MAX8614AETD+T Maxim Integrated Products, MAX8614AETD+T Datasheet - Page 11

• Manufacturer Part Number: MAX8614AETD+T
• Description: IC DC-DC CONV DL CCD 14TDFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8614AETD+T

• Applications: Converter, CCD
• Voltage - Input: 2.7 ~ 5.5 V
• Number Of Outputs: 2
• Voltage - Output: Adjustable up to 24V, Adjustable down to -10V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 14-TDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

the inverter output, load disconnect is implemented by
turning off the inverter’s internal power switch.
The MAX8614B allows an inductor current limit of 0.8A
on the step-up converter and 0.75A on the inverter. The
MAX8614A allows an inductor current limit of 0.44A on
the step-up converter and 0.33A on the inverter. This
allows flexibility in designing for higher load-current
applications or for smaller, more compact designs when
less power is needed. Note that the currents listed
above are peak inductor currents and not output cur-
rents. The MAX8614B output current is 50mA at +15V
and 100mA at -7.5V. The MAX8614A output current is
25mA at +15V and 50mA at -7.5V.
The MAX8614A/MAX8614B match the load regulation to
the voltage droop seen during load transients. This is
sometimes called voltage positioning. This results in mini-
mal overshoot when a load is removed and minimal volt-
age drop during a transition from light load to full load.
The use of voltage positioning allows superior load-tran-
sient response by minimizing the amplitude of overshoot
and undershoot in response to load transients. DC-DC
converters with high control-loop gains maintain tight
DC load regulation but still allow large voltage drops of
5% or greater for several hundred microseconds during
transients. Load-transient variations are seen only with
an oscilloscope (see the Typical Operating
Characteristics). Since DC load regulation is read with a
voltmeter, it does not show how the power supply reacts
to load transients.
The positive output voltage is set by connecting FBP to
a resistive voltage-divider between the output and GND
(Figure 1). Select feedback resistor R2 in the 30kΩ to
100kΩ range. R1 is then given by:
where V
The negative output voltage is set by connecting FBN
to a resistive voltage-divider between the output and
REF (Figure 1). Select feedback resistor R4 in the 30kΩ
to 100kΩ range. R3 is then given by:
FBP
Load Transient/Voltage Positioning
= 1.01V.
Applications Information
R
______________________________________________________________________________________
1
=
Adjustable Output Voltage
R
2



V
V
BST
FBP
Current-Limit Select
−
1



Dual-Output (+ and -) DC-DC
where V
The MAX8614A/MAX8614B high switching frequency
allows for the use of a small inductor. The 4.7µH and
2.2µH inductors shown in the Typical Operating Circuit is
recommended for most applications. Larger inductances
reduce the peak inductor current, but may result in skip-
ping pulses at light loads. Smaller inductances require
less board space, but may cause greater peak current
due to current-sense comparator propagation delay.
Use inductors with a ferrite core or equivalent. Powder
iron cores are not recommended for use with high
switching frequencies. The inductor’s incremental satura-
tion rating must exceed the selected current limit. For
highest efficiency, use inductors with a low DC resistance
(under 200mΩ); however, for smallest circuit size, higher
resistance is acceptable. See Table 1 for a representa-
tive list of inductors and Table 2 for component suppliers.
The MAX8614A/MAX8614B high switching frequency
demands a high-speed rectifier. Schottky diodes, such
as the CMHSH5-2L or MBR0530L, are recommended.
Make sure that the diode’s peak current rating exceeds
the selected current limit, and that its breakdown volt-
age exceeds the output voltage. Schottky diodes are
preferred due to their low forward voltage. However,
ultrahigh-speed silicon rectifiers are also acceptable.
Table 2 lists component suppliers.
The primary criterion for selecting the output filter
capacitor is low effective series resistance (ESR). The
product of the peak inductor current and the output fil-
ter capacitor’s ESR determines the amplitude of the
high-frequency ripple seen on the output voltage.
These requirements can be balanced by appropriate
selection of the current limit.
For stability, the positive output filter capacitor, C1,
should satisfy the following:
where R
D+ is 1 minus the step-up switch duty cycle and is:
CS
REF
Converters for CCD
C1 > (6L I
= 0.015 (MAX8614B), and 0.035 (MAX8614A).
= 1.25V and V
R
3
=
BSTMAX
D+ = V
R
4
×



FBN
CC
V
V
) / ( R
REF
FBN
Capacitor Selection
/ V
= 0V.
Output Filter Capacitor
Inductor Selection
−
−
CS
BST
V
V
FBN
IMV
Diode Selection
D+ V



BST
2
)
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