LTC1628IG Linear Technology, LTC1628IG Datasheet - Page 17

• Manufacturer Part Number: LTC1628IG
• Description: IC SW REG STEP-DOWN 28-SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1628IG

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: Adj to 0.8V
• Current - Output: 3A
• Frequency - Switching: 220kHz
• Voltage - Input: 3.5 ~ 30 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Other names: Q1109473

APPLICATIO S I FOR ATIO
Manufacturers such as Nichicon, United Chemicon and
Sanyo can be considered for high performance through-
hole capacitors. The OS-CON semiconductor dielectric
capacitor available from Sanyo has the lowest (ESR)(size)
product of any aluminum electrolytic at a somewhat
higher price. An additional ceramic capacitor in parallel
with OS-CON capacitors is recommended to reduce the
inductance effects.
In surface mount applications multiple capacitors may
need to be used in parallel to meet the ESR, RMS current
handling and load step requirements of the application.
Aluminum electrolytic, dry tantalum and special polymer
capacitors are available in surface mount packages. Spe-
cial polymer surface mount capacitors offer very low ESR
but have lower storage capacity per unit volume than other
capacitor types. These capacitors offer a very cost-effec-
tive output capacitor solution and are an ideal choice when
combined with a controller having high loop bandwidth.
Tantalum capacitors offer the highest capacitance density
and are often used as output capacitors for switching
regulators having controlled soft-start. Several excellent
surge-tested choices are the AVX TPS, AVX TPSV or the
KEMET T510 series of surface mount tantalums, available
in case heights ranging from 2mm to 4mm. Aluminum
electrolytic capacitors can be used in cost-driven applica-
tions providing that consideration is given to ripple current
ratings, temperature and long term reliability. A typical
application will require several to many aluminum electro-
lytic capacitors in parallel. A combination of the above
mentioned capacitors will often result in maximizing per-
formance and minimizing overall cost. Other capacitor
types include Nichicon PL series, NEC Neocap, Pansonic
SP and Sprague 595D series. Consult manufacturers for
other specific recommendations.
INTV
An internal P-channel low dropout regulator produces 5V
at the INTV
the drivers and internal circuitry within the LTC1628. The
INTV
and must be bypassed to ground with a minimum of
4.7 F tantalum, 10 F special polymer, or low ESR type
electrolytic capacitor. A 1 F ceramic capacitor placed
directly adjacent to the INTV
CC
CC
Regulator
pin regulator can supply a peak current of 50mA
CC
pin from the V
U
U
IN
CC
supply pin. INTV
and PGND IC pins is highly
W
U
CC
powers
recommended. Good bypassing is necessary to supply
the high transient currents required by the MOSFET gate
drivers and to prevent interaction between channels.
Higher input voltage applications in which large MOSFETs
are being driven at high frequencies may cause the maxi-
mum junction temperature rating for the LTC1628 to be
exceeded. The system supply current is normally domi-
nated by the gate charge current. Additional external
loading of the INTV
needs to be taken into account for the power dissipation
calculations. The total INTV
either the 5V internal linear regulator or by the EXTV
input pin. When the voltage applied to the EXTV
less than 4.7V, all of the INTV
internal 5V linear regulator. Power dissipation for the IC in
this case is highest: (V
is lowered. The gate charge current is dependent on
operating frequency as discussed in the Efficiency Consid-
erations section. The junction temperature can be esti-
mated by using the equations given in Note 2 of the
Electrical Characteristics. For example, the LTC1628 V
current is limited to less than 24mA from a 24V supply
when not using the EXTV
Use of the EXTV
ture to:
Dissipation should be calculated to also include any added
current drawn from the internal 3.3V linear regulator. To
prevent maximum junction temperature from being ex-
ceeded, the input supply current must be checked operat-
ing in continuous mode at maximum V
EXTV
The LTC1628 contains an internal P-channel MOSFET
switch connected between the EXTV
When the voltage applied to EXTV
internal regulator is turned off and the switch closes,
connecting the EXTV
supplying internal power. The switch remains closed as
long as the voltage applied to EXTV
This allows the MOSFET driver and control power to be
T
T
J
J
CC
= 70 C + (24mA)(24V)(95 C/W) = 125 C
= 70 C + (24mA)(5V)(95 C/W) = 81 C
Connection
LTC1628/LTC1628-PG
CC
input pin reduces the junction tempera-
CC
CC
IN
and 3.3V linear regulators also
)(I
pin to the INTV
CC
INTVCC
CC
pin as follows:
CC
current can be supplied by
current is supplied by the
), and overall efficiency
CC
CC
rises above 4.7V, the
CC
remains above 4.5V.
IN
and INTV
.
CC
pin thereby
CC
CC
17
pin is
pins.
1628fb
CC
IN