MAX1747EUP Maxim Integrated Products, MAX1747EUP Datasheet - Page 11

• Manufacturer Part Number: MAX1747EUP
• Description: Charge Pumps
• Manufacturer: Maxim Integrated Products

Specifications of MAX1747EUP

• Function: Step Up, Step Down
• Output Voltage: 4.5 V to 5.5 V, +/- 35 V
• Output Current: 200 mA
• Maximum Operating Temperature: + 85 C
• Package / Case: TSSOP-20
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

in the Typical Operating Characteristics). The main out-
put voltage is controlled to be in regulation within 4096
clock cycles (1/f
power charge pumps are controlled to be in regulation
within 2048 clock cycles.
Upon power-up or exiting shutdown, the MAX1747
starts a power-up sequence. First, the reference pow-
ers up. Then the primary charge pump powers up with
soft-start enabled. Once the main charge pump reach-
es 90% of its nominal value (V
tive charge pump turns on. When the negative output
voltage reaches approximately 90% of its nominal value
(V
Finally, when the positive output voltage reaches 90%
of its nominal value (V
ready signal (RDY) goes low (see Power Ready).
Once RDY is low, and if any output falls below its fault
detection threshold, RDY goes high impedance.
For the reference, the fault threshold is 1.05V. For the
main charge pump, the fault threshold is 88% of its
nominal value (V
pump, the fault threshold is approximately 88% of its
nominal value (V
pump, the fault threshold is 88% of its nominal value
(V
Once an output faults, all outputs later in the power
sequence shut down until the faulted output rises
above its power-up threshold. For example, if the nega-
tive charge-pump output voltage falls below the fault-
detection threshold, the main charge pump remains
Figure 4. Positive Charge-Pump Block Diagram
FBN
FBP
< 1.1V).
OSC
< 125mV), the positive charge pump starts up.
MAX1747
GND
FBN
OSC
FB
V
1.25V
______________________________________________________________________________________
REF
< 1.1V). For the negative charge
> 140mV). For the positive charge
). The negative and positive low-
FBP
PGND
SUPP
DRVP
FBP
Power-Up Sequencing
> 1.125V), the active-low
FB
C3
V
V
POS
REF
R4
> 1.125V), the nega-
Fault Detection
= 1.25V
= [1 + (R3/R4)]
V
R3
SUPP
D2
D1
= 2.7V TO 13V
✕
Triple Charge-Pump TFT LCD
V
C4
V
REF
POS
active while the positive charge pump stops switching
and its output voltage decays, depending on output
capacitance and load. The positive charge-pump out-
put will not power up until the negative charge-pump
output voltage rises above its power-up threshold (see
Power-Up Sequencing).
Power ready is an open-drain output. When the power-
up sequence is properly completed, the MOSFET turns
on and pulls RDY low with a typical 125Ω R
is detected, the internal open-drain MOSFET appears
as a high impedance. Connect a 100kΩ pullup resistor
between RDY and IN for a logic level output.
The voltage at REF is nominally 1.25V. The reference
can source up to 50mA with excellent load regulation
(see Typical Operating Characteristics). Connect a
0.22µF bypass capacitor between REF and GND.
During shutdown, the reference is disabled.
The efficiency characteristics of the MAX1747 regulat-
ed charge pumps are similar to a linear regulator. They
are dominated by quiescent current at low output cur-
rents and by the input voltage at higher output currents
(see Typical Operating Characteristics). Therefore, the
maximum efficiency may be approximated by:
Figure 5. Frequency Adjustment
Efficiency ≅ V
charge pump
Efficiency ≅ - V
low-power charge pump
MAX1747
OSC
DC-DC Converter
OUT
NEG
/ (2
Efficiency Considerations
/ (V
✕
R
R
AND f
SHDN
SUPN
FREQ
FREQ
Design Procedure
GND
V
IN
SUPM
OSC
= k
IS IN kΩ, k
Voltage Reference
FREQ
IS IN MHz.
✕
) for the main
N) for the negative
✕
(V
FREQ
R
ON
FREQ
Power Ready
- 0.7V)/f
IS 45.5MHz/mA,
V
ON
ON
OSC
= V
. If a fault
C
IN
IN
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