L6591 STMicroelectronics, L6591 Datasheet - Page 30

• 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
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Figure 48. Oscillator waveforms and their relationship with gate-driving signals
Adaptive UVLO
A major problem when optimizing a converter for minimum no-load consumption is that the
voltage generated by the self-supply system under these conditions falls considerably as
compared even to a few mA load. This very often causes the IC's supply voltage Vcc to drop
and go below the UVLO threshold of the controller so that the operation becomes
intermittent, which is undesired. A low UVLO threshold would be helpful but it could be an
issue to drive the MOSFETS with a sufficient gate-drive voltage at heavy load during power
off.
To help the designer overcome this problem, the L6591, besides reducing its own
consumption during burst-mode operation, also features a proprietary adaptive UVLO
function. It consists of shifting the UVLO threshold downwards at light load, namely when
the voltage at pin COMP falls below a threshold V
more headroom. To prevent any malfunctioning during transients from minimum to
maximum load the normal (higher) UVLO threshold is re-established when the voltage at pin
COMP exceeds V
UVLO threshold (see
load conditions the MOSFETS will be driven with an appropriate gate voltage.
Figure 49. Adaptive UVLO block
COMP
(*) V
7
V
COMPL
CC OF F2
-
+
< V
Clock
OSC
HVG
LVG
PFC _STOP
CC OFF1
PFC_ ST OP
COMPL
logic
8
is selected when Q is high
Figure 51
R
S
(with some mV hysteresis) and Vcc has exceeded the normal
V
CC OFF1
Q
+
-
Doc ID 14821 Rev 5
). The normal UVLO threshold ensures that under heavy
T
d
V
S W
CC OFF2
Vcc
9
+
(*)
-
UVLO
T
L6591
on
COMPL
T
sw
(*) V
V
VCOMP
V
V
CC OF F1
CC OF F2
COMPO
COMPL
T
internally fixed, so as to provide
Vcc
d
Q
T
d
t
t
t
t
L6591
t
t
t