STEVAL-ISA033V1 STMicroelectronics, STEVAL-ISA033V1 Datasheet - Page 8
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STEVAL-ISA033V1
Manufacturer Part Number
STEVAL-ISA033V1
Description
BOARD EVAL L5991/STP12NK80Z
Manufacturer
STMicroelectronics
Type
Supervisory Circuitsr
Specifications of STEVAL-ISA033V1
Main Purpose
AC/DC, Primary Side
Outputs And Type
3, Isolated
Power - Output
55W
Voltage - Output
13.8V, 3.8V, 25V
Current - Output
3A, 350mA, 200mA
Voltage - Input
88 ~ 300VAC
Regulator Topology
Flyback
Board Type
Fully Populated
Utilized Ic / Part
L5991, STP12NK80Z
Input Voltage
88 V to 300 V
Output Voltage
3.8 V to 25 V
Product
Power Management Modules
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Frequency - Switching
-
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
For Use With/related Products
L5991, STP12NK80Z
Other names
497-8226
STEVAL-ISA033V1
STEVAL-ISA033V1
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
STEVAL-ISA033V1
Manufacturer:
STMicroelectronics
Quantity:
1
L5991 - L5991A
STANDBY FUNCTION
The standby function, optimized for flyback topol-
ogy, automatically detects a light load condition
for the converter and decreases the oscillator fre-
quency on that occurrence. The normal oscillation
frequency is automatically resumed when the out-
put load builds up and exceeds a defined thresh-
old.
This function allows to minimize power losses re-
lated to switching frequency, which represent the
majority of losses in a lightly loaded flyback, with-
out giving up the advantages of a higher switching
frequency at heavy load.
This is accomplished by monitoring the output of
the Error Amplifier (V
on the peak primary current, except for an offset.
If the the peak primary current decreases (as a re-
sult of a decrease of the power demanded by the
load) and V
(V
lower value (f
increases and V
(V
value (f
prevents undesired frequency change when
power is such that V
threshold. This operation is shown in fig. 21.
Both the normal and the standby frequency are
externally programmable. V
nally fixed but it is possible to adjust the thresh-
olds in terms of input power level.
APPLICATION INFORMATION
Detailed Pin Function Description
Pin 1. SYNC (In/Out Synchronization). This func-
tion allows the IC’s oscillator either to synchronize
other controllers (master) or to be synchronized to
an external frequency (slave).
As a master, the pin delivers positive pulses dur-
ing the falling edge of the oscillator (see pin 2). In
slave operation the circuit is edge triggered. Refer
to fig. 23 to see how it works. When several IC
work in parallel no master-slave designation is
needed because the fastest one becomes auto-
Figure 22. Synchronizing the L5991.
8/23
1
RCT
T1
T2
L5991
SYNC
), the oscillator frequency will be set to a
) the oscillator frequency is set to the normal
2
osc
16
4
R
ST-BY
B
). An appropriate hysteresis (V
VREF
(a)
R
COMP
C
A
SB
T
). When the peak primary current
COMP
falls below a fixed threshold
COMP
exceeds a second threshold
COMP
L5991
1
2
SYNC
RCT
) that depends linearly
T1
R
moves close to the
OSC
and V
(MASTER)
17
L4981A
18
16
T2
C
OSC
are inter-
SYNC
T2
(b)
-V
RCT
1
(SLAVE)
T1
L5991
ST-BY
2
)
16
4
Figure 21. Standby dynamic operation.
matically the master.
During the ramp-up of the oscillator the pin is
pulled low by a 600 A internal sink current gener-
ator. During the falling edge, that is when the
pulse is released, the 600 A pull-down is discon-
nected. The pin becomes a generator whose
source capability is typically 7mA (with a voltage
still higher than 3.5V).
In fig. 22, some practical examples of synchroniz-
ing the L5991 are given.
Since the device automatically diminishes its op-
erating frequency under light load conditions, it is
reasonable to suppose that synchronization will
refer to normal operation and not to standby.
Pin 2. RCT (Oscillator). Two resistors (R
and one capacitor (C
fig. 23, allow to set separately the operating fre-
quency of the oscillator in normal operation (f
and in standby mode (f
C
mal operation (STANDBY = HIGH), through R
only in standby ( STANDBY = LOW). See pin 16
description to see how the STANDBY signal is gen-
erated.
When the voltage on C
tor is quickly internally discharged. As the voltage
has dropped to 1V it starts being charged again.
P
P
VREF
NO
SB
T
R
C
is charged from Vref through R
A
T
Pin
1
R
B
RCT
C
T
D97IN728A
R
B
2
R
2
(MASTER)
16
A
L5991
ST-BY
4
T
V
VREF
VCOMP
SB
1
), connected as shown in
T 1
T
Normal operation
).
reaches 3V, the capaci-
SYNC
3
SYNC
(c)
Stand-by
A
and R
R
16 17
OSC
(SLAVE)
L4981A
V
A
T 2
B
and R
4
in nor-
18
f
f
C
osc
SB
osc
OSC
B
A
)
)