ltc6992-2-ltc6992-3 Linear Technology Corporation, ltc6992-2-ltc6992-3 Datasheet - Page 12

• Manufacturer Part Number: ltc6992-2-ltc6992-3
• Description: Timerblox Voltage-controlled Pulse Width Modulator Pwm
• Manufacturer: Linear Technology Corporation

PIN FUNCTIONS
LTC6992-1/LTC6992-2/
LTC6992-3/LTC6992-4
V
ply should be kept free from noise and ripple. It should be
bypassed directly to the GND pin with a 0.1μF capacitor.
DIV (Pin 2/Pin 4): Programmable Divider and Polarity
Input. The DIV pin voltage (V
into a 4-bit result (DIVCODE). V
a resistor divider between V
to ensure an accurate result. The DIV pin and resistors
should be shielded from the OUT pin or any other traces
that have fast edges. Limit the capacitance on the DIV pin
to less than 100pF so that V
DIVCODE (POL) determines if the PWM signal is inverted
before driving the output. When POL = 1 the transfer func-
tion is inverted (duty cycle decreasing as V
SET (Pin 3/Pin 3): Frequency-Setting Input. The voltage
on the SET pin (V
amount of current sourced from the SET pin (I
grams the master oscillator frequency. The I
range is 1.25μA to 20μA. The output oscillation will stop
if I
nected between SET and GND is the most accurate way to
set the frequency. For best performance, use a precision
metal or thin film resistor of 0.5% or better tolerance and
50ppm/°C or better temperature coefficient. For lower ac-
curacy applications an inexpensive 1% thick film resistor
may be used.
12
+
SET
(Pin 1/Pin 5): Supply Voltage (2.25V to 5.5V). This sup-
drops below approximately 500nA. A resistor con-
SET
) is regulated to 1V above GND. The
DIV
(DCB/S6)
+
and GND. Use 1% resistors
DIV
settles quickly. The MSB of
DIV
) is internally converted
may be generated by
MOD
SET
increases).
SET
current
) pro-
MOD (Pin 4/Pin 1): Pulse-Width Modulation Input. The
voltage on the MOD pin controls the output duty cycle. The
linear control range is between 0.1 • V
(approximately 100mV to 900mV). Beyond those limits,
the output will either clamp at 5% or 95%, or stop oscil-
lating (0% or 100% duty cycle), depending on the version.
GND (Pin 5/Pin 2): Ground. Tie to a low inductance ground
plane for best performance.
OUT (Pin 6/Pin 6): Oscillator Output. The OUT pin swings
from GND to V
30Ω. The duty cycle is determined by the voltage on the
MOD pin. When driving an LED or other low-impedance
load a series output resistor should be used to limit the
source/sink current to 20mA.
Limit the capacitance on the SET pin to less than 10pF
to minimize jitter and ensure stability. Capacitance less
than 100pF maintains the stability of the feedback circuit
regulating the V
+
V
+
with an output resistance of approximately
R
SET
SET
MOD
GND
SET
voltage.
LTC6992
OUT
6992 PF
DIV
V
+
C1
0.1μF
SET
V
+
R1
R2
and 0.9 • V
69921234fb
SET