ADP1882-1.0-EVALZ Analog Devices Inc, ADP1882-1.0-EVALZ Datasheet - Page 20

• Manufacturer Part Number: ADP1882-1.0-EVALZ
• Description: 1 MHz Synchronous Current-Mode Buck Controller Eval. Board
• Manufacturer: Analog Devices Inc

Specifications of ADP1882-1.0-EVALZ

• Silicon Manufacturer: Analog Devices
• Application Sub Type: PWM Buck Controller
• Kit Application Type: Power Management - Voltage Regulator
• Silicon Core Number: ADP1882
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADP1882/ADP1883
PROGRAMMING RESISTOR (RES) DETECT CIRCUIT
Upon startup, one of the first blocks to become active is the RES
detect circuit. This block powers up before a soft start begins. It
forces a 0.4 V reference value at the DRVL output (see Figure 68)
and is programmed to identify four possible resistor values:
47 kΩ, 22 kΩ, open, and 100 kΩ.
The RES detect circuit digitizes the value of the resistor at the
DRVL pin (Pin 6). An internal ADC outputs a 2-bit digital code
that is used to program four separate gain configurations in the
current-sense amplifier (see Figure 69). Each configuration
corresponds to a current-sense gain (A
and 24 V/V, respectively (see Table 5 and Table 6). This variable
is used for the valley current-limit setting, which sets up the
appropriate current-sense signal gain for a given application
and sets the compensation necessary to achieve loop stability
(see the Valley Current-Limit Setting and Compensation
Network sections).
Table 5. Current-Sense Gain Programming
Resistor (kΩ)
47
22
Open
100
Figure 69. RES Detect Circuit for Current-Sense Gain Programming
CS GAIN SET
DRVL
Figure 68. Programming Resistor Location
A
3.25
6.5
26
13
AMP
CS
CS
PROGRAMMING
RES
ADP1882
(V/V)
ADC
CS GAIN
DRVH
DRVL
SW
RES
CS
0.4V
) of 3 V/V, 6 V/V, 12 V/V,
Q1
Q2
SW
PGND
Rev. 0 | Page 20 of 40
VALLEY CURRENT-LIMIT SETTING
The architecture of the ADP1882/ADP1883 is based on valley
current-mode control. The current limit is determined by three
components: the R
fier output voltage swing (COMP), and the current-sense gain.
The COMP range is internally fixed at 1.5 V. The current-sense
gain is programmable via an external resistor at the DRVL pin
(see the Programming Resistor (RES) Detect Circuit section).
The R
and usually has a positive T
temperature); therefore, it is recommended that the current-
sense gain resistor be programmed based on the rated R
the MOSFET at 125°C.
Because the ADP1882/ADP1883 are based on valley current
control, the relationship between I
where:
I
I
K
desired average load current (see Figure 10).
Establishing K
Inductor Selection section), but in most cases, K
When the desired valley current limit (I
the current-sense gain can be calculated by using the following
expression:
where:
A
R
CLIM
LOAD
I
CS
ON
is the ratio between the inductor ripple current and the
is the current-sense gain multiplier (see Table 5 and Table 6).
is the channel impedance of the lower-side MOSFET.
I
I
is the desired valley current limit.
is the current load.
CLIM
CLIM
ON
Figure 70. Valley Current Limit to Average Current Relation
of the lower-side MOSFET can vary over temperature
= I
=
A ×
LOAD
CS
1
I
5 .
helps to determine the inductor value (see the
LOAD CURRENT
×
V
R
VALLEY CURRENT LIMIT
ON
ON
⎛
⎜
⎝
1
of the lower-side MOSFET, the error ampli-
−
K
2
I
⎞
⎟
⎠
C
(meaning that it increases with
RIPPLE CURRENT =
CLIM
CLIM
and I
) has been determined,
LOAD
I
LOAD
is as follows:
I
3
= 0.33.
ON
of