L6591 STMicroelectronics, L6591 Datasheet - Page 32

• Manufacturer Part Number: L6591
• Description: IC CTRLR PWM PROG CM HV 16SOIC
• Manufacturer: STMicroelectronics

Specifications of L6591

• Output Isolation: Isolated
• Frequency Range: 168 ~ 192kHz
• Voltage - Input: 8.7 ~ 22 V
• Power (watts): 750mW
• Operating Temperature: -40°C ~ 150°C
• Package / Case: 16-SOIC (0.154", 3.90mm Width)
• Output Voltage: 5 V
• Input Voltage: 25 V
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: SMD/SMT
• Duty Cycle (max): 50 %
• For Use With: 497-8335 - BOARD EVAL FOR L6591
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-8286

Application information
6.9
32/41
Equation 6
Which, solved for R
Equation 7
While the line undervoltage is active the start-up generator keeps on working but there is no
PWM activity, thus the Vcc voltage continuously oscillates between the start-up and the
UVLO thresholds, as shown in the timing diagram of
The LINE pin, while the device is operating, is a high impedance input connected to high
value resistors, thus it is prone to pick up noise, which might alter the OFF threshold or give
origin to undesired switch-off of the IC during ESD tests. It is possible to bypass the pin to
ground with a small film capacitor (e.g. 1-10 nF) to prevent any malfunctioning of this kind.
Tie to Vcc (#9) with a 220 to 330 kΩ resistor if the function is not used.
Soft-start and delayed latched shutdown upon overcurrent
At device start-up, a capacitor (Css) connected between the SS pin (#4) and ground is
charged by an internal current generator, I
clamped. During this ramp, the overcurrent setpoint progressively raises from zero the final
value (0.8 V). The time needed for the overcurrent setpoint to reach its steady state value,
referred to as soft-start time, is approximately:
Equation 8
During the ramp, the MOSFET duty cycle increases progressively, hence controlling the
start-up inrush current. Furthermore, all the functions that monitor the voltage on pin COMP
are disabled.
The soft-start pin is also invoked whenever the control voltage (COMP) saturates high,
which reveals an open-loop condition for the feedback system. This condition very often
occurs at start-up, but may be also caused by either a control loop failure or a converter
overload/short circuit.
Vin
H
ON
R
R
and R
H
−
H
. 1
=
25
Vin
L
, yield:
=
15
ON
Doc ID 14821 Rev 5
15
⋅
−
10
⋅
10
Vin
−
6
−
6
OFF
T
SS
+
. 1
SS1
;
R
=
25
L
0
, from zero up to about 2 V where it is
8 .
R
C
I
SS
L
SS
=
1
Figure 52
R
Vin
H
Vin
OFF
R
OFF
. 1
H
−
.
25
. 1
−
25
. 1
25
=
. 1
R
25
L
L6591