MAX8758ETG+T Maxim Integrated Products, MAX8758ETG+T Datasheet - Page 17

• Manufacturer Part Number: MAX8758ETG+T
• Description: IC REG STEP UP 24-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8758ETG+T

• Applications: Converter, TFT, LCD
• Voltage - Input: 1.8 ~ 5.5 V
• Number Of Outputs: 1
• Voltage - Output: 5V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The input capacitor reduces the current peaks drawn
from the input supply and reduces noise injection into
the IC. Two 10µF ceramic capacitors are used in the
Typical Applications Circuit (Figure 1) because of the
high source impedance seen in typical lab setups.
Actual applications usually have much lower source
impedance since the step-up regulator often runs
directly from the output of another regulated supply.
Typically, the input capacitance can be reduced below
the values used in the Typical Applications Circuit.
The MAX8758’s high switching frequency demands a
high-speed rectifier. Schottky diodes are recommend-
ed for most applications because of their fast recovery
time and low forward voltage. In general, a 2A Schottky
diode complements the internal MOSFET well.
The output voltage of the step-up regulator can be
adjusted by connecting a resistive voltage-divider from
the output (V
ed to FB (see Figure 1). Select R2 in the 10kΩ to 50kΩ
range. Calculate R1 with the following equation:
where V
is 1.25V. Place R1 and R2 close to the IC.
Choose R
cy integrator gain for fast transient response. Choose
C
maintain loop stability.
For low-ESR output capacitors, use the following equa-
tions to obtain stable performance and good transient
response:
To further optimize transient response, vary R
20% steps and C
transient-response waveforms.
COMP
R
C
COMP
Step-Up Regulator Input Capacitor Selection
FB
(C7 in Figure 1) to set the integrator zero to
Step-Up Regulator Output Voltage Selection
COMP
COMP
, the step-up regulator’s feedback set point,
OUT
Step-Up Regulator Loop Compensation
R
≈
1
(R3 in Figure 1) to set the high-frequen-
≈
) to GND with the center tap connect-
COMP
______________________________________________________________________________________
315
=
10
Step-Up Regulator Rectifier Diode
R
Step-Up Regulator with Switch Control
2
×
×
and Operational Amplifier for TFT LCD
×
in 50% steps while observing
V
I
V
MAIN MAX
L
MAIN
IN



×
V
MAIN
V
×
(
I
FB
MAIN MAX
×
V
MAIN
C
)
(
−
MAIN
×
1



R
×
)
COMP
C
MAIN
COMP
in
Place C
add an additional high-frequency pole. UseC
between 10pF and 47pF.
The soft-start capacitor should be large enough that it
does not reach final value before the output has
reached regulation. Calculate the soft-start capacitor
(C
where C
the maximum output voltage, and I
inrush current allowed, I
current, and V
The load must wait for the soft-start cycle to finish
before drawing a significant amount of load current.
The duration after which the load can begin to draw
maximum load current is:
For highest efficiency, always choose the lowest num-
ber of charge-pump stages that meet the output volt-
age requirement.
The number of positive charge-pump stages is given by:
where n
stages, V
V
the forward voltage drop of the charge-pump diode.
The number of negative charge-pump stages is given by:
where n
stages, V
V
the forward voltage drop of the charge-pump diode.
MAIN
MAIN
SS
C
) value using:
SS
Selecting the Number of Charge-Pump Stages
is the main step-up regulator output, and V
is the main step-up regulator output, and V
COMP2
NEG
MAIN
POS
=
GOFF
GON
21
n
×
n
is the number of positive-charge-pump
is the number of negative-charge-pump
Step-Up Regulator Soft-Start Capacitor
IN
is the total output capacitance, V
NEG
POS



(C8 in Figure 1) from COMP to GND to
×
t
is the positive-charge-pump output,
is the negative charge-pump output,
MAX
is the minimum input voltage.
V
IN
10
=
=
−
×
= 6.77 x 10
V
6
2
I
V
V
MAIN
INRUSH
×
V
MAIN
MAIN
MAIN
GON
C
MAIN
−
V
−
−
GOFF
−
−
is the maximum output
−
V
5
2
IN
2
x C
V
I
MAIN
MAIN
×
×
INRUSH
×
Charge Pumps
SS
V
V
V
D
D
MAIN
×
V
is the peak
MAIN
MAIN
COMP2



D
D
17
is
is
is