TK75020TL/75020 TOKO [TOKO, Inc], TK75020TL/75020 Datasheet - Page 7

• Manufacturer Part Number: TK75020TL/75020
• Description: ZVS RESONANT CONTROLLER
• Manufacturer: TOKO [TOKO, Inc]

the DRV pin is held low. The drive latch may be set either
by the output of comparator CMP
OR gate G
CMP
comparator detects if the voltage at the ZVD pin dropped
below 2 V. Note that gate G
through the ZVD pin only when the voltage at the C
higher than 1.5 V and the current limit latch is in the reset
state. The reason for disabling the ZVD path at C
voltages lower than 1.5 V is to prevent an immediate turn-
on of the MOSFET after it was turned off. CMP
detect if the C
When the voltage of the timing capacitor is falling (due to
the discharging current set by the external resistors between
the output of the error amplifier and the T
as between the T
allowed to go high. The charge and discharge currents are
enabled exclusively.
ZERO VOLTAGE DETECTION PIN (ZVD)
This pin is connected to the drain of the power MOSFET
switch of the converter or inverter through a high value
resistor or a diode. When the MOSFET is turned off, the
drain voltage increases at first and then decreases, due to
the resonant action in the loading network of the switch.
When the drain voltage is above the supply voltage of the
IC, the ZVD pin voltage is clamped to the supply voltage
through the internal diode D
below the supply voltage, the voltage of the ZVD pin begins
to follow it. When the ZVD pin voltage drops below 2 V, the
output of the ZVD comparator goes high and sets the drive
latch through gates G
condition, the DRV pin goes high and turns on the MOSFET
switch. By having the ZVD feature, the circuit automatically
sets the optimum off time, essentially independently from
the value of the resistor between the T
ground.
ERROR AMPLIFIER PIN (EA
The EA
The output stage of the amplifier is an open-collector
transistor. It is normally connected to the T
external resistor. The non-inverting input of the error
amplifier is internally tied to a trimmed 1.25 V reference.
The error amplifier is short-circuit protected.
January 1999 TOKO, Inc.
3
detects if the timing voltage reached 3 V, the ZVD
OUT
2
pin is the output of the internal error amplifier.
or by the ZVD comparator through G
T
pin voltage is higher than 1.5 V.
ON
/SS pin and ground), the DRV pin is
1
and G
1
1
allows setting the drive latch
. As the drain voltage drops
OUT
2
. Unless there is a fault
)
3
through the two-input
PIN DESCRIPTION (CONT.)
ON
OFF(MAX)
ON
/SS pin, as well
/SS pin via an
4
is used to
1
pin and
and G
T
pin is
T
pin
2
.
ERROR AMPLIFIER INPUT PIN (EA
The EA
serves for receiving either an external voltage-feedback or
an external current-feedback signal. The compensating
network of the feedback loop is usually connected between
the EA
TURN-ON TIMING / SOFT-START PIN (T
The on-time is inversely proportional to the current flowing
in the resistor connected between this pin and the EA
pin. The T
at turn-on. Soft-Start can be achieved by connecting the
series combination of a resistor and capacitor between the
T
IC is enabled (either because the V
upper UVLO threshold or because the IC is turned on by
the Enable pin), the Soft-Start capacitor, which was initially
discharged, begins to charge up through the series resistor.
The charging current adds to the current flowing in the on-
time-setting resistor and sets a shorter on time. As the
voltage builds up across the soft-start capacitor the charging
current gradually decreases and the on time gradually
increases.
At normal operation a voltage-to-current converter formed
by A
The current flowing through R
connected to the T
Q
diode-connected section of the second mirror is shorted
with the transistor Q
is reset.
MAXIMUM TURNOFF TIMING PIN (T
An external resistor connected between this pin and ground
sets the current that charges the timing capacitor. The
maximum possible off time is inversely proportional to the
value of that current. As discussed previously, when the off
period is terminated by the zero-voltage detector, the
actual off time becomes shorter than the value set by this
resistor.
At normal operation the voltage of the T
at 2 V with the help of a voltage-to-current converter
formed by the amplifier A
flowing through the off time setting resistor and R
ON
3
and Q
/SS pin and ground. When the normal operation of the
2
and Q
INV
INV
4
and the EA
ON
into a second mirror formed by Q
pin (the inverting input of the error amplifier)
2
/SS pin is also useful for providing Soft-Start
keeps the voltage of the T
ON
7
/SS pin and ground is mirrored with
via Q
OUT
1
pins.
8
and transistor Q
when the current switch latch
2
and the external resistor
CC
voltage exceeds the
INV
OFF(MAX)
OFF (MAX)
ON
)
TK75020
/SS pin at 2 V.
ON
1
5
. The current
and Q
/ SS)
)
pin is kept
Page 7
6
. The
1
OUT
is