MAX662A データシートの表示（PDF） - Maxim Integrated

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MAX662A

+12V, 30mA Flash Memory Programming Supply

Maxim Integrated 

+12V, 30mA Flash Memory

Programming Supply

_______________Detailed Description

Operating Principle

The MAX662A provides a regulated 12V output voltage

at 30mA from a 5V ±5% power supply, making it ideal

for flash EEPROM programming applications. It uses

internal charge pumps and external capacitors to gen-

erate +12V, eliminating inductors. Regulation is provid-

ed by a pulse-skipping scheme that monitors the

output voltage level and turns on the charge pumps

when the output voltage begins to droop.

Figure 1 shows a simplified block diagram of the

MAX662A. When the S1 switches are closed and the

S2 switches are open, capacitors C1 and C2 are

charged up to VCC. The S1 switches are then opened

and the S2 switches are closed so that capacitors C1

and C2 are connected in series between VCC and

VOUT. This performs a voltage tripling function. A pulse-

skipping feedback scheme adjusts the output voltage

to 12V ±5%. The efficiency of the MAX662A with VCC =

5V and IOUT = 30mA is typically 76%. See the

Efficiency vs. Load Current graph in the Typical

Operating Characteristics.

During one oscillator cycle, energy is transferred from

the charge-pump capacitors to the output filter capaci-

tor and the load. The number of cycles within a given

time frame increases as the load current increases or

as the input supply voltage decreases. In the limiting

case, the charge pumps operate continuously, and the

oscillator frequency is nominally 500kHz.

5V

0V

12V

5V

200µs/div

CIRCUIT OF FIGURE 3, VCC = 5V, IOUT = 200µA

Figure 2. MAX662A Exiting Shutdown

SHDN

VOUT

Shutdown Mode

The MAX662A enters shutdown mode when SHDN is a

logic high. SHDN is a TTL/CMOS-compatible input sig-

nal that is internally pulled up to VCC. In shutdown

mode, the charge-pump switching action is halted and

VIN is connected to VOUT through a 1kΩ switch. When

entering shutdown, VOUT declines to VCC in typically

13ms. Connect SHDN to ground for normal operation.

When VCC = 5V, it takes typically 400µs for the output

to reach 12V after SHDN goes low (Figure 2).

__________Applications Information

Compatibility with MAX662

The MAX662A is a 100%-compatible upgrade of the

MAX662. The MAX662A does not require capacitor C3,

although its presence does not affect performance.

Capacitor Selection

Charge-Pump Capacitors, C1 and C2

The capacitance values of the charge-pump capacitors

C1 and C2 are critical. Use ceramic or tantalum capaci-

tors in the 0.22µF to 1.0µF range. For applications requir-

ing operation over extended and/or military temperature

ranges, use 1.0µF tantalum capacitors for C1 and C2

(Figure 3b).

Input and Output Capacitors, C4 and C5

The type of input bypass capacitor (C4) and output filter

capacitor (C5) affects performance. Tantalums, ceramics

or aluminum electrolytics are suggested. For smallest size,

use Sprague 595D475X9016A7 surface-mount capacitors,

which are 3.51mm x 1.81mm. For lowest ripple, use low-

ESR through-hole ceramic or tantalum capacitors. For low-

est cost, use aluminum electrolytic or tantalum capacitors.

Figure 3a shows the component values for proper opera-

tion over the commercial temperature range using mini-

mum board space. The input bypass capacitor (C4) and

output filter capacitor (C5) should both be at least 4.7µF

when using Sprague’s miniature 595D series of tantalum

chip capacitors. Figure 3b shows the suggested compo-

nent values for applications over extended and/or mili-

tary temperature ranges.

The values of C4 and C5 can be reduced to 2µF and

1µF, respectively, when using ceramic capacitors. If

using aluminum electrolytics, choose capacitance values

of 10µF or larger for C4 and C5. Note that as VCC

increases above 5V and the output current decreases,

the amount of ripple at VOUT increases due to the slower

oscillator frequency combined with the higher input volt-

age. Increase the input and output bypass capacitance

to reduce output ripple.

Table 1 lists various capacitor suppliers.

4 _______________________________________________________________________________________

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