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Data Sheet

ADP5053

Rev. B | Page 17 of 36

SEPARATE SUPPLYAPPLICATIONS

The ADP5053 supports separate input voltages for the four

buck regulators. This means that the input voltages for the four

buck regulators can be connected to different supply voltages.

The PVIN1 voltage provides the power supply for the internal

regulators and the control circuitry. Therefore, if the user plans

to use separate supply voltages for the buck regulators, the PVIN1

voltage must be above the UVLO threshold before the other

channels begin to operate.

To ensure that PVIN1 is high enough to support the outputs in

regulation, use precision enabling to monitor the PVIN1 voltage

and to delay the startup of the outputs. For more information,

see the Precision Enabling section.

The ADP5053 supports cascading supply operation for the four

buck regulators. As shown in Figure 32, PVIN2, PVIN3, and

PVIN4 are powered from the Channel 1 output (VOUT1). In this

configuration, the Channel 1 output voltage must be higher

than the UVLO threshold for PVIN2, PVIN3, and PVIN4.

PVIN1

BUCK 1

BUCK 2

VOUT1

PVIN2

PVIN4

VOUT2 TO VOUT4

VIN

Figure 32. Cascading Supply Application

LOW-SIDEDEVICESELECTION

The buck regulators in Channel 1 and Channel 2 integrate 4 A

high-side power MOSFET and low-side MOSFET drivers. The

N-channel MOSFETs selected for use with the ADP5053 must be

compatible with the synchronized buck regulators. In general, a

low RDSON N-channel MOSFET achieves higher efficiency;dual

MOSFETs in onepackage (for both Channel 1 and Channel 2) are

recommended to save space on the printed circuit board (PCB).

For more information, see the Low-Side Power Device Selection

section.

BOOTSTRAP CIRCUITRY

Each buck regulator in the ADP5053 has an integrated bootstrap

regulator. The bootstrap regulator requires a 0.1 µF ceramic

capacitor (X5R or X7R) between the BSTx and SWx pins to

provide the gate drive voltage for the high-side MOSFET.

ACTIVE OUTPUT DISCHARGESWITCH

Each buck regulator in the ADP5053 integrates a discharge switch

from the switching node to ground. This switch is turned on

when its associated regulator is disabled, which helps todischarge

the output capacitor quickly. The typical value of the discharge

switch is 250 Ω for Channel 1 to Channel 4.

Enable or disable the discharge switch function for all four buck

regulators by factory fuse.

PRECISION ENABLING

The ADP5053 has an enable control pin for each regulator. The

enable control pin(ENx) features a precision enable circuit with a

0.8 V reference voltage.A voltage greater than 0.8 V at the ENxpin

enables the regulator. A voltage less than 0.725 V at the ENx pin

disables the regulator. An internal 1MΩ pull-down resistor

prevents errors when the ENx pin is left floating.

The precision enable threshold voltage allows easy sequencing

of channels within the device, as well as sequencing between the

ADP5053 and other input/outputsupplies. The ENx pin can also

be used as a programmable UVLO input using a resistor divider

(see Figure 33). For more information, see the Programming

the UVLO Input section.

0.8V

DEGLITCH

TIMER

INTERNAL

ENABLE

ENx

1MΩ

INPUT/OUTPUT

VOLTAGE

ADP5053

Figure 33. Precision Enable Diagram for One Channel

OSCILLATOR

The switching frequency (fSW) of the ADP5053 can be set to a

value from 250 kHz to 1.4 MHz by connecting a resistor from

the RT pin to ground. Calculate the value of the RT resistor as

follows:

RRT (kΩ) = [14,822/fSW (kHz)]1.081

Figure 34 shows the typical relationship between the switching

frequency (fSW) and the RT resistor. The adjustable frequency

allows users to make decisions based on the trade-off between

efficiency and solution size.

1.6M

1.4M

1.2M

1.0M

800k

600k

400k

200k

RT RESIST

OR (kΩ)

Figure 34. Switching Frequency vs. RT Resistor

For Channel 1 and Channel 3, the frequencycan be set to half the

master switching frequency set by the RT pin. This setting can be

selected by factory fuse. If the master switching frequency is less

than 250 kHz, this halving of the frequency for Channel 1 or

Channel 3 is not recommended.

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