Ω.

at 4.75V.

Ω, or approximately 8.2kΩ.

Input Noise Considerations

Because low power requirements often demand high-

impedance circuits, effects from radiated noise are more

significant. Thus, traces between the op-amp or com-

parator inputs and any resistor networks attached should

be kept as short as possible.

Crosstalk

Reference

Internal crosstalk to the reference from the comparator

45mV for the plastic DIP package and 32mV for the SO

package. Applications using the reference for the op

amp or external circuitry can eliminate this crosstalk by

using a simple RC lowpass filter, as shown in Figure 5.

Op Amp

Internal crosstalk to the op amp from the comparator is

package dependent, but not input referred. Typical val-

and 280µV for the SO package.

Op-Amp Stability and Board Layout

Considerations

Unlike other industry-standard micropower CMOS op

amps, the op amps in the MAX951–MAX954 maintain

stability in their minimum gain configuration while driving

heavy capacitive loads, as demonstrated in the

MAX951/MAX953 Op-Amp Percent Overshoot vs.

Capacitive Load graph in the

Typical Operating

Characteristics.

Although this family is primarily designed for low-fre-

quency applications, good layout is extremely impor-

tant. Low-power, high-impedance circuits may increase

the effects of board leakage and stray capacitance. For

example, the combination of a 10M

Ω resistance (from

leakage between traces on a contaminated, poorly

designed PC board) and a 1pF stray capacitance pro-

vides a pole at approximately 16kHz, which is near the

amplifier’s bandwidth. Board routing and layout should

minimize leakage and stray capacitance. In some

cases, stray capacitance may be unavoidable and it

may be necessary to add a 2pF to 10pF capacitor

across the feedback resistor to compensate; select the

smallest capacitor value that ensures stability.

Input Overdrive

With 100mV overdrive, comparator propagation delay

is typically 6µs. The

Typical Operating Characteristics

show propagation delay for various overdrive levels.

Supply current can increase when the op amp in the

MAX951–MAX954 is overdriven to the negative supply rail.

For example, when connecting the op amp as a compara-

tor and applying a -100mV input overdrive, supply current

rises by around 15µA and 32µA for supply voltages of

2.8V and 7V, respectively.

R

V

V

R

R

R

V

V

V

R

R

B

REF

IHYST

A

S H

REF

IHSYT

A

=

+

(

) ( )( )



 −

+

(

)

+

(

)

( )

2

2

2

R

R

V

V

for V

V

A

SHYST

DD

SHYST

IHYST

≈

>>

2

,

Ultra-Low-Power, Single-Supply

Op Amp + Comparator + Reference

10

______________________________________________________________________________________

R2

R1

2pF to 10pF

AMPOUT

AMPIN+

REF

0.1

µF

0.1

µF

L1

330mH

390pF

1

(2

330pF

20-60pF

10M

5.1M

1.0M

100k

1.2V

20k

COMP

ANTENNA

AMP

LAYOUT-SENSITIVE AREA,

METAL RFI SHIELDING ADVISED

MAX952

L1 x C1 =

Figure 3. Compensation for Feedback-Node Capacitance

Figure 4. Low-Frequency Radio Receiver Application