LT3433IFE Linear Technology, LT3433IFE Datasheet - Page 10

• Manufacturer Part Number: LT3433IFE
• Description: IC CONV DC/DC 200KHZ SW 16-TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost)r

Specifications of LT3433IFE

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 3.3 ~ 20 V
• Current - Output: 500mA
• Frequency - Switching: 200kHz
• Voltage - Input: 4 ~ 60 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

LT3433
APPLICATIO S I FOR ATIO
The requirement for avoiding current mode instability is
that the rising slope of sensed inductor ripple current (S1)
is greater than the falling slope (S2). At duty cycles greater
than 50% this is not true. To avoid the instability condition,
a false signal is added to the sensed current with a slope
(S
or S1 + S
If the forward voltages of a converter’s catch and pass
diodes are defined as V
Solving for L yields a relation for the minimum inductance
that will satisfy slope compensation requirements:
The LT3433 maximizes available dynamic range using a
slope compensation generator that generates a continu-
ously increasing slope as duty cycle increases. The slope
compensation waveform is calibrated at 80% duty cycle to
generate an equivalent slope of at least 0.05A/ s. The
equation for minimum inductance then reduces to:
For example, with V
(cold):
10
X
S
S2 = (V
L
L
L
) that is sufficient to prevent current mode instability,
MIN
MIN
MIN
X
S2(2DC – 1)/DC
= (V
= (V
= (5 + 1.1)(15e-6) = 91.5 H
X
Typical Minimum Inductor Values vs V
350
250
200
100
300
150
OUT
50
OUT
OUT
Slope Compensation Requirements
4
S2. This leads to the following relations:
+ V
+ V
+ V
6
F1
U
F1
F1
OUT
+ V
8
+ V
+ V
F1
10
F2
= 5V and using V
V
F2
)/L
F2
U
and V
OUT
12
)(15e-6)
)(2DC – 1)/(DC • S
(V)
14
F2
, then:
16
W
18
3433 AI01
F1
20
OUT
+ V
U
X
)
F2
= 1.1V
Converter Capabilities
The output current capability of an LT3433 converter is
affected by a myriad of variables. The current in the
switches is limited by the LT3433. Switch current is
measured coming from the V
directly translate to a limitation in load current. This is
especially true during bridged mode operation when the
converter output current is discontinuous.
During bridged mode operation, the converter output
current is discontinuous, or only flowing to the output
while the switches are off (not to be confused with discon-
tinuous switcher operation). As a result, the maximum
output current capability of the converter is reduced from
that during buck mode operation by a factor of roughly
1 – DC, not including additional losses. Most converter
losses are also a function of DC, so operational duty cycle
must be accurately determined to predict converter load
capabilities.
Application variables:
V
V
V
DC = Operational duty cycle
f
I
I
less half the ripple current (I
R
R
L = Inductor value
O
MAX
SW
IN
OUT
BST
I
SWH
SWL
L
= Switching frequency
= Converter input supply voltage
= Inductor ripple current
= Average switch current or peak switch current
= Peak switch current limit
= Boosted supply voltage (V
= Converter programmed output voltage
= Grounded switch “on” resistance
= Boosted switch “on” resistance
LT3433
SW_H
SW_L
V
IN
L
D2
MAX
IN
supply, and does not
– I
3433 AI02
BST
V
D1
OUT
L
– V
/2)
SWH
)
3433f