LTC3428 Datasheet, PDF (8/12 Pages) Linear Technology – 4A, 2MHz Dual Phase Step-Up DC/DC Converter in 3mm 3mm DFN

LTC3428
APPLICATIO S I FOR ATIO
Table 2. Capacitor Vendor Information
Supplier Phone
Fax
Website
AVX
[phone] [phone] www.avxcorp.com
Sanyo
[phone] [phone] www.sanyovideo.com
TDK
[phone] [phone] www.component.tdk.com
Murata
[phone] [phone] www.murata.com
Taiyo Yuden [phone] [phone] www.t-yuden.com
Output Diode Selection
For high efficiency, a fast switching diode with low reverse
leakage and a low forward drop is required. Schottky diodes
are recommended for their low forward drop and fast
switching times. When selecting a diode, it is important to
remember that the average diode current in a boost
converter is equal to the average load current: I_D = I_LOAD
When selecting a diode, make sure that the peak
forward current and average power dissipation ratings
meet the application requirements. See Table 3 for a list
of Schottky diode manufacturers. Example diodes are
Philips PMEG1020, PMEG2010, On-Semi MBRA210, IR
10BQ015, Microsemi UPS120E, UPS315.
Table 3. Diode Vendor Information
Supplier Phone
Philips
[phone]
Microsemi [phone]
On-Semi [phone]
International [phone]
Rectifier
Fax
[phone]
[phone]
Website
www.philips.com
www.microsemi.com
www.onsemi.com
www.irf.com
Thermal Considerations
To deliver maximum power, it is necessary to provide a
good thermal path to dissipate the heat generated within
the LTC3428’s package. The large thermal pad on the IC
underside can accomplish this requirement. Use multiple
PC board vias to conduct heat from the IC and to a copper
plane that has as much area as possible.
If the junction temperature gets too high, the LTC3428 will
stop all switching until the junction temperature drops to
safe levels. The typical over temperature threshold is
150°C.
Closing the Feedback Loop
The LTC3428 uses current mode control with internal,
adaptive slope compensation. Current mode control elimi-
nates the 2nd order pole in the loop response of voltage
mode converters due to the inductor and output capacitor,
simplifying it to a single pole response. The product of the
modulator control to output DC gain and the error amp
open-loop gain equals the DC gain of the system.
G_DC
=
G_CONTROL
• G _EA
•
V_REF
V_OUT
G_CONTROL
=
2 • V_IN
I_OUT
G_EA ≈ 100
The output filter pole is given by:
f_POLE
=
π
I_OUT
• V_OUT • C_OUT
Hz
where C_OUT is the output filter capacitor value. The output
filter zero is given by:
f_ZERO
=
2•
π
1
• R_ESR
• C_OUT
Hz
where R_ESR is the output capacitor equivalent series
resistance.
A complication of the boost converter topology is the right
half plane (RHP) zero and is given by:
f_RHP =
V_IN2 •R_{O Hz}
2
2 • π • L • V_O
3428f
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