MAX5073 View Datasheet(PDF) - Maxim Integrated
Part Name
Description
Manufacturer
MAX5073 Datasheet PDF : 25 Pages
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2.2MHz, Dual-Output Buck or Boost Converter
with Internal Power MOSFETs
Input Capacitor
The input current for the boost converter is continuous
and the RMS ripple current at the input is low. Calculate
the capacitor value and ESR of the input capacitor
using the following equations.
CIN
=
4
∆IL × D
× fSW × ∆VQ
ESR = ∆VESR
∆IL
where
∆IL
=
(VIN − VDS ) ×
L × fSW
D
where VDS is the total voltage drop across the internal
MOSFET plus the voltage drop across the inductor
ESR. ∆IL is the peak-to-peak inductor ripple current as
calculated above. ∆VQ is the portion of input ripple due
to the capacitor discharge and ∆VESR is the contribu-
tion due to ESR of the capacitor.
Output Capacitor
For the boost converter, the output capacitor supplies
the load current when the main switch is ON. The
required output capacitance is high, especially at high-
er duty cycles. Also, the output capacitor ESR needs to
be low enough to minimize the voltage drop due to the
ESR while supporting the load current. Use the follow-
ing equation to calculate the output capacitor for a
specified output ripple tolerance.
ESR = ∆VESR
IO
COUT
=
IO ×
∆VQ
DMAX
× fSW
IO is the load current, ∆VQ is the portion of the ripple
due to the capacitor discharge and ∆VESR is the contri-
bution due to the ESR of the capacitor. DMAX is the
maximum duty cycle at minimum input voltage.
Power Dissipation
The MAX5073 includes a high-frequency, low RDS_ON
switching MOSFET. At +85°C, the RDS_ON of the inter-
nal switch for converter 1 and converter 2 are 290mΩ
and 630mΩ, respectively. The DC loss is a function of
the RMS current in the switch while the switching loss is
a function of switching frequency and input voltage. Use
the following equations to calculate the RMS current,
DC loss, and switching loss of each converter. The
MAX5073 device is available in a thermally enhanced
package and can dissipate up to 2.7W at +70°C ambient
temperature. The total power dissipation in the package
must be limited so the junction temperature does
not exceed its absolute maximum rating of +150°C at
maximum ambient temperature.
For the buck converter:
IRMS =
(I2DC
+I2PK
+
(IDC
×
IPK ))
×
DMAX
3
PDC = I2RMS × RDS(ON)MAX
where
IDC
= IO
−
∆IL
2
IPK
= IO
+
∆IL
2
See the Electrical Characteristics table for the
RDS(ON)MAX value.
PSW = VINMAX × IO × (tR + tF) × fSW
4
For the boost converter:
IRMS =
(I2DC
+I2PK
+
(IDC
×
IPK
))
×
DMAX
3
IIN
=
VO × IO
VIN × η
∆IL
=
(VIN − VDS )
L × fSW
×
D
IDC
=
IIN
−
∆IL
2
IPK
=
IIN
+
∆IL
2
18 ______________________________________________________________________________________
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