MAX889SESA Maxim Integrated Products, MAX889SESA Datasheet - Page 7

• Manufacturer Part Number: MAX889SESA
• Description: Charge Pumps f-Reg 200mA Invert Charge Pump
• Manufacturer: Maxim Integrated Products

Specifications of MAX889SESA

• Function: Inverting
• Output Voltage: - 2.5 V to - 5.5 V
• Output Current: 200 mA
• Maximum Operating Temperature: + 85 C
• Package / Case: SOIC-8 Narrow
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT

Adjust the output voltage to a negative voltage from
-2.5V to -V
shown in Figures 1 and 4. FB servos to GND. Choose
R1 to be 100kΩ or less. Calculate R2 for the desired
output voltage:
where V
source.
Typically, choose a voltage-divider current of at least
30µA to minimize the effect of FB input current and
capacitance:
The appropriate capacitors used with the MAX889
depend on the switching frequency. Table 1 provides
suggested values for C
Surface-mount ceramic capacitors are preferred for
C
and low ESR. To ensure proper operation over the
entire temperature range, choose ceramic capacitors
with X7R (or equivalent) low-temperature-coefficient
(tempco) dielectrics. See Table 2 for a list of suggested
capacitor suppliers.
The output capacitor stores the charge transferred from
the flying capacitor and services the load between
oscillator cycles. A good general rule is to make the
output capacitance at least five-times greater than the
flying capacitor.
Output voltage ripple is largely dependent on C
Choosing a low-ESR capacitor of sufficient value is impor-
tant in minimizing the peak-to-peak output voltage ripple,
which is approximated by the following equation:
where C
the output capacitor’s ESR, and f
switching frequency. Ceramic capacitors have the lowest
ESR and are recommended for C
capacitance at low cost is desired, a low-ESR tantalum
capacitor may be used for C
suggested capacitor suppliers.
To ensure stability over the entire operating temperature
range, choose a low-ESR output capacitor using the fol-
lowing equation:
IN
, C
OUT
REF
OUT
, and C
IN
2 x I
V
can be either V
is the output capacitor value, ESR
RIPPLE
with external resistors R1 and R2 as
V
R2 = R1 (V
OUT
OUT
R2 < -V
FLY
_______________________________________________________________________________________
R1 ≤ V
=
ESR
= -V
due to their small size, low cost,
IN
2 x f
, C
COUT
REF
OUT
REF
OUT
FLY
OUT
OSC
I
IN
OUT
/ 30µA
Capacitor Selection
(R2 / R1)
/ 30µA
, and C
/ -V
. See Table 2 for a list of
or a positive reference
C
OUT
REF
OSC
OUT
)
OUT
is the MAX889
. Where larger
+
200mA, Inverting Charge Pump
.
COUT
High-Frequency, Regulated,
OUT
is
.
where C
minimum oscillator frequency in the Electrical
Characteristics table.
To ensure stability for regulated output mode, suitable
output capacitor ESR should be determined by the follow-
ing equation:
The power dissipated in the MAX889 depends on the
input voltage, output voltage, and output current. Device
power dissipation is accurately described by:
where I
less than the package dissipation rating (see Absolute
Maximum Ratings). Pay particular attention to power dis-
sipation limits when generating small negative voltages
from large positive input voltages.
The MAX889’s high oscillator frequencies demand
good layout techniques that ensure stability and help
maintain the output voltage under heavy loads. Take
the following steps to ensure optimum layout:
1) Mount all components as close together as possible.
2) Place the feedback resistors R1 and R2 close to the
3) Keep traces short to minimize parasitic inductance
4) Use a ground plane with C
FB pin, and minimize the PC trace length at the FB
circuit node.
and capacitance.
star ground configuration (see the MAX889SEVKIT
layout).
C
R
ESR
OUT
Q
OUT
is the device quiescent current. P
P
≤
≥
DISS
is the output capacitor value, and f

 




19.2 x 10
15.5
f
MIN
= I
I
OUT
OUT






R1 + R2
-3
(V
R1

 

IN
Layout Considerations



- (-V
1
IN
+



and C
OUT
Power Dissipation
R2
R1
I
OUT
)) + (I



OUT
Q
placed in a
DISS
✕
V
MIN
IN
must be
)
is the
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