifier and the COMP pin is the error amplifier output.
These pins are used to compensate the voltage-control
feedback loop of the converter.
EN
This pin is the open-collector enable pin. Pull this pin below
1V to disable the converter. In shutdown, the soft-start pin is
discharged and the UGATE and LGATE pins are held low.
GND
Signal ground for the IC. All voltage levels are measured
with respect to this pin.
PHASE
Connect the PHASE pin to the upper MOSFET source. This
pin is used to monitor the voltage drop across the MOSFET
for overcurrent protection. This pin also provides the return
path for the upper gate drive.
UGATE
Connect UGATE to the upper MOSFET gate. This pin
provides the gate drive for the upper MOSFET. This pin is also
monitored by the adaptive shoot through protection circuitry to
determine when the upper MOSFET has turned off.
BOOT
This pin provides bias voltage to the upper MOSFET driver.
A bootstrap circuit may be used to create a BOOT voltage
suitable to drive a standard N-Channel MOSFET.
PGND
This is the power ground connection. Tie the lower MOSFET
source to this pin.
LGATE
Connect LGATE to the lower MOSFET gate. This pin provides
the gate drive for the lower MOSFET. This pin is also
5
FN9122.2
April 13, 2005