UC1854
UC2854
UC3854
PIN DESCRIPTIONS (cont.)
GT Drv
(Pin 16) (gate drive): The output of the PWM is a
totem pole MOSFET gate driver on GT Drv. This output is
internally clamped to 15V so that the IC can be operated
with V
CC
as high as 35V. Use a series gate resistor of at
least 5 ohms to prevent interaction between the gate im-
pedance and the GT Drv output driver that might cause
the GT Drv output to overshoot excessively. Some over-
shoot of the GT Drv output is always expected when driv-
ing a capacitive load.
TYPICAL CHARACTERISTICS at T
A
= T
J
= 25°C
Current Amplifier Gain and Phase vs Frequency
120
Voltage Amplifier Gain and Phase vs Frequency
120
Phase
Margin
degrees
100
80
60
Phase
Margin
degrees
100
80
60
Open-Loop
40
20
Gain
dB
0
-20
0.1
1
10
100
1000
10000
Open-Loop
40
20
Gain
dB
0
-20
0.1
1
10
100
1000
10000
Frequency
kHz
Frequency
kHz
Gate Drive Rise and Fall Time
700
600
500
Fall Time
Rise Time
Gate Drive Maximum Duty Cycle
100%
95%
90%
ns
400
300
200
100
0
0
0.01
0.02
0.03
0.04
0.05
Duty
85%
Cycle
80%
75%
70%
1
10
100
Load Capacitance,
µ
F
R
SET
, k
Ω
Multiplier Output vs Voltage on Mult
600
Mult Out=3V
Mult Out=2V
Oscillator Frequency vs R
SET
and C
T
1000
500
Mult Out=1
Mult Out=0V
400
Multiplier
Output
300
µA
200
Frequency
kHz
100
V
RMS
=2V, VA Out=5V
100pF
200pF
500pF
1nF
100
10nF 5nF 3nF 2nF
0
0
100
200
300
400
500
10
600
700
800
1
10
100
I
AC
,
µ
A
R
SET
, k
Ω
5
TI [ TEXAS INSTRUMENTS ]
