Datasheet

0.9
1.0
1.10
45
50
55
SOFT-START CURRENT (PA)
TEMPERATURE (
o
C)
-50 0 50 100 150
|
|
490
492
494
496
498
500
502
504
506
508
510
CURRENT LIMIT THRESHOLD
@
CS1, CS2
(
mV
)
-50 0 50 100 150
TEMPERATURE (
o
C)
LM5034
SNVS347A –FEBRUARY 2005–REVISED APRIL 2013 www.ti.com
Typical Performance Characteristics (continued)
Soft-start Pin Current vs. Temperature Current Limit Threshold at CS1, CS2 vs. Temperature
Figure 18. Figure 19.
FUNCTIONAL DESCRIPTION
The LM5034 contains all the features necessary to implement two independently regulated current mode dc/dc
converters, or a single high current converter comprised of two parallel interleaved channels using the Forward/
Active Clamp topology. The two controllers operate 180° out of phase from a common oscillator, thereby
reducing input ripple current. Each regulator channel contains a complete PWM controller, current sense input,
soft-start circuit, main gate driver output, and active clamp driver output. Common to both channels are the
startup and V
CC
regulators, line under-voltage lockout, 2 MHz capable oscillator, maximum duty cycle control,
overlap time setting, and the hiccup mode fault protection circuit.
The main gate driver outputs (OUT1, OUT2) are designed to drive N-channel MOSFETs. Their compound
configuration reduces the turn-off-time, thereby reducing switching losses. The active clamp outputs (AC1, AC2)
are designed to drive P-channel MOSFETs. The adjustable overlap time of the active clamp outputs relative to
the main outputs produces a deadtime between the main switch and the P-channel active clamp switch.
Additional features include thermal shutdown, slope compensation, and the oscillator synchronization capability.
Line Under-Voltage Lock Out, UVLO, Shutdown
The LM5034 contains a line under-voltage lockout circuit (UVLO) designed to enable the V
CC
regulator and
output drivers when the system voltage (V
PWR
) exceeds the desired level (see Figure 20). V
PWR
is the voltage
normally applied to the transformer primary, and usually connected to the VIN pin (see the schematic on Page
1). The threshold at the UVLO comparator is 1.25V. An external resistor divider connected from V
PWR
to ground
provides 1.25V at the UVLO pin when V
PWR
is increased to the desired turn-on threshold. When V
PWR
is below
the threshold the V
CC
regulator and output drivers are disabled, and the internal 20 µA current source is off.
When V
PWR
reaches the threshold, the comparator output switches low to enable the internal circuits and the 20
µA current source. The 20 µA flows into the external divider’s junction, raising the voltage at UVLO, thereby
providing hysteresis. Internally the voltage at UVLO also drives the Maximum Duty Cycle Limiter circuit
(described below), which may influence the values chosen for the UVLO pin resistors. At maximum V
PWR
, the
voltage at UVLO should not exceed 6V. Refer to Applications Information for a procedure to calculate the
resistors values.
The LM5034 controllers can be shutdown by forcing the UVLO pin below 1.25V with an external switch. When
the UVLO pin is low, the outputs and the V
CC
regulator are disabled, and the LM5034 enters a low power mode.
If the VCC pins are not powered from an external source, the current into VIN drops to a nominal 500 µA. If the
VCC pins are powered from an external source, the current into VIN is nominally 50 µA, and the current into the
VCC pins is approximately 4.3 mA. To disable one regulator without affecting the other, see the description of the
Soft-start section.
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