SLUSEY7 Data sheet

SLUSEY7 December 2022 TPSM82816

PRODUCTION DATA

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)

SIE|14

Thermal pad, mechanical data (Package|Pins)

Orderable Information

slusey7_oa

8.3.3 COMP/FSET

This pin allows the user to set three different parameters independently:

Internal compensation settings for the control loop (two settings available)
The switching frequency in PWM mode from 1.8 MHz to 4 MHz
Enable / disable spread spectrum clocking (SSC)

A resistor from COMP/FSET to GND changes the compensation as well as the switching frequency. The change in compensation allows the user to adopt the device to different values of output capacitance. The resistor must be placed close to the pin to keep the parasitic capacitance on the pin to a minimum. The compensation setting is sampled at the start-up of the converter, so a change in the resistor during operation only has an effect on the switching frequency, but not on the compensation.

To save external components, the pin can also be directly tied to VIN or GND to set a pre-defined switching frequency or compensation. Do not leave the pin floating.

The switching frequency has to be selected based on the maximum input voltage in the application and the output voltage to meet the specifications for the minimum on time.

Example: V_IN = 5.5 V, V_OUT = 1 V

Equation 1.

f_{S w, m a x} = \frac{V_{O U T}}{V_{I N} \times t_{O N, m i n}} = \frac{1 V}{5.5 V \times 67 n s} = 2.71 M H z

The compensation range has to be chosen based on the effective minimum capacitance used. The capacitance can be increased from the minimum value as given in Table 8-1, up to the maximum of 470 µF in both compensation ranges. If the capacitance of an output changes during operation, for example when load switches are used to connect or disconnect parts of the circuitry, the compensation has to be chosen for the minimum capacitance on the output. If the output capacitance exceeds 72 µF × V / VOUT[V], use the second compensation setting to get the best load transient response. If the output capacitance only exceeds 32 µF × V / VOUT[V], use the first compensation setting. Compensating for large output capacitance but having too little effective capacitance on the output can lead to instability.

The switching frequency for the different compensation setting is determined by the following equations.

For compensation (comp) setting 1 with spread spectrum clocking (SSC) disabled:

Equation 2.

R_{C F} [k Ω] = \frac{18 M H z \times k Ω}{f_{S} [M H z]}

For compensation (comp) setting 1 with spread spectrum clocking (SSC) enabled:

Equation 3.

R_{C F} [k Ω] = \frac{60 M H z \times k Ω}{f_{S} [M H z]}

For compensation (comp) setting 2 with spread spectrum clocking (SSC) disabled:

Equation 4.

R_{C F} [k Ω] = \frac{180 M H z \times k Ω}{f_{S} [M H z]}

Table 8-1 Switching Frequency and Compensation

COMPENSATION	R_CF	SWITCHING FREQUENCY	MINIMUM OUTPUT CAPACITANCE
For smallest output capacitance (comp setting 1) SSC disabled	10 kΩ ... 4.5 kΩ	1.8 MHz (10 kΩ) ... 4 MHz (4.5 kΩ) according to Equation 2	32 µF × V / V_OUT[V]
For smallest output capacitance (comp setting 1) SSC enabled	33 kΩ ... 15 kΩ	1.8 MHz (33 kΩ) ... 4 MHz (15 kΩ) according to Equation 3	32 µF × V / V_OUT[V]
For best transient response (larger output capacitance) (comp setting 2) SSC disabled	100 kΩ ... 45 kΩ	1.8 MHz (100 kΩ) ... 4 MHz (45 kΩ) according to Equation 4	72 µF × V / V_OUT[V]
For smallest output capacitance (comp setting 1) SSC disabled	Tied to GND	Internally fixed 2.25 MHz	32 µF × V / V_OUT[V]
For best transient response (larger output capacitance) (comp setting 2) SSC enabled	Tied to V_IN	Internally fixed 2.25 MHz	72 µF × V / V_OUT[V]

The minimum output capacitance required for stability depends on the output voltage as stated in Table 8-1. Refer to Output Capacitor for further details on the output capacitance required depending on the output voltage.

A too-high resistor value for R_CF is decoded as "tied to V_IN" and a value below the lowest range is decoded as "tied to GND". The minimum output capacitance in Table 8-1 is for capacitors close to the output of the device. If the capacitance is distributed, a lower compensation setting can be required.