UP9503P datasheet(12/39 Pages) UPI

12 / 39 page

uP9503P

uP9503P-DS-F0000, June 2017

www.upi-semi.com

Functional Description

DAC Reference Voltage

The uP9503P embeds separate precise bandgap reference

voltage generation circuits for VDD and VDDA controllers.

Figure 4 shows the reference voltage generation circuit.

The output voltage of bandgap reference circuit is 1.55V

with respect to FBRTN (FBRTNA for VDDA).

The uP9503P utilizes plural resistors to generate precise

reference voltages ranging from 6.25mV to 1.55V, with

6.25mV step. All the voltages connect to a multiplexer

(MUX). According to SVI2 command, the MUX outputs the

selected VID (VDAC) to the current limit buffer input. The

DAC voltage is generated as the reference voltage to the

DAC pin (DACA pin for VDDA). The DAC voltage for VDDA

is generated by the same method except that it is referred

to FBRTNA pin. Table 6 shows the VID voltage and the

SVI2 code.

VBG

FBRTN

1.55V

FBRTN

1.55V

6.25mV

MUX

6.25mV~1.55V

Step=6.25mV

VDAC

SVI2

Interface

Current

Limited

Buffer

Figure 4. Reference Voltage Generation Circuit

Dynamic VID Change and Slew Rate

The controller accepts SetVID command via SVI2 bus for

output voltage change during normal operation. This allows

the output voltage to change while the DC/DC converter is

running and supplying current to the load. This is commonly

referred to as VID on-the-fly (VID OTF). A VID OTF event

may occur under either light or heavy load condition. This

voltage change direction can be upward or downward. The

default value of VID upward slew rate is 12mV/us. The value

of VID downward slew rate is 1/3 of VID upward slew rate.

The upward slew rate of VDD and VDDA can be separately

further programmed by the controllers SMBus register

0x26h. The upward slew rate can be set from 8mV/us to

22mV/us with a total of 7 steps and 2mV/LSB resolution.

The default value of upward slew rate is 12mV/us.

Output Voltage Differential Sense

The uP9503P uses differential sense by a high-gain low

offset error amplifier for output voltage differential sense as

shown in Figure 5. The GPU voltage is sensed by the FB

and FBRTN pins (FBA and FBRTNA for VDDA). FB pin is

connected to the positive remote sense pin VDD_SENSE

of the GPU via the resistor R

FB. FBRTN pin is connected to

the negative remote sense pin VSS_SENSE of GPU

directly. (VDDA_SENSE and VSSA_SENSE for VDDA).

The error amplifier compares the V

FB with VEAP (=VDAC - IMON

x R

DRP) to regulate the output voltage.

RCOMP_INT

COMP

RFB

VDD_SENSE

Positive voltage remote

sense pin of GPU

CSP

CSN

EAP

DAC

RDRP

FBRTN

CDAC

VSS_SENSE

Negative voltage remote

sense pin of GPU

CCOMP

RCSN

CCSN

Reference

Voltage

RCOMP

IMON

Figure 5. Output Voltage Differential Sense

Total Load Current Sense

The uP9503P uses a low input offset current sense amplifier

(CSA) to sense the total load current flowing through

inductors for droop function by CSP and CSN (CSPA and

CSNA for VDDA) as shown in Figure 6.

RPH2

RPH3

1ohm

PH1

PH2

PH3

1ohm

VDD_1

VDD_2

VDD_3

CCSN

RCSN

CSP

CSN

RPH1

IMON

Figure 6.Total Load Current Sense

The voltage across C

CSN is proportional to the total load

current, and the output current of CSA (I

MON) is also

proportional to the total load current of the voltage regulator.

The sensed current I

MON represents the total output current

of the regulator, and it is directly used for droop function,

total output over current protection, and output current

reporting. I

MON is calculated as follows.

CSN

OUT

MON

In this inductor current sensing topology, R

PH and CCSN must

be selected according to the equation below:

CSN

where R

DC is the DCR of the output inductor L, P is the

operation phase number. Theoretically, k should be equal

to 1 to sense the instantaneous total load current. But in

real application, k is usually between 1.2 to 1.8 for better

load transient response. Note that the resistance value of

CSN must be less than 2k

Ω

to ensure the current sensing

circuit in normal operation.

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