TOP242-250
TOPSwitch-GX
Family Functional
Description
Frequency (kHz)
Auto-restart
I
CD1
132
I
B
I = 125
µA
L
Like
TOPSwitch, TOPSwitch-GX
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 7.
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, thermal shutdown,
the
TOPSwitch-GX
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, LINE-SENSE, and
EXTERNAL CURRENT LIMIT (available in Y, R or F
package) or one terminal MULTI-FUNCTION (available in P
or G package) have been added to implement some of the new
functions. These terminals can be connected to the SOURCE
pin to operate the
TOPSwitch-GX
in a
TOPSwitch-like
three
terminal mode. However, even in this three terminal mode, the
TOPSwitch-GX
offers many new transparent features that do
not require any external components:
1. A fully integrated 10 ms soft-start limits peak currents
and voltages during start-up and dramatically reduces or
eliminates output overshoot in most applications.
2. DC
MAX
of 78% allows smaller input storage capacitor, lower
input voltage requirement and/or higher power capability.
3. Frequency reduction at light loads lowers the switching
losses and maintains good cross regulation in multiple output
supplies.
4. Higher switching frequency of 132 kHz reduces the
transformer size with no noticeable impact on EMI.
5. Frequency jittering reduces EMI.
6. Hysteretic over-temperature shutdown ensures automatic
recovery from thermal fault. Large hysteresis prevents
circuit board overheating.
7. Packages with omitted pins and lead forming provide large
drain creepage distance.
8. Tighter absolute tolerances and smaller temperature
variations on switching frequency, current limit and PWM gain.
The LINE-SENSE (L) pin is usually used for line sensing by
connecting a resistor from this pin to the rectified DC high
voltage bus to implement line overvoltage (OV), under-voltage
(UV) and 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 starting from a line voltage
above the under-voltage threshold. See Table 2 and Figure 11.
I
L
= 190
µA
I <I
L
L(DC)
30
I
C
(mA)
Auto-restart
I
CD1
78
Duty Cycle (%)
I
B
Slope = PWM Gain
38
I
L
= 125
µA
I <I
L
L(DC)
10
I
L
= 190
µA
TOP242-5 1.6 2.0
TOP246-9 2.2 2.6
TOP250 2.4 2.7
I
C
(mA)
5.2
5.8
6.5
6.0
6.6
7.3
Note: For P and G packages I
L
is replaced with I
M
.
PI-2633-011502
Figure 7. Relationship of Duty Cycle and Frequency to CONTROL
Pin Current.
The pin can also be used as a remote ON/OFF and a
synchronization input.
The EXTERNAL CURRENT LIMIT (X) pin is usually used
to reduce the current limit externally to a value close to the
operating peak current, by connecting the pin to SOURCE
through a resistor. This pin can also be used as a remote
ON/OFF and a synchronization input in both modes. See
Table 2 and Figure 11.
For the P or G packages the LINE-SENSE and EXTERNAL
CURRENT LIMIT pin functions are combined on one MULTI-
FUNCTION (M) pin. However, some of the functions become
mutually exclusive as shown in Table 3.
The FREQUENCY (F) pin in the Y, R or F package sets the
switching frequency to the default value of 132 kHz when
connected to SOURCE pin. A half frequency option of
66 kHz can be chosen by connecting this pin to CONTROL pin
instead. Leaving this pin open is not recommended.
M
12/04
5
POWERINT [ POWER INTEGRATIONS, INC. ]
