
4
4325.1
November 3, 2005
Functional Pin Description
RT (Pin 1)
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:
Conversely, connecting a pull-up resistor (R
T
) from this pin to
VCC reduces the switching frequency according to the
following equation.:
OCSET (Pin 2)
Connect a resistor (R
OCSET
) from this pin to the drain of the
upper MOSFET. R
OCSET
, an internal 200
μ
A current source
(I
OCS
), and the upper MOSFET on-resistance (r
DS(ON)
) set
the converter over-current (OC) trip point according to the
following equation:
An over-current trip cycles the soft-start function.
SS (Pin 3)
Connect a capacitor from this pin to ground. This capacitor,
along with an internal 10
μ
A current source, sets the soft-
start interval of the converter.
COMP (Pin 4) and FB (Pin 5)
COMP and FB are the available external pins of the error
amplifier. The FB pin is the inverting input of the error
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 (Pin 6)
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 (Pin 7)
Signal ground for the IC. All voltage levels are measured with
respect to this pin.
PHASE (Pin 8)
Connect the PHASE pin to the upper MOSFET source. This
pin is used to monitor the voltage drop across the MOSFET
for over-current protection. This pin also provides the return
path for the upper gate drive.
UGATE (Pin 9)
Connect UGATE to the upper MOSFET gate. This pin
provides the gate drive for the upper MOSFET.
BOOT (Pin 10)
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.
VCC (Pin 14)
Provide a 12V bias supply for the chip to this pin.
Typical Performance Curves
FIGURE 1. R
T
RESISTANCE vs FREQUENCY
FIGURE 2. BIAS SUPPLY CURRENT vs FREQUENCY
10
100
1000
SWITCHING FREQUENCY (kHz)
R
)
10
100
1000
R
T
PULLUP
TO +12V
R
T
PULLDOWN
TO V
SS
100
200
300
400
500
600
700
800
900
1000
40
35
30
25
20
15
10
5
0
I
C
SWITCHING FREQUENCY (kHz)
C
GATE
= 3300pF
C
GATE
= 1000pF
C
GATE
= 10pF
8
9
10
11
12
13
14
7
6
5
4
3
2
1
OCSET
SS
EN
COMP
FB
RT
VCC
NC
NC
BOOT
UGATE
PHASE
GND
NC
Fs
200kHz
------------------
6
T
+
≈
(R
T
to GND)
Fs
200kHz
------------------
7
T
–
≈
(R
T
to 12V)
I
PEAK
I
-------------------------------------------
R
DS ON
)
=
HIP6013