LT1336IS-PBF 查看數據表（PDF） - Linear Technology

零件编号

产品描述 (功能)

生产厂家

LT1336IS-PBF

Half-Bridge N-Channel Power MOSFET Driver with Boost Regulator

Linear Technology 

LT1336

Applications Information

Using the components as shown in Figure 2 the flyback

regulator will run at around 800kHz. To lower the frequency

CFILTER can be increased and to increase the frequency

CFILTER can be decreased.

D1

1N4148

T1*

24V 1000pF 6.2k

CFILTER

0.1µF

RSENSE

2Ω

1/4W ISENSE

SV+

PV+

1N4148

SWITCH

S

SWGND

BOOST

LT1336

TSOURCE

1:1

+

–VBOOST

TGATEDR

D2

1N4148

40V

+

CBOOST

1µF

HV =

60V MAX

+

TGATEFB

* COILTRONICS CTX100-1P

1336 F02

Figure 2. Using the Flyback Regulator

The flyback regulator works as follows: when switch S is

on, the primary current ramps up as the magnetic field

builds up. The magnetic field in the core induces a voltage

on the secondary winding equal to V+. However, no power

is transferred to VBOOST because the rectifier diode D2 is

reverse biased. The energy is stored in the transformer’s

magnetic field. When the primary inductor peak current

is reached, the switch is turned off. Energy is no longer

transferred to the transformer causing the magnetic field

to collapse. The collapsing magnetic field induces a change

in voltage across the transformer’s windings. During this

transition the Switch pin’s voltage flies to 10.6V plus a diode

above V+, the secondary forward biases the rectifier diode

D2 and the transformer’s energy is transferred to VBOOST.

Meanwhile the primary inductor current goes to zero and

the voltage at ISENSE decays to the lower inductor current

threshold with a time constant of (RSENSE)(CFILTER), thus

completing the cycle.

Power MOSFET Selection

Since the LT1336 inherently protects the top and bottom

MOSFETs from simultaneous conduction, there are no size

or matching constraints. Therefore, selection can be made

based on the operating voltage and RDS(ON) requirements.

The MOSFET BVDSS should be at least equal to the LT1336

absolute maximum operating voltage. For a maximum

operating HV supply of 60V, the MOSFET BVDSS should

be from 60V to 100V.

The MOSFET RDS(ON) is specified at TJ = 25°C and is gen-

erally chosen based on the operating efficiency required

as long as the maximum MOSFET junction temperature is

not exceeded. The dissipation in each MOSFET is given by:

( ) P = D IDS 2 (1+ ∂)RDS(ON)

where D is the duty cycle and ∂ is the increase in RDS(ON)

at the anticipated MOSFET junction temperature. From this

equation the required RDS(ON) can be derived:

( ) RDS(ON) = D

IDS

P

2 (1+ ∂)

For example, if the MOSFET loss is to be limited to 2W

when operating at 5A and a 90% duty cycle, the required

RDS(ON) would be 0.089Ω/(1 + ∂). (1 + ∂) is given for

each MOSFET in the form of a normalized RDS(ON) vs

temperature curve, but ∂ = 0.007/°C can be used as an

approximation for low voltage MOSFETs. Thus, if TA = 85°C

and the available heat sinking has a thermal resistance of

20°C/W, the MOSFET junction temperature will be 125°C

and ∂ = 0.007(125 – 25) = 0.7. This means that the required

RDS(ON) of the MOSFET will be 0.089Ω/1.7 = 0.0523Ω,

which can be satisfied by an IRFZ34 manufactured by

International Rectifier.

Transition losses result from the power dissipated in each

MOSFET during the time it is transitioning from off to on,

or from on to off. These losses are proportional to (f)(HV)2

and vary from insignificant to being a limiting factor on

operating frequency in some high voltage applications.

1336fa

12

Share Link: