TK83854
PIN DESCRIPTION
GROUND PIN (GND)
All voltages are measured with respect to GND. V
CC
and
V
ref
should be bypassed directly to GND with a 0.1
µF
or
larger ceramic capacitor. The timing capacitor discharge
current also returns to this pin, so the lead from the
oscillator timing capacitor to GND should also be as short
and as direct as possible.
PEAK LIMIT (PKLMT)
The threshold for PKLMT is GND. Connect this input to the
negative voltage on the current sense resistor as shown in
Figure 1. Use a resistor to V
ref
to offset the negative current
sense signal up to GND.
CURRENT AMPLIFIER OUTPUT (CA
OUT
)
This is the output of a wide-bandwidth op-amp that senses
line current and commands the Pulse Width Modulator
(PWM) to force the correct current. This output can swing
close to GND, allowing the PWM to force zero duty cycle
when necessary. The current amplifier will remain active
even if the IC is disabled.
CURRENT SENSE MINUS
(I
SENSE
)
This is the inverting input to the current amplifier. This input
and the non-inverting input MULT
OUT
remain functional
down to and below GND. Care should be taken to avoid
taking these inputs below –0.5 V, because they are
protected with diodes to GND.
MULTIPLIER OUTPUT AND CURRENT SENSE PLUS
(MULT
OUT
)
The output of the analog multiplier and the non-inverting
input of the current amplifier are connected together at
MULT
OUT
. The cautions about taking I
SENSE
below –0.5 V
also apply to MULT
OUT
. As the multiplier output is a
current, this is a high impedance input similar to I
SENSE
, so
the current amplifier can be configured as a differential
amplifier to reject GND noise. Figure 1 shows an example
of using the current amplifier differentially.
INPUT AC CURRENT (IAC)
This input to the analog multiplier is a current. The multiplier
is tailored for very low distortion from this current input (IAC
to MULT
OUT
), so this is the only multiplier input that should
January 1999 TOKO, Inc.
Page 7
be used for sensing instantaneous line voltage. The nominal
voltage on IAC is 6 V, so in addition to a resistor from IAC
to rectified line, connect a resistor from IAC to V
ref
. If the
resistor to V
ref
is one-fourth of the value of the resistor to
the rectifier, then the 6 V offset will be cancelled, and the
line current will have minimal crossover distortion.
VOLTAGE AMPLIFIER OUTPUT (VA
OUT
)
This is the output of the op-amp that regulates output
voltage. Like the current amplifier, the voltage amplifier will
also stay active even if the IC is disabled with either ENA
or V
CC
. This means that large feedback capacitors across
the amplifier will stay charged through momentary disable
cycles. Voltage amplifier output levels below ~1 V will
inhibit multiplier output.
RMS LINE VOLTAGE (V(rms))
The output of a boost PWM is proportional to the input
voltage, so when the line voltage into a low-bandwidth
boost PWM voltage regulator changes, the output will
change immediately and slowly recover to the regulated
level. For these devices, the V(rms) input compensates for
line voltage changes if it is connected to a voltage
proportional to the RMS input line voltage. For best control,
the V
RMS
voltage should stay between 1.5 V and 3.5 V.
VOLTAGE REFERENCE OUTPUT (V
ref
)
V
ref
is the output of an accurate 7.5 V voltage reference.
This output is capable of delivering 10 mA to peripheral
circuitry and is internally short circuit current limited. V
ref
is
disabled and will remain at 0 V when V
CC
is low or when
ENA is low. Bypass V
ref
to GND with a 0.1
µF
or larger
ceramic capacitor for best stability.
ENABLE (ENA)
ENA is a logic input that will enable the PWM output,
voltage reference, and oscillator. ENA also will release the
soft start clamp, allowing SS to rise. When unused, connect
ENA to a +5 V supply or pull ENA high with a 22 k resistor.
The ENA pin is not intended to be used as a high-speed
shutdown to the GTDRV output.
TOKO [ TOKO, INC ]
