TOP264-271
PI-5579-012210
+
R
LS
4 MΩ
V
UV
= I
UV
× R
LS
+ V
V
(I
V
= I
UV
)
V
OV
= I
OV
× R
LS
+ V
V
(I
V
= I
OV
)
For R
LS
= 4 MΩ
Auto-Restart
78
Duty Cycle (%)
Slope = PWM Gain
V
UV
= 102.8 VDC
V
OV
= 451 VDC
DC
MAX
@100 VDC = 76%
DC
MAX
@375 VD
C = 41%
C
DC
Input
Voltage
D
V
CONTROL
S
X
R
IL
12 kΩ
For R
IL
= 12 kΩ
I
LIMIT
= 61%
See Figure 35 for
other resistor values
(R
IL
) to select different
I
LIMIT
values.
-
Figure 4.
CONTROL
Current
Package Line Sense and Externally Set Current Limit.
TOP264-271 Functional Description
Like TOPSwitch-HX, TOP264-271 is an integrated switched
mode power supply chip that converts a current at the control
input to a duty cycle at the open drain output of a high voltage
power MOSFET. During normal operation the duty cycle of the
power MOSFET decreases linearly with increasing CONTROL
pin current as shown in Figure 5.
In addition to the three terminal TOPSwitch features, such as
the high voltage start-up, the cycle-by-cycle current limiting,
loop compensation circuitry, auto-restart and thermal shut-
down, the TOP264-271 incorporates many additional functions
that reduce system cost, increase power supply performance
and design flexibility. A patented high voltage CMOS technology
allows both the high-voltage power MOSFET and all the low
voltage control circuitry to be cost effectively integrated onto a
single monolithic chip.
Three terminals, FREQUENCY, VOLTAGE-MONITOR, and
EXTERNAL CURRENT LIMIT have been used to implement
some of the new functions. These terminals can be connected
to the SOURCE pin to operate the TOP264-271 in a TOPSwitch-
like three terminal mode. However, even in this three terminal
mode, the TOP264-271 offers many transparent features that do
not require any external components:
1. A fully integrated 17 ms soft-start significantly reduces or
eliminates output overshoot in most applications by sweeping
both current limit and frequency from low to high to limit the
peak currents and voltages during start-up.
2. A maximum duty cycle (DC
MAX
) of 78% allows smaller input
storage capacitor, lower input voltage requirement and/or
higher power capability.
3. Multi-mode operation optimizes and improves the power
supply efficiency over the entire load range while maintaining
good cross regulation in multi-output supplies.
4. Switching frequency of 132 kHz reduces the transformer size
with no noticeable impact on EMI.
5. Frequency jittering reduces EMI in the full frequency mode at
high load condition.
Drain Peak Current
To Current Limit Ratio (%)
100
55
25
CONTROL
Current
Full Frequency Mode
132
Low
Frequency
Mode
Frequency (kHz)
66
Jitter
30
I
CD1
I
B
I
C01
Variable
Frequency
Mode
Multi-Cycle
Modulation
I
C02
I
C03
I
COFF
CONTROL
Current
PI-5665-110609
Figure 5.
Control Pin Characteristics (Multi-Mode Operation).
6. Hysteretic over-temperature shutdown ensures thermal fault
protection.
7. Packages with omitted pins and lead forming provide large
drain creepage distance.
8. Reduction of the auto-restart duty cycle and frequency to
improve the protection of the power supply and load during
open loop fault, short circuit, or loss of regulation.
9. Tighter tolerances on I
2
f power coefficient, current limit
reduction, PWM gain and thermal shutdown threshold.
The VOLTAGE-MONITOR (V) pin is usually used for line sensing
by connecting a 4 MW resistor from this pin to the rectified DC
high voltage bus to implement line overvoltage (OV), under-
voltage (UV) and dual-slope line feed-forward with DC
MAX
reduction. In this mode, the value of the resistor determines the
OV/UV thresholds and the DC
MAX
is reduced linearly with a dual
slope to improve line ripple rejection. In addition, it also
provides another threshold to implement the latched and
4
Rev. B 03/10
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